Preparation Of Composite Metal Oxide (Mn,Ce Based)@ZSM-5 Catalyst And Study Of NO_x Elimination Performance

Nitrogen oxides（NO_x）from human activities mainly originate from the combustion of fossil fuels,and the emission of large amounts of NO_x can lead to acid rain,photochemical smog,eutrophication of water bodies and other serious and environmental pollution problem,it is urgent to achieve NO_x emission reduction.The NH₃-SCR technology is the most mature and widely used technology to control NO_xemissions,which mainly uses NH₃ as the reducing agent to selectively catalyze the reduction of NO_x to N₂,which has many advantages such as high NO_x conversion efficiency and good N₂ selectivityprocess stability.In the practical application process of this technology,catalyst is the most core part,whose performance directly affects the overall denitration efficiency and stability of SCR system,and the life also determines the annual cost and process stability of SCR technology.However,the flue gases emitted from stationary sources contain a large number of other harmful species in addition to NO_x,such as alkali metals（K,Na）,alkaline earth metals（Mg,Ca）,acid substances（S,Cl,P）,etc.Among which K and SO₂ are the most toxic substances that have the greatest influence on the performance of catalysts,and the study of anti-poisoning denitrification catalysts has become a development trend.In this paper,Ce WO_x@ZSM-5 and Mn Sm O_x@ZSM-5 series catalysts were designed and prepared for NO_x elimination in stationary sources by using the shielding effect of shell layer.In this paper,Ce WO_x@ZSM-5 and Mn Sm O_x@ZSM-5 series catalysts were designed and prepared for the removal of nitrogen oxides by using the shielding effect of shells.The denitrification activities,anti-alkali metal poisoning and anti-SO₂properties of Ce WO_x@ZSM-5 and Mn Sm O_x@ZSM-5 catalysts were investigated.The influence of catalyst structure on the whole catalytic reaction was further discussed.In the first part of this paper,a series of novel catalysts（Ce WO_x@ZSM-5）with core-shell structure were prepared by a one-pot two-step dry-gel conversion method.The Ce WO_x@ZSM-5 catalyst has good denitrification and resistance to K-poisoning performance.The shell layer of zeolite is rich in acid sites,which can be used as sacrificial sites to preferentially bind to K and avoid direct contact between K and Ce WO_x active component,thus slowing down/inhibiting the alkali metal poisoning process of the catalyst.Even after loading with 1 wt.%K,the NO_x conversion of this catalyst remained above 80%in the 300-500°C interval,and the loaded catalyst Ce WO_x/ZSM-5 and the oxide catalyst Ce WO_x were also prepared to compare the effect of structural differences on the catalytic performance.This study provides a new idea for the development catalysts with high resistance to alkali metal poisoning performance.Based on the research in the first part,the resistance of catalyst to compound poisoning was further explored.In the second part,ZSM-5 molecular sieve was used as the shell layer,and a series of catalysts with core-shell structure（Mn Sm O_x@ZSM-5）were prepared by improving the experimental method and shortening the catalyst synthesis time.It was found that SO₂ induced K migration on the K-poisoned Mn Sm O_x@ZSM-5 catalysts,which retarded the catalyst poisoning and activity recovery.Further investigation of the relevant catalysts revealed that the introduction of K occupied both the redox and acidic sites of the catalysts,reducing the reactivity of the Mn Sm O_x@ZSM-5 catalysts,and the K-poisoned catalysts reacted in the reaction gas with SO₂ atmosphere,and SO₂ induced migration with K on the K-Mn Sm O_x@ZSM-5 catalysts,again exposing the K-poisoned The active site,which is synergistically promoted by regulating the balance between redox and acid centers,improve the high-temperature de NO_x performance of the K-Mn Sm O_x@ZSM-5+SO₂catalyst.This part of the work contributes to the understanding of the specific interactions between alkali metals and SO₂ on denitrification catalysts and provides a new catalyst for the development of anti-complex poisoning resistance for realistic working conditions of NO_x elimination.