The Study Of Mn/TiO₂ Series Catalysts For Low-Temperature SCR Prepared By Ultrasonic Spray Pyrolysis Method

Nitrogen oxides (NOx) are the main pollutants in the atmosphere, and selective catalytic reduction (SCR) is the most widely used technology for NOx removal of the flue gas from power plant. In recent years, low-temperature SCR technology becomes very attractive. However, it is found that the preparation of catalyst is not convenient enough, and the dispersion of the active component is limited. The preparation of the catalysts is the key factor of their activity. For the advantage of ultrasonic spray pyrolysis method, it is used to prepare Mn/TiO2 catalysts for low-temperature SCR.Firstly, the activity of the catalysts with different Mn loading is investigated. With the increasing of Mn loading, both of the crystallinity and the crystal size of the catalysts decreases, while NOx conversion shows a "volcano" change. The catalyst reaches the highest activity with Mn/Ti=0.5. When Mn/Ti is 0.6, the dispersion of the active component is limited, and crystal MnOx appears, which leads to the decrease of activity accompanied with lower redox ability. As for other parameters, it is found that the calcine temperature, the type and flow rate of the carried gas has significant effect on the crystallinity, the dispersion and the redox ability of the catalysts. The catalysts should be calcined at 500 ℃ with 2 L/min of N2.In order to further enhance the activity at low temperature, three-component catalysts were prepared by doping transition metal, such as Fe, Ce, Zr and Sn. It shows that the Fe-doped catalyst has the highest NOx removal activity at low temperature, and the doping amount should be 0.05. From the results of XRD and XPS, it is found that Fe-doping can enhance the interaction of metal oxides, and increase the surficial concentration of active components and the active oxygen, which has positive effect on catalytic activity.Finally, the kinetics study of Mn(0.5)/TiO2 and Fe(0.05)-Mn(0.5)/TiO2 was investigated. The reaction order of NO, NH3 and O2 are 1,0 and 0.5, respectively. The apparent activation energy was calculated to be 27.65 and 14.46 kJ/mol for Mn(0.5)/TiO2 and Fe(0.05)-Mn (0.5)/TiO2, respectively. It indicates that Fe (0.05)-Mn(0.5)/TiO2 should have higher activity for NO removal at low temperature.