MnO_x/CeO₂/SiO₂Catalysts Prepared By Adsorption Phase Reaction Technique For Selective Catalytic Reduction Of NO_x At Low-Temperature

NOx is one of the main air pollutants and it can be removed efficiently through Selective Catalytic Reduction (SCR) technique. Recently, low-temperature SCR has been widely researched for its energy conservation.In order to further investigate the relationship between catalysts structure and low-temperature catalytic performances, we prepared MnOx/CeO2/SiO2catalysts through adsorption phase reaction technique based on our previous studies.Firstly, we prepared Mn-based catalysts which were respectively modified by Ce, Cu, Fe, Co and Zr through adsorption phase reaction technique. After the characterization and activity test of these catalysts, we found that the addition of CeO2could improve the dispersity, the oxygen storage capacity and the acidity of the catalysts. Therefore, the activity of these catalysts increased. Then we varied the contents of CeO2, and found that Mn ions on the surface of the catalysts could enter the crystal lattice of CeO2and lead to the formation of oxygen vacancies. It was confirmed that the catalytic activity was affected by the concentration of the oxygen vacancies. Finally, we varied the contents of Mn, the results showed that the concentration of oxygen vacancies was not the only determinant of the catalytic activity.In order to improve the interaction between Mn and Ce and further regulate the concentration of oxygen vacancies, we changed the means of adding raw materials, the absorption sequence and the alcohol thermal synthesis temperature during the preparation of the catalysts. The results manifested that the catalytic activity was affected by the concentration of oxygen vacancies. However, when the concentration of oxygen vacancies reached a certain value, the catalytic activity didn’t increased sharply. We guessed that the catalytic activity may be restricted by the adsorption of NH3on the acidic sites when the oxygen vacancies were adequate.In order to demonstrate whether the acidity is the main restrict of the catalytic activity when the oxygen vacancies were adequate, we changed the kind of absorbate, the concentration of water and the addition of CA during the preparation of the catalysts. The results indicated that improving the acidity can lead to the increasment of the activity of the catalyst when the oxygen vacancies were adequate.