CO2 hydrogenation on Rh/TiO2 previously reduced at different temperatures

Hydrogenation of CO2 was studied on 1% Rh/TiO2 reduced at different temperatures. The interaction of CO2 with the catalyst and that of the CO2 + H-2 mixture was also studied. FTIR and TPD measurements revealed that CO2 dissociation depends on the reduction temperature of the catalyst. In the surface reaction, besides Rh carbonyl hydride, formate groups and different carbonates and surface formyl species were also formed. The surface concentration of the formyl group depended on the reduction temperature. The initial rate of CO2 hydrogenation significantly increased with increasing reduction temperature but after some time it drastically decreased. The promotion effect of the reduction temperature was explained by the formation of oxygen vacancies on the perimeter of the Rh/TiO2 interface, which can be re-oxidized by the adsorption of CO2 and H2O.