Tailoring the surface structures of iron oxide nanorods to support Au nanoparticles for CO oxidation

Abstract

AbstractIron oxide supported Au nanomaterials are one of the most studied catalysts for low-temperature CO oxidation. Catalytic performance not only critically depends on the size of the supported Au nanoparticles (NPs) but also strongly on the chemical nature of the iron oxide. In this study, Au NPs supported on iron oxide nanorods with different surface properties through β-FeOOH annealing, at varying temperatures, were synthesized, and applied in the CO oxidation. Detailed characterizations of the interactions between Au NPs and iron oxides were obtained by X-ray diffraction, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. The results indicate that the surface hydroxyl group on the Au/FeOOH catalyst, before calcination (Au/FeOOH-fresh), could facilitate the oxygen adsorption and dissociation on positively charged Au, thereby contributing to the low-temperature CO oxidation reactivity. After calcination at 200 °C, under air exposure, the chemical state of the supported Au NP on varied iron oxides partly changed from metal cation to Au0 along with the disappearance of the surface OH species. Au/FeOOH with the highest Au0 content exhibits the highest activity in CO oxidation, among the as-synthesized catalysts. Furthermore, good durability in CO oxidation was achieved over the Au/FeOOH catalyst for 12 h without observable deactivation. In addition, the advanced identical-location TEM method was applied to the gas phase reaction to probe the structure evolution of the Au/iron oxide series of the catalysts and support structure. A Au NP size-dependent Ostwald ripening process mediated by the transport of Au(CO)x mobile species under certain reaction conditions is proposed, which offers a new insight into the validity of the structure-performance relationship.