Distribution Effect of the Second Phase in Disperse Silica/X Oxides (X = Al2O3, TiO2, GeO2) on Their Surface Properties

Highly disperse oxides X/SiO 2 (synthesized by using high-temperature hydrolysis of a SiCl 4 and MCl n (M = Al, Ti) blend or chemical vapor deposition (CVD) technique for preparation of CVD-X (X = TiO 2, GeO 2 ) on a fumed silica substrate) were studied by means of 1 H 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/SiO 2 surfaces, e.g., type, concentration, and strength of active surface sites such as Brønsted (B) and Lewis acid (L) sites. Also, these surface features affect the interaction of X/SiO 2 with different adsorbates and other properties, which depend nonlinearly on the C X value and exhibit an extreme character.