Interfacial Site Density Engineering of ZnO/Cu Cube Inverse Catalysts for CO2 Hydrogenation Reactions

We report an approach to engineer the ZnO-Cu interfacial site density without changes of the interfacial site structure on ZnO/Cu inverse catalysts by controlling the sizes of cubic Cu nanocrystals (c-Cu) and the loadings of ZnO. The acquired ZnO/c-Cu inverse catalysts exhibit similar apparent activation energies of around 72.2 kJ/mol in the reverse water-gas shift (RWGS) reaction and of around 47.2 kJ/mol in the CO2 hydrogenation to methanol reaction (methanol synthesis (MS)). By correlating the catalytic performance to the density of various Cu sites, we unambiguously identify that the ZnO-Cu(I)Cu interface of ZnO/c-Cu inverse catalysts is the active site for the typical RWGS and MS reactions, while the defective site on bare c-Cu of ZnO/c-Cu is the active site for the RWGS reaction under the MS reaction condition. The ZnO-Cu(I)Cu interfacial site of ZnO/c-Cu inverse catalysts is more related to the Cu defective site than to the Cu terrace site. In situ diffuse reflectance infrared Fourier transform spectroscopy characterization results demonstrate that the MS and RWGS reactions catalyzed by the ZnO-Cu interface follow formate and carboxylate hydrogenation pathways, respectively.