Performance And Mechanism Studies On W-Modified Ce-Zr Catalysts For Selective Catalytic Reduction Of NO

For the marine low-pressure SCR denitration system,the temperature of exhaust gas on the diesel engine is low（<300°C）and contains a certain concentration of SO₂,so it is urgent to investigate and improve the catalytic activity and anti-sulfur poisoning performance of SCR catalysts.Compared with traditional V-based catalysts,Ce-based catalysts have high oxygen storage capacity and reversible conversion between Ce⁴⁺and Ce³⁺.Therefore,Ce-Zr catalyst is selected as the research object,the low-temperature activity and sulfur resistance of the catalyst are significantly improved by doping transition metals and optimizing the synthesis process,and then the SCR reaction mechanism and anti-sulfur reaction mechanism of W-modified Ce-Zr catalyst are deeply discussed.This investigate can provide strong technical support and theoretical guidance for the development of efficient marine low-voltage SCR denitration products in the future.The main contents and conclusions of this paper are as follows:（1）Different transition metals such as Mo,Nb,and W were used to modifying Zr O₂supports,and its effect on the SCR performance and the reaction mechanism of Ce_0.4/Zr O₂catalysts was studied.The activity results showed that W was the optimal modified metal,and the NO_x conversion efficiency of Ce_0.4/W_0.1Zr O_x catalyst is always higher than 80%in the temperature range of 226-446°C.The characterization results showed that the presence of W not only inhibited the formation of monoclinic Zr O₂,but also favored the high dispersion of the active component Ce O₂ on the surface of the support.In addition,the interaction between W and Zr generated W-Zr-O_x solid solution superacid,which increased the number of acidic sites on the surface of Ce_0.4/W_0.1Zr O_x catalyst,and was conducive to the large number of Ce³⁺and chemically adsorbed oxygen（Oα）species,thusing increasing the medium and low temperature SCR activity of Ce_0.4/W_0.1Zr O_x catalyst.According to the results of In-situ DRIFTS analysis,the SCR reaction of Ce_0.4/W_0.1Zr O_x catalyst follows both E-R and L-H mechanisms.（2）On the basis of the above research,the influence of synthesis process on SCR performance of W-modified Ce-Zr catalyst was further investigated,and then the SCR reaction mechanism and anti-SO₂ poisoning mechanism were explored.The results showed that,with W as the active component and Ce_0.4Zr O_x as the support,the NO_x conversion efficiency of W_0.1/Ce_0.4Zr O_x catalyst was higher than 80%in the temperature range of 210-450°C.Moreover,it also exhibited excellent anti-SO₂ poisoning performance at 300°C.The characterization showed that W replaced the position of the Zr atom in the Ce-Zr solid solution,the Ce-O-W valence bond formed would induce electron redistribution on the surface of the catalyst,promoted the formation of surface Ce³⁺and oxygen vacancies,and improved the redox performance of the W_0.1/Ce_0.4Zr O_x catalyst.In addition,the acidity of W species also increased the NH₃ species adsorption on the surface of the W_0.1/Ce_0.4Zr O_x catalyst.These factors lead to W_0.1/Ce_0.4Zr O_x catalyst exhibited excellent low-temperature catalytic performance.The results of In-situ DRIFTS analysis showd that the W_0.1/Ce_0.4Zr O_x catalyst also followede the E-R and L-H reaction mechanism.Among them,double-tooth nitrate and bridge nitrate are important reaction intermediates.In the presence of SO₂,the W species inhibits the adsorption of stable nitrate species on the catalyst surface and reduces the non-selective oxidation of NH₃,which makes W_0.1/Ce_0.4Zr O_x catalyst have excellent SO₂ resistance.