Origin of synergistic effects in bicomponent cobalt oxide-platinum catalysts for selective hydrogenation reaction

The synergistic nature of bicomponent catalysts remains a challenging issue, due to the difficulty in constructing well-defined catalytic systems. Here we study the origin of synergistic effects in CoO(x)-Pt catalysts for selective hydrogenation by designing a series of closely contacted CoO(x)Pt/TiO(2) and spatially separated CoO(x)/TiO(2)/Pt catalysts by atomic layer deposition (ALD). For CoO(x)/TiO(2)/Pt, CoO(x) and platinum are separated by the walls of titania nanotubes, and the CoO(x)-Pt intimacy can be precisely tuned. Like CoO(x)Pt/TiO(2), the CoO(x)/TiO(2)/Pt shows higher selectivity to cinnamyl alcohol than monometallic TiO(2)/Pt, indicating that the CoO(x)-Pt nanoscale intimacy almost has no influence on the selectivity. The enhanced selectivity is ascribed to the increased oxygen vacancy resulting from the promoted hydrogen spillover. Moreover, platinum-oxygen vacancy interfacial sites are identified as the active sites by selectively covering CoO(x) or platinum by ALD. Our study provides a guide for the understanding of synergistic nature in bicomponent and bifunctional catalysts.