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Abstract:
Gold nanoparticles (Au NPs) on oxygen-free supports were examined using near ambient pressure X-ray photoelectron spectroscopy under CO oxidation conditions, and ex situ using scanning electron microscopy and transmission electron microscopy. Our observations demonstrate that Au NPs supported on carbon materials are inactive, regardless of the preparation method. Ozone (O<sub>3<sub>) treatment of carbon supports leads oxygen-functionalization of the supports. When subsequently exposed to a CO feed, CO is oxidized by the functionalized sites of the carbon support via a stoichiometric pathway. Microscopy reveals that the reaction with CO does not change the morphology of the Au NPs. In situ XPS reveals that the O<sub>3</sub> treatment gives rise to additional Au 4f and O 1s peaks at binding energies of 85.25–85.6 and 529.4–530 eV, respectively, which are assigned to the presence of Au oxide. A surface oxide phase is formed during the activation of Au NPs supported on Au foil by O<sub>3</sub> treatment. However, this phase decomposes in vacuum and the remaining low-coordinative atoms do not have sufficient catalytic properties to oxidize CO, so the size reduction of Au NPs and/or oxidation of Au NPs is not sufficient to activate Au.
