| In view of the catalytic activity of NH3-SCR catalysts is closely related to its surface acidity. In this research, solid acid supported transition metal oxides were studied for the NH3-SCR of NOx. It found that Cr/W/Zr and W/Fe catalysts showed high deNOx activity. The structure of these catalysts were characterized by X-ray diffraction (XRD), XPS, H2-TPR. The reaction mechanism on NH3-SCR catalysts were studied by the in situ infrared reflectance spectroscopy.2Cr/12.5W/Zr catalyst prepared by incipient impregnation method showed high activity, with nearly 90% NOsx conversion achieved in the temperature range of 300-450℃. Moreover, high tolerance to water and sulfur poisoning was observed. The doping of Cr improved the dispersion of W, enhancing the redox property of the catalyst. The strong surface acidity over W/Zr catalysts was beneficial to the adsorption and activation for reactants on the catalyst surface, producing more reactive intermediates, thus promoting the NH3-SCR of NOx to proceed.The catalytic performance over solid acid is closely related to the calcined temperature and W content. The optimal calcined temperature is 550℃ and the optimal W content is 10%. Over 10W/Fe, more than 90% NOX conversion was obtained in the range of 275-425℃ with a GHSV of 100,000 h-1. Meanwhile,high N2 selectivity and water sulfur resistance were exhibited. The interaction between W and Fe reduced the crystallinity of Fe particles. It also leaded the Fe3+ and W6+ to be more easily reduced, improving the redox performance. By in situ infrared reflectance It was found that W and Fe formed solid acid geatly enhanced the acidity of the catalyst. It reduced the stability of nitrate adsorbed on the catalyst basic sites, simultaneously increased the acidity of ammonia adsorption activity center, making the gas phase NH3, NH3 combined with L acid sites and ammonia oxidizing species be involved in the reaction. All of these contribute to enhancing the catalytic performance. |
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