Mechanistic Understanding of Dissociated Hydrogen in Cu/CeO2-Catalyzed Methanol Synthesis

Abstract

The hydrogen dissociation and spillover mechanism on oxide-supported Cu catalysts play a pivotal role in the hydrogenation of carbon dioxide to methanol. This study investigates the hydrogen spillover mechanism on Cu/CeO₂ catalysts using in situ spectral characterization under high-pressure reaction conditions and density functional theory (DFT) simulations. The research confirms that the Cu sites serve as the initial dissociation points for the hydrogen molecules. The chemically adsorbed hydrogen (H*) then spills over onto the CeO₂ support and interacts with the lattice oxygen to form special hydroxyl groups, while simultaneously reducing the surrounding Ce⁴⁺ to form Ce³⁺. Interestingly, the temperature-programmed desorption (TPD) results found that heating the hydroxyl-containing surface mainly reverses H₂ dissociation by desorbing H₂ instead of forming H₂O, while no significant vacancy formation was detected. The DFT calculation identified a subsurface pathway favoring hydrogen migration, which explained the dominating H₂ in the TPD products. A chemical loop study after CO₂/H₂ cofeeding on the catalyst reveals that hydrogen spillover facilitates the highly reduced surface serving as the active centers, enabling a secondary methanol synthesis in a vacuum. This study provides a model of the formation and desorption pathways of hydrogen species on Cu/CeO₂ catalysts and illustrates the key role of the hydrogen spillover mechanism in promoting the CO₂ hydrogenation to methanol reaction through important experimental analysis.