Deactivation of Modified Iron Oxide Materials in the Cyclic Water Gas Shift Process for CO-Free Hydrogen Production

The iron oxide Fe2O3 is a potential oxygen storage material for the production of hydrogen in the cyclic water gas shift (CWGS) reaction. The deactivation of modified iron oxides during repeated reduction and reoxidation cycles was investigated. Sintering was found to be the main reason for deactivation during the CWGS cycles. The influence of CeO2, La2O3, and Ce0.5Zr0.5O2 as promoters in the system was investigated, as well. CeO2- or La2O3-promoted iron oxide deactivated significantly during the progression of the redox cycles due to the solid−solid transformation of oxide structures (CeFeO3 or LaFeO3) which had a lower oxygen capacity. Iron oxide promoted by Ce0.5Zr0.5O2 showed high stability and activity in the CWGS process. The influence of the Fe2O3−Ce0.5Zr0.5O2 oxide composition ratio and the effect of Mo, Cu, and Mg metal additives on the lifetime stability and activity have been declared. A sample containing 80 wt % Fe2O3 gave the highest activity during the reduction and reoxidation cycles compared to the other oxide composition ratios. The Mo species impregnated on Fe2O3−Ce0.5Zr0.5O2 inhibited the interaction between iron oxide particles during the redox cycles and resulted in mitigated sintering of the iron species. The Mo-impregnated sample was stable over 100 redox cycles.