Storage and Supply of Pure Hydrogen from Methane Mediated by Modified Iron Oxides

Abstract

Storage and supply of pure hydrogen through the reduction of Fe3O4 with methane and the subsequent oxidation of the formed iron metal with water vapor were demonstrated. The modification of iron oxides with Cr cations prevented the sintering of Fe3O4/Fe particles during the redox, whereas the mediator without Cr cations was deactivated quickly, because of the sintering. The addition of Cu species into the iron oxides modified with Cr cations enhanced both the reduction with methane and the oxidation with water vapor at lower temperatures. The iron oxides modified with Cu and Cr (denoted as Cu−Cr−FeOx) can store and supply pure hydrogen repeatedly through the reduction with methane and the subsequent oxidation with water vapor. During the redox of Cu−Cr−FeOx, the Cu species were always present as copper metal and Cr cations were always stabilized on the B-sites in ferrite CrxFe3-xO4. Copper metal in the Cu−Cr−FeOx must activate methane in the reduction and water in the oxidation. The CrxFe3-xO4 ferrite in the Cu−Cr−FeOx might prevent the sintering of iron metal particles by blocking their contacts with each other.