Preparation And Sm-Modification Of Mn-Ti-Based Low-Temperature NH₃-SCR Catalyst

With the rapid development of our country’s economy,the energy structure dominated by coal resources has resulted in the generation of large amounts of nitrogen oxides,which pose varying degrees of threat to the ecological environment and human health.The main industrial method for removing nitrogen oxides is the selective catalytic reduction of NO_xusing ammonia gas as a reducing agent.However,the active temperature window required for the catalyst in the industry is usually in the range of 300°C to 400℃,some of the flue gas needs to be reheated to reach this temperature,increasing industrial operating costs.Because the catalyst is applied prior to the dedusting and desulfurization units,it is extremely susceptible to dust coverage and sulfation,which greatly reduces the service life of the catalyst.Therefore,low temperature NH₃-SCR is favored by more and more researchers.In this paper,two Mn and Ti are used as active catalyst components,and the effects of different preparation conditions such as calcination temperature,calcination time,citric acid amount,and different metal sources on the structure and physicochemical properties of Mn-Ti-based catalysts are investigated by sol-gel method.Through analysis of various characterization results,it is found that the calcination time and p H value show little effect on the structure and catalytic activity of the catalyst.The changes in preparation conditions such as calcination temperature,different metal sources and citric acid content show great impact on the catalyst structure and low-temperature de NO_xactivity.The catalytic performance is improved by increasing the specific surface area,redox performance and surface chemisorped oxygen.When the preparation conditions are citric acid:metal ion=6:1,roasting temperature400℃,roasting time 5 h,p H=6,Mn（manganese nitrate）:Ti（tetrabutyl titanate）=2:1,the prepared Mn-Ti catalyst shows the best low temperature catalytic activity.When the reaction temperature is 135℃,the catalyst can achieve 100%NO_xconversion,and the catalyst has the widest active temperature window of 95°C to 315℃.In order to further improve the catalyst’s low-temperature NH₃-SCR catalytic activity and sulfur resistance,the Mn-Ti-based catalyst was doped with Sm by the impregnation method,sol-gel method and co-current co-precipitation method,separately.The effects of different preparation methods,Sm content and calcination temperature on the Sm-Mn-Ti composite oxide catalyst were investigated.The changes of the catalytic activity and sulfur resistance of the catalyst modified by Sm were analyzed.The results show that0.1Sm-Mn-Ti-400 composite oxide catalyst prepared by concurrent co-precipitation method showed the best catalytic activity.The catalytic activity results of low-temperature NH₃-SCR show that the doping of Sm in the 0.1Sm-Mn-Ti-400 catalyst further improves the NO_xconversion in the low temperature region,and it generates the widest active temperature window of 60°C to 315℃.Through comprehensive comparison and analysis of various characteristics,it is found that the addition of Sm element not only improves the low-temperature catalytic activity of the catalyst by improving the specific surface area,redox performance,chemical adsorption of oxygen and surface Mn⁴⁺species content,but also inhibits the conversion of SO₂to SO₃and improves the sulfur resistance of the catalyst.