Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration.

Catalytic and catalytic photo-assisted hydration of propene to form 2-propanol in gas-solid regime at atmospheric pressure and 85 °C were carried out by using a heteropolyacid (POM) supported on different oxides. Binary materials were prepared by impregnation of H3PW12O40 on different commercial and home prepared supports (TiO2, SiO2, WO3, ZrO2, ZnO, Al2O3). Some of the composites were active both for catalytic and catalytic photo-assisted reactions. The Keggin type POM was completely and partially degraded, when supported on ZnO and Al2O3, respectively, and these binary solids always resulted as inactive for both catalytic and catalytic photo-assisted reactions. The supported Keggin POM species played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary presence of heat and UV light improved the activity of almost all POM supported materials. All materials were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM), diffuse reflectance spectroscopy (DRS), determination of the conduction and valence band energy by photovoltage measurements, Fourier transform infrared spectroscopy (FTIR), NH3-TPD experiments and time resolved microwave conductivity (TRMC).

Photocatalytic activity of TiO2/SiO2 systems.

Silica-supported TiO(2) powders were synthesized by a wet method under mild conditions. The aim of the work was the preparation of TiO(2)/SiO(2) additives for photocatalytic cements. Three types of commercial SiO(2) were used as supports: Cabot, Axim and Fly Ash. Cabot silica was ultra-pure whereas the other two silica contained different percentages of various oxides. The TiO(2)/SiO(2) samples, denoted TiO(2)/Cabot, TiO(2)/Axim and TiO(2)/Fly Ash, were prepared by boiling suspensions obtained by addition of silica to a solution of TiCl(4) in water (volume ratio 1:10). The photocatalytic activity was evaluated in a gas-solid system both in batch and in continuous reactors using 2-propanol as probe molecule. SEM-EDX analysis revealed that titanium dioxide was quantitatively deposited on silica. TiO(2)/Axim and TiO(2)/Fly Ash were scarcely active whereas a good photoactivity was exhibited by the TiO(2)/Cabot sample both in the batch and in the continuous system. Consequently only the last sample was tested for both NO(x) abatement and for 4-nitrophenol photodegradation in a liquid-solid system.

Preparation of N-doped TiO(2): characterization and photocatalytic performance under UV and visible light.

Nanocrystalline N-doped TiO(2) samples were prepared by using TiCl(4) or TiOSO(4) as precursors. The powders were characterized by X-ray diffraction, BET specific surface area measurements, scanning electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested using the photodegradation of 4-nitrophenol under UV and visible light.Some samples were more active than commercial Degussa P25. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed in the samples obtained from TiCl(4). Two absorption edges were observed in the samples derived from TiOSO(4) and calcined at 400 degrees C: the main edge due to TiO(2) and the second one due to the presence of a localised midgap band that induces the visible light activity.