ABSTRACT
A systematic study is presented on the effect of crystallite size of Anatase (Hombikat, Sachtleben), varied by calcination at different temperatures up to 800 degrees C, on photocatalytic activity in cyclohexane selective oxidation. Two different reactors were used to test the materials: a top illumination reactor and an in situ ATR-FTIR cell. Properties such as crystallinity and associated availability of holes and electrons for surface reactions, as well as the amount of surface OH-groups, are shown to have a significant influence on TiO(2) activity, (surface) selectivity, and stability. Upon increasing the crystallite size, productivity (g(-1)(catalyst)) decreases, while (i) the TOF (moles of cyclohexanone formed per minute per OH-site), (ii) the rate of cyclohexanone desorption, (iii) catalytic site stability, and (iv) the cyclohexanol/cyclohexanone ratio increase. The results are discussed on the basis of a reaction scheme, and a simple reaction rate equation.
ABSTRACT
Time resolved microwave conductivity (TRMC) measurements show that the presence of Au on anatase Hombikat UV100 significantly reduces the lifetime of mobile electrons formed by photo-excitation of this photocatalyst at 300 nm, providing evidence for the widely acclaimed electron localization effect of Au in promoting TiO(2) photocatalysts. Electron localization efficiency of Au was even higher for Au-promoted Hombikat calcined at 400 degrees C, explained by enlargement of the anatase particle size and the associated, relatively larger fraction of anatase particles in direct contact with Au.
