Modulation of inter-elemental synergy and oxygen vacancy content of CdZrOx solid solution catalysts by Ga for effective CO2 hydrogenation to methanol

Abstract

CO₂ conversion into valuable chemical products such as methanol using green hydrogen generated from renewable energy sources is an effective way to reduce CO₂ emissions. However, preparing catalysts with high activity and methanol yield remains a significant challenge. Here, we found that the synergistic effect of Ga, Cd and Zr produced by introducing Ga into CdZrO_x solid solution catalysts significantly facilitated the methanol synthesis from CO₂ hydrogenation. The Ga-promoted CdZrO_x solid solution catalyst (5 %GaCdZrO_x) exhibited a CO₂ conversion of 8.6 % and a methanol space time yield of 457 mg/g_cat·h, which is remarkably higher than the unmodified CdZrO_x, and displayed excellent long-term stability. Multiple characterization results indicate that Ga acts as a promoter, leading to changes in the electronic structure of the CdZrO_x solid solution, which generates a large number of oxygen vacancies on the catalyst surface, and thus promotes the methanol generation. A series of chemisorption experiments and in situ DRIFTS revealed that the Ga, Cd and Zr components in the 5 %GaCdZrO_x solid solution catalyst exhibited a stronger synergistic effect with enhanced CO₂ and H₂ adsorption and activation compared to CdZrO_x. Both the strengthened synergistic effect of the solid solution structure and the elevated oxygen vacancies promoted the adsorption of CO₂ and the formation of more CO₃* species, while increased H₂ adsorption and activation capacity further accelerated the hydrogenation of CO₃* species into HCOO* and CH₃O* species. This study provides specific insights into the modification of solid solution catalysts with bimetallic oxide components for the CO₂ hydrogenation.