CARBON-DIOXIDE AND CARBON-MONOXIDE HYDROGENATION OVER GOLD SUPPORTED ON TITANIUM, IRON, AND ZINC-OXIDES

Gold deposited on TiO2, Fe2O3, ZnO and ZnFe2O4 with high dispersion was found to be active for the hydrogenation of both carbon dioxide and carbon monoxide at temperatures between 150 and 400 degrees C. Over the above catalysts, methanol was produced more readily from carbon dioxide than from carbon monoxide. Tn particular, Au/ZnO and Au/ZnFe2O4 showed high methanol selectivities from carbon dioxide, which were comparable to those obtained for copper catalysts. As for methanol synthesis from carbon monoxide, only Au/ZnO gave appreciable yields with similar selectivity as copper catalysts. The comparison between experimental and thermodynamic data proved that over ah the catalysts except for Au/TiO2 three reactions, namely between carbon dioxide and methanol, carbon monoxide and methanol, carbon dioxide and carbon monoxide, simultaneously reached equilibria at temperatures above 300 degrees C and that the methanol yield decreased with further increase in temperature. Hydrocarbons were formed at high temperatures and the resulting water was also involved in the above equilibria. As a main hydrocarbon product, methane was obtained much more selectively from carbon dioxide than from carbon monoxide. Ethane and propane were also produced from carbon dioxide and carbon monoxide over gold supported on reduced iron oxides.