Preparation And Charaterization Of Porous Metal Composite Oxides(Co-Ce,Mn-Ce)Catalysts And Their Catalytic Performance For The Oxidation Volatile Organic Compounds

Volatile organic compounds（VOCs）are the main components of atmospheric pollutants,which have a serious impact on people’s living environment and endanger people’s health.VOCs mainly come from petroleum processing,refining,coking and other industries,including hydrocarbons,lipids,aldehydes and ketones,alcohols and ethers,aromatic hydrocarbons,etc.Catalytic oxidation is one of the most important methods for VOCs removal at the end.The catalysts for catalytic oxidation are mainly noble metal catalysts and non-noble metal catalysts.Noble metal catalysts have excellent catalytic performance,but they are expensive and lack of resources.The non-noble metal catalysts have the advantages of low price,easy availability of raw materials,high electronic fluidity,variable valence and excellent catalytic performance,which have become the focus of current catalyst research.In this paper,Co-Ce and Mn-Ce composite metal oxide catalysts were prepared by direct thermal decomposition using metal oxides as active components and citric acid as assistant,metal nitrates as metal sources.The effects of different preparation conditions on the structure and catalytic performance of the catalysts were systematically investigated.XRD,SEM,TEM,BET and H₂-TPR were used to characterize the physicochemical properties of the catalysts,and toluene and ethyl acetate were used as probes to evaluate the performance of the catalysts for VOC removal.The results show that both Co-Ce and Mn-Ce catalysts have polycrystalline structure.The average pore size distribution is narrow,about 10-15 nm.The appearance of the catalysts is"bird’s nest"and the pore structure is developed.Under the conditions of toluene（or ethyl acetate）concentration of 1000 ppm,space velocity of 20 000 mL·g^-1·h^-1and VOC/O₂ molar ratio of 1:400,the optimum 90%conversion temperature of Co-Ce catalyst（CC-3 catalyst）for toluene oxidation reaches 199 ℃ with a specific surface area of39.9 m²·g^-1 and an average pore size of 13.5 nm.TPR results show that the redox temperature of Co-Ce catalyst is significantly 268,323 and 443 ℃.In the original peak,the total amount of H₂ consumption can reach 20.3 mmol·g^-1.While,the 90%conversion of ethyl acetate is 190 ℃ in the sample of Mn-Ce catalyst,and the specific surface area and average pore size of Mn-Ce catalyst are 69.9 m²·g^-1 and 15.9 nm,respectively.The reduction peak of hydrogen occurs near 300 and 700 ℃,respectively.The total consumption of H₂ is the largest in this group of catalysts,which is 10.4 mmol·g^-1,but much lower than that of CC-3 catalysts.The catalytic performance of bimetallic Co-Ce and Mn-Ce oxides for the oxidation of toluene or ethyl acetate is related to their specific surface area,porous Micro-Nanostructure and low temperature reduction performance.