Micro-Structure Engineering in Pd-InO x Catalysts and Mechanism Studies for CO 2 Hydrogenation to Methanol.

Significant interest has emerged for the application of Pd-In 2 O 3 catalysts as high-performance catalysts for CO 2 hydrogenation to CH 3 OH. 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 Pd 2 In 3 . Lower Pd loadings exhibited Pd-O(H)-In sites, while higher loadings resulted in Pd 2 In 3 intermetallic compounds. These variations impacted catalytic performance, with Pd-O(H)-In catalysts showing heightened activity at lower temperatures due to the enhanced CO 2 adsorption and H 2 activation, and Pd 2 In 3 catalysts performing better at elevated temperatures due to the further enhanced H 2 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 Pd 2 In 3 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 CO 2 conversion catalysts.