Causation of catalytic activity of Cu-ZnO for CO₂ hydrogenation to methanol

The catalytic active sites over the universal Cu-ZnO based catalysts for CO₂ hydrogenation to methanol are still the subject of intense debate. Herein, unified first-principle calculations for the CO₂ conversion processes over the controversial catalytic active sites, i.e., Cu crystal steps, Zn-doped Cu sites, Cu/ZnO interfaces, and the Cu and Zn closest packing crystal facets, are implemented, which is verified with the experimental facts based on support-free catalysts of porous hollow nanospheres that eliminate the interferences from the catalyst supports. We discover that the enhanced catalytic activity corresponds to the uplifted and spin-polarized density of states owing to the hybridization of Cu and Zn species, and prove that Cu/ZnO interfaces and Zn-doped Cu sites play significant roles among the catalytic active sites, and successively participate in the CO₂ conversion, of which initial step should primarily be the hydrogen-free CO₂ dissociation, differing from the preconceived viewpoint of hydrogen-assisted dissociation of CO₂.