SILICA-SUPPORTED ZIRCONIA .1. CHARACTERIZATION BY INFRARED-SPECTROSCOPY, TEMPERATURE-PROGRAMMED DESORPTION, AND X-RAY-DIFFRACTION

Silica-supported zirconia samples have been prepared by aqueous impreg nation of a nonporous fumed silica with zirconyl nitrate giving 5, 10, or 20 wt % ZrO2 on SiO2 after calcining at 450 degrees C. The surface areas were comparable to that of the parent silica (200 m(2)/g), and IR spectra showed OH peaks characteristic of SiO2 and of monoclinic Zr O2. The intensity of the SiOH peak decreased with ZrO2 loading, and a new IR band near 945 cm(-1) was attributed to the formation of ZrOSi l inkages. The ZrO2 is dispersed as clusters on SiO2, and free SiOH is s till available even at the highest ZrO2 loading. X-ray diffraction sho ws either that SiO2/ZrO2 is amorphous or that the ZrO2 crystallites ar e too small to be detected. Infrared spectroscopy of adsorbed ammonia and pyridine have shown that sites for coordination exist on all mixed oxides and on pure ZrO2, The number of sites for coordination of NH3 increases as the ZrO2 loading increases, Moreover, there are very weak Bronsted acid sites on SiO2/ZrO2 which can protonate NH3; these are a bsent on ZrO2. Temperature-programmed desorption of adsorbed NH3 has s hown that the number of sites available for coordination, protonation, or H-bonding to ZrOH is about 2.5-3-fold greater than the number of s ites for H-bonding to SiOH groups on pure SiO2. Finally, IR of adsorbe d CO2 (a probe of surface basicity) has shown that SiO2/ZrO2 is less b asic than of pure ZrO2.