Surface Properties of Carbided Molybdena–Alumina and Its Activity for CO2Hydrogenation

The surface properties of carbided molybdena–alumina were investigated through O2-TPD and TPSR along with the catalytic activities of the supported catalysts for CO2hydrogenation. The 1173 K-carbided catalyst exhibited the highest activity for the reaction on the CO adsorption basis. H2pretreatment of the passivated 973 K-carbided catalyst at 773 K did not affect the activity for CO2hydrogenation but a change was visible for the unpassivated catalyst. Through O2-TPD, it was found that the adsorbed oxygen oxidizes the surface carbon of the molybdenum carbide to form CO2and CO. A possible reaction scheme for the hydrogenation of CO2is given, along with an explanation for the lowered activity of the passivated catalysts. η-Mo3C2serves as an active site for CO2hydrogenation. TPSR results were correlated with the activity to reveal that the number of Mo carbides depends on the activity for CO2hydrogenation.