Interfacial Site\nDensity Engineering of ZnO/Cu Cube\nInverse Catalysts for CO<sub>2</sub> Hydrogenation Reactions

We report an approach to engineer the ZnO–Cu interfacial\nsite density without changes of the interfacial site structure on\nZnO/Cu inverse catalysts by controlling the sizes of cubic Cu nanocrystals\n(c-Cu) and the loadings of ZnO. The acquired ZnO/c-Cu inverse catalysts\nexhibit similar apparent activation energies of around 72.2 kJ/mol\nin the reverse water–gas shift (RWGS) reaction and of around\n47.2 kJ/mol in the CO<sub>2</sub> hydrogenation to methanol reaction\n(methanol synthesis (MS)). By correlating the catalytic performance\nto the density of various Cu sites, we unambiguously identify that\nthe ZnO–Cu(I)<sub>Cu</sub> interface of ZnO/c-Cu inverse catalysts\nis the active site for the typical RWGS and MS reactions, while the\ndefective site on bare c-Cu of ZnO/c-Cu is the active site for the\nRWGS reaction under the MS reaction condition. The ZnO–Cu(I)<sub>Cu</sub> interfacial site of ZnO/c-Cu inverse catalysts is more related\nto the Cu defective site than to the Cu terrace site. In situ diffuse\nreflectance infrared Fourier transform spectroscopy characterization\nresults demonstrate that the MS and RWGS reactions catalyzed by the\nZnO–Cu interface follow formate and carboxylate hydrogenation\npathways, respectively.