CVD-titania/silica gel carbonized due to pyrolysis of cyclohexene

Titania/silica gels covered by a carbon layer using pyrolysis of cyclohexene at 973 K and containing different amounts of titania (C-TiO2) and carbon deposit (Cc) have been studied by means of pyrolysis kinetics, nitrogen adsorption/desorption, TEM, IR spectroscopy, differential thermogravimetry, and theoretical methods. The pyrolysis rate depends on the concentration and the characteristics of a titania phase, as anatase, which forms at a lower synthetic temperature in comparison with rutile, catalyzes this process more strongly than rutile does. The adsorbent mesoporosity decreases with increasing concentrations of titania and carbon covering the oxide surface mainly in mesopores, but in the case of C/SiO2, carbon can be also grafted onto the outer surface of silica. The microporosity (maximal for binary systems C/SiO2 or TiO2/SiO2) of carbon/titania/silica gels is relatively low and changes slightly with increasing deposit concentration. The influence of carbon on the specific surface area of the adsorbents is weaker than that of titania due to not only the difference in the morphology of these deposits per se but also the types of their distributions and contacts between grafted matters and substrate surfaces. Carbon deposit reduces the amount of adsorbed water to a greater extent than titania does. Theoretical modeling of C/TiO2/SiO2 and pyrolysis of cyclohexene has been performed using different quantum chemical methods and molecular mechanics.