Preparation And Modification Of Mn/TiO₂ Zeolite Catalyst For Wide Temperature Scr Denitration

Nitrogen oxides?abbreviated as NO_x?are the general names of oxynitrides.They mainly exist in the form of no and NO₂ in the air,which are extremely harmful to nature and human beings,such as photochemical smog,acid rain,etc.Since the 13th five year plan,China has strictly controlled the acid gas emission and rectified the pollution sources of the industry.At present,selective catalytic reduction?SCR?is used to remove NO_x from flue gas.At present,high temperature catalyst is mostly used,and the reaction temperature is 350?-500?.However,the temperature of smelting flue gas is usually only 150?-200?,and the effect of high temperature SCR catalyst is poor,so it is an urgent task to develop a high activity SCR denitration catalyst suitable for a wide temperature range.As the most common catalyst for SCR denitration at low temperature,Mn-TiO₂system has the disadvantages of poor thermal stability,small specific surface area,and less adsorption of NH₃ with catalyst at low temperature.In this paper,titanium dioxide nanotubes were prepared to increase the specific surface area,and composite support was used to improve the thermal stability and adsorption of the catalyst.The conclusions are as follows:1. When the concentration of CTAB is 0.04M and the ultrasonic power is 180W,the tubular catalyst with uniform pore diameter and tube length is obtained.The ratio of length to diameter is 8:1,the specific surface area is 154m²/g,and the average pore diameter is 10.4nm.The denitration rate of the TiO₂nanotube loaded with Mn can reach 85%at 200?,which is higher than 75%of the denitration activity of TiO₂at the same temperature.When Zr O₂ was added to Mn/Ti NT,the catalytic activity increased to 90%,and was stable in the range of 200?-350?,which may be related to the increase of specific surface area and the dispersion of active components.2. The mixed TiO₂/ZSM-5 composite support was prepared by mechanical grinding method,and the Mn/TiO₂-ZSM-5 catalyst was prepared by impregnation method.The specific surface area and pore size distribution of the composite support are between two kinds of single carriers,and the crystal structure has not changed significantly.However,the adsorption of NH₃ on the mixed carrier has significantly improved its denitrification activity,which is stable at more than 95%,and stable at175?-350?.It may be related to the dispersion of active components caused by the addition of molecular sieves with large specific surface.3. Mn/TiO₂ and Mn/ZSM-5 were mixed to obtain the mixed catalyst.It was found that the catalyst with the ratio of 12wt%Mn/ZSM-5+8wt%Mn/TiO₂ had better activity,which was similar to the activity of Mn/TiO₂-ZSM-5,indicating that there was competitive adsorption between TiO₂ and ZSM-5.Through the characterization of H₂-TPR and XPS,it is found that the active component of TiO₂ is mostly Mn⁴⁺,which is favorable for the reaction with higher no conversion.Through the characterization of composite carrier NH₃-TPD and NO-TPD,it is found that ZSM-5 component of the mixed catalyst has better adsorption performance for the reaction gas.When the temperature rises,NO will be converted from physical adsorption to chemical adsorption,and the adsorption capacity will be reduced.The reaction mechanism will be transformed from L-H mechanism followed in the low temperature stage to E-R mechanism.