Mononuclear AuIII and AuI Complexes Bonded to Zeolite NaY:  Catalysts for CO Oxidation at 298 K

Mononuclear gold complexes in zeolite NaY were synthesized from initially physisorbed Au(CH3)2(C5H7O2) and characterized in reactive atmospheres by X-ray absorption and infrared spectroscopies. Under conditions of CO oxidation catalysis at 298 K and 760 Torr in a flow reactor, the gold remained as mononuclear species, as demonstrated by extended X-ray absorption fine structure spectra indicating the lack of Au−Au contributions. X-ray absorption near edge structure data and infrared spectra in the νCO region indicate that the initially present AuIII was reduced to AuI as the catalyst lost activity during operation in the flow reactor, and the data give no evidence of the formation of clusters of zerovalent gold. The AuIII complex is an order of magnitude more active as a catalyst than the AuI complex. These results are the first evidence of supported mononuclear cationic gold complexes as CO oxidation catalysts.