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.