Palladium enhanced resistance to deactivation of titanium dioxide during the photocatalytic oxidation of toluene vapors

摘要

Different Pd/TiO_2 samples were prepared with metal loading ranging from 0.1 to 1% (w/w) and using two different titanium dioxide powders samples as support.The XRD data reveal that the incorporation of palladium can increment slightly the rutile to anatase ratio,but it does not change the textural parameters of TiO_2 extensively.The H_2 chemisorption measuremkents indicate that the dispersion of palladium decreases on increasing the metal loading.The Pd particles remain in a metallic state after reduction in hydrogen and the subsequent exposure to atmospheric air,as revealed by UV-Vis DRS.Most of the Pd/TiO_2 catalysts show a considerable increment of the conversion of toluene vapor afte rprolonged UV-irradiation,meanwhile the benzaldehyde production decreases slightly with respect to bare TiO_2.However,this enhancement of the photoactivity is not observed initially and it is independent of the palladium content and dispersion.Therefore,the main effect of palladium is to hinder the deactivation of the photocatalysts.On the other hand,the addition of palladium is slightly detrimental for the photoactivity.The presence of water vapor in the feed stream is beneficial for the photo9activity for both Pd-loaded and neat TiO_2.In contrast,a moderate increment in the operation temprature is not beneficial for the photoactivity,despit Pd/TiO_2 samples present a significant thermal activity in the dark.FTIR analyses of the used Pd/TiO_2 catalysts indicate that the surface of both the metallic particles and the support are partly covered with by-products of the photo-oxidation of toluene.A limited oxidation of the palladium particles also takes place during photoreaction.