宽工作温度烟气脱硝催化剂制备及反应机理研究

以溶胶-凝胶法制备介孔TiO₂载体，采用分步浸渍法制备了V₂O₅-WO₃/TiO₂催化剂，借助BET、NH₃-TPD、H₂-TPR、SEM、活性评价、In-situ FT-IR等手段，考察了催化剂的结构、酸性、还原性、脱硝活性及反应机理等。介孔TiO₂载体比表面积为158.6 m²/g，制成催化剂后比表面积略有降低，约为136.7 m²/g。针对模拟烟气在φ_NH3/φ_NO=0.8的条件下测试催化剂的脱硝活性温度窗口为250~400 ℃，脱硝转化率达到80%。NH₃-TPD和H₂-TPR表征结果表明，催化剂在活性温度范围内具有典型的表面酸性位，载体TiO₂与V₂O₅之间存在的相互作用使得V₂O₅还原温度降低。利用In-situ FT-IR研究NH₃和NO在V₂O₅-WO₃/TiO₂催化剂表面吸附和氧化的反应过程发现，NH₃可同时吸附在L酸位和B酸位，NH₃在活性位上氧化脱氢形成NH₂物种是SCR脱硝反应的控制步骤。研究NO+O₂+NH₃反应时发现，吸附NH₃的催化剂引入NO和O₂后，共价吸附的NH₃首先消失。选择性催化还原反应发生在吸附态NH₃和气态或弱吸附态的NO之间，该反应遵从Eley-Rideal反应机理。

Preparation of catalyst with wide working-temperature and the reaction mechanism of flue gas denitration

The V₂O₅-WO₃/TiO₂ catalyst using the mesoporous support of TiO₂ made by sol-gel method was prepared with two-step impregnation method and tested for the selective catalytic reduction (SCR) of NO by NH₃. The characterization of the catalyst with BET, NH₃-TPD, H₂-TPR, SEM, activity evaluation and in-situ FT-IR was made to have a deep understanding of the structure, acidity, redox property, catalytic performance, de-NO_x activity and the reaction mechanism. The mesoporous TiO₂ has a surface area of 158.6 m²/g, and the prepared de-NO_x catalyst has a slightly decreased surface area of 136.7 m²/g. The V₂O₅-WO₃/TiO₂ catalyst enables the NO conversions to reach to about 80% at 250~400 ℃ and φ_NH3/φ_NO = 0.8, showing the feature of wide working-temperature for the catalyst. The surface adsorption of reactants characterized by in-situ FT-IR shows that NH₃ is adsorbed on both the Lewis and Brnsted acidic sites to generate a few different transformation species. The transformation from NH₃ to NH₂ is the rate-determining step for de-NO_x reaction in NH₃-SCR. It is found that the NH₃-SCR reaction occurs between the adsorbed NH₃ and gaseous NO, which follows the Eley-Rideal reaction mechanism.