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.