SURFACE CHARACTERIZATION OF AU HY BY XE-129 NMR AND DIFFUSE-REFLECTANCE IR SPECTROSCOPY OF ADSORBED CO - FORMATION OF ELECTRON-DEFICIENT GOLD PARTICLES INSIDE HY CAVITIES/

The Au/HY (4 wt.%) system, prepared by autoreduction of [Au(en)(2)](3) in inert gas flow at 423 K, has been studied by TEM, Xe-129 NMR and diffuse reflectance infrared spectroscopy of adsorbed CO. 80% of the m etallic clusters were in the 1-4 nm size range, and the average linear diameter was found to be 2.6 nm. Some large particles (>5 nm) were al so seen. Xenon adsorption and Xe-129 NMR spectroscopy proved the prese nce of gold clusters inside HY cavities and showed clearly that gold c lusters are weak adsorption sites for xenon. Heterogeneity in the part icle size distribution was suggested by Xe-129 NMR spectroscopy. Diffu se reflectance IR spectroscopy showed an intense asymmetric absorption band of CO linearly adsorbed on the gold surface. Two weak shoulders at ca. 2110-2120 and 2170 cm(-1) were ascribed to neutral particles an d oxidized gold sites, respectively. The main absorption band at about 2140 cm(-1) is observed for the first time for CO adsorbed on a gold surface and was attributed to CO species interacting with electron-def icient gold particles Au-n(sigma+) inside the HY lattice and in contac t with protons. CO was more strongly adsorbed on these Au-n(sigma+) pa rticles than on other gold sites; the corresponding IR stretching vibr ation was observed even after evacuation for 30 min at room temperatur e.