The Preparation Of Mn/TiO₂ Series Low-temperature SCR DeNO_x Catalysts And Its Reaction Mechanism

The selective catalytic reduction (SCR) is an important commercial process to control NO_x from stationary sources. Recently, low-temperature SCR has attracted interests for its energy efficiency and potential application. However, the activity of the catalysts is still not very high in low-temperature range, and the dispersion of active component is not good enough. Furthermore, the reaction mechanism is not very clear. These disadvantages limit the industrial application of low-temperature SCR. In order to solve these problems, the low-temperature SCR system was investigated by using the catalysts base on Mn/TiO₂.Firstly, to improve the dispersion of active component in the catalysts, sol-gel catatlyst preparing method was introduced. From the comparison of catalysts prepared by sol-gel, impregnation and coprecipitation methods, it was found that the nano-structure and the dispersion of active component of catalysts prepared by sol-gel method were both improved, leading to higher catalytic activity. Therefore, sol-gel method was a potential one to prepare low-temperature SCR catalyst.Secondly, base on the catalysts prepared by sol-gel method, the operating parameters were investigated, including the ratio of Mn/Ti, the calcination temperature, O₂ concentration, NH3 concentratoin, and the transient effect of the O₂ and NH₃. Furthermore, the kinetic study of the reaction was carried out. The reaction order and the rate constant were determined, and the apparent activation energy was also calculated.To retard the sintering of the active component, the transition metals were added to the catalysts. From the characterization of the catalysts by BET, XRD, XPS and TEM, it was found that the nano-structure of the catalysts and the dispersion of the active component were both improved, which contributed to higher NO removal.Furthermore, the reaction process and the mechanism were studied. With the addition of transition metal Fe, the coordinated NH3 was easier to be formed. The stability of the nitrate decreased, and nitrate was transformed to be an active intermediate in the reaction. Thus, the reaction could take place in another way.Finally, the resistance to SO₂ of the catalysts was also investigated. Zr was added to the catalyst. TG-DSC, XPS and DRIFT were used to investigate the state of S over the catalysts and its influence on the reaction. The mechanism of deactivation was studied. And it was found that the resistance to SO₂ of the Zr modified catalysts was enhanced.