Catalytic Combustion Of Toluene Over Cerium-based Catalysts And Their Kinetics Analysis

Volatile Organic Compounds（VOCs）are air pollutants that cause great harm to both the environment and human health,which was also one of the source of particular matter in the atmosphere.Catalytic oxidation is one of the most recognized and effective methods in the treatment of VOCs.Toluene is one of the typical VOCs,which was often as probe molecular for the development of VOCs abatement catalyst.Design and synthesize catalysts with high activity,high stability and low cost is critical task for the catalytic oxidation of VOCs.CeO_2,due to its excellent oxygen capacity and redox properties,has been widely applied in environmental catalysis.In this paper,the relationship between the oxygen storage performance and catalytic activity of cerium-based catalysts were studied by adjusting their oxygen storage performance and redox characteristics with addition of different transition metals and alternation in preparation methods.Moreover,kinetic analysis were also conducted to investigate the mechanism.The main research contents and conclusions of this paper are as follows:A series of MCeO_x catalysts were synthesized via addition of transition metal M（M=Cu,Mn,Co,Ni,Fe）into commercial CeO₂ by impregnation method.We studied the effects of different transition metals on the redox characteristics,oxygen storage capacity and oxygen vacancy of the catalysts,and their roles on the catalytic performance of MCeO_x for toluene oxidation.It was found that the sequence of activity in catalytic oxidation of toluene is as follows:Cu CeO_x>Co CeO_x>Mn CeO_x>Fe CeO_x>Ni CeO_x.Among the tested MCeO_xcatalysts,Cu CeO_x catalyst showed the best catalytic activity for toluene oxidation,with its T₁₀,T₅₀ and T₉₀being 233°C,264°C and 303°C,respectively.T₁₀ of the Cu CeO_x catalyst decreased by 115°C compared to CeO_2.Structural characterization showed that the addition of transition metal did not change the crystal structure of CeO₂,but varied the oxygen storage capacity（oxygen storage,oxygen storage rate）of the catalyst.The linear relationship between oxygen storage capacity and catalytic activity was established,indicating that the oxygen storage capacity was the vital for the catalytic oxidation of toluene.Kinetic analysis results indicated that Cu CeO_x catalytic oxidation of toluene proceed Mv K mechanism.Furthermore,rod-shaped MCeO_x-R catalysts（M=Fe,Cu,Mn,Ca,Ni,Zr）were synthesized via bimetal co-hydrothermal synthesis methods.It is found that Zr CeO_x-R catalyst exhibited the best catalytic performance for the oxidation of toluene with its T₁₀,T₅₀ and T₉₀ of Zr CeO_x-R were 201°C,236°C and 334°C respectively.The structural characterization showed that the addition of Zr could effectively increase the content of lattice oxygen and Ce³⁺,generating more oxygen vacancies,and then enhance the catalytic performance of toluene reaction.Kinetic analysis results indicated that the catalytic oxidation of toluene on Zr CeO_x-R also follows the Mv K mechanism.The above work clarified the effect of transition metal addition on the oxygen storage performance and the reaction mechanism over cerium based catalyst for catalytic oxidation toluene,which would provide guidance for the designation and application of new cerium based catalysts for catalytic oxidation of toluene in the future.