Study On Performance And Anti-SO₂ Mechanism Of Metal Oxides Modified Mn/ACN Series Catalysts For NH₃-SCR Of NO_x At Low Temperature

Coal accounts for more than half of China’s primary energy consumption for many years.The nitrogen oxides（NO_x）family produced during the usage of coal is one of the main air pollutants.Due to the comprehensive application of selective catalytic reduction（SCR）denitrification technology,the thermal power industry has successfully achieved long-term and effective NO_x control.Nowdays,the NO_x emission control of flue gas from non-electric industries,such as steel industries and building materials industries,has become the main task of air pollution prevention and control.Commercial SCR catalysts,widely used in the thermal power industry,do not possess low-temperature catalytic activity,thereby they are difficult to be directly applied to low-temperature（<250^oC）industrial flue gas in non-electric industries.Although the low-temperature SCR catalysts developed in recent years exhibite good catalytic activity,they are easily deactivated by SO₂ poisoning,which severely restricts their industrial application.Therefore,the development of alternative low-temperature SCR denitrification catalysts with good low-temperature catalytic activity and high sulfur resistance is extremely important for promoting the reduction of NO_x pollutants in the non-electric industries flue gas,and realizing green production and sustainable development.Considering the advantages of carbon-based materials with large specific surface area,rich pore structure,good adsorption performance,abundant resources,and low-cost,the preparation and performance tests of nitric acid modified carbon-based materials（ACN）supported manganese oxide（MnO_x）Mn/ACN series catalysts were systematically carried out.The effects of different metal oxides modification on the low-temperature SCR denitrification performance,physicochemical properties,and anti-SO₂ poisoning performance of Mn/ACN were studied.The mechanisms of improved anti-SO₂poisoning performance of Mn/ACN by different metal oxides modification were clarified.This study provided a valuable theoretical basis for the development of low-temperature SCR denitration catalysts with high catalytic activity and anti-SO₂poisoning performance.The performance tests of different carbon-based materials and corresponding catalysts were carried out for screening suitable carbon-based supports and obtaining the basic formula of carbon-based low-temperature SCR denitrification catalyst.Nitric acid modification increased the acidic oxygen-containing functional groups of carbon-based materials,promoting the adsorption and activation of reaction gases.Nitric acid modified commercial activated carbon（ACN）and self-made activated carbon（BACN）showed obviously higher denitration performance.The denitrification performance of ACN and BACN supported by different metal oxides were also studied,showing that both ACN and BACN were suitable for being used as low-temperature SCR catalyst supports,and MnO_x was selected as the basic active component.The effects of CeO_x modification on the physicochemical properties,low-temperature denitration performance and anti-SO₂ poisoning performance of Mn/ACN catalysts were studied.The mechanism of CeO_x modification on the performance improvement of Mn/ACN catalyst and the reaction mechanism of Mn-Ce/ACN catalyst were analyzed.The low-temperature denitration performance,nitrogen selectivity,stability,and anti-SO₂ poisoning performance of the Mn-Ce/ACN catalyst were significantly better than those of the Mn/ACN catalyst.CeO_x modification promoted the dispersion of MnO_x on the surface of ACN,and provided more oxygen vacancies and Mn⁴⁺.The low-temperature NH₃-SCR reaction of Mn-Ce/ACN mainly followed the L-H mechanism.The effects of VO_x modification on the low-temperature denitration performance and anti-SO₂ poisoning performance of the Mn-Ce/ACN catalyst were studied,and the anti-SO₂poisoning mechanism was also analyzed.Mn-Ce（0.4）-V/ACN catalyst exhibited better denitration performance,higher N₂ selectivity,wider active temperature range,and better anti-SO₂poisoning performance than Mn-Ce（0.4）/ACN.The NO conversion of Mn-Ce（0.4）-V/ACN in the temperature range of 100～300^oC was higher than 90%.VO_x modification significantly enriched the surface chemisorption oxygen,promoted the adsorption and activation of the reaction gases,and inhibited the consumption of reducing agent NH₃ by SO₂.Both of the inhibitory effect of strong surface acidity on SO₂ adsorption and the trapping effect of V₂O₅ on SO₂ alleviated the sulfation of SO₂ on MnO_x and CeO_x.The performance and anti-SO₂poisoning mechanism study on FeO_x and CeO_xco-modification of Mn/ACN catalyst showed that co-modification of FeO_x and CeO_xeffectively improved the low-temperature catalytic activity and anti-SO₂poisoning performance.The NO_x conversion of Mn-Fe（0.4）-Ce（0.4）/ACN at 100～250^oC was higher than 95%.FeO_x and CeO_x co-modification significantly improved the redox performance,enriched the surface chemisorption oxygen and Mn⁴⁺,and enhanced the strength and concentration of surface acid through the interaction among Mnⁿ⁺,Feⁿ⁺and Ceⁿ⁺,effectively promoting the adsorption and activation of both NH₃ and NO.The strong surface acidity of the Mn-Fe（0.4）-Ce（0.4）/ACN catalyst effectively inhibited the adsorption of SO₂,and the adsorbed SO₂ directly reacted with CeO₂.The low-temperature SCR reaction process of Mn-Fe（0.4）-Ce（0.4）/ACN catalyst followed both of the L-H mechanism and the E-R mechanism,and was dominanted by the L-H mechanism.