Improved performance of TiO2 in the selective photo-catalytic oxidation of cyclohexane by increasing the rate of desorption through surface silylation

The effect of silylation on the performance of an anatase TiO2 catalyst in the selective photo-oxidation of cyclohexane was investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and an illuminated slurry reactor. The rate of cyclohexanone formation showed a dependency on the availability of surface active OH sites and on the desorption rate of cyclohexanone. Two classes of catalysts could be identified: (1) containing less than 1.0 wt.% Si where the cyclohexanone formation rate is decreased by silylation due to a decrease in OH availability and (2) containing more than 1.0 wt.% Si where the improved desorption rate becomes dominant over the decreasing OH availability, and the cyclohexanone formation rate observed in an illuminated slurry reactor is increased. ATR-FTIR results confirmed the linear increase in the rate of cyclohexanone desorption as a function of increasing Silane content of the TiO2 surface. Because of this enhanced desorption, silylation also resulted in a decrease in rate of formation of surface deactivating carbonate and carboxylate species on TiO2.