Considerations for catalyst properties required for S-I thermochemical cycle applications

One promising route for hydrogen production involves the splitting of water by thermochemical sulfur-based cycles that employs the catalytic decomposition of sulfuric acid into SO2 and O2. We have arrived at the following criteria for catalyst selection: Potential catalysts will probably need d or f electrons. Though having d electrons, supported noble metals catalysts will not work because of sintering effects. Materials must be stable under the extreme oxidizing conditions of a H2SO4 environment at 850 °C. Therefore, they should probably be oxides. In addition, they should be transition metal, or rare earth, oxides that do not sinter, sublime or disproportionate (e.g., with melting points above about 2300 °C). Because of the harsh, oxidizing environment, constituent metals should be in the highest oxidation state. Oxides should not form undesirable compounds such as very stable sulfates. Finally, oxides should be reasonably economical, and should not present major environmental issues.