Contrastive Study On The SCR Mechanism Of The Modified Vanadium Titanium-based Catalysts

The majority of industrial chemical processes driven by fossil fuel combustion cause excessive emissions of atmospheric pollutants such as NOx,which will seriously damage the ecological environment and endanger human health.Selective catalytic reduction?SCR?technology is currently the main way to control NOx emissions.As the core of SCR technology,the research and development of efficient and practical new SCR catalyst is a difficult problem.In this paper,based on further exploration of the catalytic mechanism of vanadium-titanium system,the preparation of multistage transition metal oxide loading catalysts and the properties study of rare earth metal composite oxides,the modification of traditional vanadium titanium-based catalyst was studied.XRD,BET,SEM,Raman,H₂-TPR,NH₃-TPD,in situ IR,XPS and other characterization methods were used to characterize the structure,performance and SCR mechanism of different types of modified catalysts.The V-WOx/TiO₂ catalysts with vanadium loads of 1wt%to 13wt%were prepared by impregnation method.When the vanadium load reach 9wt%,the vanadium species on the support surface changed from oligomer to crystalline state.The deNOx activity of the catalysts keep the best in the range of 150-450?at 30000h^-1 space velocity.At this point,the V⁴⁺/V⁵⁺ratio reached the maximum?1.73?,and the apparent activation energy required for the reaction was the lowest(15.7 kJ·mol^-1).Surface chemical adsorption oxygen?O?/?O?+O??=0.38?and proton acid sites?B/L=0.514?are the most abundant.Macroscopic adjustment of vanadium loading changed the relative content of vanadium in different valence states on the support surface and NH₃ is more easily adsorbed by V⁴⁺-OH and V⁵⁺=O to form a transition state,which promotes the catalytic reaction.The?Mn-Ce?VW/TiO₂ composite metal oxide catalysts were prepared by impregnation method.When the molar ratio of?Mn-Ce?VW:TiO₂ is 0.2,four active components can aggregate slightly on the support surface and no crystalline phase is formed.The NO conversion and N₂ selectivity of the catalysts are more than 90%at150-400?and 40000h^-1 space velocity.The strong synergistic effect among various active components changes the relative content of different valence elements and improves the reduction performance of the catalyst,which is the main reason for maintaining the high NO conversion of the catalyst.Ce_XM_1-XO₂?M=Ti,Zr,Mn;X=0.1,0.3,0.5,0.7,0.9?composite metal oxides were prepared by coprecipitation method.When the ratio of Ce:M is Ce:Ti=3:7,Ce:Zr=9:1and Ce:Mn=1:9,the deNOx performance among them is the best at 40000h^-1 space velocity.The composite oxides with different lattice structures formed by adding various elements in different proportions,which have different effects on SCR performance.Ce_0.9Z_r0.1O₂/TiO₂ composite support was prepared by deposition precipitation method and loaded with vanadium oxide of different content.When the molar ratio of Ce_0.9Zr_0.1O₂:TiO₂=1:1 and the vanadium loading is 3wt%,the catalyst has the best deNOx activity and the NO conversion reaches 94.5%at 250?.VOx loading increases the number of proton acidic sites and the concentration of chemisorbed oxygen on the catalyst surface,thereby improving the catalytic activity.