Zinc oxide morphology-dependent CuOx-ZnO interactions and catalysis in CO oxidation and CO2 hydrogenation

CuO/ZnO catalysts with different ZnO morphologies, i.e. nanoplates (p-ZnO) and nanorods (r-ZnO), have been prepared to test for CO oxidation and CO2 hydrogenation. Strong morphology-dependent CuOx-ZnO interactions were observed, which are tightly associated with the ZnO morphology. p-ZnO predominantly exposing polar {002} facets greatly promote the CuOx-ZnO interactions, contributing to the stabilities of CuOx/ZnO catalysts in both reactions. Experimental evidences reveal that CuO-ZnO interfaces act as the active sites in CO oxidation. CuO/p-ZnO catalyst with stronger CuO-ZnO interactions can facilitate the generations of fine CuO and interfacial Cu(I) species, responsible for the adsorption and reactivity of CO and subsequently the high (intrinsic) activity in CO oxidation. However, CuO/ZnO catalysts undergo in situ restructuring to generate Cu/ZnO in CO2 hydrogenation, whose catalytic performance are determined by the key step of CO2 activation. Consequently, Cu/r-ZnO catalyst possessing more surface basic sites exhibits better catalytic performance. These results greatly deepen the fundamental understanding of Cu-based catalysts in both reactions and broaden the concept of morphology-dependent catalysis of oxide-based nanocrystal catalysts that varies with the reactions catalyzed.