Mechanistic Study of Pd–Cu Bimetallic Catalysts for Methanol Synthesis from CO2 Hydrogenation

Abstract

Density functional theory (DFT) calculations were carried out to explore the adsorptions of reactive species and the reaction mechanisms on Pd–Cu bimetallic catalysts during CO2 hydrogenation to methanol. All the possible preferred adsorption sites, geometries, and adsorption energies of the relative intermediates on pure Cu(111) and three PdCu(111) surfaces were determined, revealing that both the adsorption configuration and corresponding adsorption energy are changed by doping with Pd atoms. The strengthened COOH* adsorption and the greatly weakened OH* adsorption change the rate-limiting step from CO2 hydrogenation forming trans-COOH* on Cu(111), Pd3Cu6(111), and Pd6Cu3(111) surfaces to cis-COOH* decomposition forming CO* and OH* on Pd ML surface. Additionally, the highest activation barriers for the overall reaction pathway are reduced in the following trend: Cu(111) > Pd6Cu3(111) > Pd3Cu6(111) > Pd ML (monolayer). Compared to the reaction on clean Cu(111) surface, the complete reaction pathways for ...