How the nature of the promoter –Ga vs. Zn– shapes copper-based CO2 hydrogenation catalyst structures evaluated via metadynamics

• Comparison of Ga and Zn as promoters of Cu NPs in methanol synthesis. • Both promoters are favorably segregated towards the nanoparticle surface. • Zn can desorb while Ga remains adsorbed, favoring stable GaCu core–shell structures. • CuZn nanoparticles interact more strongly with the SiO 2 support than the CuGa ones. • When oxygen adsorbs, Ga fully oxidizes, whereas Zn only partially does so Cu-based catalysts are considered references and “gold” standards in the selective hydrogenation of CO 2 to methanol, a chemical feedstock and an intermediate to sustainable fuels. Improving catalyst performances, i.e., higher activity and methanol selectivity, relies on the use of promoters such as Ga and Zn, which are known to alloy with Cu. Nevertheless, establishing detailed, molecular-level relationships between structure and activity remains challenging as multi-metallic catalysts readily and dynamically respond to reaction conditions associated with specific chemical potentials. Notably, CO 2 hydrogenation reaction conditions affect the catalyst structure by being reducing for Cu, but oxidizing for Ga or Zn, hence the possible dynamics. Furthermore, these systems always contain a support, which is used to keep the active phase dispersed, but also generates additional interfaces and complexity. Here, we evaluate the structures and dynamics of CuGa and CuZn alloys using ab initio molecular dynamics combined with metadynamics, focusing in particular on i) alloying stability for CuGa and CuZn NPs across promoter loadings (10.5–52.6 %), ii) the effect of the support, here silica, on the alloy structure, and iii) how simulations of different oxygen coverages, as a proxy of CO 2 hydrogenation conditions, favor GaO x and ZnO x phases, to understand and rationalize the catalytic activity of these materials. Remarkably, both promoters (Ga and Zn) prefer to locate at the Cu particle surface, with increasing promoter loadings, and Zn atoms readily desorb from the particle. CuZn particles interact significantly more strongly with amorphous SiO 2 than CuGa ones. Under CO 2 hydrogenation conditions, considering the addition of O adatoms, Ga completely oxidizes to Ga III when enough oxygen is present. In contrast, Zn only partially oxidizes, and a small fraction remains metallic and alloyed with Cu. These differences explain why Zn exhibits better tolerance to high promoter concentrations compared to Ga, and likely why Zn is preferred over Ga at the industrial level.