Highly dispersed X/SiO2 and C/X/SiO2 (X = alumina, titania, alumina/titania) in the gas and liquid media

Fumed oxides, such as silica, alumina, titania, and mixed XI silicas (X = A l2O3 (AS), TiO2 (TS), CVD-TiO2, Al2O3/TiO2 (AST)), pristine or covered by c arbon deposits formed due to pyrolysis of cyclohexene, were studied using n itrogen adsorption-desorption, photon correlation spectroscopy particle siz ing, and electrophoresis. A significant influence of the nature of surface- active sites and structural features of oxides (individual silica, mixed fu med, or prepared using chemical vapor deposition (CVD)) on the pyrolysis of cyclohexene is observed with respect to the pore size distributions due to differences between primary particles in aggregates and on their outer sur faces in the filling of channels by pyrocarbon, resulting also in a decreas e in fractal dimension. Structural characteristics and dependences of the p article size distribution and electrokinetic potential of X/SiO2 and C/X/Si O2 on the pH of aqueous suspensions suggest that the carbon deposit covers mainly acidic sites at the X/SiO2 interfaces and X phase patches possessing catalytic activity in pyrolysis, as the negative charge of particles is re duced by pyrocarbon grafting, (C) 2000 Academic Press.