Enhanced low temperature CO oxidation by pretreatment: Specialty of the Au-Co₃O₄ oxide interfacial structures

In this study, the morphologically uniform Co₃O₄ cubes (c-Co₃O₄), hexagonal plates (h-Co₃O₄) and tetrakaidecahedrons (t-Co₃O₄) were carefully synthesized and the crystalline facets of (001), (111), and (112) were identified. Au nanoparticles (3.1-3.3 nm) were deposited on the three Co₃O₄ entities, which were achieved to obtain specific Au-Co₃O₄ interfaces. A detailed comparison was made on the basis of their unique interfacial structures and catalytic behaviors. H₂-TPR and XPS investigations revealed the important variations in reactivity of surface oxygen, surface Co³⁺/Co²⁺ ratio, evolution of surface oxygen vacancies as well as Au oxidation state upon Au loading and pretreatments. The enhanced CO oxidation by Au deposition, and particularly He- and in situ-pretreatments, has been elucidated in light of the structural specialties associated with the three facets of Co₃O₄ substrates and the corresponding Au-Co₃O₄ interfaces. The consequent activity enhancement for Co₃O₄ substrate and Au-Co₃O₄ interface was verified: (001) > (112) > (111), and Au/(112) > Au/(001) > Au/(111). The results of Au/h-Co₃O₄ also suggest that both Au cluster and Co₃O₄ structural feature can have a profound effect on the catalytic behaviour of generated interface. The present study extends the insights into the interface-dependent CO oxidation over the controllably prepared Au-Co₃O₄ interfacial structures.