SURFACE CHARACTERIZATION OF ZIRCONIA-COATED ALUMINA AND SILICA CARRIERS

Silica- and alumina-supported zirconia samples have been prepared by i mpregnation of the supports with a solution of zirconium alkoxide (n-p ropoxide) in n-propanol containing ZrO2 in the ranges 1.2-28.6 and 2.2 -23.2 wt%, respectively. The samples were characterized by the S-BET m ethod, XRD, XPS, and FTIR. The x-ray diffraction showed that zirconia on silica was amorphous for all concentrations of ZrO2. Zirconia on al umina was amorphous up to 17.1 wt% ZrO2; beyond this value crystallite s were formed. The increase in the XPS IZr 3d/ISi 2p indicates that Zr O2 appears as a monolayer on silica near the theoretical monolayer cov erage (about 28.6 wt%), whereas for alumina-supported zirconia samples the monolayer is formed at lower ZrO2 content (between 12.9 and 17.1 wt%). It was observed by pyridine adsorption that the strong Lewis aci d sites on alumina decreased after deposition of zirconia. However, th e number of Lewis acid sites on silica-supported zirconia samples, evo ked by an increase of the positive charge on Zr atoms compared to pure zirconia, increases with increasing ZrO2 content. Some Bronsted acid sites were detected on ZrO2/SiO2 samples due to the slightly higher el ectron density on the oxygen associated with Si atoms detected by XPS. (C) 1997 Academic Press.