Ca₂Fe₂O₅-Based WGS Catalysts to Enhance the H₂ Yield of Producer Gases

Ca2Fe2O5-based catalysts were synthesized from siderite and calcite precursors, which were processed in the form of pelletized samples and tested as water gas shift catalysts. Catalytic tests were performed in a tubular reactor, at temperatures in the range 400-500 degrees C and with different H2O:CO ratios, diluted with N-2; this demonstrates the positive impact of Ca2Fe2O5 on conversion of CO and H-2 yield, relative to corresponding tests without catalyst. The catalytic performance was also remarkably boosted in a microwave-heated reactor, relative to conventional electric heating. Post-mortem analysis of spent catalysts showed significant XRD reflections of spinel phases (Fe3O4 and CaFe2O4), and SiO2 from the siderite precursor. Traces of calcium carbonate were also identified, and FTIR analysis revealed relevant bands ascribed to calcium carbonate and adsorbed CO2. Thermodynamic modelling was performed to assess the redox tolerance of Ca2Fe2O5-based catalysts in conditions expected for gasification of biomass and thermochemical conditions at somewhat lower temperatures (<= 500 degrees C), as a guideline for suitable conditions for water gas shift. This modelling, combined with the results of catalytic tests and post-mortem analysis of spent catalysts, indicated that the O-2 and CO2 storage ability of Ca2Fe2O5 contributes to its catalytic activity, suggesting prospects to enhance the H-2 content of producer gases by water gas shift.