Nanostructured chromium–iron mixed oxides: Physicochemical properties and catalytic activity

Chromium–iron bulk mixed oxides were prepared by a sol–gel method using 2-propanol solutions of the nitrate salts of both metals, and propylene oxide as a gelation promoter. Composites with iron content of 10%, 50% and 90% were prepared and compared with the corresponding pure oxides, α-Fe2O3 and Cr2O3. The mixed oxides were characterized by XRD, TEM, FT-IR, and N2 adsorption. The XRD analysis indicated the formation of solid solutions of the mixed oxides which exhibited significantly modified textural characteristics, as indicated by N2 adsorption studies. The characteristics of the mixed oxides were dependent on the Cr/Fe ratio and the composite with 50% Fe, in particular, exhibited significantly higher specific surface areas and porosity than other composites and pure oxides. The catalytic conversion of methanol was studied at 225 °C. The catalytic activities exhibited by the mixed oxides were significantly higher than those of the pure oxides. The yields of the products, dimethyl ether (DME), methyl formate (MF), and CO2 were dependent on the Cr/Fe ratio.