Gold Supported on La2O3: Structure and Reactivity with CO2and Implications for CO Oxidation Catalysis

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A sample consisting of gold dispersed on high-area porous lanthanum oxide was prepared by adsorption of dimethylgold acetylacetonate. X-ray absorption spectroscopy and infrared (IR) spectroscopy were used to characterize the gold species and their ligands, and CO as a probe molecule was used with IR spectroscopy to follow the changes in the gold species under various reaction conditions, with a focus on oxidation−reduction processes. Gold on the initially prepared sample was present as Au 3+ species, but only a small fraction of them were apparently reactive with the CO probe molecule. After evacuation at elevated temperatures, the gold was first reduced to give clusters incorporating positively charged gold species, which in turn were converted to neutral gold species. CO and O 2 reacted with the reduced sample in a process that appears to be autocatalytic and related to the existence of oxidized gold species that facilitate oxygen activation and CO oxidation catalysis. Surprisingly, it was also established that—although they are inert toward O 2 at room temperature—the supported gold nanoparticles are readily oxidized by CO 2, a result that suggests that CO 2 may be the actual oxidant of gold in CO oxidation catalysis. The supported zerovalent gold nanoparticles are also easily oxidized by NO and by NO 2 .