Gas-phase photo-assisted mineralization of volatile organic compounds by monolithic titania catalysts

A new monolithic catalyst based on Pt/TiO2 has been developed for the photocatalytic destruction of traces of organic pollutants present in gaseous emissions. The influence of both the raw materials used in the preparation of the support (titanias and magnesium silicates) and the nature of the doping phase (Pt or V2O5) on the properties of the catalysts have been studied. Finally, a hydroxylated titania gel was selected as a catalyst precursor, a mixture of magnesium silicates as inorganic binders and platinum as the doping phase. The developed monolithic catalyst can be described as composed of platinum dispersed over the surface of titania-anatase particles, which were intimately mixed with the fibrous magnesium silicate. Using the selected catalyst, trichloroethylene photocatalytic oxidation tests showed complete mineralization at operating temperatures between 80 degrees C and 110 degrees C, and residence times lower than 0.03 s without any thermocatalytic contribution. Although toluene did not reach appreciable photoactivity between 130 degrees C and 200 degrees C and a residence time of 0.06 s, this compound can be completely oxidized between 250 degrees C and 300 degrees C with the help of infrared radiation without significant production of by-products. Consequently, the operating conditions needed to achieve the complete mineralization of the VOC by photocatalytic oxidation are strongly dependent on the type of compound to be removed. (C) 1998 Elsevier Science B.V.