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.