Construction Of Flexible Mn-based Catalysts And SCR Denitrification Sulfur Resistance Mechanism Investigation

SO2 in industrial flue gas can lead to permanent deactivation of the active center on the catalyst surface,and improving the low-temperature SO2 resistance of Mn-based catalysts has been a great challenge.Porous catalysts with larger specific surface area and more active sites have become a hot research topic in the field of environmental catalysis.With the excellent performance of flexible porous materials,their application in the field of low-temperature denitrification catalysis is expected to further optimize and enhance the catalytic performance.Based on the Mn,Co and Ce metal oxides with good low-temperature denitrification performance studied by the group,this work constructs self-assembled porous flexible catalysts based on the common rules of catalysts with excellent lowtemperature performance,and elucidates the catalytic reaction mechanism and resistance enhancement mechanism by investigating the conformational relationship.In this study,the MnCo-CMS catalysts were firstly synthesized in situ on carbonized melamine sponge substrate by stepwise hydrothermal method,and the screened MnCo-CMS catalysts could maintain more than 90%NOx conversion and 80%N2 selectivity in the range of 120-240℃.The surface of MnCo-CMS catalysts was rich in active surface oxygen,large amount of Mn3+ and Mn4+ and Lewis acid sites.The three-dimensional interconnected mesh structure and pinning morphology can increase the effective active sites per unit surface area of the catalyst and improve the adsorption characteristics of gas molecules.In order to further optimize the catalyst structure and simplify the preparation process,MnMe-N(Me represents Ce,Co,Fe)nanowire aerogel catalysts were synthesized by a one-step hydrothermal method,and the mechanism of the three-dimensional interconnected mesh structure on the catalyst activity and SO2 resistance was explored more deeply.It was found that Mn-Ce-N has great specific surface area,strong redox property and surface acidity,and the NOx conversion at 100-400℃ is higher than 90%,and the NOx conversion is almost not inhibited by SO2.Meanwhile,the obtained nanowire structure will weaken the nitrate adsorption on Mn-Ce-N,provide more adsorption sites for NH3 adsorption,and effectively inhibit SO2 adsorption,which is the main reason for its excellent sulfur resistance performance.Finally,phosphotungstic acid modification was used to optimally enhance the water resistance and N2 selectivity of nanowire aerogel catalysts,and the regulatory mechanism and influence mechanism were analyzed.The modified HPW-Mn-CeN catalyst has excellent NOx conversion(close to 100%at 150-400℃)and N2 selectivity(higher than 90%at 50-400℃).In the presence of 10 vol%H2O,the NOx conversion of the modified Mn-N and Mn-Ce-N catalysts was enhanced by 14%and 5%,respectively.The formation of Ce4+-O-W species reduced the high redox capacity of the Mn-Ce-N catalyst,reduced NH3 oxidation,and enhanced N2 selectivity.the presence of HPW changed the reaction path of the Mn-Ce-N catalyst and increased NH3 adsorption,while significantly enhancing the generation of active bidentate nitrate species and promoting the L-H mechanism reaction.