Disentangling Local Interfacial Confinement and Remote Spillover Effects in Oxide–Oxide Interactions

Supported oxides are widely used in many important catalytic reactions, in which the interaction between the oxide catalyst and oxide support is critical but still remains elusive. Here, we construct a chemically bonded oxide-oxide interface by chemical deposition of Co₃O₄ onto ZnO powder (Co₃O₄/ZnO), in which complete reduction of Co₃O₄ to Co⁰ has been strongly impeded. It was revealed that the local interfacial confinement effect between Co oxide and the ZnO support helps to maintain a metastable CoO_x state in CO₂ hydrogenation reaction, producing 93% CO. In contrast, a physically contacted oxide-oxide interface was formed by mechanically mixing Co₃O₄ and ZnO powders (Co₃O₄-ZnO), in which reduction of Co₃O₄ to Co⁰ was significantly promoted, demonstrating a quick increase of CO₂ conversion to 45% and a high selectivity toward CH₄ (92%) in the CO₂ hydrogenation reaction. This interface effect is ascribed to unusual remote spillover of dissociated hydrogen species from ZnO nanoparticles to the neighboring Co oxide nanoparticles. This work clearly illustrates the equally important but opposite local and remote effects at the oxide-oxide interfaces. The distinct oxide-oxide interactions contribute to many diverse interface phenomena in oxide-oxide catalytic systems.