Preparation And Performance Of Manganese Modified Carbon-Based Low-Temperature SCR Denitration Catalysts

Large NO_x emissions can cause a variety of environmental problems.Selective catalytic reduction（SCR）denitrification technology is a key tool for reducing NO_x emissions,and current research is focused on the preparation of low-temperature SCR denitrification catalysts.Activate carbon is regarded as an efficient catalyst carrier,and can be employed in the preparation of low-temperature SCR denitrification catalysts by introducing manganese and other active ingredients.Manganese modified activated carbon possesses excellent denitrification performance at low temperature in flue gas.However,the unsatisfying physicochemical characteristics of activated carbon and the non-uniform dispersion of active ingredients limit the denitrification performance of MnO_x/AC catalysts prepared by conventional preparation methods.In this study,the loading conditions of Mn and the structural properties of catalyst carriers were optimized to improve the low temperature denitrification efficiency of MnO_x/AC.1.Preparation and performance of manganese modified carbon-based denitrification catalysts assisted with ethanolTo improve the dispersion and chemical form of Mn,a new method was proposed to prepare MnO_x/AC assisted with ethanol.Commercial activated carbon was employed as the carrier.The effects of manganese nitrate solution type,calcination conditions（temperature and atmosphere）on the denitrification performance of MnO_x/AC were systematically investigated.The relevant mechanism was further analyzed and the preparation conditions were optimized.Compared with the conventional method using aqueous manganese nitrate solution during the loading of manganese,using ethanol solvent could not only improve the dispersion of Mn,but also reduce the agglomeration phenomenon.In addition,the relative content of Mn⁴⁺ in MnO_x was also greatly increased,which could effectively improve the denitrification performance of MnO_x/AC.The MnO_x/AC prepared at calcination temperature of 200℃ and manganese loading of 8 wt%was donoted as E-8MnO_x/AC-200A,which exhibited best denitrification performance.The NO conversion rate of the E-8MnO_x/AC-200A catalyst was as high as 96.3%at air speed of 20,000 h^-1 and denitrification temperature of 150℃.2.Effect of nitric acid preoxidation on the performance of manganese modified carbon-based denitrification catalystsThe catalyst carrier structure and its surface functional groups have a significant role in the denitrification performance of the catalyst.A series of activated carbon was prepared with pretreatment of nitric acid solution in different concentrations and temperatures,and further were modified by manganese（MnO_x/OAC）.The effects of nitric acid preoxidation on the physicochemical characteristics and denitrification performance of the catalysts were systematically analyzed.The results showed that the nitric acid preoxidation could increase the oxygen content,enrich the oxygen-containing functional groups and increase the relative content of Oα in the catalyst,which led to the strong NH3 adsorption capacity and excellent redox performance,thus improving the denitrification efficiency of the catalyst.The denitrification efficiency was positively correlated with nitric acid concentration at low preoxidation temperature（20℃）,while exhibited a tendency of increasing first and then decrasing with the increase of nitric acid concentration at higher preoxidation temperatures（50℃ and 80℃）.The MnO_x/OAC prepared at nitric acid concentration of 6 mol/L and preoxidation temperature of 50℃,denoted as MnO_x/OAC-6-50,which exhibited best denitrification performance.The relevant catalytic efficiency was as high as 97.5%at air speed of 40,000 h^-1 and denitrification temperature of 150℃.