Characterization and activity of Pd-modified TiO2 catalysts for photocatalytic oxidation of NO in gas phase

Pd-modified TiO2 prepared by thermal impregnation method was used in this study for photocatalytic oxidation of NO in gas phase. The physico-chemical properties of Pd/TiO2 catalysts were characterized by X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller measurements (BET), X-ray photoelectron spectrum analysis (XPS), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), UV-vis diffuse reflectance spectra (UV-vis DRS) and photoluminescence spectra (PL). It was found that Pd dopant existed as PdO particles in as-prepared photocatalysts. The results of PL spectra indicated that the photogenerated electrons and holes were efficiently separated after Pd doping. During in situ XPS study, it was found that the content of hydroxyl groups on the surface of Pd/TiO2 increased when the catalyst was irradiated by UV light, which could result in the improvement of photocatalytic activity. The activity test showed that the optimum Pd dopant content was 0.05 wt.%. And the maximum conversion of NO was about 72% higher than that of P25 when the initial concentration of NO was 200 ppm, which showed that Pd/TiO2 photocatalysts could be potentially applied to oxidize higher concentration of NO. (C) 2008 Elsevier B.V. All rights reserved.