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

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journal contribution
posted on 2017-11-07, 00:00 authored by Lingna Liu, Fei Fan, Zhao Jiang, Xiufeng Gao, Jinjia Wei, Tao Fang
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 CH3OH synthesis on PdCu(111) surfaces, especially on Pd ML, were facilitated and the yields of byproducts CO and CH4 are suppressed, which corroborates well with experimental reports showing that Pd–Cu bimetallic catalysts have a strong synergistic effect on CO2 hydrogenation to methanol. The present insights are helpful for the design and optimization of highly efficient Pd–Cu bimetallic catalysts used in CH3OH formation from CO2 hydrogenation.