The Reverse Water Gas Shift (RWGS) reaction, which has been known since the mid-1800’s, has been combined with water electrolysis (WE) to provide a testbed for the development of autonomous control software to produce data to model the RWGS/WE system and to develop process improvements at Kennedy Space Center. The RWGS reaction combines carbon dioxide (CO₂) with hydrogen (H₂) over a copper catalyst at 673 kelvin (K) in an endothermic reaction (ΔH = 37.6 kJ/mol) to produce water (H₂O) and carbon monoxide (CO). The H₂O is electrolyzed to produce oxygen (O₂) and H₂, which is recirculated to the RWGS reactor. This system would be a useful tool on Mars where atmospheric CO₂ is a convenient raw material. The system is important even if water is present on Mars, since it provides not only O₂ but also CO, which is a useful raw material for metal oxide reduction and production of hydrocarbons and other organic materials. Therefore, we have continued to develop our understanding of the RWGS/WE system, with primary objectives to reduce the system complexity and improve the overall efficiency of the process.

The baseline data for the system are given in the table, which provides a matrix of operating parameters, including the reactor feed to raw material (RM) feed ratio with the compressor. Several trends in the RWGS reaction are shown by the data. For example, as the total flow rate increases (runs 1, 2, and 3), the conversion is almost unchanged; as the ratio of CO₂ to H₂ increases (runs 2, 4, and 5), the conversion increases; as the reactor temperature increases (runs 2, 6, 7, 8, and 9), the conversion increases; as the pressure in the reactor increases (runs 2, 10, and 11), the conversion remains unchanged; and as the reactor feed to RM feed ratio increases, the conversion appears to go through a maximum. These data in the table will be used to select the optimum operating conditions for the system.

One of the initial problems with the design of the reactor was illustrated by the temperature differential across the bed, which ranged from 40 to 50 degrees Celsius. Since the bed was heated from the outside and the reaction is endothermic, it was difficult to transfer heat across the bed. This difference is made worse by the insulating characteristics of the catalyst bed, which is copper-impregnated - alumina. To correct the problem, copper turnings were added to the catalyst, and the temperature difference dropped to less than 10 degrees. Other changes in the initial design include a change in the method of analysis (from a mass spectrometer to a gas chromatograph).