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_xPt/TiO₂ and spatially separated CoO_x/TiO₂/Pt catalysts by atomic layer deposition (ALD). For CoO_x/TiO₂/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_xPt/TiO₂, the CoO_x/TiO₂/Pt shows higher selectivity to cinnamyl alcohol than monometallic TiO₂/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.