Mechanistic study on the hydrogenation of CO2 to methanol over Cu-Mn-La-Zr catalysts prepared by different methods

Abstract

AbstractThe reaction routes for the CO2 hydrogenation to methanol over a series of Cu-Mn-La-Zr catalysts prepared by different methods, viz., CMLZ-CP by co-precipitation, CMLZ-S by sol-gel method and CMLZ-H by hydrothermal method, were comparatively investigated by in-situ DRIFT and H2-TPD characterization. The results indicate that the surface hydroxyl groups on these catalysts contribute to the CO2 hydrogenation to methanol and the reaction may follow the formate (HCOO*) and carboxylate (COOH*) routes. The carboxylate pathway is preferred for the reaction over the CMLZ-CP and CMLZ-H catalysts, whereas the formate pathway dominates in the reaction over the CMLZ-S catalyst. The CMLZ-CP catalyst shows the strongest ability to activate H2 and thus exhibits the highest CO2 conversion and methanol yield. In contrast, the CMLZ-H catalyst has high percentage of medium to strong basic sites and oxygen defects, which favor the hydrogenation of intermediate species to methanol, and thus exhibits the highest selectivity to methanol.