Study On The Anti Poisoning Design Strategy And Mechanism For Lead/Potassium Over SCR Catalysts

In recent years,global NOx emissions have remained high,posing a serious threat to the ecological environment and human health.NH3 selective catalytic reduction(NH3-SCR)is a stable technology choice for achieving ultra-low NOx emissions.Currently,the global nonelectric industry has low environmental protection investment and multiple types of pollutants,while the electricity industry has complex fuel blending and complex flue gas components.This presents a new challenge for the economic efficiency,operational stability,and complex flue gas adaptability of traditional environmental catalyst raw materials.Developing low-cost,hightolerance,multi-component,and highly adaptable new green catalysts has become the key to addressing these challenges.This thesis aims to study the mechanism of heavy metal Pb and alkali metal K poisoning on SCR catalysts for stable removal and deep purification of NOx under complex flue gas components.Based on the separation and regulation strategy of catalytic active sites and toxic metal binding sites on the catalyst surface,SCR catalysts with high tolerance to heavy metal Pb and alkali metal K were designed and synthesized,achieving the following research results:Anti-Pb poisoning catalyst design strategy and anti-Pb poisoning mechanism of acid carrier targeted capture:I An acid carrier,α-Fe2O3,was extracted from industrial aluminum refining waste red mud(RM)to replace the traditional TiO2,and Ce-W/RM catalyst was designed and synthesized.The NOx conversion of fresh Ce-W/RM catalyst and Ce-W/Ti catalyst were both 100%in the temperature range of 275-400℃,and both catalysts exhibited good denitrification activity.After being poisoned with 5.00 wt%Pb,the NOx conversion of Ce-W/Ti catalyst decreased significantly,reaching a maximum of only 87.5%at 325 ℃.However,the NOx conversion of Pb-poisoned Ce-W/RM catalyst only slightly decreased,and remained above 90.0%in the range of 225-400℃.II In-situ characterization and theoretical calculation results showed that for Ce-W/Ti catalyst,Pb combined with the surface WO3 species of the catalyst to form inactive PbWO4 species,which increased the bonding strength between adsorbed NH3 species and acid sites,thereby affecting the further dehydrogenation activation of adsorbed NH3 species and leading to a decrease in denitrification activity.For Ce-W/RM Catalyst,it had a higher Ce3+/Ce4+ ratio,and red mud，as a carrier,provided support for active species while the main component a-Fe2O3 of the red mud also provided a large number of acid sites as active components.After Pb contacted with Ce-W/RM catalyst surface,it would preferentially combine with α-Fe2O3,which to some extent avoided the combination of Pb with WO3 species,reduced the formation of inactive PbWO4 species,and ensured a higher NOx conversion.Anti-K poisoning catalyst design strategy and anti-K poisoning mechanism of interlayer proton precise capture:I Based on the exchange-coordination mechanism,a new type of the acid-treated birnessite-type MnO2(OL-1(H))catalyst with excellent ion exchange properties was designed and developed.The acid-treated birnessite-type MnO2 catalyst exhibited excellent low-temperature denitrification activity,with a NOx conversion of 100%at 200℃.After introducing 1.00 wt%K,its denitrification activity increased instead of decreased,and even when the K poisoning load was increased to 7.00 wt%,the NOx conversion still reached 97.8%at 200℃.The low-temperature activity of the acid-treated ordinary MnO2 catalyst(MnO2(J)was poor.After being poisoned with 1.00 wt%K,the NOx conversion of MnO2(H)catalyst further decreased,with a maximum of only 56.8%at 250℃.Ⅱ In situ characterization and theoretical calculation results indicated that for MnO2(H)catalyst,K destroy the Mn active sites and form K2O,leading to its deactivation.As for the OL-1(H)catalyst,when attacked by K+,K+would overcome several steps of energy barriers,smoothly migrated from the outer surface to the interlayer of birnessite-type MnO2,preferentially reacted with the H protons,and ultimately were accurately trapped in the interlayer of acid-treated birnessite-type MnO2 and coordinated with 6-8 surface O2-,improving its alkali metal K resistance.In addition,the introduction of an appropriate amount of K(1.00 wt%)would lead to changes in the coordination state and chemical bonds on catalyst surface,attracting the arrangement of electron clouds around the K species,thereby enhancing the negative charge of the surrounding Mn and O atoms,reducing Br(?)nsted acid sites,and increasing Lewis acid sites,promoting the catalytic reduction of NOx.