Gold Nanoclusters Entrapped in the α-Cages of Y Zeolites:  Structural Characterization by X-ray Absorption Spectroscopy

Au(CH3)2(C5H7O2) was used as a precursor to synthesize mononuclear gold complexes in faujasites, NaY zeolite, and dealuminated Y zeolite. Treatment of these supported complexes in flowing helium as the temperature was increased led to the gradual reduction of the gold and formation of gold nanoclusters in each zeolite, which were characterized by X-ray absorption spectroscopy. After treatment at the highest temperature, 573 K, the average diameters of the gold clusters were approximately 10 and 8 Å in NaY zeolite and dealuminated Y zeolite, respectively; these clusters are smaller than the diameters of the α-cages of the zeolite. The results indicate that the supported clusters were trapped within these cages and that the cages limited their sizes; in contrast, clusters formed similarly on the surfaces of metal oxides are significantly larger than those formed in the zeolites.