Investigation Of Selective Catalytic Reduction Of NO And Reaction Mechanism Over MnCeZr Mixed Oxides At Low Temperature

With the improvement of our country industrialization and people’s life standard, serious environmental problems occured in recent years. And they have brought great distress to people’s life and work, especially atmospheric haze. The key pollutant of haze is nitrogen oxides (NOx), so the effective removal of NOx has become the main research direction. Selective Catalytic Reduction (SCR) has been studied by many scholars, and they prove that ammonia (NH3) remove NOx as the reducing agents for SCR efficiently. At present, the commercial denitration catalyst is vanadium based catalyst, which has many disadvantages, including high reaction temperature, and the narrow temperature window. Therefore, researches on the characteristics of catalyst with high catalytic activity and a wide temperature window, have become focus on denitration. The characteristics of composite metal oxide catalysts have been extensively studied for its high rate of NOx conversion, and a wide temperature window. Although manganese based composite metal oxide catalyst has better performance, its NOx conversion needs to improve at low temperature. Aiming at this problem, this thesis contrasts CeZr and MnCeZr composite metal oxide catalysts prepared by one-step co-precipitation method. Activity and physical chemical properties of catalyst were investigated through Brunauer-Emmertt-Teller (BET), X-ray Diffration (XRD), X-ray Photoelectron Spectroscopy (XPS), H2-Temperature Program (H2-TPR) and In situ FTIR characterization. The main research results are as follows:1. A series of CeZr catalysts was synthesized by citric acid method, homogeneous precipitation and co-precipitation method. And the NOx conversion of catalysts in the following order is prepared by co-precipitation, homogeneous precipitation, and citric acid method. By comparison, CeZr catalysts had the best catalytic activity, which were synthesized by co-precipitation method, and these BET were 52.41 m2/g. And the main distribution of pore size was about 0.04 nm, and pore was slit pore. At the same time, the high reduction temperature of Ce4+ affect the activity of CeZr catalysts at low temperature.2. The reaction conditions were [NO]=[NH3]=500 ppm; the concentration of O2 was 5%; reaction Gas Hourly Space Velocity was 30,000 h-1. Mn0.25Ce0.5Zr0.25Ox was prepared with a molar Mn and Zr ratio of 1:1 by co-precipitation method, and then calcined at 550℃. the NOx conversion of Mn0.25Ce0.5Zr0.25Ox catalyst was above 80% in the temperature range of 60-350℃. And Mn0.25Ce0.5Zr0.25Ox catalyst has the high degree of crystallization, larger BET, lower temperature reduction and the better activity in NH3-SCR at low temperature.3. The reaction of Mn0.25Ce0.5Zr0.25Ox catalyst followed E-R reaction mechanism under the condition of high reaction temperature and O2 by investigating the IR spectroscopic characterization. And its reaction process is that adsorbed NH3 reacted with reaction gas and generated the intermediates NH2NO, NH4NO2. And they decomposed into N2 and H2O eventually for its instability.