Micro-Structure Engineering in Pd-InO_x Catalysts and Mechanism Studies for CO₂ Hydrogenation to Methanol

Significant interest has emerged for the application of Pd-In₂O₃ catalysts as high-performance catalysts for CO₂ hydrogenation to CH₃OH. However, precise active site control in these catalysts and understanding their reaction mechanisms remain major challenges. In this investigation, a series of Pd-InO_x catalysts were synthesized, revealing three distinct types of active sites: In-O, Pd-O(H)-In, and Pd₂In₃. Lower Pd loadings exhibited Pd-O(H)-In sites, while higher loadings resulted in Pd₂In₃ intermetallic compounds. These variations impacted catalytic performance, with Pd-O(H)-In catalysts showing heightened activity at lower temperatures due to the enhanced CO₂ adsorption and H₂ activation, and Pd₂In₃ catalysts performing better at elevated temperatures due to the further enhanced H₂ activation. In situ DRIFTS studies revealed an alteration in key intermediates from *HCOO over In-O bonds to *COOH over Pd-O(H)-In and Pd₂In₃ sites, leading to a shift in the main reaction pathway transition and product distribution. Our findings underscore the importance of active site engineering for optimizing catalytic performance and offer valuable insights for the rational design of efficient CO₂ conversion catalysts.