Ni and ZrO2 promotion of In2O3 for CO2 hydrogenation to methanol

Transition metals, such as Ni, Pd, and Pt, and ZrO2 are known as efficient promoters in M-In2O3-ZrO2 catalysts for CO2 hydrogenation to methanol. Herein, we systematically investigated the role of Ni and ZrO2 promoters by preparing ternary NiO-In2O3-ZrO2 catalysts and binary counterparts by flame spray pyrolysis. The highest methanol rate was obtained for the Ni(6 wt%)-In2O3(31 wt%)-ZrO2(63 wt%) composition. DRIFTS-SSITKA shows that formate is the key intermediate in the hydrogenation of CO2 to methanol. Kinetic analysis shows the competition between methanol and CO formation. The rate-limiting step in methanol formation is likely the hydrogenation of surface methoxy species. Ni and ZrO2 play different promoting roles without showing synergy with respect to each other. Ni promotes hydrogenation of surface formate and methoxy species, while ZrO2 maintains a high In2O3 dispersion, the smaller In2O3 size likely stabilizing formate and other intermediates during their conversion to methanol.