Distribution effect of the second phase in disperse silica/X oxides (X = Al2O3, TiO2, GeO2) on their surface properties

Highly disperse oxides X/SiO2 (synthesized by using high-temperature hydrolysis of a SiCl4 and MCln (M = Al, Ti) blend or chemical vapor deposition (CVD) technique for preparation of CVD-X (X = TiO2, GeO2) on a fumed silica substrate) were studied by means of H-1 NMR, one-pass temperature-programmed desorption time-of-flight mass spectrometry (OPTPD-TOFMS), optical and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The nature and the concentration of the X phase (C-X) its distribution in (or on) the silica matrix, and pretreatment conditions have a strong influence on the features of the X/SiO2 surfaces, e.g., type, concentration, and strength of active surface sites such as Bronsted (B) and Lewis acid (L) sites. Also, these surface features affect the interaction of X/SiO2 with different adsorbates and other proper ties, which depend nonlinearly on the C-X value and exhibit an extreme character.