Formation of Nonclassical Carbonyls of Au3+in Zeolite NaY: Characterization by Infrared Spectroscopy

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Abstract
Adsorption of CO on gold supported in zeolite NaY at 85 K led to the formation of (i) various carbonyls and isocarbonyls typical of the zeolite and (ii) carbonyls formed at cationic gold sites (observed in the 2186−2171 cm-1 region). Analysis of the behavior of the bands allows their assignment to carbonyls of Au3+ ions. At temperatures higher than 220 K, CO adsorption led to the formation of a new type of Au3+−CO species (2207 cm-1). Once formed, these complexes could be transformed into the dicarbonyls Au3+(CO)2 when the sample was cooled to 85 K in the presence of CO. The results are explained by migration of Au3+ ions to more accessible positions within the zeolite at increasing temperatures. When a CO molecule is already adsorbed, it stabilizes the Au3+ ion in the new position, and a second CO molecule can be coordinated, thus forming a geminal species. These results are the first evidence of Au3+(CO)2 complexes.

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