Preparation Of Mn-based Medium-low Temperature Denitration Catalysts And Its Application In NH₃-SCR Reaction

With the accelerated urbanization and the rapid development of industry,NO_x（one of the main pollutants in the atmosphere）emitted from industrial exhaust emission has caused great harm to the atmosphere and human health,so it is highly desired to control the emission of NO_x.In the context of the national vigorous advocacy of ecological environmental protection,the emission of NO_xis becoming more and more strict.Among emission reduction technologies,ammonia selective catalytic reduction（NH₃-SCR）is a highly efficient,environmentally friendly and economical stationary source denitrification technology.The key to NH₃-SCR technology is the preparation of catalysts with excellent performance.Commercial V-based catalysts（V₂O₅-WO₃/Ti O₂）have shown excellent denitrification performance in industrial applications,but they are not suitable for medium-low temperature denitrification.Therefore,its further application in the industry is limited.In this study,a series of Mn-based catalysts with different structures were prepared and improved to broaden the reaction temperature of the whole catalytic process,and to improve their water resistance and N₂selectivity.The specific research contents are as follows:1.A series of Mn O_x,Mn₄Fe O_x,Mn Fe O_xand Mn Fe₄O_xcatalysts with different structures were obtained by one-pot solvothermal method and air calcination method.The effects of different ratios of Mn Fe oxides on NO removal were investigated,and the effects of Fe species doping on the crystal structure and SCR performance of Mn-based catalysts were explored.The results showed that Mn Fe O_xhad better catalytic activity and water resistance at low temperature.The NO conversion was 96%at 200℃and kept above 85%in the range of 120-280℃.Through the characterizations of XRD,SEM,N₂ad/desorption,H₂-TPR,XPS and FTIR,it was found that manganese and iron species were highly dispersed in the Mn Fe O_xcatalyst.Moreover,the Mn Fe O_xcatalyst not only possessed a large specific surface area and pore volume but also had a better reduction ability and abundant oxygen vacancies to adsorb and activate the reaction gases.More importantly,the charge transfer between the active species Mn and Fe in Mn Fe O_xcatalyst could effectively inhibit H₂O poisoning and improve the stability of the catalyst.The results of in situ DRIFTs experiments suggested that the low temperature NH₃-SCR reaction of Mn Fe O_xcatalyst followed L-H mechanism.2.Titanium-Manganese oxide octahedral molecular sieve（Ti-OMS-2）catalyst was prepared by hydrothermal method,and PTFE modified Ti-OMS-2 catalyst Ti-OMS-2/b%PTFE（b is the mass percentage）was prepared by introducing polytetrafluoroethylene（PTFE）on the surface of Ti-OMS-2 by impregnation method.The effect of PTFE content in Ti-OMS-2/b%PTFE catalyst on the catalytic activity for low-temperature NH₃-SCR of NO under the existence of water vapor was investigated by adjusting the concentration of PTFE.After the introduction of PTFE on the surface of Ti-OMS-2,the adsorption of water molecules by Ti-OMS-2 could be effectively inhibited and the consumption of active species was reduced,thus exhibiting good catalytic activity and water resistance.The activity of Ti-OMS-2/20%PTFE catalyst could reach more than 80%when water vapor was introduced at 180℃.More importantly,Ti-OMS-2/20%PTFE catalyst did not readily bind the active species(Mn⁴⁺,Mn³⁺and O_ads)and maintained the adsorption and activation of NH₃ species.