NH₃-SCR Performance Of Mangance Modifies Rare Earth Tailings Catalyst Activated-with Microwave And Sulphuric Acid

Currently,commercial denitrification catalysts are mainly vanadium-based catalysts,but V2O5 is a toxic substance affecting the environment and human health.In recent years,minerals have been used for the preparation of catalysts,especially the catalyst preparation of elemental modified minerals,because of their characteristics of environmental friendliness,wide source and multi-metallic elements.In this thesis,we studied the preparation of rare earth tailings denitrification catalysts using microwave roasting,sulfuric acid activation and manganese modification with the object of Baiyun Ebo rare earth tailings.The effects of microwave roasting of rare earth tailings,microwave roasting after sulfuric acid activation of rare earth tailings,and microwave roasting after manganese modification of sulfuric acid activation of rare earth tailings on denitrification performance were investigated respectively,and the mechanisms of the effects of microwave roasting,sulfuric acid activation and manganese modification on denitrification performance of rare earth tailings catalysts were investigated using XRD,BET,XPS,NH3-TPD and H2-TPR characterization methods,and the main findings are as follows:Suitable microwave roasting conditions can improve the denitrification performance of rare-earth tailings.When the microwave roasting temperature is 200℃,roasting time is20 min,and roasting power is 1100 W,the denitrification efficiency of the catalyst at 400℃is 47%.The thermal stress generated by microwave roasting exposes more active sites in the rare-earth tailings,but too high roasting temperature and long roasting time can lead to the collapse of pore channels in the rare-earth tailings,which reduces the contact between the gas and active components and leads to a decrease in denitrification activity efficiency.The denitrification efficiency of the rare earth tailings catalyst increased firstly and then decreased with the increase of sulfuric acid modification amount,and the temperature window of the catalyst widened from 350 to 450℃.The denitrification efficiency of the catalyst was highest when the sulfuric acid concentration was 3 mol/L,which was 67% at400℃.Sulfuric acid reacts with iron oxide ore,fluorocerium ore and dolomite minerals in the rare earth tailings to produce the corresponding sulfate,and the increase of sulfuric acid concentration increases the degree of reaction,and too much calcium and magnesium salts attach to the catalyst surface,which is not conducive to the catalyst performance.The sulfate in sulfate provides acidic sites for the catalyst,which is beneficial to the adsorption of NH3 and improves the denitrification efficiency of the catalyst.When the manganese modification amount was 5% and the sulfuric acid concentration was 0 mol/L,0.5 mol/L and 1 mol/L,the denitrification efficiency of Mn-modified catalyst increased firstly and then decreased with the increase of sulfuric acid modification amount,and the catalyst activity temperature shifted to the low temperature in the range of 150～250℃.When the sulfuric acid concentration was 0.5 mol/L,the denitrification efficiency reached 90% in the overall reaction temperature range,and the N2 selectivity was above 80%.The higher the sulfuric acid concentration,the higher the N₂ selectivity of the catalyst.