|
SUMMARIES OF FY 1996
RESEARCH IN THE CHEMICAL
SCIENCES |
Chemical Energy:
Offsite Projects
University of Arizona
Tucson, AZ 85721
Department of Chemistry
A Model Approach to Hydrodenitrogenation Catalysis
Despite the importance of removing nitrogen from petroleum feedstocks to providing more
processable and environmentally sound fuels, the mechanisms of metal-catalyzed,
hydrodenitrogenation (HDN) reactions are not well understood. We are continuing studies of
soluble model compounds that mimic HDN substrate-catalyst interactions and demonstrate
purported HDN reactions. Our primary focus is on the six-membered heterocyclic compounds
such as pyridine and its derivatives. Recent studies allow us to support the following conclusions:
1. The 
2(N,C) binding
mode renders a pyridine ligand susceptible to nucleophilic attack and results in C-N bond
cleavage. 2. The overall reaction between an 2(N,C) pyridine complex and an attacking nucleophile can be
partitioned into two stages: nucleophilic attack at the metal center followed by ligand migration to
the 2 ligand. 3. In our
model system, ligand migration is rate-limiting and the ligand migrates to the substrate as a 
nucleophile. 4. The C-N bond scission
appears to be driven by the formation of a strong metal-nitrogen multiple bond and made possible
by the reduction in pyridine C-N bond order that arises from 2 coordination. 5. Carbon-carbon bond scissions of a
ring-opened pyridine ligand are possible at the same metal site when the pyridine is highly
substituted. 6. Although the first step of quinoline HDN involves hydrogenation to
tetrahydroquinoline, tetrahydroquinoline has not been induced to bind in the 2(N,C) mode. These results offer
new, significant insight into HDN related processes, including the manner by which nitrogen
heterocycles may be further degraded after C-N bond cleavage.
Boston College
Chestnut Hill, MA 02167
Department of Chemistry
High-Temperature Chemistry of Aromatic Hydrocarbons
This work focuses on the fundamental molecular processes involved in the rearrangements and
interconversions of polycyclic aromatic hydrocarbons (PAHs) under conditions of thermal
activation. PAH ring systems figure prominently in the molecular architecture of coal, but prior to
this systematic program of study, little was known about the chemical transformations that PAHs
undergo at high temperatures, such as those employed in the uncatalyzed gasification and
liquefaction of coal. This year several additional examples of fullerene fragment formation from
bay region PAH at high temperatures have been discovered, e.g., the production of
cyclopent[cd]fluoranthene from benz[a]anthracene, dicyclopenta[cd,fg]pyrene from
benz[e]pyrene, inter alia. The possible intermediacy of bay region diradicals in such processes is
supported by the generation of pyracylene from cyclopent[def]phenanthrenone by
decarbonylation-rearrangement. Isotopic labelling experiments with
13C2-picene further support our proposed unified mechanism for
high temperature transformations of this type. The spectacular triple cyclodehydrogenation of
decacyclene to triacenaphthotriphenylene, a 36-carbon bowl-shaped fullerene fragment, has also
been observed at 1200-1300 °C. The long-range objectives of this research are to uncover all
the principal reaction channels available to PAHs at high temperatures and to establish the factors
that determine which channels will be followed in varying circumstances.
California Institute of Technology
Pasadena, CA 91125
Department of Chemistry
Synthetic and Mechanistic Investigations of Olefin Polymerization Catalyzed by Early
Transition Metal Compounds
The objectives of this research program are (1) to discover new types of chemical transformations
between hydrocarbons and transition-metal compounds; (2) to investigate their mechanisms; and
(3) to explore the possibilities of coupling these transformations with others to catalyze chemical
reactions for the preparation of fuels, commodity chemicals, and polymeric materials. A current
focus is the catalytic polymerization of olefins. Ziegler-Natta catalysis is a well-established and
commercially very important process; however, it is clear that new (and superior) polymers with
different microstructures and new homo-block copolymers could be made from the same readily
available monomers if sufficient control over the catalytic process could be achieved.
C2-symmetric yttrocene derivatives with linked cycopentadienyl ligands have
been prepared. The alkyl and hydride derivatives function as well-defined, single component,
isospecific alpha olefin polymerization catalysts well suited to mechanistic investigations. A ligand
capable of affording only one enantiomer of a chiral catalyst has been synthesized. The absolute
facial preferences for olefin insertion into Y-H and Y-C bonds has been established for a chiral,
highly deuterated olefin using NMR methods. Recently a new class of zirconocene catalysts have
been developed that produce highly syndiotactic poly alpha-olefins. A modified version allows the
preparation of polypropylenes with tacticities varying from isotactic to syndiotactic.
University of California, Davis
Davis, CA 95616
Department of Chemical Engineering
Effects of Supports on Metal Complexes and Clusters: Structure and Catalysis
The research is a fundamental investigation of the effects of supports on the structure and
catalytic properties of metal complexes and clusters. The metals are Rh and Ir. The supports are
MgO, 
-Al2O3, and zeolite LTL. The former are
used as high-area powders and as ultrathin layers on metal single crystals. Like the oxides, the
zeolite is basic, incorporating K+ and Ba2+ exchange ions. With
precursors such as [Ir(CO)2(acac)], metal subcarbonyls such as
[Ir(CO)3(OMg)3] are formed (where the braces around MgO
denote groups terminating the MgO). With precursors such as
[HIr4(CO)11]- and
[Ir6(CO)15]2-, supported clusters such as
Ir4 and Ir6 are formed. The supported species are being
characterized structurally with IR, EXAFS, and NMR spectroscopies, TPD, H2
chemisorption, and imaging methods. The samples are being tested as catalysts for ethylene
hydroformylation toluene hydrogenation, and n-butane hydrogenolysis. The goals are to
determine how the support structure and composition affect the structure of the well-defined
supported metal complexes and clusters and their reactivities and catalytic properties. For
example, tetrairidium clusters on MgO were oxidized to give iridium oxide clusters of nearly 4
atoms each, and these were reduced in H2 to give back Ir4. These
latter clusters on MgO catalyze toluene hydrogenation, and the catalytic reaction rate depends
only modestly on the MgO surface hydroxyl content.
University of California, Irvine
Irvine, CA 92697-2025
Department of Chemistry
Synthesis and Chemistry of Yttrium and Lanthanide Metal Complexes
| Investigator(s) |
Evans, W.J.
|
$127,381 |
| Phone | 714-824-5174 |
| E-mail |
wevans@uci.edu |
The purpose of this project is to study the chemistry of complexes of yttrium and the lanthanide
metals, a series of 15 metals readily available in the United States, so that the special properties of
these metals can be utilized in energy-saving optical and magnetic materials and in the catalysis of
conversions of abundant low-value substrates such as CO and CO2 into more
useful chemicals. To achieve this goal, more information is needed on ligands which solubilize the
metals as complexes, which allow full characterization of the chemistry, and which are compatible
with the practical applications. Alkoxide and aryloxide ligands have been found to be effective in
making polymetallic complexes including soluble manipulatible complexes which have interior
structures similar to metal oxides. The nitrogen analogs of aryloxides, arylamido ligands, have
also been found to be valuble ligands for these metals providing a wide range of structural types.
Investigation of "dehydrated" CeCl3 extensively used in organic
synthesis for its unique reactivity in alkylations as CeCl3/RLi has shown that this
ligand system is not as simple as previously assumed. The "dehydrated" material is
actually [CeCl3(H2O)(THF)]n , a fact which
requires reevaluation of reaction mechanisms for this popular reagent.
University of California, Riverside
Riverside, CA 92521
Department of Chemistry
Study of the Surface Chemistry of Hydrocarbon Radicals and of Carbonium Ions on Metal
Oxide Surfaces
This project focus on the development of two separate directions related to the characterization of
the surface chemistry of hydrocarbons on metal oxide surfaces. In the first, the oxidation of nickel
surfaces to form thin nickel oxide films spectroscopies is been investigated. In particular, the
effect of argon ion bombardment on the oxidation of nickel films was studied by using X-ray
photoelectron spectroscopy (XPS). In the absence of any ion beams, exposure of nickel surfaces
to an oxygen atmosphere leads to the moderately rapid formation of a thin (3-5 monolayers thick)
nickel oxide overlayer. At room temperature the oxygen uptake stops once this limit is reached,
but at higher temperatures the slow growth of a thicker oxide is seen. The diffusion coefficient for
oxygen through the forming NiO film was determined to be on the order of
2x10-18 cm2/s at 625 K. The simultaneous impingement of argon
ions on the surface during oxygen exposures was found to enhance the oxidation process. Indeed,
ion beam current densities as low as 0.01 µA/cm2 were found to be
sufficient to induce nickel oxidation past the 3-5 ML limit even at room temperature.
The oxidation rate was found to be roughly proportional both to the ion flux and to the square of
the oxygen pressure. The build-up of a NiO film during this Ar+-ion/oxygen
treatment was also found to slow down at higher temperatures, presumably because of the
combined effect of a higher probability for desorption of molecular oxygen from the surface and a
higher atomic oxygen mobility into the bulk. The oxide films prepared at low temperatures appear
to be quite disordered, and display an extra feature in the Ni 2p XPS spectra around 853.2 eV
which could be assigned to partially reduced nickel. Annealing of those films to temperatures
above 400 K leads to the possible ordering of the surface and to the disappearance of the signal
for the Ni+x species in the XPS, and further heating above 600 K leads to the
diffusion of oxygen atoms into the bulk and to the partial reduction of the surface nickel to its
metallic state. Finally, the presence of water in the gas phase during the nickel Ar ions/oxygen
treatment was seen to result in the production of a surface hydroxyl layer, the same as when the
oxidation is carried out in the absence of ion excitation. The second direction of this project has
been to study the conversion of alkyl groups chemisorbed on the oxide surfaces prepared as
described above. On clean nickel surfaces, alkyl species decompose via a combination of
beta-hydride and reductive elimination steps to yield a mixture of alkanes and alkenes.
On the other hand, most of the surface reactivity is inhibited by the presence of surface oxygen,
and only the products of total oxidation reactions, namely, CO, CO2 and
H2O, desorb from fully oxidized surfaces under vacuum. The interesting aspect of
this research is the fact that formation of acetone, a partial oxidation product, was observed for
the reaction of 2-propyl iodide with low oxygen precoverages. The desorption temperature of that
partial oxidation reaction, when compared to the desorption of acetone from Ni(100), suggests
that its formation is reaction limited. The experimental results obtained so far suggest that alkyl
halides adsorb and dissociate on the nickel atoms first, forming the desired alkyl groups. At
slightly higher temperatures, around 200 K, most of those moieties undergo the beta-hydride and
reductive elimination reactions to alkenes and alkanes, respectively, typical of the metallic
function, but a small fraction migrates to the oxygen functionality and to form alkoxy groups,
which then dehydrogenate above 300 K to produce the ketone.
University of California, Santa Barbara
Santa Barbara, CA 93106
Department of Chemical and Nuclear Engineering
Alkane Activation and Reactivity on Iridium, Platinum, and Ruthenium Surfaces
The research objective is to quantify alkane activation on various transition metal surfaces
including Ir(110) and Ir(111). We have employed molecular beam techniques to investigate the
molecular trapping and trapping-mediated dissociative chemisorption of perhydrido- and
perdeutero-ethane and propane, as well as c-C3H6 on Ir(110) at
low beam translational energies, Ei 
5 kcal/mol, and surface temperatures, TS, from 85 to
1200 K. In each of these cases, the cleavage of C-H (C-D) bonds through the trapping-mediated
mechanism is unactivated with respect to a gas-phase energy zero, i.e., the activation energy for
reaction from the physically adsorbed state, Er, is less than the activation energy
for desorption, Ed, from this state. We have also measured the initial adsorption
probability of CH4 and CD4 on Ir(111) under both low pressure
(< 10-3 Torr) and high pressure (1 Torr) conditions. Under low pressure
conditions trapping-mediated chemisorption is the dominant mechanism of methane dissociation
with activation energies of 16.0 and 17.0 kcal/mol for CH4 and
CD4. By diluting the methane in argon at a total pressure of 1 Torr, we have also
examined the direct activation of methane. Under these conditions the translational energy of the
methane is characterized by a Maxwell-Boltzmann distribution at the surface temperature. For
this case the apparent activation energies of methane activation are 17.0 kcal/mol for
CH4 and 17.9 kcal/mol for CD4. For both CH4
and CD4, the rate of reaction is greater for the high pressure experiments than the
low pressure experiments.
University of California, Santa Barbara
Santa Barbara, CA 93106
Department of Chemistry
Studies Relevant to the Catalytic Activation of Carbon Monoxide
This research is concerned with quantitative investigations of fundamental reactions relevant to
the catalytic activation of carbon monoxide and other C1 compounds. New
carbonylation catalysts based on rhodium(III) heterogenized on polyvinyl pyridine polymers have
been developed and these are active in Reppe type hydroformylation and hydrogenation of
alkenes. In addition, exploratory studies have been carried out to use sodium formate as the
reductant in the catalytic reduction of chlorinated organic compounds. Time resolved spectral
techniques have been used to prepare and to investigate the spectra and dynamics of
organometallic intermediates relevant to the activation of hydrocarbon C-H bonds and to
formation of carbon-carbon bonds via CO migratory insertion into metal-alkyl bonds. The latter is
the key reaction in the carbonylations of various organic substrates. The goals are to delineate the
quantitative details of these fundamental processes, to understand chemical principles relevant to
the activity and selectivity of molecular catalysts for activating hydrocarbons and
C1 compounds such as CO, and to define guidelines for designing new,
environmentally friendly and more efficient applications of energy and chemical feedstocks.
Carnegie-Mellon University
Pittsburgh, PA 15213
Department of Chemical Engineering
H2SO4-Modified ZrO2 and
ZrO2/SiO2 Aerogels as Solid Superacids
Manipulation of sulfate content, silica content, and activation temperature provided the means for
controlling the strength of surface Brønsted acid sites in the zirconia-silica-sulfate system. This
approach allowed the development of an acid strength hierarchy, based on the adsorption of
pyridine and isomerization of 1-butene and n-butane, as a rational basis for acid catalyst design.
Introduction of silica into zirconia-sulfate co-gels also provided insight into the activation
behavior of this important class of materials. Silica retarded sintering upon heat treatment, thereby
delaying crystallization of zirconia to higher temperatures. Activation of sulfate to a form capable
of catalyzing the isomerization of n-butane was also delayed to higher heat treatment
temperatures, confirming the role of crystallization in initiating the activation sequence.
Colorado State University
Fort Collins, CO 80523
Department of Chemistry
Polyoxoanion-Stabilized Transition Metal Nanoclusters: Soluble Analogs of Heterogeneous
Catalysts
The first examples of a new type of metal-particle catalyst, polyoxoanion and
Bu4N+-stabilized transition-metal nanoclusters, were discovered recently under
our DOE grant support. Presently, the following knowledge is being gathered, information
necessary to construct a paradigm covering their catalytic applications: an understanding of what
gives rise to their stabilization and isolability, an understanding of how this stabilization can be
enhanced to generate higher temperature-stable nanocluster catalysts, and an understanding of the
nanocluster's catalytic reactions and their underlying mechanisms. Ultimately, our goal is a full
understanding of the strengths and weaknesses of this exciting new subclass of soluble
metal-particle catalysts.
Colorado State University
Fort Collins, CO 80523
Department of Chemistry
Diosmacycloalkanes as Models for the Formation of Hydrocarbons from Surface
Methylenes
Protonation of mono- and dinuclear dialkyl and olefin osmium complexes gives cationic alkyl,
alkylidene, and olefin complexes. In the case of
Os(CO)4(C2H4), both the kinetic and
thermodynamic sites of protonation are Os, but C2H4 inserts into
the Os-H bond in the presence of as weak a coordinating ligand as Et2O. We
have examined the reactivities of these cationic Os complexes toward olefins, alkynes, and CO,
and have found insertion reactions but no utility as polymerization catalysts. In collaboration with
Elliott Burnell of the U. of British Columbia, we have rethought our analysis of the structure of
the parent diosmacyclobutane from nematic phase NMR data. We have prepared
diosmacyclobutanes from strained olefins such as norbornene and cyclobutene. We will now
assess (1) the effect of ring strain on the relative binding affinities and (2) the potential for strained
diosmacyclobutanes to cleave C-C and Os-Os bonds to form tethered alkylidene complexes:
(CO)4Os=CHR-RHC=Os(CO)4.
University of Colorado
Boulder, CO 80309
Department of Chemistry and Biochemistry
Syntheses and Reactions of Pyrrole and Indole Complexes
The objectives of the project are (1) to synthesize new transition metal pyrrole and indole
complexes and (2) to investigate how the metal ion coordination affects the reactivity of the
heterocycle. An understanding of how coordinated heterocycles might be activated toward
reduction, ring opening, or nucleophilic addition reactions may provide a basis for understanding
basic mechanisms of the hydrodenitrogenation catalysts. A series of new 5 pyrrolyl complexes of
ruthenium(II) have been synthesized, and the heterocyclic ligand was found to be activated
toward nucleophilic substitution reactions at the alpha carbon atom. Reactions with alkyl and aryl
lithium reagents and with amide nuleophiles led to the preparation of new derivatives with
substituted pyrrolyl ligands. 2,5-Disubstituted pyrroylyl ligands have also been prepared in some
cases. The new pyrrole ligands can be readily displaced from the ruthenium ion by protonation
reactions, and the free ligands have been isolated. The results demonstrate that these reactions
have potential useful applications for the preparation of new substituted pyrrole rings. In a related
project 5-tetramethylpyrrole, 6-indole, 6-indolyl, and 6-indoline complexes of pentamethylcyclopentadienyl Ir(III) have
been synthesized. Reactions of these complexes with nucleophiles and reducing agents have been
studied. For example, [(5-HNC4Me4)Ir(C5Me5)](OTf)2, 1, undergoes a quasi-reversible
two-electron reduction at - 1.34 V vs Fc. Reaction of 1 with a hydride donor resulted in
a reduced Ir(I) product in which nucleophilic hydride addition to the Cp* ligand had occurred. In
contrast reactions of the indole and indoline complexes with nucleophiles resulted in attack on the
carbocyclic ring of the heterocycle. Further studies of these systems are in progress.
Columbia University
New York, NY 10027
Department of Chemistry
Model Studies in Hydrocarbon Oxidation
The research performed during the last grant period has continued with an investigation of the
chemistry of molecular terminal chalcogenido complexes. By studying the chemistry of a series of
complexes with M=O, M=S, M=Se, and M=Te bonds, it is hoped that this research will provide
results that are relevant to systems concerned with both hydrocarbon oxidation and
hydrodesulfurization processes. For example, we have synthesized the first series of oxo, sulfido,
selenido, and tellurido derivatives of hafnium Cp
2Hf(E)(NC5H5)
(E=O, S, Se, Te), and the first mononuclear telluroformaldehyde complex of tantalum
Cp*2Ta(2-TeCH2)H. Studies on these complexes have
revealed interesting differences in the chemistry of the systems as a function of the chalcogen. For
example, coupling and cleavage reactions play an active role in a variety of important
transformations. However, in spite of the potential importance of reactions involving the
interconversion of [M](E)2 and [M](2-E2) moieties, relatively few well-characterized
examples of such transformations have been described. Significantly, we have reported the first
examples of such transformations for tellurium, thereby suggesting that such reactions are more
facile for tellurium than its lighter congeners. We have also compared the ability of molybdenum
and tungsten centers to activate C-H bonds and have demonstrated that the
hexakis(trimethylphosphine)molybdenum complex only forms aryloxy-hydride complexes in its
reactions with phenols, whereas the corresponding tungsten complex undergoes intramolecular
C-H bond activation. Nevertheless, although C-H bond activation by the molybdenum center is
thermodynamically unfavored, magnetization transfer studies demonstrate that it is kinetically
capable of such reactions.
University of Connecticut
Storrs, CT 06269
Department of Chemistry
Synthetic Todorokite: Preparation, Characterization, and Applications
The goals of this project are to prepare new octahedral molecular sieve (OMS) and octahedral
layer (OL) materials by several methods including sol-gel, reflux, autoclave methods; to prepare
and characterize isomorphously substituted OMS and OL materials; to develop new
characterization methods for OMS and OL systems such as diffuse reflectance UV-visible
spectroscopy; and to optimize catalytic properties of OMS and OL for dehydrogenation of
alkanes to terminal olefins and oxidation of alkanes to terminal alcohols. Materials with transition
metals substituted into framework or tunnel sites of OMS and OL have been prepared.
Characterization of such systems will be done with a variety of methods in order to study
structural, compositional, surface, electronic, electrical, morphological, thermal, magnetic,
electron transfer, redox, and catalytic properties. Characterization of changes in the OMS and OL
catalysts during reaction are being studied. Some reactions of interest are oxidative
dehydrogenation of cyclohexane, decomposition of hydrogen peroxide, and styrene formation.
University of Delaware
Newark, DE 19716
Center for Catalytic Science and Technology
Synthetic Reactions of Oxametallacycles and Related Intermediates on Transition Metal
Surfaces
The goal of this research is to identify the requirements for and competition between activation of
C-H, C-C, and C-O bonds in the synthesis and decomposition of oxygenates on transition metal
surfaces. Current research is focused on surface oxametallacycle chemistry. These intermediates
are implicated in a variety of reactions in homogeneous catalysis, heterogeneous catalysis and
surface science, including epoxide synthesis and carbonylation and decarbonylation processes.
However, spectroscopic evidence for oxametallacycles is generally lacking and the patterns of
reactivity of these intermediates are not well established. We are employing both experimental
techniques (Temperature Programmed Desorption, High Resolution Electron Energy Loss
Spectroscopy, and X-ray Photoelectron Spectroscopy) and theoretical methods (Density
Functional Theory) in these studies. A primary goal is to demonstrate the synthesis of surface
oxametallacycles, and thus to determine the factors which control their formation and the
selectivity of their reactions, and to identify new reactions with ramifications for catalysis. Our
research has produced the first evidence for the participation of oxametallacycles in higher alcohol
chemistry on certain transition metal surfaces, and most recently it has produced the first evidence
both for stable oxametallacycle formation and for novel cyclization chemistry of these
intermediates. This work holds the potential of establishing new principles for surface organic
syntheses, of discovering new chemistry, and thus of providing guidance for the development of
new catalysts and processes for oxygenate synthesis.
University of Delaware
Newark, DE 19716
Department of Chemistry and Biochemistry
Oxidation Catalysis with Tris(pyrazolyl)borate Metal Complexes
This project involves the development of catalysts for the oxidation of organic substrates using
dioxygen as the source of the oxygen. In particular, the approach involves coordination and
symmetric cleavage of the O2 molecule into two reactive metal-oxo moieties by
hindered tris(pyrazolyl)borate complexes of late transition metals. The feasibility of this scheme
has been previously demonstrated using a set of cobalt complexes. In the initial phase of the
research the mechanism of the cobalt mediated stoichiometric reaction will be elucidated in detail,
and some reactions of the cobalt system [Tpt-Bu,MeCo,
Tpt-Bu,Me = hydridotris(3-t-butyl-5-methylpyrazolyl)borate] related to oxidation
catalysis will be investigated. Building on this, the metal complexes will be modified to facilitate
catalytic turnover. To this end the ligands must be "hardened" against oxidative
degradation. This will be done by appropriate substitution of the ligand and/or the metal. In the
long term, catalytic oxidations of various substrates as well as the design of ligands for regio- and
stereo-selective oxidations will be investigated.
University of Florida
Gainesville, FL 32611
Department of Chemistry
Bimetallic Complexes as Methanol Oxidation Catalysts
The project involves preparation of bimetallic Pt/Ru and Pt/Mo complexes as catalysts for the
electrooxidation of methanol. The currently accepted mechanisms for methanol oxidation at Pt/Ru
anodes involve C-H activation at Pt and "active oxygen transfer" from Ru. Since
these reactions are known individually for mononuclear complexes, the catalysts are designed to
mimic the anode behavior. Design features of the complexes include bridging ligands such as
1,10-phenanthrolinedione or bidentate phosphines to prevent dissociation of the metal centers,
low-valent starting materials that allow a series of oxidation states for each metal to be generated
during oxidation studies, and incorporation of ligands that are relevant to the methanol oxidation
process. Both chemical and electrochemical oxidation of the complexes are being examined and
reaction of the oxidized species with methanol is being investigated. The complexes whose
solution electrochemistry is most promising for methanol oxidation will be deposited on
electrodes for studies of electrocatalysis under the aqueous conditions found in direct methanol
fuel cells.
Harvard University
Cambridge, MA 02138
Department of Chemistry
Model Microcrystalline Mixed-Metal Oxides for Partial Oxidation and Desulfurization
The broad objective of this proposal is to investigate how the constituents of bimetallic materials
function in important catalytic processes. We are currently investigating the activity of mixed Co-S
and Co-O phases supported on Mo(110) for hydrocarbon oxidation, deoxygenation and
desulfurization. A general method for synthesizing small (~100 angstroms) metal clusters on
Mo(110) has been devised, allowing us to compare the chemistry of small particles to that of uniform
films. The reactivity of the small Co clusters is substantially different than a uniform monolayer.
For example, methanol does not react on the Co clusters whereas it decomposes to CO and
dihydrogen on the uniform monolayer at ~375 K. Currently, the reactions of methyl radicals with
adsorbed oxygen and hydroxyl are being investigated on the uniform phases and Co clusters with
the goal of synthesizing methanol. Scanning tunneling microscopy and theoretical studies are
planned to develop an understanding of the contributions of geometric and electronic structure
effects in determining the reactivity differences. These studies have broad significance in that they
serve as a test of aspects of the cluster-surface analogy and may provide a means of manipulating
product distributions in catalytic processes via variation in particle sizes.
University of Illinois at Urbana-Champaign
Urbana, IL 61801
School of Chemical Sciences
Electron Transfer Activation of Coordinated Thiophene
The presence of organic sulfur compounds in fossil fuels poses very serious environmental and
engineering challenges. The most effective method for addressing these problems is through the
hydrodesulfurization (HDS) process whereby the sulfur is removed by hydrogenolysis of C-S
bonds in the fossil fuel matrix. The project objectives are threefold: (1) elucidate mechanisms for
metal-catalyzed HDS, (2) develop new methods for desulfurization of fossil fuels, and (3) develop
new uses for organosulfur components of fossil fuels. Most of these studies employ thiophenes as
representative substrates. Experiments focus on HDS pathways that involve electron transfer to a
metal-thiophene ensemble followed by protonation, i.e., heterolytic hydrogen activation. The
stereochemistry and energetics for individual steps are examined for model systems based on
ruthenium complexes. New desulfurization methods and new uses for the organosulfur
components in fossil fuels are developed through the addition of nucleophiles to metal thiophene
ensembles.
Indiana University
Bloomington, IN 47405
Department of Chemistry
Chemical Principles Relevant to Materials Precursor Design and Synthesis
The project objective is to determine, by a series of case studies, which chemical routes are
particularly facile for the conversion of mixed-metal alkoxides to solid-state oxide materials. The
transformation from molecule to infinite lattice solid will be effected by thermolysis, hydrolysis,
and plasma treatment. The groups L to be considered include simple hydrocarbon-derived
alkoxides, heavily fluorinated alkoxides, and vicinal diolates. These are chosen to incorporate
progressively more complex chemical features, each of whose typical reaction patterns are
well-established. Chemically-facile routes are expected in certain cases because elimination of
known neutral organic molecules can be envisioned. Such "weak" bonds will cause
the precursor-to-product process to occur under very mild conditions. This research involves
establishing whether such expectation will be realized under CVD processing conditions.
Incorporation of mobile protons will also be considered as a "trigger" for precursor
processing at especially low temperatures. In every case, mechanistically diagnostic experiments
will be executed in order to allow generalization of these results to make more rational the design
of effective molecular precursors to technologically-valuable solid materials.
Indiana University
Bloomington, IN 47405
Department of Chemistry
Alkoxide Ligands in Organometallic Chemistry and Catalysis
Alkoxide and related aryloxide and siloxide ligands are hard 
-donor ligands and complement the now traditional soft -acceptor ligands such as tertiary phosphines, carbonyls and -hydrocarbyl ligands. We are using the former with
hard metals such as early transition elements, lanthanides and group 2 and 3 main group elements
as ancillary ligands for the development of a new field of organometallic chemistry. Current areas
of research include (i) the development of selective hydrogenation catalysts for conjugated dienes
employing W2(OR)6 compounds; (ii) the use of bidentate and tridentate diols and triols to impose
specific coordination geometries at the metal atoms; (iii) studies of opening of sulfur, nitrogen and
oxygen containing aromatic rings as models for steps in HDS, HDN and HDO catalysis and (iv)
the development of single site metal alkoxide catalysts for the ring-opening of epoxides and
strained cyclic esters.
Indiana University
Bloomington, IN 47405
Department of Chemistry
A Model Approach to Vanadium Involvement in Crude Oil Refining
The project is directed toward characterizing the initial fate of crude oil vanadyl impurities under
the reducing and sulfur-rich conditions of industrial hydrodemetallation (HDM) and
hydrodesulfurization (HDS) processes. The impurities are ultimately converted to insoluble
vanadium sulfides (primarily V2S3 and
V3S4), which lower the activity of, and eventually poison, the
Mo heterogeneous catalyst. Recent work has concentrated on detailed characterization of various
V/S clusters that represent models for intermediate stages of V sulfide polymer growth. A number
of di- and trinuclear species have ben prepared and studied by a range of techniques, including
x-ray crystallography, VT magnetic susceptibility measurements, VT 1H NMR
studies, and EHT MO calculations. Selected complexes under study include
[V3Cl6(SCH2CH2S)3]3-,
[V2(SCH2CH2S)4]z- (z=1 or 2) and [VxOy(pyt)z]
(pyt=pyridine-2-thiolate), which represent models of small V species adsorbed on the surface of
the growing V2S3/V3S4 phases.
The V/pyt complexes have been investigated by EI mass spectrometry, the observed MS
fragmentation patterns (C-S and C-N bond cleavage) being employed as a model system for the
fragmentation pathways of organovanadium impurities during the high temperature conditions of
crude oil refining. The work has most recently been extended to include a variety of
V/O/carboxylate clusters; the latter organic functionality is common in crude oils. A number of
tetranuclear and pentanuclear species have been prepared and characterized by crystallographic
and physical methods, including magnetochemistry. Aggregation methodology has been
developed for the stepwise conversion of mononuclear vanadyl species to penta-, ennea-, and
pentadecanuclear products, and all these species have undergone detailed characterization. The
reaction of such species with H2S is also being investigated as a model system
for V sulfide polymer formation under refining conditions.
University of Iowa
Iowa City, IA 52242
Department of Chemistry
Synthesis and Chemistry of Cationic d0 Metal Alkyl Complexes
The objective of this research is to design and synthesize new types of electrophilic organometallic
complexes for use in fundamental studies of olefin polymerization and C-H activation chemistry,
and for exploitation in catalysis. Earlier studies of Cpp2Zr(R)(L)+
complexes identified the key features required for high insertion reactivity in early metal systems:
an electrophilic metal center, a do metal electron configuration, and one or more
vacant (or virtual) coordination sites cis to the M-R ligand. Current work is directed to the
development of new classes of cationic early metal alkyls, which incorporate these features in
non-Cp2M ligand environments. A series of Zr and Hf alkyl complexes
(N4-macrocyle)M(R)2 (R = CH3,
CH2Ph, CH2SiMe3) containing dianionic
tetra-aza macrocycles (N4-macrocycle = Me8-taa,
Me4-taen) in place of Cp ligands has been prepared. The pockets of these
macrocycles are too small to accommodate the large group 4 metal ions, so the metal sits out of
the N4-plane and cis structures are imposed. Base-stabilized cations
[cis-(N4-macrocycle)M(R)(L)][BPh4] (L = THF, RCN,
PMe2Ph), and base-free cationic systems
[(N4-macrocycle)M(R)][B(C6F5)4], have been prepared by protonolysis routes. The base-free systems are moderately active
ethylene polymerization catalysts. One example,
(Me8-taa)Hf(CH3)+, also undergoes clean single insertion of
vinyltrimethylsilane, and clean double insertion of dimethylacetylene. Ortho C-H activation of
2-methylpyridine and vinyl C-H activation of 2-vinylpyridine have also been observed with these
cationic systems. Cationic alkyls based on tetradentate Schiff base ligands, e.g.,
(F6-acen)Zr(R)+, have been prepared more recently. These systems are active
olefin polymerization catalysts in the presence of AIR3 cocatalysts. Chiral
analogues catalyze the stereoselective polymerization of propylene to isotactic polypropylene.
Current efforts are focused on more highly electron-withdrawing chelating ligands, which should
maximize the electrophilicity of the metal center in these systems and thus increase reactivity.
Additionally, studies of other ligand systems, including bidentate O,N donors and chiral chelating
bis-amide ligands are being pursued.
Kansas State University
Manhattan, KS 66506
Department of Chemistry
Homogeneous Models of Ammoxidation Catalysis
| Investigator(s) |
Maatta, E.
|
$121,587 |
| Phone | 913-532-6687 |
| E-mail |
eam@ksu.ksu.edu |
We continue to exploit the discoveries of simple and efficient routes to a wide variety of
organoimido-substituted derivatives of the hexamolybdate cluster,
[Mo6O19]2-. Since the hexamolybdate displays
an MoO6 coordination environment conspicuously similar to that within the
ammoxidation catalyst component MoO3, attention has focused on the
preparation of benzyl- and allylimido-hexamolybdates, which would represent the closest
approximation yet available of purported ammoxidation surface species. Reaction of the
hexamolybdate with the benzylimido delivery reagent
Ph3P=NCH2Ph in acetonitrile in fact yields benzonitrile in 37%
yield, presumably through the intermediacy of the benzylimido hexamolybdate
[Mo6O18(NCH2Ph)]2-, thus
providing the first example of a functional ammoxidation mimic. This reaction also produces a
substantial amount (34%) of PhCH=NCH2Ph; this product derives from reaction
of benzyl amine, which itself arises as a result of unwanted hydrolysis of the benzylimido ligand.
The intermediates in this ammoxidation mimicry are being sought and attempts are underway to
transfer this chemistry into solvents which can be dried more efficiently.
Lehigh University
Bethlehem, PA 18015
Department of Chemical Engineering
Molecular Structures and Reactivity of Mixed Metal Oxide Monolayer Catalysts
| Investigator(s) |
Wachs, I.E.
|
$183,000 |
| Phone | 610-758-4274 |
| E-mail |
iew0@Lehigh.EDU |
Metal oxide monolayer catalysts, supported metal oxide catalysts possessing the active metal
oxide components as a surface phase, find extensive applications in the energy industries of
petroleum refining, pollution control from power generation plants, and automotive pollution
control. To help bridge the knowledge gap between model and industrial metal oxide monolayer
catalysts, a fundamental research program will address the relationships between the molecular
structures and surface acidity and the molecular structures and surface redox chemistry of mixed
metal oxide monolayer catalysts. For the fundamental surface acidity portion of the research
program the alumina-supported tungsten oxide system will be the focus of the investigation, and
for the fundamental surface redox chemistry portion of the research program the
alumina-supported vanadium oxide system will be the focus. The influence of secondary metal
oxides upon the molecular structures and reactivity of these systems will be investigated. The
molecular structures will be primarily determined with in situ Raman spectroscopy, but
complementary structural spectroscopies (solid state nuclear magnetic resonance (NMR) and
extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure
(XANES)) will also be applied. The surface chemistry will be probed by surface acidity and
surface redox measurements. This fundamental information should allow better understanding of
the synergistic interactions that occur in mixed surface metal oxides.
Lehigh University
Bethlehem, PA 18015
Department of Chemistry
Mechanisms and Controlling Characteristics of the Catalytic Oxidation of Methane
| Investigator(s) |
Klier, K.; Simmons, G.W.; Herman, R.G.
|
$122,000 |
| Phone | 610-758-3577 |
| E-mail |
kk04@Lehigh.EDU |
The general objectives addressed in this research are: the mode of methane activation on metals,
the structure-sensitivity of the C-H bond activation, the nature of surface species originating from
methane, oxygen, and dopants, the relationship between surface structure and dynamics of
elementary catalytic steps, and the controlling characteristics of partial oxidation of methane.
Palladium is the metal of choice because of its ability to activate methane at relatively low
temperatures and a weak Pd-O surface bond. Methane was found to dissociatively chemisorb on Pd surfaces
at <400K with an observed structure sensitivity of Pd(679) > Pd(311) > Pd(111).
New fundamental methodology involving angle-resolved X-ray photoelectron spectroscopy
(ARXPS), surface core level shifts, and X-ray photoelectron diffraction (XPD) at high energy
resolution and valence band (VB) spectroscopy has also been developed. It was shown from XPD
behavior of O/Pd surface core level shifts that O induced Pd surface states to exponentially decay
to 5 subsurface layers. The resultant model of angular dependence in the photoelectron intensity
attenuation has been extended to other overlayer systems (i.e. CO, S, Cl, and NO on Pd[100]), as
well as to studies of the initial state atomic orbital character of trigonal prismatic layered
MoS2. Upon doping the MoS2(0002) surface with Cs, no
Cs-induced surface relaxation was observed, but a new photoemission peak 1.6 eV above the VB
edge of MoS2 was observed corresponding to an electron donor-acceptor surface
complex (J. Phys. Chem. 1996, 100, 10739;
http://acsinfo.acs.org/plweb/journals/jpchax/100/i25/abs/jp9605865.html). Hartree-Fock and
density functional theory calculations are being performed on model Pd surfaces to better
understand the Pd-adsorbate bonding interactions. Computational efforts to elucidate the
electronic structure of MoS2 and Cs/MoS2 are also in progress.
Louisiana State University
Baton Rouge, LA 70803
Department of Chemistry
Polynuclear Aromatic Hydrocarbons with Curved Surfaces: Models and Precursors for
Fullerenes
The remarkable discovery that buckminsterfullerene or "buckyball,"
C60, is a stable molecule has led to a flood of research focused on this new family
of three-dimensional carbon cages known as fullerenes. These unique structures can be produced
by laser vaporization of graphite or coal. Metal derivatives show promise as superconductors.
This program deals with the synthesis, structural analysis, and chemistry of polynuclear
hydrocarbons with carbon frameworks represented on the buckminsterfullerene surface
("buckyball" fragments referred to as "buckybowls"). These curved-surface hydrocarbons are
expected to serve as models for the fullerenes in some of their chemical and physical properties.
The simplest example of such a hydrocarbon is corannulene,
C20H10, which represents the polar cap of buckminsterfullerene.
However, corannulene undergoes rapid bowl-to-bowl inversion that may lessen its utility as a
fullerene model. Consequently, a goal of this program was to produce a "locked"
bowl-shaped hydrocarbon; this was accomplished by the addition of a second five-membered ring
to corannulene to afford cyclopentacorannulene. More recently, this program produced the first
semibuckminsterfullerenes (C30H12) representing half of the
C60 surface. In theory, the C30H12 with 3-fold
symmetry might be dimerized to produce buckminsterfullerene itself, and this exciting reaction is
being explored. The synthesis of additional fullerene related hydrocarbons is a current goal of the
program.
University of Louisville
Louisville, KY 40292
Department of Chemistry
Metallocarboxylate Chemistry
Compounds having a carbon dioxide ligand bound to a metal center are models for surface-bound
CO2 in catalytic processes. Our work is centered on the synthesis and
characterization of such compounds, especially those with carbon dioxide bridged between two
metal centers. In the present period, new compounds of the symmetric
µ2-3 type have been structurally characterized; these, together with
others of the same type, allow correlation of the IR 
asym band of the ligated CO2 to be made with the
coordination geometry of the metal center which binds the carboxyl oxygens. The sym band varies only slightly
with changes in the metallocarboxylate. New synthetic routes have been established for
compounds having the carboxyl oxygens bound to zirconium by using transmetalation reactions of
related tin complexes. A further new direction involves the synthesis and chemistry of ruthenium
complexes with chelating nitrogen ligands (bipyridyl, terpyridyl, etc.) that also bear
C1 ligands; such compounds are little-known but are implicated as intermediates
in reductions of CO2 catalyzed by ruthenium complexes. Thus, the reaction of
Ru(bpy)2(CO)(CHO)+ PF6- with
water in the presence of oxygen leads to the corresponding µ2-2 CO2-bridged
complex; furthermore, the reaction can be photoassisted.
University of Maryland at College Park
College Park, MD 20742
Department of Chemistry and Biochemistry
Odd-Electron Organometallic Chemistry of Relevance to Hydrocarbon Functionalization
Investigations of transition metal hydride complexes that are potential precursors to highly
unsaturated odd-electron organometallics has continued. The structure of
Cp*MoH3(dppe) has revealed an unexpected and unprecedented
pseudo-trigonal prismatic geometry, while a product of protonation,
[Cp*MoH(MeCN)2(dppe)]2+ shows the expected
pseudo-octahedral structure. These studies, as well as a structural study on
CpMoH3(PMe2Ph)2 and parallel theoretical
investigations, have allowed a better understanding of the mechanism of hydride fluxionality in
these trihydride complexes of Mo(IV). The electrochemical oxidation of
Cp*MoH3(dppe) affords the EPR active 17-electron
[Cp*MoH3(dppe)]+, which decomposes over
several hours at room temperature. The decomposition involves reductive elimination of
H2 and trapping by a donor solvent to afford a stable
[Cp*MoH(S)(dppe)]+ radical, which has been isolated and is
currently being characterized. The radical can be reversible deprotonated by a number of bases.
The deprotonated radical, presumably
[Cp*Mo(S)2(dppe)]+, has also been isolated. The
decomposition of [Cp*MoH3(dppe)]+ using
nondonor solvents, which presents the potential of generating highly reactive 15-electron
[Cp*MoH(dppe)]+ or Cp*Mo(dppe) species, will
be a subject of future investigation. The generation of such intermediates in the presence of
substrates whose C-H and C-C bonds can be selectively activated will be a particular focus of
our research. Further knowledge has been gained on the role of external bases
for the mechanism and stoichiometry of oxidation/deprotonation of transition metal hydrides. The
ubiquitous external base for bulk electrochemical oxidations of hydride complexes is water.
Investigation of oxidations of CpMoH(L)(CO)2 (L =
PMe3 or PPh3) and
CpMoH(PMe3)3 in the presence or absence of water has
revealed: (i) the action of the base as a "proton shuttle", featuring proton capture
from the 17-electron hydride cation and later delivery to the 18-electron hydride precursor,
followed by irreversible elimination of H2; (ii) formation, isolation, and
crystallographic characterization of a Mo(III) hydroxo complex,
[CpMo(OH)(PMe3)3]+ and a Mo(IV) oxo
complex, [CpMo(O)(PMe3)2]+.
Massachusetts Institute of Technology
Cambridge, MA 02139
Department of Chemistry
High-Pressure Heterogeneous Catalysis in a Low-Pressure, Ultrahigh Vacuum
Environment
| Investigator(s) |
Ceyer, S.T.
|
$109,000 |
| Phone | 617-253-4537 |
| E-mail |
StCeyer@mit.edu |
The major thrust of this project is to carry out high-pressure, heterogeneous catalytic reactions in
a low-pressure, ultrahigh vacuum environment. These studies have now become possible because
of the culmination of several investigations in the laboratory over the last five years resulting in
the development of new physical processes and techniques: collision-induced absorption;
collision-induced recombinative desorption; bulk vibrational spectroscopy; and the synthesis of
adsorbed, reactive intermediates by translational and collision-induced activation. These new
processes allow the simulation of a high-pressure environment while maintaining the
single-collision conditions in which microscopic reaction steps and intermediates can be elucidated
and detected by molecular beam scattering coupled with high-resolution electron energy loss
spectroscopy. Results to date show that bulk H is the reactive species in the high pressure
reaction involving the hydrogenation of C2H4.
Massachusetts Institute of Technology
Cambridge, MA 02139
Department of Chemistry
Controlled Synthesis of Polyenes by Catalytic Methods
| Investigator(s) |
Schrock, R.R.
|
$130,000 |
| Phone | 617-253-1596 |
| E-mail |
RRS@MIT.EDU |
A way has been found to synthesize totally new polyenes in a controlled living fashion from
dipropargyl derivatives employing well-characterized alkylidene complexes of the type
M(CHCMe2R)(NAr)(OR')2 (M = Mo or W, R = Me or Ph, Ar =
2, 6 diisopropylphenyl, R' = OCMe3,
OCMe2(CF3), OCMe(CF3)2, or
various phenoxides) as catalysts. Dipropargyl derivatives of the type HC
CCH2XCH2CCH (X = NR, O,
C(CO2R)2, SiMe2, and so forth) are
cyclopolymerized to give soluble polyenes that contain either six-membered rings (head-to-tail
cyclopolymerization) or five-membered rings (tail-to-tail cyclopolymerization). The reaction can
be controlled by varying the solvent and the type of catalyst so that "dangling"chains
resulting from simple insertion of one of the propargyl groups are absent. Addition of one of the
acetylene bonds to an alkylidene to yield a new disubstituted alkylidene normally would essentially
terminate polymerization, since the disubstituted alkylidene would not react readily with more
terminal acetylene. This problem is avoided by the speed of the intramolecular cyclization reaction
to give a five-membered ring and a new monosubstituted alkylidene. This new polymerization
reaction will lead to a large number of new materials since the conditions of polymerization are
relatively mild (versus Ziegler-Natta conditions) and many functionalities therefore tolerated. In
addition to investigating the scope and details of this new controlled cyclopolymerization reaction,
the properties (nonlinear, conductivity, electrochemical, and so forth) of these new materials as a
function of chain length will be studied, a fundamental question that remains largely unresolved in
the area of unsaturated polymers (polyanilines, polythiophenes, polyparaphenylene, and so forth).
It seems possible that, owing to the control excercised in their preparation, a wide variety of new materials will become available that may rival the
more established unsaturated polymers in applications, as well as in fundamental research.
A catalyst has now been prepared that
cyclopolymerizes dipropargyl diethylmalonate to only six-membered rings, and another that
polymerizes o- trimethylsilyphenylacetylene in a living manner to give low polydispersity polyenes
that contain between 10 and 100 double bonds. Nonlinear optical measurements on both types of
polymers are being carried out in order to correlate 
and with chain
length and structure.
University of Massachusetts at Amherst
Amherst, MA 01003
Department of Chemical Engineering
Zeolite Characterization and Dynamics: The Effect on Molecular Transport and Catalyst
Selectivity
| Investigator(s) |
Conner, W.C.; Laurence, R.L.; Ragle, J.L.
|
$92,000 |
| Phone | 413-545-0316 |
| E-mail |
wconner@ecs.umass.edu |
Zeolitic materials are most often crystalline alumina-silicates with microporosity (less than
20Å) created by interconnected ring-like structures. These channels give sorbing molecules
access to the intraparticle surface where chemisorption and reactions occur. Since the channels
within the lattice are similar in size to sorbing molecules, the term "configurational
diffusion" has been used to describe intraparticle transport. The limited size of the
products for the reactions of hydrocarbons, selective sorption, and selectivity in isomerization and
trans-alkylation reactions have been ascribed to this "shape selectivity." This research
focuses on three related aspects of zeolites: the mutual interactions between adsorbing molecules
and the zeolite lattice, the nature of the pore structure of the zeolite characterized during
adsorption, and the influence of extreme steric constraints on cracking and isomerization reactions
for cycloalkanes. Earliest perceptions of the pore structure within a zeolite have depended on the
visualization of the Si(Al)-oxygen crystalline bond network. This representation and analysis
depends upon an image of a fixed pore configuration based primarily upon X-ray diffraction
(XRD) studies of the solid structure. Recent studies employing solids nuclear magnetic resonance
(NMR) and in situ XRD have documented that the shape of the adsorbing pores can change on
adsorption. More recently, detailed spectroscopic studies of adsorption and of adsorbing
molecules have begun to provide a picture of the pore structure and the sorbing species during
sorption. In situ infrared spectrometry (specifically far-FTIR) and thermal or gravimetric analyses
(DTA and TGA) can also be employed to understand the dynamic configurational changes in the
sorbing species and the energetics of these interactions. Several of these techniques have been
developed, and each will be used in concert to understand the effects of the interactions between
adsorbing molecules, their transport, and their reactivity. Specifically, 29Si,
129Xe, and 15N NMR will be employed in conjunction with high
resolution adsorption, HRADS, with DTA-TGA, and with FTIR for the initial studies of the
adsorption of C6 and C7 cycloalkanes within ten- and twelve-member ring zeolites. In addition,
the rate of adsorption/diffusion will be quantified by solids-gas chromatography (SGC). The
cracking and isomerization reaction of these cycloalkanes will be studied to understand the
symbiotic relationship between dynamic pore/adsorbate interactions and the resultant reactions of
these cycloalkanes.
University of Memphis
Memphis, TN 38152
Department of Chemistry
Towards Computer Aided Catalyst Design: Three Effective Core Potential Studies of C-H
Activation
We have focused on methane activation. Study of this reaction also provides the impetus for improved
modeling of inorganic systems. Research has focused primarily on methane activation by transition
metal (TM) imidos (L n M=NZ), and mercury complexes. Since hydrocarbons other
than methane are present in natural gas, a conversion catalyst must operate in a
multisubstrate environment. To complement experiments by Wolczanski, we studied CH
activation of hydrocarbons larger than methane by Zr-imidos. This work provides new insight into
substrate effects in CH activation allowing us to address questions relevant to selectivity. A
major question of interest in catalysis involves modifying a complex to make it more active.
Previous work has focused on the role of metal and ancillary ligands in methane activation. Our
most recent research indicates it is difficult to tailor imido reactivity through electronic
modification of imido substituents (Z), because most substituents studied are found to exert
their influence primarily through inductive effects localized on the sigma framework. This
suggests several profitable areas to be pursued. Hg(II) and complexes of related electrophilic, late
TMs have attracted much experimental interest. A main impediment to their development is lack
of an intimate understanding of the CH activation mechanism. Our objective is to study how
prototypical hard and soft anionic ligands control the kinetics and thermodynamics of methane
activation by Hg(II) complexes. The great sensitivity shown by these systems to ligand
modification suggests that these ligands can be modified to effect lower CH activation barriers. This
research suggests several logical extensions to greater activity including replacing mercury with
related metals and going to cationic complexes.
University of Michigan
Ann Arbor, MI 48109
Department of Chemistry
The Role of Hydrogen in C-N, C-C, and C-S bond activation on Ni and Pt surfaces
C-N, C-C, and C-S bond activation reactions play an important role in catalytic processes used in
both the fuels and chemical industries. We are examining the role of hydrogen in bond activation
reactions on Ni and Pt surfaces in order to establish a basic understanding of the primary factors
which control bond activation. The primary methods include spectroscopic characterization of
adsorbed intermediates using a combination of surface spectroscopies and transient kinetic studies
of stoichiometric surface reactions. Over the year we have focused our research primarily on
developing a fundamental information regarding two reaction systems on nickel. Phenylthiolate is
the dominant intermediate independent of hydrogen availability during C-S bond activation in
phenylthiol. Hydrogen appears to be directly involved in C-S bond activation on Ni. For C-S bond
activation, tilted orientations of the adsorbed phenylthiolate intermediates appear to be most
favorable for hydrogenolysis. Adsorption in perpendicular or nearly perpendicular orientations
limits bond activation as well as interactions with the attached phenyl group. Coadsorbed
hydrogen does not activate C-C bonds in small hydrocarbons. However, we have found that
energetic forms of hydrogen activate strained C-C bonds in cyclic hydrocarbons at low
temperature. After initial atomic hydrogen addition from the gas phase to form an adsorbed alkyl
group, coadsorbed hydrogen adds to form the alkane. Efforts to activate C-C bonds in unstrained
ring systems like cyclohexane, cyclohexene, and toluene were unsuccessful suggesting that even
these reactions are kinetically controlled on the surface. These studies establish a method of
probing hydrogen induced C-C bond activation and also provide a new approach for preparing
adsorbed alkyl species on Ni. In summary, over the past year we have developed substantial new
understanding of the role of hydrogen in C-S and C-C bond activation reactions on Ni.
University of Minnesota
Minneapolis, MN 55455
Department of Chemical Engineering and Materials Science
Homogeneous--Heterogeneous Combustion: Chemical and Thermal Coupling
The roles of homogeneous and heterogeneous reactions in catalytic oxidation processes are being
studied experimentally and theoretically by measuring rates and concentration and temperature
profiles near reacting surfaces and by calculating these profiles for known kinetics. Laser-induced
fluorescence methods are being developed to measure the concentrations of free-radical
intermediates near reacting surfaces for several combustion reactions on polycrystalline platinum
and rhodium as functions of surface temperatures and reactant composition, pressure, and
temperature. Concentrations of stable and radical intermediates with and without homogeneous
reaction will be measured directly. Concentration and temperature profiles are also being
calculated for various reaction processes and flow conditions. Of particular interest is the
occurrence of multiple steady states and oscillations for various models of
homogeneous-heterogeneous processes. Reaction rate expressions for individual surface and
homogeneous reactions are used to simulate the experimentally observed behavior. Particular
interest centers on the selectivity of partial oxidation reaction such as production of CO and
hydrogen from methane oxidation, olefins by oxidative dehydrogenation of alkanes, and
oxygenates by oxygen addition to alkanes. The objective of this research is to understand the
contributions of each type of reaction in practical situations in catalytic reactors and combustors
in order to determine their implications in reactor selectivity for chemical synthesis and for
pollution abatement.
University of Missouri at Columbia
Columbia, MO 65211
Department of Chemistry
Late Transition Metal Oxo and Imido Complexes
This project involves the exploration of the chemistry of late-transition metal oxygen and nitrogen
bonds and is of relevance to catalytic processes in chemical manufacturing and pollution control.
Recent highlights include the chemical and structural characterization of the only model for the
binding of dinitrogen inside the nitrogenase Mo/Fe cluster, the synthesis and characterization of a
dioxo centered M/Au (M = Rh, Ir) clusters with square pyramidal coordination geometry about
oxygen stabilized by Au-Au and Au-M bonds, and the synthesis and characterization of
unexpectedly stable dppm and dppm-H imido complexes. The nitrogenase model complex is our
previously synthesized gold complex
[(LAu)3N2(AuL)3]2+ (L =
PPh3). Our recently completed structural characterization of this complex reveals
that it contains a dinitrogen unit inside a cluster of six Au atoms. Each nitrogen atom is bonded to
three metal atoms as has been proposed by Rees and others for the bonding of dinitrogen inside
the Mo/Fe cluster of nitrogenase. Reduction of
[(LAu)3N2(AuL)3]2+ in the
presence of a proton source produces ammonia indicating that
[(LAu)3N2(AuL)3]2+
structurally and chemically models nitrogenase. The dioxo clusters
[(COD)2M2(O)2(AuL)4]2+ (M = Rh, Ir; L = PPh3) were prepared by the reaction of
[(LAu)3(O)]+ and [(COD)MCl]2 and contain oxygen atoms in an
usual square pyramidal coordination geometry. These clusters are related to a class of complexes
containing all-gold metal atoms which are stabilized by "aurophilic" Au-Au bonds.
Our dioxo clusters contain not only stabilizing Au-Au bonds but also stabilizing Au-M bonds
indicating the likely existence of a new class of complexes related to the all-gold complexes.
Finally, we have succeeded in expanding our previously reported dimeric Pt oxo complexes
[L4Pt2(O)2] (L = a phosphine) to the analogous
imido complexes. However, while the oxo complexes were prepared for a large variety of
phosphine ligands the only effective phosphine for the imido complexes is dppm and dppm-H.
This unique ability of the dppm and dppm-H ligand to stabilize the imido complexes is not
understood at this time.
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599
Department of Chemistry
Mechanistic Studies of Transition Metal-Catalyzed Alternating Copolymerizations of Carbon
Monoxide with Olefins
| Investigator(s) |
Brookhart, M.
|
$105,000 |
| Phone | 919-962-0362 |
| E-mail |
caulder@unc.edu |
Polyketones are a significant new class of polymers prepared from alternating copolymerization of
CO and olefins. The basic objective of the program is to elucidate the fundamental mechanisms of
these copolymerization reactions catalyzed by Pd(II) and Ni(II) species. Well-defined Pd(II)
catalysts of the type (N-N)PdCH3(solv)+
BAr'4- (N-N = bipyridine, phenanthroline; Ar' =
3,5-(CF3)2-C6H3-) have been
prepared. A highly detailed mechanism of copolymerization of ethylene and CO has recently been
reported (J. Am. Chem. Soc. 1996, 118, 4746-4764). All potential intermediates in the catalytic
cycle have been independently generated including the alkyl ethylene complexes (N-N)Pd(C[sub
2}H4)R+, alkyl carbonyl complexes
(N-N)Pd(CO)R+, acyl carbonyl complexes (N-N)Pd(CO)COR+,
acyl ethylene complexes (N-N)Pd(C2H4)COR+
and chelate complexes (N-N)PdCH2CH2COR+
and (N-N)PdC(O)CH2CH2COR+. Migratory
insertion rates for all carbonyl and olefin complexes have been measured as well as relative
binding affinities of ethylene and CO to key species. This kinetic and thermodynamic data has
been combined to provide a detailed picture of the mechanism of copolymerization and which
intermediates are of significance in the catalytic cycle. The data obtained accurately predicts the
observed turnover frequency and the observed kinetic dependence (first-order in ethylene, inverse
order in CO). Work has continued on the development of chiral bis-oxazoline-based Pd(II)
catalysts for synthesis of isotactic, optically active polyketones based on styrenic monomers.
Unique ligand exchange processes have been developed which provide a new method of synthesis
of stereoblock polyketones and a deeper understanding of chain-end versus enantiomorphic site
control of polymer microstructure. A fundamental study of substituent effects on migratory
insertion rates in a series of substituted styrene complexes
(phenantroline)Pd(CH3)(CH2 =
CHC6H4X)+ (X = H, CF3, Cl,
CH3, OCH3) has been completed (J. Am. Chem. Soc. 1996,
118, 2436-2448). These studies clearly show that ground state energies are more sensitive to
substituent variation than transition state energies and electron-donating substituents stabilize the
ground state and thus retard the overall rate of migratory insertion. Work is in progress on the
complete mechanistic analysis of copolymerizations catalyzed by bidentate phosphine-based
systems and the development of new bidentate ligands for use with both Pd(II) and Ni(II)
systems.
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599
Department of Chemistry
Reductive Coupling of Carbon Monoxide to C2 Products
| Investigator(s) |
Templeton, J.L.
|
$98,350 |
| Phone | 919-966-4575 |
| E-mail |
joetemp@unc.edu |
A variety of synthetic routes to tungsten nitrene complexes have been developed. Nitrene transfer
from cationic tungsten nitrene monomers to trimethylphosphine has been achieved, and a copper
catalyst for nitrene transfer from PhINTs to olefins has been prepared. These results are
encouraging for developing systems that will transfer the neutral nitrene NR fragment to
electron-rich olefins to form aziridines. Another result in M-N-C chemistry is the selective
regiochemistry for electrophile addition to W=N-CR2 units. With an ancillary
alkyne ligand in the coordination sphere, a coordinated imine ligand forms
(M-NH=CR2+). The regioselectivity of proton addition is
reversed when the nitrogen lone pair is involved in a simple 2-center-2-electron bond as
protonation then occurs at carbon to form a nitrene ligand
(M=N-CHR2+). The Tp'(CO)2W fragment avidly
seeks three electrons, and the stability of six-coordinate monomers incorporating a three-electron
donor into the sixth site has allowed us to isolate analogous N, NH+, and CH
complexes. In addition to the CH carbyne complex, alkyl carbyne derivatives
Tp'(CO)2WCCH2CH2R and their vinyl and allyl
isomers have been prepared. By combining complementary carbyne reagents,
Tp'(CO)2MoCCl and deprotonated
Tp'(CO)2WCCH3, dimers containing the CCH2C
linkage can be synthesized. These dimers are susceptible to deprotonation and oxidation to form
simple CCC bridged dinuclear products.
Northwestern University
Evanston, IL 60208
Department of Chemical Engineering
Solid-State, Surface, and Catalytic Studies of Oxides
| Investigator(s) |
Kung, H.H.
|
$138,000 |
| Phone | 847-491-7492 |
| E-mail |
hkung@nwu.edu |
Multicomponent oxides are catalysts for a number of technologically important reactions,
including the selective conversion of low-priced saturated hydrocarbons by oxidation (selective
oxidation) to unsaturated hydrocarbons, aromatics, alcohols, aldehydes, or acids that are of much
higher value, and for the removal of nitorgen oxides, which is an atmospheric pollutant from
exhausts of lean-burn, gasoline engines (lean NOx conversion). The emphasis of
this project is to identify the properties of oxidic catalysts that determine their catalytic properties
in these reactions. In selective oxidation, it was found that modification of a silica-supported
vanadium oxide catalysts with phosphorus resulted in significant increases in the selectivity for the
formation of maleic anhydride. Spectroscopic characterization of the samples suggested that the
high selectivity could be correlated with the formation of a phosphorus-vanadium oxide
compound. Indeed, impregnation of a solution of this compound onto a silica support produced a
catalyst of high selectivity close to a commercial sample. The vanadium ions in this sample were in
a lower average oxidation state than for the less selective samples. In lean NOx
reduction, it was found that effective catalysts contained transition metal oxides highly dispersed
in an inert matrix. The desired catalytic properties could be correlated with the inability of the
catalyst to activate oxygen rapidly. Thus, alumina-supported Au and Ag catalysts could also be
made effective for NOx reduction when the crystallite size of Au or Ag particles
was such that the sample did not activate oxygen rapidly.
Northwestern University
Evanston, IL 60208
Department of Chemistry
Organometallic Adsorbates and Models Chemistry, Spectroscopy, and Catalysis
| Investigator(s) |
Marks, T.J.
|
$106,400 |
| Phone | 847-491-5658 |
| E-mail |
t-marks@nwu.edu |
The project goal is to characterize chemisorptive processes responsible for dramatic
enhancements in catalytic activity when actinide, lanthanide, and early transition element
organometallic complexes are adsorbed on Lewis acidic surfaces. Surface reaction chemistry is
studied by chemical and spectroscopic techniques, while catalytic properties (e.g., olefin
hydrogenation) are characterized by kinetic measurements, isotopic labeling, product
stereochemistry, and spectroscopy. On Lewis acid supports,
Cp2MR2 complexes (Cp = cyclopentadienyl-type ligand; M = Th,
U, Zr; R = alkyl group) undergo R- abstraction to yield electrophiles, highly
electrophilic Cp2MR+ species, which are shown to be active
catalytic centers by CPMAS NMR spectroscopy. Importantly, these species can be
spectroscopically, structurally, and functionally modeled in solution by isolable
Cp2MR+ X- complexes, where X-
is a weakly coordinating fluroarylborate anion. The chemisorptive process as well as the pathway
by which methylalumoxane, "[Al(CH3O]n" activates
organo-group 4 complexes for industrial scale olefin polymerization processes can be modeled
using fluroarylborane organo-Lewis acids as abstraction reagents. Finally, these catalysts can be
employed to produce completely new types of functionalized polyolefins via a ring-opening
processes in which exo-methylene substituted cycloalkanes open to yield exo-methylene
substituted polyethylenes.
Northwestern University
Evanston, IL 60208
Department of Chemistry
Chemical Interactions in Multimetal-Zeolite Catalysts
| Investigator(s) |
Sachtler, W.M.H.; Ipatieff, V.N.
|
$110,500 |
| Phone | 847-491-5263 |
| E-mail |
wmhs@nwu.edu |
The problem of changing the selectivity of Rh catalysts in CO hydrogenation from hydrocarbon
production to synthesis of oxygenates by "promoting" the catalyst with manganese
has been addressed. By using zeolite supported samples, it was possible to synthesize samples
with identical Rh content but with the manganese being present either as Mn2+
ions or as MnO particles. In the former case, no oxygenates were formed;
in the latter case a high yield of ethanol and ethyl acetate was obtained, suggesting that
acetate ions are primary products. Subsequent catalyst characterization revealed that MnO and Rh
clusters are located inside zeolite cavities and in direct physical contact with each other.
Research towards zeolite supported acids, such as sulfated
ZrO2, has been initiated.
Northwestern University
Evanston, IL 60208
Department of Chemistry
Organometallic and Surface Chemistry of Mixed-Metal Systems
Our research focuses on the reactions of ligands attached to clusters and the relation of these
reactions to reactions on metal surfaces. Because of their importance in surface chemistry and
catalysis, most of this research concerns carbonyl, sulfur dioxide, oxo, sulfido, carbido, and
hydrido ligands and their derivatives. We have demonstrated that bridging CO in clusters can be
attached by electrophiles and subsequently converted to C, CCO, C2, and
C4 ligands in polymetal clusters. Similarly, the attack of nucleophiles on
SO2 bound to metal clusters and the conversion of coordinated
SO2 to coordinated S or SO was demonstrated. We are currently studying the
relative reactivities of bridging CO and SO2 ligands and extending vibrational
spectroscopic characterization of the products. The latter information is relevant to the
identification of ligands on metal surfaces. Recent studies center on the reaction of the
SO2 analog OSNPh with either Ru3(CO)12 or
Ru3(CO)10(NCCH3)2. Products
from these reactions include
Ru3(CO)9(µ3-NPh),
(µ3-S), Ru4, 2SnPh)(µ4-S) and
Ru4(CO)11(µ4, 2-SNPh)(µ4-NPh), which have been
structurally and spectroscopically characterized.
University of Oklahoma
Norman, OK 73019
Department of Chemistry and Biochemistry
Transition Metal-Mediated Thermal and Photochemical Carbon Dioxide Activation
The overall goals of this project are to elucidate the patterns of reactivity, both thermal and
photochemical, of coordinated CO2 and to develop catalytic processes based on
these patterns. Activities during the past year have been focused in two areas: 1) attempts to
produce the first cis, bis- CO2 complex as a potential precursor to oxalate
derivatives via C-C bond formation and 2) exploratory studies of transition metal-mediated
insertion of CO2 into C-C and C-H bonds. Regarding (1) we have sought to
prepare cis-(tetraphos)Mo(CO2)2. In several experiments an
unstable compound (IR: 1700, 1620 cm-1), believed to be the desired
CO2 adduct has been isolated, but we have been unable to obtain it in pure form.
Towards (2) we have initiated CO2 reactivity studies of a metallacyclobutane
complexes [LnM= L2Cl2Pt,
L2Ni, Cp*Rh(PMe3)], derivable from cyclopropanes, to model
prospective systems for catalytic cyclopropane carboxylation. While several Pt(IV) derivatives
failed to react with CO2, insertion has been observed with some of the Ni- and
Rh- derivatives; characterization and reactivity studies of the resulting metallalactone complexes
are underway. We are also investigating the possibility of CO2 trapping of
reactive metallacycles generated in metal-catalyzed isomerization of strained hydrocarbons, e.g.
quadricyclane 
norbornadiene. We have also been examining the interaction of CO2 with several
systems known to activate C-H bonds (e.g. Rh(I), Mo(O), Cu(I), and Ru(O) complexes) with the
potential for effecting hydrocarbon carboxylation. Finally, our study of the reactivity and
mechanism of the thermal decarbonylation of a set of
Cp'2Nb(CO2)R complexes, the first systematic reactivity study of
a set of related CO2 complexes, has been published.
Pennsylvania State University, University Park
University Park, PA 16802
Department of Chemical Engineering
Activity and Selectivity Enhancements in Liquid-Phase Reactions by Metal-Support
Interactions
The project objectives are to study metal-support interactions that have a pronounced influence
on adsorption and catalytic behavior and to use these effects to alter hydrogenation reactions such
as those involved in fine chemicals production. In addition to determining kinetic behavior,
emphasis is on characterizing adsorbed molecules as well as the chemical and physical state of the
metal and support. Benzaldehyde hydrogenation on Pt/TiO2 was found to have
turnover frequencies 10-100 times greater than those on Pt/SiO2 and
Pt/Al2O3 while benzyl alcohol hydrogenation was inhibited. This
resulted in a 100% selectivity to the desired intermediate -- benzyl alcohol -- up to conversions
above 80%. Special sites formed at the Pt-TiO2 interface are proposed to explain
this behavior. As a test of this hypothesis, TiO2 was placed on the surface of
UHP Pt powder and the improvements in activity and selectivity were replicated. A reaction
model was proposed which fit the kinetic data well. Turnover frequencies for phenylacetaldehyde
hydrogenation were measured and again the most active Pt/TiO2 catalyst gave
values 2-5 times higher than typical supported Pt catalysts. At conversions up to 60%, this
catalyst also gave the highest selectivity to phenylethanol (70%) compared to 0-30% for the other
Pt catalysts. A study of the hydrogenation of benzene/toluene mixtures over supported Pd showed
that the ratio of rates in an equimolar mixture, RTol/RBz, was
consistently near 0.65 and thus favored benzene. This ratio was essentially independent of
support, pretreatment temperature, or reaction temperature. A detailed kinetic analysis revealed
that previous interpretations of rate parameters were inappropriate and an improved reaction
model was proposed. A new high-pressure reactor system has now been constructed to allow the
study of liquid-phase hydrogenation reactions. Reactants to be initially examined include an
organic acid, an aromatic hydrocarbon, and a conjugated aldehyde. Acetic acid adsorbed on Pt
and TiOx-covered Pt surfaces is concurrently being studied by HREELS, XPS,
AES and TPD.
Pennsylvania State University, University Park
University Park, PA 16802
Department of Chemistry
Transition-Metal-Mediated Transformations of Small Molecules
Catalytic transformations by transition metals and their compounds is of fundamental scientific, as
well as practical, importance because of the high efficiency, high specificity, and low energy
demands usually associated with such systems. The current research is focused on transition metal
catalyzed polymerizations. The study specifically encompasses homogeneous metal catalyzed
systems for the synthesis of several different kinds of copolymers incorporating the carbonyl
functionality in the backbone. The carbonyl functionality is derived form carbon monoxide, an
inexpensive monomer. Such polymers are of great current interest because of their
photodegradability and because they are precursors to a wide range of functionalized polymers.
The principal research goals are: (a) the design of living copolymerization systems that would
allow the directed synthesis of block terpolymers involving the copolymerization of two different
olefins with carbon monoxide, as well as block polymers incorporating polyolefin and
olefin-carbon monoxide blocks, (b) the synthesis of regiospecific, stereospecific and, ultimately,
chiral alternating olefin-carbon monoxide copolymers using appropriate catalysts, (c) the synthesis
of star, comb, and graft polymers with alternating olefin-carbon monoxide segments, (d) the
synthesis of alternating copolymers of functionalized olefins with carbon monoxide, and finally (e)
the direct synthesis of polycarbonates and polyoxalates from carbon monoxide and diols.
Pennsylvania State University, University Park
University Park, PA 16802
Intercollege Materials Research Laboratory
Carbon Deposition and Deactivation of Metallic Catalysts
The overall objective of this program is to achieve conditions where it is possible to control the
catalytic properties of a given metal by inducing geometric and electronic perturbations to the
reactive surfaces of the crystallites. One of the consequences of such an action would be to enable
one to alter the catalytic reactivity in such a manner so as to optimize the performance for a
desired reaction pathway, while simultaneously suppressing the rate of detrimental side reactions,
such as certain forms of carbon deposition. Our strategy has centered around a study of the effect
of introducing selected adatoms into the host metal and using the decomposition of ethylene to
probe the manner by which the chemistry of the various faces of the crystallites is modified. It is
well known that iron, cobalt and nickel undergo rapid deactivation when heated in hydrocarbon
environments at temperatures in excess of 500°C, and this is believed to be due to the
formation of graphite overlayers. In the current program we are endeavoring to prevent premature
catalyst deactivation by forcing the carbon species to follow an alternative route. Instead of
accumulating on the metal surfaces where reactant molecules undergo dissociative chemisorption,
the carbon species are diverted from these faces and following diffusion through the metal
crystallites, eventually precipitate at other faces to form a nanofiber structure. Under such
circumstances the active faces remain relatively clean and available to perform the desired
hydrocarbon conversion reactions. We have demonstrated that this condition can be achieved by
the introduction of a small amount of selected adatoms, including copper, silver or tin, into the
ferromagnetic metal. While the total amount of carbon deposited during reaction was increased
significantly with the bimetallics, the growth features were such that it did not interfere with the
desired reaction and as a consequence, catalytic activity of the particles was maintained for
prolonged periods of time. The modification in the carbon depositing characteristics of the metal
are rationalized according to the notion that the presence of the additive promotes surface atom
reconstruction of particles and also induces electronic perturbations in the catalyst system.
Pennsylvania State University, University Park
University Park, PA 16802
Department of Materials Science and Engineering
Determination of the Distribution of Hydrogen in Coal by Fourier Transform Infrared (FTIR)
Spectroscopy
The purpose of this research is to determine the role of hydrogen-containing functional groups in
coal. Work in the last year has focused predominantly on measuring parameters that describe the
strength and extent of hydrogen bonding interactions using FTIR. By studying model phenolic
systems we have found that intramolecular interactions play a key role. These parameters are then
used in a model that describes coal swelling and its relationship to structure (cross-link density,
etc.) Our previous work has demonstrated that present theories need to be modified to account
for the high degree of cross-linking found in coal and we have developed a new theory based on a
non-Gaussian model in order to address this problem.
University of Pennsylvania
Philadelphia, PA 19104
Department of Chemical Engineering
Support Effects Studied on Model Supported Catalysts
We are studying support effects associated with precious-metal catalysts, with particular
application to automotive emissions control. In automotive catalysis, the oxide support plays an
important role in maintaining oxygen stoichiometry through the use of a reducible oxide(ceria).
We have shown that this appears to occur through an oxygen transfer from the ceria to the
precious metal, which can be observed through TPD experiments with CO (which desorbs as
CO2) and through steady-state CO oxidation measurements, where a second
reaction mechanism is observed. Large crystallites and single crystals of ceria are not able to
transfer oxygen, demonstrating structure sensitivity of the ceria. To study the structure sensitivity,
we are using simulated annealing studies of small ceria clusters and oxygen TPD experiments.
Difficulties associated with growth of ceria crystallites are avoided in real catalysts through the
use of ceria-zirconia mixtures. Therefore, we are also studying the effect of mixed oxides to
determine the way in which stabilization occurs.
University of Pennsylvania
Philadelphia, PA 19104
Department of Chemistry
Inorganic Polymers and Materials
This project is focused on the development of new polymeric-precursor synthetic routes of
technologically important ceramics in processed forms. Current studies are conducted on the
syntheses, properties, ceramic-conversion reactions, and applications of new boron-based
polymers, including polyvinylborazine, polyborazylene, borazine-modified polysilazanes, and both
decaborane and carborane-based polymers. In addition, investigations are being conducted on the use of
these polymers as reagents for the synthesis of a wide range of metal boride, metal nitride, and
metal silicide ceramics. Major achievements of the last year have included the development of
melt-spinnable polymeric precursors to both BN and composite SiNCB ceramic fibers and a new
efficient synthetic route to lanthanum metal boronitride intermetallics, such as the
La3Ni2B2N3 superconductor. The continued development of the
fundamental synthetic methodology needed to produce new inorganic monomers and polymers is
also a key component of this project.
University of Pennsylvania
Philadelphia, PA 19104
Department of Chemistry
Catalytic Hydrogenation of Carbon Monoxide
Central objectives for this program encompass the development of new strategies for conversion
of carbon monoxide and hydrocarbons into organic oxygenates at mild conditions of pressure and
temperature. A primary focus is placed on designing transition metal complexes with
thermodynamic properties and potential mechanistic pathways that promote the formation and
transformation of intermediates that determine the selectivity and rate for substrate reactions. The
seminal observation that rhodium porphyrin complexes have the unusual thermodynamic
capability to produce metalloformyl (M-CHO) species at low pressures of H2 and
CO is utilized in guiding the design of metal complexes that have both the thermodynamic and
kinetic properties necessary for catalytic CO hydrogenation. Production of formyl species from
H2 and CO has now been shown to be a general property for rhodium complexes
of nitrogen donor macrocycles and has also recently extended to complexes of nonmacrocyclic
tetradentate ligands with both nitrogen and oxygen donors. Structurally flexible nonmacrocyclic
ligand complexes manifest reaction pathways excluded to macrocyclic ligand complexes, and have
the capability of achieving oxidative addition, reductive elimination, and migratory insertion steps
integral to selective CO hydrogenation to alcohols. An alternate reaction pathway to form organic
oxygenates that occurs through initial CO reductive coupling has been observed for rhodium
porphyrins and the scope of rhodium complexes that can reduce and couple CO is currently being
evaluated. New materials are also being designed to achieve simultaneous activation of CO and
CH4 to give organic formyl and acyl functional groups.
University of Pittsburgh
Pittsburgh, PA 15261
Department of Chemical and Petroleum Engineering
Fundamental Aspects of Selective Reduction of NOx and Low Temperature
Methane Activation Catalyzed by Zeolites
| Investigator(s) |
d'Itri, J.L.; Hall, K.W.
|
$133,000 |
| Phone | 412-624-9634 |
| E-mail |
jditri@pitt.edu |
Medium pore-sized zeolites containing a wide variety of charge-compensating cations are active
catalysts for selective reduction of NO by hydrocarbons and for low-temperature activation of
CH4 by NO. The objective of the proposed research is to develop a fundamental
understanding of the surface chemistry which governs both of these chemical processes.
Metal-loaded zeolites will be prepared by ion exchange under controlled conditions which will be
systematically changed in order to vary the type and concentration of metal species. The catalysts
are to be characterized by a variety of techniques including FTIR, MAS-NMR,
temperature-programmed reactions with probe molecules, and isotopic exchange reactions.
Fundamental information regarding the individual steps involved in the reaction mechanism and
which of these steps are rate limiting will be developed by isotopic transient investigations. The
role of parameters such as zeolite acidity, structure, and the reducibility of the
charge-compensating cations will be probed through reaction studies and catalyst
characterization, and relationships will be developed between these catalyst properties and key
reaction steps such as the activation of methane. Moreover, the importance of components such
as H3CNO2 and NO2 in forming a N-N bond in
these systems will be investigated.
University of Pittsburgh
Pittsburgh, PA 15260
Department of Chemistry
Vibrational Spectroscopic Studies of Surface Chemical Interactions in Chemisorption and
Catalysis
Catalytic reactions are being studied using vibrational spectroscopy methods coupled with
electron and photon stimulation of the reactions. The vibrational spectroscopic methods include
Fourier transform infrared reflection absorption spectroscopy (IRAS) on model single-crystal
catalysts and transmission infrared spectroscopy (TIR) on high area powdered catalysts. Current
problems include: (1) study of the role of defect sites on catalytic reactions; (2) study of the
activation of chemical bonds by coordinatively unsaturated surface sites on supported metal
catalysts; and (3) study of the dynamical motion of adsorbates on single-crystal surfaces and the
anisotropic nature of these motions. For project (3) the ESDIAD (electron stimulated desorption
ion angular distribution) method is employed. A particularly important goal of project (2) is to
learn how to thermally activate C-H bonds in alkanes. Following up on our
photochemical work in which coordinatively unsaturated
Rh(I)CO/Al2O3 species were found to activate C-H bonds, a
study of the thermal activation of alkanes on these sites is underway.
Purdue University
West Lafayette, IN 47907
Department of Chemistry
Novel Intrazeolite Metal-Oxo Catalysts and Alloy Clusters
The focus of this project is the design of novel catalysts based on transition metal complexes and
oxo species encapsulated in the cages of zeolites. These systems are expected to offer both improved
control over the active species in heterogeneous catalysis and novel reactant and product
selectivities. We combine the catalytic activity of transition metal catalysts with the shape
selectivity and well-defined pore structure of zeolite pores. Recent work has focused on
intrazeolite manganese triazacyclononane chelate complexes and their activity in highly selective
olefin epoxidation and other reactions. The selectivity of these catalysts exceeds that of many
previous zeolite/metal complex-based epoxidation catalysts. Furthermore, we are also exploring
homogeneous oxidation catalysis with this family of complexes as a basis for the design of future
hybrid catalysts, and we have substantially improved the activity of the complexes compared to
previous work. Molybdenum oxo species encapsulated in zeolite hosts were also found to be
highly selective epoxidation catalysts. First successful developments in the design of asymmetric,
zeolite-encapsulated epoxidation catalysts have been achieved. Using chiral Mn-salen complexes
in large-pore hosts such as EMT, asymmetric epoxidation of cis-olefins has been observed. We
perform comprehensive characterization with spectroscopic and structural techniques including
EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy utilizing synchroton radiation,
in situ FT-IR coupled to thermodesorption, Micro Raman, UV-NIR, and ESR spectroscopies.
Catalytic studies of hydrocarbon conversions address issues such as the location of catalytically
active sites, stability against migration, and shape selectivity.
Purdue University
West Lafayette, IN 47907
Department of Chemistry
Catalytic Arene Hydrogenation Using Early Transition Metal Hydride Compounds
During the last year a concerted effort has been focused on gaining a better understanding of the
mechanism of arene hydrogenation catalyzed by Group 5 metal hydride compounds. The kinetics
of the hydrogenation of aryl-phosphines (e.g., PPh3, RPPh2), etc.
by niobium aryloxide systems has been studied and successfully modeled. The stereochemistry of
the reactions have been explored by a variety of methods and shown to occur in a predominantly
all-cis fashion. The stoichiometric reaction of tantalum polyhydrides,
[Ta(OAr)2(Cl)(H)2(L)x] (x=1,2) and
[Ta(OAr)2(H)3(L)2] with cyclohexene,
cyclohexadiene and related olefinic substrates has been surveyed. The organometallic products
obtained are found to be highly dependent on the nature of the aryloxide ancillary ligation. The
mechanism of styrene hydrogenation by
[Ta(OAr)2(Cl)(H)2(PMe2Ph)2](OAr=2,6-diphenylphenoxide) is being studied. The regio and stereoselectivities of various surface
supported Group 5 metal species are also being evaluated. In particular, the nature of the oxide
support on the hydrogenation of arene substrates is being studied.
Purdue University
West Lafayette, IN 47907
Department of Chemistry
Fundamental Studies of Reactive Intermediates in Homogeneous Catalysis
Mass spectrometry and gas-phase ion chemistry techniques are employed to investigate the
thermodynamics and intrinsic reactivity of organic and organometallic models for reactive
intermediates in combustion and homogeneous catalysis. Energy-resolved collision induced
dissociation (CID) in a flowing afterglow-triple quadrupole apparatus has been used to
determine M-CO bond dissociation energies for a series of homoleptic metal carbonyl anions. We
have now completed measurements and analyses of the sequential M-CO bond strengths in a
series of cyclopentadienyl (Cp) metal carbonyl ion complexes,
CpM(CO)n+/-(Cp=c-C5H5).
These data provide an instructive picture of the variable influence of this important polydentate
organic ligand on M-CO bonding. Moreover, the trends exhibited by the bond strengths in
isoelectronic CpM(CO)n+, CpM(CO)n and
CpM(CO)n- complexes provide quantitative insights into the
interplay between back-bonding and M-CO bond strengths. Unlike the
M(CO)n- ions, which display remarkably constant M-CO bond
energies around 40 kcal/mol, the CpM(CO)n- ions show
spectacular variations in their sequential M-CO bond strengths, which range from about 24
kcal/mol for the "slipped" 3-CpCo(CO)2- ion to more than
70 kcal/mol for 5-CpCoCO-. Energy-resolved CID has also been
used in conjunction with other gas-phase ion experiments to determine absolute heats of
formation for organic fragments such as phenyl radical, the isomeric benzynes,
cyclopropenylidene, the isomeric dehydrotoluenes and phenyl carbene. These data are being used
to derive sequential C-H bond energies for simple hydrocarbons such as benzyne, toluene and
cyclopropane. Construction is nearly completed of a new flowing afterglow-guided ion beam
instrument, which will be use for refined measurements of thermodynamic data for a wider variety
of organic and organometallic intermediates. We have developed a new method for preparing
negative ions of biradicals in the gas phase, and have used this method in collaboration with the
Lineberger group in Boulder to determine electron affinities and singlet-triplet splittings for
trimethylenemethane, meta-benzyne and para-benzyne. We have successfully developed an
electrospray ionization (ESI) source for our flowing afterglow-triple quadrupole apparatus. The
ESI source is being used to examine the properties and reactivity of massive transition metal
complexes transported from polar solutions directly into the gas-phase flow reactor. A preliminary
value for the Ru-bipy (bipy=2,2'-bipyridine) bond dissociation energy in
Ru2+(bipy)3 of 46 kcal/mol has been determined from
energy-resolved CID. The tandem ESI-flowing afterglow-triple quadrupole instrument will
ultimately be used to examine directly the components of catalytically-active homogeneous
solutions.
Rensselaer Polytechnic Institute
Troy, NY 12180
Department of Chemistry
I. Metal Carbonyl - Hydrosilane Reactions and Hydrosilation Catalysis; II. Catalytically
Relevant Chemistry of (5-Indenyl)Ru Alkyl Complexes.
| Investigator(s) |
Cutler, A.R.
|
$108,000 |
| Phone | 518-276-8447 |
| E-mail |
cutlea@rpi.edu |
The reactions of hydrosilanes [e.g., Me2PhSiH,
Ph2SiH2] towards manganese p-substituted benzoyl complexes
(CO)5MnC(O)C6H4Y (Y =H, Me, OMe, t-Bu,
CF3) provided either ArCH2OSiMe2Ph (90%)
and variable amounts of (CO)5MnSiMe2Ph or exclusively
(CO)5MnCH(OSiHPh2)Ar. Similar studies with
(L)(CO)4MnCOAr and (L)(CO)4MnCOCH3 [L
=PPh3, PMe3, P(OMe)3] were thwarted by facile
decarbonylation reactions for the former and ill-defined degradation reactions for the latter. In
particular, the acetyl complexes yielded mostly disiloxanes: 2 equiv. of Me2PhSiH
consumed L =P(OMe)3 (all-cis, in 15 min.), PPh3 (50%-cis, 45
min), and PMe3 (all-cis, 3 days). These Mn complexes and
(L)(CO)4MnH [L =CO, P(p-tolyl)3, P(OMe)3]
were surveyed as hydrosilation precatalysts (Me2PhSiH,
Ph2SiH2) towards acetone or ethyl acetate. The manganese acyls
L(CO)4MnC(O)R [L =CO, R =CH3, Ph; L
=PPh3, R =CH3] also catalyzed the PhSiH3
hydrosilation-reduction of Cp(CO)2FeC(O)CH3 to give
[FpCH(CH3)O]3-xHxSiPh [x =0-2] and
FpCH2CH3. The PhSiH3 (1.6 equiv) /
RhCl(PPh3)3 (3%) system, however, converted
Cp(L)(CO)FeC(O)R to their alkyl derivatives, Cp(L)(CO)FeCH2R (49 to 87%
isolated yields), plus some vinyl complexes Cp(L)(CO)FeCH=CH2: [FpC(O)R, R
=Me, Ph, i-Pr, t-Bu; Cp(L)(CO)FeC(O)CH3, L =PPh3,
P(OMe)3, and P(OPh)3]. The facile carbonylation of
(Ind)Fe(CO)(L)R apparently entails 5-3 indenyl ring slippage commensurate with stereospecific,
backside association of CO prior to the alkyl-CO migration. Thus,
[Fe13]CH3 and CO provided only
[Fe13]COCH3, where [Fe13] =Cp or
(Ind)Fe(13CO)(PPh3). Studies on the stereochemistry of
carbonylation of optically active [Fe]Et to [Fe]COEt, [Fe] =CpFe(CO)(PR3) and
(Ind)Fe(CO)(PR3), were initiated. Catalytic PhSiH3
hydrosilation-reduction of resolved [Fe]COCH3 (L = PPh3)
provided [Fe]Et, which underwent carbonylation (80 psig, 0 °C) to give racemic [Fe]COEt.
Epimerization of the CpFe and (Ind)Fe systems occurred under very mild conditions via the ethyl
intermediates.
University of Rochester
Rochester, NY 14627
Department of Chemical Engineering
Dimensional Effects in Controlled Structures Support Catalysts Derived from Layered
Synthetic Microstructures (LSMs)
A new class of supported catalysts has been produced using solid-state fabrication techniques
typical of the microelectronics industry. Deposition of alternating, nanometer thick layers of
catalyst and support on an inert wafer, followed by etching perpendicular to the flat surfaces to
reveal only the edges of the layers, provides a catalyst surface in the form of nanometer-wide,
micrometer-long lines (the edge of a thin plate). These Layered Synthetic Microstructures
(LSMs), with Ni and silica as catalyst and support, duplicate the size effect ("structure
sensitivity") which is observed during ethane hydrogenolysis on traditional silica supported
Ni clusters of nanometer "diameter". In principle, any catalyst/support system can be
manufactured so that the catalyst and support are uniform in size and geometry with arbitrary
nanometer dimensions. Surface studies can be carried out on a totally accessible surface and one
which behaves catalytically like a supported cluster. The objective of this research is to develop
this new structure as a tool for understanding supported catalysts. LSMs
(Ni/SIO2) will be fabricated using ion milling to provide higher catalyst surface
areas per unit wafer area. Other supports will be studied (Al2O3
carbon, MgO, and silica-alumina). The Ni/SIO2 LSMs will be tested using other
structure sensitive and structure insensitive catalytic reactions. These include the reaction of CO
and H2 which shows a rate maximum with 4 nanometer clusters; cyclopropane
hydrogenation exhibits shows a rate maximum with 2 nanometer clusters; and benzene
hydrogenation which is unresolved. Characterization will be carried out concurrently. TEM can be
used to examine the edge array, Auger analysis will provide a spatially averaged composition, and
both STM (AFM) and TPD will be used. Fabrication of Pt based LSMs will be carried out.
Platinum catalyzed reactions which would be candidates for study include: hydrogen plus oxygen
at 273 K since in excess hydrogen the rate is structure sensitive while in excess oxygen it is
insensitive; the hydrogenation of cyclohexene which is structure insensitive; and skeletal
isomerization of methylcyclopentane which exhibits selectivity changes (rather than rate changes)
with cluster size greater than 2 nanometers.
University of Rochester
Rochester, NY 14627
Department of Chemistry
Transition Metal Activation and Functionalization of Carbon-Hydrogen Bonds
The investigation of homogeneous C-H bond activation has been continued with a variety of
metal complexes. The reactive fragment [Cp*Rh(PMe3)] has been
found to react with a variety of alkanes and arenes to give C-H oxidative addition products, and
with fused polycyclic hydrocarbons to give eta-2 complexes and/or C-H bond activation products.
The project has now been expanded to include C-C bond activation. Reaction of this same
fragment with biphenylene results in aryl-aryl bond cleavage and the formation of rhodium biaryl
complex. Mechanistic studies indicate that this product is a rhodium biaryl complex formed via
initial aromatic C-H bond oxidative addition followed by intramolecular rearrangement to the C-C
inserted product. A homogeneous catalyst has also been found for the hydrogenolysis of the
aryl-aryl bond of biphenylene, giving biphenyl. C-C cleavage reactions of biphenylene have also
been observed with other rhodium and cobalt complexes. Reactions of the related metal fragment
tris-3,5-dimethyltrispyrazolylborate (Tp'Rh(CNR) where R = neopentyl) also show C-H activation
reactions with of a variety of alkanes. Competitive activation of alkanes has been examined,
showing that this fragment is more selective than either
Cp*Rh(PMe3) or Cp*Ir(PMe3).
Methane has been activated thermally at 2000 psi. Reaction with cyclopropane initially gives a
C-H activation product, which then converts intramolecularly to a four-membered metallacycle
product. Ethylene initially reacts by way of vinylic C-H activation, but then converts
intramolecularly to an eta-2 ethylene complex. The secondary derivative Tp'Rh(CNR)(i-propyl)H
has been prepared and observed to rearrange intramolecularly to Tp'Rh(CNR)(n-propyl)H. Work
with the tris-3,5-dimethylpyrazolylborate complex Tp'Rh(CNR)(CH3)H has
provided kinetic evidence for an alkane complex being involved in C-H activation reactions. The
deuterated analog Tp'Rh(CNR)(CD3)H rearranges intramolecularly to give
Tp'Rh(CNR)(CD2H)D. The kinetics of the reaction of
Tp'Rh(CNR)(CH3)H with benzene has been found to be first order in metal
complex and first order in benzene, and is interpreted in terms of an associative substitution on a
methane sigma-complex.
Rutgers, The State University of New Jersey
Piscataway, NJ 08855
Department of Chemistry
Carbon-Hydrogen Bond Functionalization Catalyzed by Transition-Metal Systems
A primary focus of this project is the development of homogeneous catalysts for the conversion of
alkanes to the corresponding alkenes. Complexes of the form
Rh(PMe3)2ClL have been discovered to catalyze efficient thermal
(non-photochemical) alkane transfer-dehydrogenation under dihydrogen atmosphere. Apparently,
the role of hydrogen is to add to the complexes, which then dissociate L to afford
H2Rh(PMe3)2Cl, which then reacts with
hydrogen-acceptors to give the fragment Rh(PMe3)2Cl; the latter
then reacts with alkanes. Recently, significant progress has been made toward the development of
hydrogen-free catalytic systems. RhL2Cl derivatives with L larger than
PMe3 were found to effect the stoichiometric dehydrogenation of cyclooctane. In
the presence of hydrogen acceptors, catalytic transfer-dehydrogenation is observed. The efficiency
of both the stoichiometric and catalytic reactions is limited by ligand degradation. A search for
degradation-resistant ligands with suitable electronic and steric properties has revealed that the
P(cyclobutyl)3 complex, [RhL2Cl]2, gives clean
and quantitative stoichiometric cyclooctane dehydrogenation, and fairly efficient catalytic
dehydrogenation. Further, the catalyst decomposition product can be regenerated with hydrogen.
A second objective of this project is the development of metal carbonyl catalysts for the
deoxygenation of organoelement oxides using CO. Several such catalyst systems have been
discovered and in all cases mechanistic studies have revealed an unanticipated pattern: the
reaction proceeds via substitution of a ligand (either phosphine or halide) by CO to give a less
electron-rich carbonyl. Although present in very minor concentration, the substitution product is
the key species which reacts (via nucleophilic attack at CO and loss of CO2) to
deoxygenate the substrate (e.g. R2SeO, R3NO,
R3AsO).
Rutgers, The State University of New Jersey
Piscataway, NJ 08855
Department of Physics and Astronomy
Morphological Instability in Model Thin Film Catalysts: Structure, Reactivity and Electronic
Properties
We are exploring new aspects of the relations between microscopic surface structure and chemical
reactivity for model bimetallic catalysts, i.e., ultrathin films of metals on metals. Our focus is on
atomically rough, morphologically "unstable" single crystal surfaces (e.g., bcc(111)
and fcc(210)) that undergo massive reconstruction and faceting when covered by ultrathin films of
metals or other adsorbed species (ca. 1 monolayer thick), upon annealing to elevated
temperatures. We use a variety of ultrahigh vacuum (UHV) surface science methods, including
atomic resolution scanning tunneling microscopy (STM) and catalytic studies in a high pressure
reactor, (i) to study metal film induced on faceting atomically rough substrates of W, Mo, Ir, Pd,
(ii) to use structure sensitive catalytic reactions, including hydrogenolysis of n-butane, and the
cyclization of acetylene to benzene, to correlate surface morphology and reactivity, and (iii) to
characterize the electronic properties of the bimetallic interfaces using synchrotron radiation. In
recent UHV STM studies of Pd-covered W(111), we find that the surface becomes completely
faceted to 3-sided pyramids upon annealing to T>750K. Atomic resolution images confirm that
facet sides have {211} orientation. Faceting is observed to occur only for elements
having Pauling electronegativity greater than 2.0, suggesting that surface electronic effects control
morphological stability. Structure sensitivity in a model catalytic reaction, n-butane
hydrogenolysis, is observed over planar and faceted Pt/W(111). We have also used synchrotron
radiation methods to characterize Pt, Pd and Au on W(111), and we find substantial substrate
core level shifts associated with interface formation.
University of South Carolina
Columbia, SC 29208
Department of Chemical Engineering
New Heterogeneous Catalysts for Selective Reduction of NOx Emissions to
Improve Vehicular Transportation
The objective of the proposed research is the rational identification of new heterogeneous
catalysts for the removal of nitrogen oxides (NOx) from automobile tailpipe
emissions through their selective catalytic reduction by hydrocarbons (hydrocarbon-SCR) under
excess oxygen ("lean") conditions. The focus will be on noble-metal-based catalysts
due to their high activity and hydrothermal stability. The proposed research will employ kinetic
and microcalorimetric measurements, in-situ spectroscopic characterization, and kinetic analysis
techniques to achieve this goal. It is anticipated that significant progress will be made towards
understanding the fundamental surface chemistry of the hydrocarbon-SCR reaction. In particular,
we expect to identify the important competing reactions, measure or at least estimate their rates,
identify the nature of important reactive intermediates, and identify the active sites of the catalyst.
Furthermore, we expect to apply this information towards the identification and synthesis of new
generations of catalysts. If successful, the proposed research will have a significant impact in the
area of emission control due to the high market potential of a commercially viable
hydrocarbon-SCR catalyst. Such a catalyst would find a commercial use in several mobile
emission control applications including diesel and "lean-burn" gasoline vehicles.
University of South Carolina
Columbia, SC 29208
Department of Chemistry and Biochemistry
Studies of the Transformations of Sulfur Containing Heterocycles by Transition Metal Cluster
Compounds
Recent studies have focused on the activation of sulfur containing strained ring heterocycles,
thiiranes and thietanes, by polynuclear metal complexes. The principal objective is to develop
catalysts for the formation of polythioether macrocycles by ring opening cyclooligmerization
reactions of the strained ring precursors. Goals include synthesis of new macrocycles and the
development of more efficient routes to known ones. Studies of activation process and the
mechanisms of the cyclooligomerizations are included. The ligand behavior of the macrocycles is
also being investigated through the preparation and x-ray crystallographic characterization of new
complexes containing these ligands.
University of Southern California
Los Angeles, CA 90089
Department of Chemistry
Chemistry of Bimetallic and Alloy Surfaces
The objectives of our research are to define the overall chemical reactivity of Pt-Sn alloys, clarify
the role of a second metal in altering surface chemistry and catalysis on Pt bimetallic and alloy
surfaces, and develop general principles for understanding the reactivity and selectivity of
bimetallic and alloy catalysts. The surfaces studied are primarily the stable, ordered surface alloys
of Sn with Pt, Ni, and Rh that can be prepared by the controlled vapor deposition of Sn onto
single crystal metal substrates. Our recent ALISS studies on Pt(100) and Ni(100) have shown that
the lattice mismatch between Sn and Ni or Pt completely controls the buckling distance of Sn in
Pt-Sn or Ni-Sn alloys independent of the surface bonding geometry or coordination, and we are
now exploring how this affects the site-blocking efficiency of Sn atoms in the surface layer.
Through TPD studies of a series of hydrocarbons on the (2 x 2) Pt3Sn(111) and
(
3 x 3)R30° Pt2Sn surface alloys, we have
found that upon increasing the Sn concentration within the surface layer on Pt(111), adsorption
energies are reduced in the order: alkynes>aromatics>alkenes>alkanes. Sharper changes
occur in the adsorption energies and dehydrogenation activities of the surfaces upon the
elimination of the 3-fold Pt sites on the (3 x 3)R30°
Pt2Sn surface alloy. We have determined that the sticking coefficients and
saturation coverages of hydrocarbons on Pt-Sn alloys do not decrease nearly as sharply with Sn
concentration as may be expected. The adsorption kinetics can be understood if the influence of a
modifier precursor state is properly included. Secondly, reaction ensembles for hydrocarbon
dehydrogenation on Pt-Sn alloy surfaces are quite small, at most a few (<5) Pt atoms, for a
number of hydrocarbon reactions. Our current work is aimed at making detailed spectroscopic
studies of hydrocarbon bonding on these surfaces. In parallel with these chemisorption studies, we
are measuring catalytic reaction kinetics over these same surfaces at higher (1-760 torr) pressures
to understand in detail how the composition and structure of Pt-Sn alloy surfaces affect catalytic
activity and selectivity for hydrocarbon reactions.
Stanford University
Stanford, CA 94305
Department of Chemical Engineering
The Dynamics of Adsorption on Clean and Adsorbate-Modified Transition Metal
Surfaces
The objectives of this research are (1) to determine the probabilities of both dissociative and
nondissociative adsorption of alkanes on clean and adsorbate-covered surfaces, (2) to gain an
understanding of the molecular dynamics of the adsorption process via experiments and molecular
dynamics simulations, and (3) to clarify the role of precursor states in adsorption. Model metal
surfaces are studied under highly controlled conditions in ultrahigh vacuum to reveal the
dynamical features of the adsorption process. Molecular beams of gases are directed at these
surfaces and the dependence of the adsorption probabilities for reactive and/or nonreactive
adsorption are measured directly. Stochastic simulations are combined with the experiments
related to nondissociative adsorption to gain insight into the energy exchange processes that lead
to trapping and adsorption. Recent focus has been on the molecular dynamics simulations to
understand the dynamical differences in the adsorption of ethane, propane and methane on
Pt(111). Using pairwise additive methyl-platinum potentials determined from fitting the
dependence of the adsorption probability of ethane on Pt(111) on the incident energy and angle,
the adsorption probabilities and the energy scaling determined experimentally for propane and
methane on Pt(111) were predicted by simulations. These results indicate that molecular
adsorption rates may be predictable from simple potentials. We have also examined the trapping
of ethane on adsorbate-covered surfaces, both experimentally and theoretically. Generally,
adsorbates increase the adsorption probability of ethane and render it nearly independent of the
angle of incidence. Stochastic simulations show the origin of these effects to be increased
corrugation of the surface; ie, microroughness of the gas-surface potential.
State University of New York at Binghamton
Binghamton, NY 13902
Department of Chemistry
Photochemistry of Intermolecular C-H Bond Activation Reactions
Photoreactivity measurements have been carried out on the intermolecular C-H activating
(HBPz'3)Rh(CO)2 (Pz'=3,5-dimethylpyrazolyl) complex in
various hydrocarbon solutions at room temperature. In each case UV-visible and FTIR spectra
recorded throughout photolysis illustrate that the parent dicarbonyl complex can be converted
readily to the corresponding alkyl or aryl hydrido product complex. The photochemical reaction
proceeds without interference from secondary or thermal reactions and the reactivity has been
measured quantitatively in the form of quantum efficiencies for intermolecular C-H bond
activation (
CH). The
results show that the C-H activation proceeds very efficiently (CH=0.13-0.32) on excitation at 366 nm but is much
less effective (CH=0.0059-0.011) on photolysis at 458 nm for each of the
hydrocarbon substrates. The quantum efficiencies on UV irradiation are consistent with rapid CO
dissociation and the formation of a monocarbonyl reaction intermediate prior to C-H activation.
Significantly, the photoefficiencies are found to be unaffected on increasing the dissolved CO
concentration, illustrating that the monocarbonyl intermediate is extremely short lived and is
solvated before CO is able to coordinate. Additionally, the lack of a CO concentration dependence
on CH illustrates that the
solvated intermediate is not subjected to a competitive back-reaction with CO prior to the C-H
activation step. Hence, the quantum efficiencies for C-H activation appear to be determined solely
by the branching ratio between the dissociative and nondissociative routes from the reactive
excited state in the complex. The lower quantum efficiencies obtained on excitation at long
wavelength may be the result of ineffective CO dissociation from a lower energy state, or may
involve a 3 to 2 ligand dechelation mechanism.
This aspect is still to be determined. At any particular excitation wavelength the photoefficiencies
are observed to be similar across the series of alkanes studied but are significantly reduced for the
aromatic solvents, even though the aryl hydrido photoproducts are found to be more
thermodynamically stable. The differences in CH are also rationalized in terms of the photophysical properties
the reactive excited state and can be related to solvent effects on the nonradiative relaxation rates
of the complex in the various hydrocarbon solutions.
State University of New York at Buffalo
Buffalo, NY 14260
Department of Chemistry
Mechanistic Examination of Organometallic Electron-Transfer Reactions
The goal of this research is to provide a mechanistic understanding of electron transfer processes
between organometallic complexes to enable utilization of the reactivity of odd-electron
complexes in catalytic reactions. It has been shown that metal carbonyl anions participate in single
electron processes with a number of organometallic complexes and by two-electron processes
with other complexes and have begun to gain an understanding of which process is expected.
Reactions of metal carbonyl anions with Fischer-type carbene complexes,
M(CO)5(C(OMe)Ph), M = Cr,W, have not shown carbene transfer reactions, but
have shown a new site for nucleophilic attack (abstraction of methyl) on carbene complexes. Such
reactions are two-electron processes (nucleophilic). In contrast, reactions of cationic carbene
complexes of iron with metal carbonyl anions give evidence for single electron reactions.
Reactions of metal carbonyl anions with Os(CO)4RR' (R,R'= H,Me) show a
smooth deprotonation and lack of reactivity by the methyl. The same reactions under CO do not
give formation of an acyl, but show interesting substitution behavior. These studies have provided
a much clearer understanding of one- and two-electron processes in organometallic reactions. We
are now exploiting this understanding to activate inert complexes in electron transfer catalyzed
reactions.
Texas A & M University
College Station, TX 77843
Department of Chemistry
Correlations between Surface Structure and Catalytic Activity/Selectivity
The project objective is to address those issues which are keys to understanding the relationship
between surface structure and catalytic activity/selectivity. Of primary concern are those questions
related to the origins of the enhanced catalytic properties of mixed-metal catalysts and the critical
active site requirements for molecular synthesis and rearrangement. The experimental approach
utilizes a microcatalytic reactor contiguous to a surface analysis system, an arrangement which
allows in vacuo transfer of the catalyst from one chamber to the other. Surface techniques being
used include Auger (AES), UV and X-ray photoemission spectroscopy (UPS and XPS), ion
scattering spectroscopy (ISS), temperature programmed desorption (TPD), low energy electron
diffraction (LEED), high resolution electron energy loss spectroscopy (HREELS), infrared
reflection-absorption spectroscopy (IRAS), and scanning probe microscopies (STM/AFM).
Currently the preparation, characterization, and determination of the catalytic properties of
ultra-thin metal and metal oxide films are being explored. Specifically, the program is proceeding
toward three goals: (1) the study of the unique catalytic properties of ultrathin metal films; (2) the
investigation of the critical ensemble size requirements for principal catalytic reaction types; and
(3) the modeling of supported catalysts using ultra-thin planar oxide surfaces.
Texas A & M University
College Station, TX 77843
Department of Chemistry
Solid-State NMR Studies of Zeolite Acidity
High-Resolution 1H nuclear magnetic resonance (NMR) will be used to
characterize hydrogen bonding to the Brønsted acid site and H--D scrambling. The latter study
may lead to a new way to characterize Brønsted acidity in zeolites. Other experiments will seek to
thoroughly understand the 1H NMR properties of HZSM-5 including the effects
of chemical exchange and diffusion. The second strategy will use in situ 13C NMR
to look for intermediates in acid catalyzed reactions in zeolites. A laser heating system will be
built for temperature jump and quench experiments that are expected to yield higher
concentrations of reactive intermediates than are observed in standard variable temperature
experiments. The focus of this project is Brønsted acidity in zeolites rather than reaction
mechanisms per se.
Texas A & M University
College Station, TX 77843
Department of Chemistry
Catalysts and Mechanisms in Synthesis Reactions
The objective of this research is to understand the role of surface-generated gas-phase radicals in
the catalytic oxidation of hydrocarbons, with emphasis on the conversion of methane to more
useful chemicals and fuels. Matrix isolation electron spin resonance (MIESR), variable ionization
energy mass spectrometry (VIEMS) and laser-induced fluorescence (LIF) methods have been
used to detect radicals that emanate from or react with metal oxide surfaces during a catalytic
reaction. The detection of methyl radicals using the MIESR system has been effective in
establishing the mechanism by which methane and ethylene react to form propylene. The
technique has been used to demonstrate that methyl radicals react with adsorbed ethylene to form
propyl radicals, which rapidly lose a hydrogen atom. The VIEMS system has been used to follow
the role of methyl radicals formed over Ba/MgO catalysts during the selective catalytic reduction
of nitric oxide to N2. It has also been demonstrated that water and oxygen react
over strongly basic oxides, such as lanthanum oxide, to form hydroxyl radicals in the temperature
range 1200 to 1350 K. The hydroxyl radicals are believed to be formed by the abstraction of
hydrogen atoms from water at reactive surface oxygen ions, and they may play an important role
in catalytic combustion.
University of Texas at Austin
Austin, TX 78712
Department of Chemical Engineering
Catalytic Hydrocarbon Reactions over Supported Metal Oxides
The primary goal of this research program is to determine how catalyst composition, redox ability,
structure, and neighboring sites control the catalytic properties of metal oxides. Molybdenum,
tungsten, chromium, and vanadium cations are supported on silica using preparation methods that
enable molecular control over the structure and oxidation state. Supported structures featuring
crystallites, isolated cations, and dimers with either a metal-metal or bridging sulfur bond are used
as model templates to investigate key steps in catalytic oxidation and hydrodesulfurization
catalysis. The research effort focuses on reaction studies over the different structures. Reduction
of the cation site and C-H abstraction are studied using oxidative dehydrogenation of butenes to
butadiene and 1-butene isomerization to cis- and trans-2-butene. Differences in
the rates of alkyl cation and allylic intermediate formation reveal information on how cations
function in oxidation catalysis. Mechanisms and site requirements for selective hydrogenolysis of
the C-heteroatom bond in thiophene hydrodesulfurization are studied. Cations, or ensembles of
cations, that can undergo a four electron transfer are most active for hydrodesulfurization
revealing key aspects of the catalytic mechanism.
University of Texas at Austin
Austin, TX 78712
Department of Chemistry
Morphological Aspects of Surface Reactions
Our work examines substrate morphology and fragments synthesized on surfaces using thermal,
electron, and photon activation techniques. Our goal is to acquire fundamental descriptions of
heterogeneous chemical processes at gas-solid interfaces in selected systems that have controlled
and characterizable morphology, are of catalytic significance, and are relevant to DOE missions.
Solid surface morphology reaction intermediate preparation, and kinetic characterization of
intermediates lie at the heart of our program. By electron irradiation of methane, weakly held on
Pt(111), we have cleanly prepared chemisorbed methyl groups, a very important hydrocarbon
fragment. The thermal reactions of these methyl groups among themselves and with coadsorbed
deuterium have been studied. Similarly, activation of cyclopropane on Pt(111) to form
metallocycles has been investigated along with companion work on other hydrocarbons containing
three carbon atoms. By starting with cyclopropane and irradiating with electrons at low
temperatures, we have prepared and kinetically characterized several interesting three-carbon
intermediates.
Tulane University
New Orleans, LA 70118
Department of Chemical Engineering
The Formation of Silica, Alumina, and Zirconia: Supported High Surface Area Monometallic
and Bimetallic Catalysts
A new generation of thermally resistant supported metal catalysts prepared by the sol-gel method
is currently under development. These catalysts derive their superior thermal properties by
minimizing sintering processes which occur through surface diffusion. Because surface diffusion is
substantially decreased when metal particle size is matched to the average pore diameter of the
support, synthetic procedures aimed at obtaining this match are under study. The resultant
materials are being tested as catalysts in the oxidation of CO, the combustion of volatile organic
compounds such as benzene, and the hydroisomerization of butane to isobutane by superacid
catalysts. Finally, the development of catalytic ceramic membrane reactors to study the
dehydrogenation of butane and i-butane is in progress. It is anticipated that the separation and
catalytic properties of palladium and platinum can synergistically be used to improve olefin yields
by shifting the position of equilibrium. Sol-gel synthesis of supported metal catalysts is performed
by a one-step synthesis process. The metal, usually introduced as an acetyl acetonate precursor
dissolved in acetone, is added to the appropriate alkoxide (tetraethoxysilane or aluminum
tert-butoxide). The homogeneous mixture is then hydrolyzed through the addition of water.
Important synthetic variables include the water/alkoxide ratio, the preparation pH and the reaction
temperature. In particular, the pore size distribution is strongly related to the water/alkoxide ratio.
Current research efforts in the area of the preparation of thermally resistant supported metal
catalysts are focused primarily on Rh, Pd, and Pt supported on silica and alumina surfaces. The
synthesis of sulfated zirconia catalysts using a two-step sol-gel method results in high surface area
materials which are capable of isomerizing n-butane at low temperatures. Unfortunately,
deactivation of these materials at relatively low times on stream is a major drawback to these very
promising materials. Our current research effort is to understand the underlying causes of this
deactivation. In particular, deactivation may occur as a result of the following:(i) loss in Brønsted
acid site activity, (ii) partial reduction of sulfur, (iii) phase changes associated with zirconia, (iv)
formation of coke, and (v) poisoning of acid sites. Several physical techniques are currently being
used to provide an explanation for the deactivation. The formation of coke is under study using a
combined TGA-mass spectrometer approach. Changes in acid site distribution are under study
using a novel in-situ infrared diffuse reflectance cell, while changes in crystal morphology are
being probed using x-ray diffraction. Ceramic membranes have the mechanical strength and
permeability required for general use, but the pores are usually too large for selective gas
separation. The sol-gel method of catalyst preparation is easily applied to membrane formation.
The formation and stabilization of colloidal particles in aqueous media are important in the
formation of very small pores. Efforts are under way to add a transition metal to the sol before
coating. This will hopefully result in a thermally stable catalytic membrane. The dehydrogenation
of n-butane is being studied as a probe reaction. The decrease in hydrogen concentration by
diffusion through the membrane results in an increase in selectivity as result of the shift in
equilibrium. The flux of hydrogen through the membrane is increased by reacting it with acetylene
on the reverse side of the membrane. This reaction results in an increase in the concentration
gradient across the membrane.
University of Utah
Salt Lake City, UT 84112
Department of Chemistry
Ligand Intermediates in Metal-Catalyzed Reactions
The first goal of this project is the synthesis, isolation, and characterization of homogeneous
transition metal complexes containing ligand types (-CHO, -CHOH, -CH2OH,
-C, =CH2, H2C=O, -OCHO, - OCH2R,
CO2, etc.) intermediate in C1/C2 catalytic
reactions. A second goal entails the characterization of ligand intermediates in other important
feedstock conversions, and the identification of new types of binding modes and bond activation
processes. A third, new goal involves the development of catalysts that can be immobilized in
fluorocarbon solvents. Mechanistic understanding of key steps and insight for the design of new
catalysts is sought. The following topics are under active investigation: (1) the determination of
relative ligand binding affinities towards Lewis acidic metal centers, including divergent kinetic
and thermodynamic O=C/C=C selectivities in bifunctional nonconjugated substrates; (2) the
characterization of nonclassical metal C-H "sigma bond" complexes as reaction
intermediates; (3) the synthesis, structure, electronic properties, and reactivity of complexes that
contain unsupported and supported C2 and C3 linkages spanning
two metals; (4) C-H bond activation reactions of aromatic nitrogen heterocycles such as pyrrole,
and new HDN processes; and (5) hydrogenation reactions with Rh(I) catalysts bearing fluorinated
phosphine ligands.
University of Utah
Salt Lake City, UT 84112
Department of Chemistry
Carbon-13 NMR of Solid-State Hydrocarbons and Related Substances
The objective of this project is the development of new nuclear magnetic resonance (NMR)
techniques to study solid organic materials to gain structural and chemical information on model
compounds and naturally occurring samples. The most important recent achievements have been:
(1) the development of new spatial correlation techniques to measure 13C
chemical shift tensors in single crystals; (2) improved theoretical methods for the calculation of
shielding tensors; (3) developing a new magic angle slow turning (MAT) method of obtaining
two-dimensional solid-state NMR spectra of powdered samples where the isotropic shift is
projected along one axis and the tensor powder patterns along the second axis; (4) extending the
theoretical and experimental shift tensor work to nitrogen containing species; and (5) construction
and utilization of a high pressure NMR sample cell for observing hydrocarbons dissolved in
supercritical fluid CO2. The single crystal correlation techniques completely
characterize all six terms of the chemical shift tensor and its orientation in the molecular frame.
The accuracy of the single crystal methods is sufficiently high that it may be used along with
quantum mechanical methods to refine crystal structures of fused aromatic hydrocarbons.
Considerable progress has been made in dealing with the single crystals of sufficient size to obtain
high quality data in a reasonable period of time. A new icosahedral flipper probe has recently been
constructed which has significantly reduced the size requirements for single crystals (e.g., 14 mg)
on a 400 MHz spectrometer. Theoretical calculations have been extended to a wide range of
polycondensed aromatic hydrocarbons and a number of corresponding heterocyclic (O, N, S)
species. A major effort has recently been mounted to obtain 15N chemical shift
tensor data on heterocyclic compounds. Enriched compounds were initially employed for studying
powder patterns in compounds containing one and two nitrogen atoms. Experimental and
theoretical correlations have shown that the nitrogen shift tensors are extremely sensitive to
intermolecular interactions. Powder pattern experiments carried out at high (400 MHz) have
demonstrated that it is possible to obtain chemical shift tensor data at the natural abundance level
on model compounds which have been doped with stable free radicals. The 13C
shift tensor data on model compounds have been extremely valuable in interpreting the MAT data
obtained on several coal samples and the 15N data will be evaluated to determine
its value in identifying the types of nitrogen species present in coals. Use of supercritical fluid
solvents is rapidly gaining importance in problems of environmental cleanup and as a method for
providing alternative cleaning solvents for a variety of industrial and commercial uses. NMR shift
and spin relaxation data provide details on the important solute-solvent interactions.
Virginia Polytechnic Institute and State University
Blacksburg, VA 24061
Department of Chemical Engineering
Influence of Surface Defects and Local Structure on Acid/Base Properties and Oxidation
Pathways over Metal-Oxide Surfaces
| Investigator(s) |
Cox, D.F.
|
$71,000 |
| Phone | 540-231-6829 |
| E-mail |
dfcox@vt.edu |
The purpose of the project is to examine the effect of surface defects (primarily oxygen vacancies)
and local structure on catalytic oxidation reactions over metal oxide materials. The
SnO2(110) surface is being investigated because of the flexibility allowed in
controlling surface cation coordination numbers, oxidation states, and the selective introduction of
two different types of surface oxygen vacancies. The relative acidity/basicity of these two surface
defects have been tested previously with probe reactions. Recently, the acid/base properties of
these specific surface sites have been investigated using NH3 and
CO2 as probe molecules. NH3 chemisorption experiments
demonstrate that four-coordinate Sn2+ sites at bridging oxygen vacancies are
stronger Lewis acid sites than Sn4+ sites on the stoichiometric surface or more
reduced sites around in-plane oxygen vacancies. These acidity measurements correlate with the
activity of the specific cation sites for the dissociation and subsequent selective oxidation of
alcohols (weak Brønsted acids). In contrast to the literature for SnO2 powders,
CO2 shows no significant interaction (i.e., carbonate formation) over the different
preparations of our extended single-crystal surface under conditions similar to those reported in
the literature for carbonate formation on SnO2 powders. New directions include
the characterization of point defects with STM, and density functional calculations of defect
geometry and electronic structure.
Virginia Polytechnic Institute and State University
Blacksburg, VA 24061-0211
Department of Chemical Engineering
Bimetallic Oxycarbides and Oxynitrides: A New Class of Hydrogenation Catalysts
| Investigator(s) |
Oyama, S.T.
|
$368,000
(39 months) |
| Phone | 540-231-5309 |
| E-mail |
oyama@vt.edu |
Considerable work has been done with single-metal carbides and nitrides showing that they have
high activity, selectivity, and life in catalytic reactions involving hydrogen transfer. This project
deals with the study of a novel class of catalysts for the processing of petroleum and chemical
feedstocks. The new materials are mixed-metal carbides and nitrides. The catalysts have multiple
capabilities that include heteroatom removal, hydrogenation, and isomerization, and can lead to
highly upgraded products. The resulting technology will improve the energy efficiency of
refineries and produce cleaner-burning fuels for the automobile industry. Preliminary work
indicates that the two metallic components give rise to enhanced catalytic properties. The new
materials have higher catalytic activity in hydrodenitrogenation than the individual monometallic
substances, and higher even than a commercial sulfided catalyst. The emphasis of this project will
be on the synthesis and characterization of a homologous series of mixed metal carbides and
nitrides. The ultimate objective is to understand the origin of the catalytic enhancement.
Substantial effort will be placed on characterization of adsorbates by infrared and Raman
spectroscopy.
University of Virginia
Charlottesville, VA 22903
Department of Chemical Engineering
Structure-Property Relationships for Binary Metal Oxide Catalysts
Alkali and alkaline earth oxides, both alone and on supports, are recognized as solid base
catalysts. However, very little is known about these materials despite their potential for many
industrially important reactions. In an attempt to explore solid base structure-property
relationships, we have been using in situ x-ray absorption spectroscopy (EXAFS and XANES) to
determine the atomic structure near rubidium and strontium supported on a variety of carriers. In
addition, IR spectroscopy and stepwise desorption of adsorbed carbon dioxide have been used to
characterize the basicity of these materials. Characterization results have been correlated to the
activity of the catalysts for decomposition of 2-propanol to acetone and propene. The x-ray
absorption studies were performed at the Rb K edge on 5wt% Rb supported on carriers of
varying acidity, based on the Sanderson electronegativity scale. Analysis of the radial structure
functions revealed that the Rb-O distance correlates roughly with support acidity. Additional in
situ investigations were conducted in the presence of 2-propanol in the gas phase. Perturbations
of the local structure due to adsorbed alcohol were observed. The rate of 2-propanol
decomposition over the catalysts, normalized per base site counted by carbon dioxide
chemisorption, varied dramatically as a function of support. Basic sites formed by Rb
incorporation onto acidic supports were less effective for the reaction than sites formed on more
basic supports. Results from x-ray absorption spectroscopy of supported Sr indicated that the
carrier does not exert a strong influence on the supported alkaline earth compound, contrasting
the results for supported alkali. These structural results were confirmed by reactivity trends for
2-propanol decomposition. Apparently the support plays a more crucial role in the formation of
surface basic sites from alkalis than from alkaline earths. Ongoing work in the laboratory focuses
on the structural determination of the active base sites for catalysis on these materials.
University of Virginia
Charlottesville, VA 22903-2442
Department of Materials Science and Engineering
Understanding and Controlling Metal-Support Interactions in Nanocrystalline Bimetallic
Catalysts
| Investigator(s) |
Howe, J.M.; Davis, R.J.
|
$317,000
(39 months) |
| Phone | 804-982-5646 |
| E-mail |
jh9s@virginia.edu |
Supported metal catalysts are vital for control of automobile emissions and to the chemical and
petroleum industries. Issues such as loss of surface area due to the migration and coalescence of
metal crystallites during service, thermal degradation of the support material or metal crystallites,
the role of the support-metal interface and the segregation behavior of the metal crystallites are all
critical to the functionality of the catalysts. The purpose of this research is to use high-resolution
transmission electron microscope (HRTEM) techniques to analyze, understand and control the
atomic and electronic structure, chemical composition, segregation behavior, wettability, thermal
stability and catalytic properties of bimetallic nanocrystalline catalysts as a function of
alloy composition and substrate reactivity. A field-emission gun HRTEM equipped with an
energy-dispersive X-ray spectrometer and Gatan imaging filter will be used to image the atomic
structures of nanocrystalline bimetallic alloys on different substrates with 0.14nm spatial
resolution and simultaneously determine the chemical compositions and electronic properties of
the crystals and support-crystallite interface with 0.5nm spatial resolution. This research will
provide a fundamental understanding of phenomena such as: 1) the effect of support reactivity on
the atomic structure, morphology and stability of bimetallic catalyst crystallites, 2) the effect of
support reactivity on the surface and interfacial segregation behavior of bimetallic crystallites, 3)
the effect of crystallite size on the morphology and segregation behavior of bimetallic particles, 4)
the mechanisms and kinetics of nanocrystalline particle sintering as a function of alloy
composition, substrate reactivity and temperature, and 5) the effect of all of the above on the
resulting catalytic properties and stability of bimetallic crystallites.
University of Washington
Seattle, WA 98195
Department of Chemistry
Oxide-Supported Metal Catalysts: Factors Controlling Particle Size and Chemisorption /
Catalytic Properties
Many catalysts for energy technology consist of transition metal particles attached to oxide
supports. Interactions at the interface between the metal and the oxide dictate the metal particle
morphology, which in turn controls catalytic activity and selectivity, yet these interactions are
poorly understood. This project involves experiments designed to clarify the geometric, dynamic
and energetic factors which control the microstructure of the metal / oxide interface, and to
rationalize the interplay between this microstructure and chemical reactivity. Specifically, the
project goal is to determine how the number, dimensions and structure of metal particle are
influenced by: oxide surface structure and defect density (on ZnO crystals), the choice of metal,
temperature, coadsorbed chlorine and hydrogen, and high-pressure gases. The chemisorption and
catalytic properties of ultrathin metal islands and isolated metal adatoms are studied, as well as the
dependence of these upon the characteristics of the underlying oxide surface. For Pt particles, the
reactions being studied are pertinent to hydrocarbon conversion catalysis. For Cu particles, they
pertain to methanol synthesis and water gas shift catalysis. Recent research highlights demonstrate
the structural sensitivity of Cu catalysts and the interesting role of ZnO in optimizing the activity
of the Cu particles.
University of Washington
Seattle, WA 98195
Department of Chemistry
Homolytic Activation of Hydrocarbons and Hydrogen by Persistent Metal Radicals
The binding and activation of hydrogen by cationic transition metal complexes such as
[RE(CNR)3(PR3)2]+ is being
explored. This highly reactive, coordinatively unsaturated rhenium complex actually binds
dihydrogen in preference to more conventional ligands such as chloride. Abstraction of a Cl atom
from methylene chloride to form the novel Re(II) chloride complex
[RE(CO)3(PR3)2Cl]+ has also
been observed. Structural investigations indicate that the Re-Cl bond is much longer in the Re(I)
complex. In related chemistry, diactionic dihydrogen complexes of osmium have been prepared by
protonation of cationic [(bipy)(PR3)2Os(CO)H]+
using triflic acid. The resulting hydrogen complex is very thermally robust but is a strong acid,
undergoing complete proton transfer to weak bases such as diethyl ether. Extension of this
chemistry to lighter elements of the iron group is under investigation.
University of Wisconsin at Madison
Madison, WI 53706
Department of Chemical Engineering
Thermodynamic and Kinetic Aspects of Surface Acidity
During the past year, most of our work on catalyst acidity has involved studies of
sulfated-zirconia catalysts for isomerization of n-butane. We have found that whereas the heat of
ammonia adsorption on our sulfated zirconia catalyst (calcined at 848 K and containing 2 wt.%
sulfur) decreases from 160 to 80 kJ/mol as the adsorbate coverage increases to 250 micro-mol/g,
only those sites with heats higher than about 130 kJ/mol (50 micro-mol/g) are active for butane
isomerization at 423 K. These heats of ammonia adsorption are similar to those measured on
various zeolites. The strong acid sites on sulfated zirconia must be present in the proper hydration
state to show high catalytic activity for butane isomerization. For example, the initial catalytic
activity decreases by over an order of magnitude as the temperature used for drying the catalyst
(following initial calcination and exposure to air) is increased from 588 to 773 K. The higher
catalytic activity can be restored for a catalyst dried at 773 K by exposure to water at a dosage of
approximately 100 micro-mol/g. The heat of water adsorption on such a sample decreases from
200 to 140 kJ/mol as the coverage by water increases to the level of 100 micro-mol/g, and this
same behavior is observed for adsorption of water on zirconia. These high heats are indicative of
dissociative adsorption of water, as confirmed by infrared and NMR spectroscopic measurements.
Spectroscopic measurements show that this level of water addition does not alter the number of
Brønsted acid sites. Rather, the role of water is to promote the catalytic activity of the sites
and/or to suppress the rate of catalyst deactivation. Reaction kinetics measurements were
conducted at 423 K on optimally-dried catalysts for the isomerization of n-butane and the
isomerization of isobutane. The reaction order with respect to the alkane reactant decreased and
approached zero order as the pressure of the reactant increased from 0.1 to 1 atm. This behavior
was also observed for the rate of butane disproportionation to form propane and pentane species,
such that the isomerization selectivity was essentially independent of the alkane pressure. These
data strongly suggest that butane isomerization takes place via an intermolecular process
involving a C8 intermediate. Studies of the rates of butane isomerization versus
time on stream showed that deactivation constants were higher during isomerization of n-butane
compared to isomerization of isobutane, and the deactivation constant increased linearly with
increasing pressure of n-butane and is independent of the isobutane pressure. The rate of catalyst
deactivation during n-butane isomerization can be decreased significantly by removing the
impurity olefins from the alkane feed stream. Thus, a primary mode of catalyst deactivation is via
decomposition of olefins on the active sites, and we have been able to operate sulfate zirconia
catalysts for prolonged periods of time through the use of an appropriate olefin-trap.
University of Wisconsin at Madison
Madison, WI 53706
Department of Chemistry
Organometallic Chemistry of Bimetallic Compounds
Four different projects at the interface between organometallic chemistry and homogeneous
catalysis are being pursued. All are designed to give increased understanding of the mechanisms of
organometallic chemistry related to homogeneous catalysis. (1) Bimetallic catalysis has almost
unlimited potential but very few systems are known in which there is direct evidence for
involvement of a bimetallic compound. The hydrogenation of alkynes by
Cp(CO)2Re(µ-H)Pt(H)(PPh3)2 to give
rhenium-alkene complexes suggests that it may be possible to develop a catalytic system based on
more labile metal-alkene complexes. The unusual lability of
indenyl(alkyne)Re(CO)2 systems is being investigated. (2) Hydroformylation with
chelating diphosphines with wide natural bite angles near 120° gives high regioselectivity for
straight chain aldehydes. Attempts to explain this selectivity with steric effects have failed and the
role of electronic effects of chelating ligands is being investigated. (3)
Cp*(CO)2Re=Re(CO)2Cp* is a
highly unusual and reactive dimer of a d6-16e fragment. The diverse reactions of
alkynes with this fascinating compound are being investigated. (4) The reaction of
Cp*3Co3(µ2-H)3(µ3-H) with acetylene to produce the bis ethylidyne cluster
Cp*3Co3(µ3-CCH3)2 is being investigated in detail with isotopically labeled materials. This
reaction is interesting in relation to transformations on metal surfaces.
University of Wisconsin at Madison
Madison, WI 53706
Department of Chemistry
Mechanism and Design in Homogeneous Catalysis
The principle goals of this proposal are the design, synthesis, characterization, and use of new
ligand structures for controlling selectivity at transition metal centers. One synthetic effort
concerns the (1) synthesis of novel chiral phosphite ligands containing aza-crown ether ligands,
(2) demonstration of the ability of these ligands to coordinate to metal centers, (3) establishing the
catalytic competence of complexes of these ligands in hydroformylation and hydrogenation
reactions, (4) synthesis of a series of novel borate-functionalized chiral diphosphine ligands, and
(5) demonstration that borate-functionalized diphosphines ligate transition metal complexes
that are catalytically active in hydrogenation reactions. We have demonstrated that chiral
aza-crown ether ligands can be readily synthesized, that these ligands form effective
hydroformylation catalysts with catalyst precursors such as Rh(acac)(CO)2, that
these catalysts show significantly enhanced activity for the hydroformylation of allylammonium
salts relative to simple phosphites, and that the hydroformylation products are enantiomerically
enriched. We have also found that these catalysts demonstrate unusual phase separation behavior
that may be exploited in simplified catalyst separation/recycling schemes. Our other synthetic
effort concerns the synthesis of borate-functionalized diphosphines based on ferrocene. We
now have both racemic and resolved versions of these novel diphosphines in hand, as well as
crystallographic structures for several variations of these ligands. We have demonstrated that
these ligands bind to Pt and Rh complexes to yield clean compounds. The rhodium complexes are
catalytically active toward alkene hydrogenation. We are now poised to study the influence of the
borate functional group on binding constants, catalytic rates, and catalytic selectivity. We also
have made significant synthetic progress toward versions of this ligand that contain guanidinium
functional group; this novel design should promote interactions with carboxylate-containing
substrates.
University of Wisconsin at Milwaukee
Milwaukee, WI 53201
Department of Chemistry
Aluminum Coordination and Active Catalytic Sites in Aluminas, Y Zeolites, and Pillared
Clays
The extension of the NMR REDOR technique to silicon from the proton of ammonia chemsorbed
by acid zeolite has provided an important distinction between the silicon atoms bridged to the
lattice aluminum by an OH. Those OH bridges which belong to a cluster
Si-(OTn), where T is another four-fold coordinated metal, here an Al, act as
Brønsted sites if n=1. Their protons are transferred to NH3 and
NH4+ is formed. NH4+ enjoy a
fast isotropic reorientation (at the NMR time scale at the room temperature). In a cluster with
n>1, the bridging OH hydrogen bonds with NH3 and is not a Brønsted site. The
number of acid OH is between 30 and 60% of the number of framework aluminum in USY and
dealuminated Y (DHY). It is about 75% FAl in dealuminated mordenite(DHM) and larger than
85% in DHZ. These are unexpected results and, among numerous consequences, they explain
why poisoning a reaction occurring on Brønsted sites requires more molecules than calculated
from FAl. The progress reported above has been made possible by the careful development of a
quantitative IR method of measuring the number of NH4+ and
NH3 coordinated by the zeolite. It has been shown also that the dispersion of the
Lewis sites on the non-framework aluminum (NFAl), that is, the ratio number of Lewis
sites/NFAl is between 25 and 75%. The use of NH3 as a probe has been definitely
improved by using 1H MAS NMR to assign the IR lines. Comparison of
chemisorbed CO and NH3 FTIR has shown that "high frequency" CO
stretching integrated absorbance at 2173-77 cm-1 is proportional to the number of
strong Brønsted sites. The latter are those in the cluster Si 4Q(1Al) but with no
next-nearest aluminum eighbors. These measurements were applied to fluorinated ultrastable Y. It
has been shown that fluorination 1) dealuminates the zeolite and thus decreases the number of
Brønsted sites, and 2) decreases the dispersion of Lewis sites. As a result the activity of the
fluorinated USY vs. pentane transformation (isomerization essentially) decreases noticeably.
University of Wisconsin at Milwaukee
Milwaukee, WI 53201
Department of Chemistry
An Investigation of Molybdenum and Molybdenum Oxide Catalyzed Hydrocarbon Formation
Reactions
Model oxide olefin metathesis catalysts consisting of MoO2,
MoO3, metallic molybdenum and oxygen overlayers on molybdenum were
characterized using various surface sensitive techniques including X-ray and ultraviolet
photoelectron, Raman and Auger spectroscopies and low energy electron diffraction and their
activities tested using an isolatable, high-pressure reactor. It is found that MoO2
mimics the activity and selectivity of alumina supported metathesis catalysts rather well for
reaction below ~650 K and provides a good model for this system. Another,
higher-temperature reaction regime is identified on the oxide with an activation energy close to
that found for the metal (~65 kcal/mol) and where the reaction selectivity decreases with
increasing reaction temperature. Reactions with ethylene on metallic molybdenum suggest that
reaction proceeds, in this case, via reaction of surface C1 species. In addition, the
formation of 2-butene from propylene is found to be rather stereoselective with cis-2-butene being
substantially favored over trans-2-butene. This effect is being investigated further. The presence
of relatively thick carbonaceous layers is found during the catalytic conversion of hydrocarbons
on both the metal and the oxide, and restart reactions indicate that catalysis proceeds in the
presence of such layers. Raman spectroscopy reveals that these consist of both graphitic particles
and a hydrocarbon layer. It is also found that hydrocarbon conversion rates are accelerated, both
for olefin metathesis and palladium-catalyzed acetylene cyclotrimerization, if hydrogen is added to
the reaction mixture even though hydrogen is not required for the reaction. A possible explanation
for this effect is that hydrogen acts to remove these strongly bound hydrocarbons exposing more
surface sites for catalysis. Unfortunately, the model MoO2 catalyst is very
unreactive in ultrahigh vacuum so that both ethylene and propylene merely adsorb and desorb
molecularly on this surface. However, it is also found that oxygen overlayers on molybdenum
effect their catalytic metathesis activity where the presence of about 0.6 monolayers of oxygen
yields the largest enhancement. Although these surfaces are not as active as the oxides, they
exhibit a rich chemistry in ultrahigh vacuum and allow the effect of oxidation to be scrutinized.
Ethylene reacts on oxygen-covered Mo(100) to form both ethane by self-hydrogenation, and
methane and photoelectron spectroscopy demonstrates that ethylene undergoes carbon-carbon
bond scission on oxygen-covered Mo(100). Carbenes (CH2) can also be grafted
onto the surface by adsorbing methylene iodide on oxygen-covered Mo(100) and it is found that
these react with adsorbed hydrogen to form methane. A similar reaction pathway involving
carbene formation and hydrogenation is proposed for methane formation from ethylene. In this
case, the methane yield increases with oxygen coverage up to a coverage of 0.6 monolayers and
decreases thereafter in an activity pattern that mimics the variation in metathesis activity. Methane
is similarly evolved in temperature-programmed desorption following adsorption of both
propylene and 2-butene on oxygen-covered Mo(100). Reaction pathways are being investigated in
these cases by grafting possible reaction intermediates by adsorbing halogenated precursors onto
these surfaces. Initial work has been carried out to synthesize more realistic model metathesis
catalysts by reacting molybdenum hexacarbonyl with planar alumina substrates in ultrahigh
vacuum. It is found that carbonyls adsorbed at low temperatures desorb intact. Higher
temperature adsorption results in complete carbonyl decomposition and the formation of a surface
carbide. This suggests that the removal of the first CO in the carbonyl is rate limiting and, once
decarbonylation is initiated, the remaining carbonyls are removed very rapidly. Heating the
carbide-covered surface to ~1300 K removes all surface carbon and desorbs CO. It is
shown, by synthesizing an oxide substrate using isotopically labelled oxygen that the carbon reacts
with the alumina substrate. The carbide can be reformed by reaction with ethylene. Finally, as part
of this project, we have been developing strategies for analyzing Near-Edge X-ray Absorption
Fine Structure spectra (in collaboration with D.K. Saldin of the University of
Wisconsin-Milwaukee) and angle-resolved X-ray Photoelectron Spectroscopy data (with D.K.
Saldin and D. R. Mullins of Oak Ridge National Laboratories).
Yale University
New Haven, CT 06520
Department of Chemical Engineering
Acidity and Effect of Acidity on Supported Metals
We are investigating the effect of acidity and counter cation on the activity and selectivity of Pt or
Pd supported in L-zeolites. The electronic state and the dispersion of the metal particles are
determined by XANES and EXAFS, respectively, and the catalytic probe reaction is neopentane
isomerization and hydrogenolysis. In the case of Pt/L-zeolite, Sn is added as a modifier to
compare these catalysts with standard Pt-Sn/Al2O3 reforming
catalysts. The physical state of both Pt and Sn is studied by X-ray absorption spectroscopy
(XANES and EXAFS). n-Hexane is used as a model reactant for catalytic reforming and the
chemical state of Pt is further catalytically probed by competitive hydrogenation of benzene and
toluene at low temperature.
Yale University
New Haven, CT 06520-8286
Department of Chemical Engineering
Pd Catalysts for Use in Vehicular Applications
Pd-based catalysts are being widely developed for new automotive applications with special focus
on fast light-off (including close-coupled convertors), enhanced hydrocarbon emission control,
and lengthened warranty periods. Pd poses particular challenges for these applications because
its physical and chemical state changes with temperature and reactant environment over the range
of conditions experienced in vehicular applications. Interaction effects with the support, dopants
and contaminants also affect Pd catalyst performance. In this research, we will study the behavior
of Pd-based catalysts on a range of supports under typical vehicular reaction conditions. A simple
in-situ technique based on UV-visible reflectance spectroscopy is being developed to monitor the
Pd's chemical state and particle size under reaction conditions. (Chemical interactions of the Pd
with other catalyst components will also be observed.) In earlier work, we used this technique to
study changes in Pd and PdO abundance, as well as formation of an aluminate-like phase during
the oxidation of methane. A variety of high-temperature supports will be used in this study,
including low and high surface area aluminas, lanthanum aluminates and metal supports derived
from etched, oxidized superalloys. Noble metal catalysts are often promoted with
CeO2, but the performance of the CeO2 is affected by changes in
catalyst state induced by the reaction environment. As reaction conditions are cycled over
temperature and composition ranges to simulate vehicular operation, we will monitor the state
and morphology of the Pd component of the catalyst, Pd-CeO2 interactions, and
the interactions of both the CeO2 and the noble metals with the supports.
Simultaneous measurements of reaction products and surface state will allow us to analyze the
physical and chemical processes of catalyst activation and deactivation.
Yale University
New Haven, CT 06511
Department of Chemistry
Catalytic Oxidation of Hydrocarbons by Binuclear Fe Complexes
This project is investigating the ability of non-heme iron metalloenzyme reactivity models to
catalyze the oxidation of alkane and arene molecules, including the conversion of methane and
ethane to methanol and ethanol, respectively. The objective of this project is to characterize the
electronic structure and reactivity properties of a series of non-heme mononuclear and dinuclear
iron complexes, characterize any intermediates formed during oxygen atom transfer chemistry,
and elucidate the mechanisms and specificity of the reactions. Comparisons to analogous
heme-based chemistry will be made. A series of diferrous, ferric/ferrous, and diferric complexes
were synthesized from simple polyamide and polycarboxylate ligands and spectroscopically
characterized. The diferrous and mixed-valence compounds are capable of catalyzing the
oxidation of alkanes, alkenes, arenes, and sulfides in the presence of oxygen atom donors.
Oxidation occurs via pathways that do not involve freely diffusing hydroxyl radicals. Both intra-
and intermolecular kinetic isotope effects are analogous to those reported for the enzymes
methane monooxygenase and cytochrome P450. Intermediates observed during catalytic turnover
and reactions with dioxygen are currently being examined.
Yale University
New Haven, CT 06511
Department of Chemistry
Some C-X Bond Cleavage Chemistry
In the latest period, the CF bond breaking chemistry discovered right at the end of the previous
period has provided some striking new results. In the most important one, we find that Freons
such as CF2Cl2 in the vapor phase are quantitatively destroyed
by a series of inorganic materials such as sodium oxalate to give carbon, sodium fluoride and
sodium chloride. The Montreal Convention's limits on ozone-destroying freons means that
convenient means of destroying CFC stockpiles could be of growing importance in the years to
come. Our finding has attracted substantial interest from industrial companies and the press and
broadcast media. The same series of materials also reacts with cyclic perfluoroalkanes to give
perfluoroarenes in high conversion and yield. In other work, we find that
Hg/NH3/hv(254 nm) leads to the functionalization of teflon and a variety of
perfluoroalkanes by a charge transfer reaction, followed by nucleophilic attack of
NH3 on the intermediate perfluoroalkene. We also find that ferrocenes react with
perfluoroalkanes under visible light illumination in THF to give charge transfer. In the presence of
lithium triflate, loss of LiF leads to the formation of perfluoroalkenes. These new reactions are of
considerable mechanistic and practical interest and we are following them up in the current grant
period.
Last updated by Harry J. Dewey, (hd@lanl.gov) on December 23,
1996.