Mechanism of Photocatalytic Reduction of CO2 to CH3OH by Cu Nanoparticle and Metal Atom (Ag, Au, Pd, Zn)-Doped Cu Catalyst: A Theoretical Study

In this study, density functional theory was used to optimize five catalyst models consisting of one Cu38nanoparticle and four Zn-, Pd-, Ag-, and Au-doped Cu37-X nanoparticles. The energy gap value of the Cu38 nanoparticle catalyst was calculated as 15.3 kcal mol–1, and the energy gap values of Cu37-X (X: Au, Ag, Zn, Pd) were 15.0 kcal mol–1, 15.2, 11.2, and 12.9 kcal mol–1, respectively. All of these catalysts are photoactive in the visible-light range and can be used as good photocatalysts. The photocatalytic mechanism of CO2 reduction on these optimized catalysts has been investigated in detail. Two possible reaction pathways for photocatalytic reduction of CO2 to CO and four possible reaction pathways for the further reduction of CO to CH3OH were investigated. In the first stage of catalytic reduction, i.e., from CO2 to CO, Au doping of the catalyst has the best photocatalytic effect on the process of catalytic CO2 reduction to CO. The optimal reaction process catalyzed by these Cu-based nanoparticles is the direct transfer of the H atom of the H2O molecule to the O atom of the CO2 molecule without surface bridging, which can determine the catalytic CO2 reduction process, but the hydrogen evolution reaction cannot occur simultaneously. During the reduction of CO to CH3OH, we propose that the photocatalytic activity of these models still follows the order Cu37-Au > Cu37-Ag ≥ Cu37-Zn > Cu37-Pd > Cu38. Our research found that doping with Zn, Ag, and Au is beneficial to improve the activity of photocatalysts.