Preparation Of Copper-Manganese-Lanthanum-Cerium Composite Catalyst And Its Degradation Mechanism Of P-Xylene

The release of volatile organic compounds（VOCs）into the atmosphere can destroy the environment and affect human physical and mental health.Catalytic oxidation technology is a promising technology.the pollutant of this study is p-xylene,The Cu-Mn-La-Ce composite catalyst was prepared by the sol-gel method for degradation experiments,The effects of preparation conditions（molar ratios and calcination temperatures）and influencing factors（initial concentration,space velocity,O₂ content,relative humidity）on catalyst performance were studied;through the characterization of the catalyst and the detection of intermediate products and final products,The reaction mechanism of p-xylene on Cu-Mn-La-Ce catalyst is discussed,which provides a theoretical basis for the degradation of benzene pollutants in the future.The conclusions are as follows:（1）The catalyst calcination temperature and element molar ratio have a greater impact on the catalyst activity.Among the Cu-Mn-Ce-M（La,Pr,Nd,Sm）composite catalysts,the Cu-Mn-Ce-La catalyst has the best degradation effect on p-xylene.The Cu-Mn-Ce-La（1:1:1:1）catalyst has a degradation rate of more than 90%at 240℃,and has good low-temperature catalytic activity.Compared with the Cu-Mn-Ce catalyst,the doping of La can increase the specific surface area and pore volume of the catalyst,increases the surface oxygen content,inhibits crystal formation,and enhances the catalytic activity.Different element ratios have a great influence on the performance of the catalyst.As the ratio of manganese element increases,the surface oxygen content,specific surface area and catalytic activity of the catalyst increase.The best element ratio is Cu-Mn-La-Ce（1:2:1:1）.At this time,the surface structure is evenly dispersed,and there are more solid solutions and oxygen vacancies.Appropriate calcination temperature will increase the activity of the catalyst,but too high calcination temperature will cause sintering and reduce the activity of the catalyst.The best calcination temperature is 400℃.The catalytic activity is highest when the ratio is Cu-Mn-La-Ce（1:2:1:1）,and its T₅₀ and T₉₀ are 217℃and 230℃.（2）Factors such as initial concentration,space velocity,O₂ content and relative humidity all have a certain influence on the degradation rate of p-xylene on the catalyst.At a space velocity of 15000 h^-1,the degradation rate of p-xylene decreases with increasing of the initial concentration;The initial concentration is 600 mg/m³,and the degradation rate of p-xylene decreases with increasing of the space velocity.At a space velocity of 15000 h^-1 and an initial concentration of 600 mg/m³,the degradation rate of p-xylene increases with increasing of the O₂ content;the degradation rate of p-xylene decreases with increasing of the relative humidity.600 mg/m³ of benzene mixed in the gas stream improves the degradation rate of p-xylene.With an initial concentration of 600 mg/m³,a space velocity of 15000 h^-1,20%O₂,and the absence of water,the Cu-Mn-Ce-La catalyst has a degradation rate of p-xylene nearly to100% at 235℃.（3）Using BET,XRD and FT-IR methods to characterize the catalyst before and after the reaction,and using GC and GC-MS to determine the degradation products.According to the product formation,the degradation mechanism of p-xylene is inferred as follows:p-xylene is oxidized to p-tolualdehyde,and oxidized to p-toluic acid to CO₂ and H₂O.It involves the MVK mechanism.