Stabilizing Iron Oxide Used in Cycles of Reduction and Oxidation for Hydrogen Production

Modified iron oxide, Fe2O3, was used to produce pure H2 using repeated cycles of reduction and oxidation. Reduction was performed in a packed bed at 1123 K with either (i) CO + N2 or (ii) H2 + N2; reoxidation was performed with (iii) steam + N2 and additionally with (iv) air + N2 in some cases. Stable yields of H2 over repeated cycles were observed if Fe2O3 was reduced only to FeO. Decreasing yields of H2 with an increasing cycle number were observed if Fe2O3 was fully reduced to Fe. Samples of modified Fe2O3 were prepared via wet impregnation with Al, Cr, Mg, and Si to give loadings of 1, 10, and 30 mol % of the metal additive. The addition of a metal additive was shown to improve and sometimes stabilize the quantity of H2 produced when Fe2O3 was reduced to Fe. Metal additives which (i) formed an intermediate with a higher melting temperature than the iron species involved, i.e., Fe2O3, Fe3O4, FeO, and Fe, and (ii) formed an intermediate that decomposed either during reduction or oxidation to release reactive iron, increased the quantity of H2 produced. Stable H2 yields over 10 cycles were obtained for the sample with 30 mol % Cr; stable H2 yields over 10 cycles were obtained for the sample with 10 mol % Al if additional oxidation in air was performed to oxidize FeO·Al2O3 to Fe2O3 and Al2O3.