Destruction of Volatile Organic Compounds (VOC's) Using TiO_2 Photocatalysis

摘要

Strong evidence is presented for a photo-thermal synergism in gas phase TiO_2 photocatalysis. Photo-oxidation efficiencies of aliphatic alcohols can be significantly improved by the simultaneous application of thermal and photonic energy. The mechanistic nature of this synergism is not yet clear. Gas phase reactions in an annular reactor with an internal UV light source and particulate film coatings of high surface area TiO_2 have been carried out on aliphatic alcohols, including ethanol, at moderate temperatures (< 250℃). Reaction products have been analyzed in-situ by Gas Chromatography. In addition, high surface area, Pt loaded TiO_2 catalysts have been prepared by a photo-deposition method. The photo-induced activity is additive to the thermal activity to temperatures near 150℃. At higher temperatures photo-illumination offers no added activity to thermal catalysis. Energy efficient and cost effective oxidation of air-borne organic contaminants is of interest to several key industries. Photo-thermal catalysis may present a more cost effective and efficient oxidation technology by capitalizing on the synergy of photo and thermal oxidation at moderate temperatures. Practical utilization of the TiO_2 for VOC oxidation may require the use of thin films dispersed on UV-transparent supports. We will describe the synthesis and characterization of TiO_2 thin films and the effect of film morphology on photoactivity. The thin films are prepared via sol-gel synthesis routes and examined by transmission electron microscopy as well as small angle x-ray scattering. Factors that have been considered are pressure drop through the UV-transparent support as well as optimal mass transfer to achieve high volumetric efficiencies.