Study on the solid solubility mechanism of Cr2O3 in Fe3O4 (γ-Fe2O3)

XRD Rietveld analysis and Mossbauer spectra show that gamma -Fe2O3 samples prepared by Fe3+(Cr3+)/Fe2+ mixed ions method lions ratio 2:1), containing 0-14 wt% Cr2O3 have 20.56-49.58% amorphous iron oxide. The amorphous iron oxide is magnetic when the content of Cr2O3 is less than 4 wt%. Above 4 wt% Cr2O3, the non-magnetic phase appears and its content increases linearly with Cr2O3 concentration. During coprecipitating of Fe3+(Cr3+)/Fe2+ mixed ions, two different kinds of primary hydrous complex are formed: Fe3+ hydrous complex mixed with Cr3+ ions, with a maximum of 4 wt% Cr2O3 content, and, the Cr3+ hydrous complex mixed with Fe3+ ions with the Cr2O3 content above 4 wt%. The Cr3+ hydrous complexes incorporate: into the Fe3+ hydrous complexes and hinder the crystallization and growth of the latter. These complexes dehydrate to form non-magnetic iron oxides containing chromium. The non-magnetic iron oxides affect the catalytic activity of Fe2O3-Cr2O3 catalysts. When Cr2O3 content is between 6-8 wt%, the catalysts have the highest water gas reaction activity for all samples.