Separation of CO2 adsorption and H2 dissociation site in Co and In doped ZrO2 catalyst enhances methanol selectivity in CO2 hydrogenation

CO2 hydrogenation to methanol over mixed oxide catalysts is hindered by the poisoning effect of strongly adsorbed CO2 and formate species, which limits their H2 dissociation ability. Addition of noble metals to mixed oxides is a common practice to promote H2 dissociation but it inadvertently reduces methanol selectivity by simultaneously promoting CO formation. Herein, we show an alternative approach of doping Co in ZrO2 to create a separate site for adsorption of CO2 and counter the poisoning effect. We synthesized a ternary oxide of Co and In doped ZrO2 (Co-In-ZrO2), which showed higher methanol productivity and selectivity (65%) as compared to individual binary oxides of Co-ZrO2 and In-ZrO2 (29% and 44%). Detailed analysis showed that Co site was responsible for CO2 and formate adsorption while neighboring In atom was responsible for H2 dissociation to promote the hydrogenation of adsorbed CO2 to methanol over Co site. The cooperative effect reduced the activation energy for methanol formation to 80 kJ mol-1 over Co-In-ZrO2 in comparison to 139 and 116 kJ mol-1 over binary oxides. Moreover, CO formation was also suppressed leading to increased methanol selectivity. This cooperative effect was not unique to Co-In system but was also be extended to Co-Zn and Co-Ga doped ZrO2 catalysts. This work presents a different approach of designing mixed oxide catalysts for CO2 hydrogenation based on preferential adsorption of substrates and intermediates instead of promoting H2 dissociation.