Based On Density Functional Theory And Reaction Kinetics, The Selection Of Low-temperature SCR Catalyst And Its Sulfur Resistance Performance

A large number of NO_xemission poses a great threat to human production,life and health,and the ecosystem is also deeply affected by its damage.With the increasing emission of NO_x,every industry in China has been greatly affected and measures must be taken to control it.Selective catalytic reduction?SCR?is currently considered to be the most effective NO_xcontrol technology.V₂O₅is a common metal oxide,which is widely used as the active component of commercial catalysts.It has the characteristics of high denitration efficiency,but its limitations are also obvious.The catalyst maintains high activity at a high temperature with a narrow temperature window?300?400??.When the temperature is lower?<200??,the catalyst can still maintain good catalytic performance,which will widen its working temperature window and can be used in iron and steel,cement and other industries where the temperature of coal-fired flue gas is low.This will reduce NO_xemissions during the production process.The efficiency of the catalyst is closely related to the acidity of the catalyst surface and its own redox performance.The stronger acidity and redox ability of the catalyst surface come with the higher catalyst activity.Based on this background,it is of great significance to develop efficient low-temperature denitration catalysts.In this paper,the active components of the catalyst were screened by quantum chemistry.By analyzing the binding energy of reactive gases on the surface of different metal oxides,the change of bond length of reactive gases before and after adsorption,the Mulliken charge analysis after adsorption,and the fractal density analysis,the two active metals Mn and Ce were finally screened for further experiments.Mn/Ti O₂and Ce/Ti O₂catalysts were prepared by sol-gel method to evaluate the activity and test the sulfur resistance of the catalyst,and the characterization of the catalyst was analyzed by using technologies such as NH₃-TPD,XPS,DRIFT and H₂-TPR.It can be found that the Mn/Ti O₂catalyst has better activity and lower N₂O selectivity than the Ce/Ti O₂catalyst at all experimental temperatures.The former has a maximum activity of 92.5%.The N₂O selectivity at 210?is 10.5%and 15.4%,respectively.In addition,the former has relatively better sulfur resistance and the activity after SO₂poisoning is 20%higher than that of Ce/Ti O₂catalyst.Moreover,it was found that Mn/Ti O₂catalyst had better redox performance through characterizations but the adsorption performance of NH₃on the catalyst surface was worse than that of Ce/Ti O₂.In order to further determine which catalyst had better catalytic performance,kinetic experiments were carried out.The kinetic model of the reaction was established,and the rate of selective catalytic reduction at different temperatures and the rate constants under different mechanisms were calculated.The effects of side reactions of non-selective catalytic reduction and excessive oxidation of NH₃on catalytic activity were investigated.Finally,it was found that the reaction rate of Mn/Ti O₂catalyst was significantly higher than that of Ce/Ti O₂catalyst,and the latter was more susceptible to the side reaction;The activation energy of the two catalysts are 20.96 k J/mol and 37.26 k J/mol,respectively.The activation energy of the Mn-based catalyst is lower and the catalytic reaction is easier to proceed.Thus,the overall catalytic activity of Mn/Ti O₂was better.In addition,the sulfur resistance of different catalysts was investigated and the catalysts were modified.By means of SEM-EDS,TG-DTG and XRD,the reasons for the change of sulfur resistance of the catalyst before and after modification were analyzed.