Enhancement effect of TiO₂ dispersion over alumina on the photocatalytic removal of NO_x admixtures from O₂–N₂ flow

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• 作者：Boris N. Shelimov ; Nikolai N. Tolkachev ; Olga P. Tkachenko ; Galina N. Baeva ; Konstantin V. Klementiev ; Alex ; er Yu. Stakheev ; Vladimir B. Kazansky
• 关键词：Air pollution ; NO_x removal ; Photocatalysis ; UV irradiation ; XAFS ; UV– ; vis spectroscopy
• 刊名：Journal of Photochemistry and Photobiology A: Chemistry
• 出版年：2008
• 出版时间：5 March 2008
• 年：2008
• 卷：195
• 期：1
• 页码：81-88
• 全文大小：781 K

文摘

The efficiencies of bulk TiO₂ Degussa P-25 and TiO₂ dispersed over alumina support in the photocatalytic removal of NO_x (NO + NO₂) admixtures from flowing NO–O₂–N₂ mixture modeling polluted air are compared. The TiO₂/Al₂O₃ samples with different Ti contents prepared by the sol–gel method are characterized by BET, XAFS and diffuse-reflectance UV–vis spectroscopy. At a TiO₂ content above approximately 20 wt % , a thermally stable anatase phase is formed in TiO₂/Al₂O₃ in which the Ti ions are six-coordinated. As the TiO₂ content diminishes from 20 to 1 wt % , the titanium coordination number gradually decreases, and the TiO₂ phase is no longer detected. Most likely, isolated Ti ions in different coordinations are predominant in such samples. It is found that, upon UV irradiation, NO oxidation to NO₂ in flowing NO–O₂–N₂ readily occurs over bulk TiO₂ and TiO₂/Al₂O₃ at TiO₂ loadings higher than 20 wt % . No photoreaction is observed on Al₂O₃ without TiO₂ and on TiO₂/Al₂O₃ at TiO₂ loadings below 10 wt % . Correlating these results with the XAFS and UV–vis data, it is concluded that the presence of a TiO₂ phase on the alumina surface is a prerequisite for the photocatalytic activity in the NO oxidation. The outlet concentrations of NO and NO₂ as a function of irradiation time are measured, and absorption capacities of the photocatalysts to NO_x are quantitatively assessed. The performance of TiO₂/Al₂O₃ is superior than that of bulk TiO₂, because much larger amounts of NO₂ formed by the photoreaction can be strongly trapped by the support. The highest adsorption capacity per unit catalyst weight is found for 50 % TiO₂/Al₂O₃. The NO_x adsorption capacity of bulk TiO₂ is found to increase upon humidification of the reaction gas mixture.