The Catalytic Oxidation Charateristics And Reaction Kinetics Analysis Of Low Concentration Benzene Over Copper-Manganese Catalyst

Volatile Organic Compounds?VOCs?pollution has attracted more and more attention of the society.Low energy density,complex composition and variable concentration all make it difficult to control.Catalytic combustion is one of the most efficient way to treat VOCs.Catalyst is become the key to restrict efficient conversion for VOCs.Especially,cheap cost for transition metal catalyst is the focus of research and development.Catalytic oxidation reaction characteristics and kinetics of VOCs by transition metals need to be further studied.In this paper,CuMn-based transition metals are used as active phase to explore the influence of carrier,preparation conditions and other factors on VOCs catalytic reaction,which is of great significance to the application and popularization of VOCs treatment technology.Benzene,one of the most typical components in VOCs,was selected as the catalytic oxidation object.Copper-manganese catalyst was been prepared by initial wet co-impregnation method.Benzene conversion over zeolite,SiO₂,?-Al₂O₃ and TiO₂supported copper-manganese catalysts and a series of SiO₂ supported copper-manganese catalysts were been compared.Micro-morphology structures,types of copper-manganese oxides,composition of active elements with different valences on catalyst surface were been inspected through BET,XRD and XPS.The oxidation laws for air flow with benzene concentration lower than 2000mg/m3were studied at atmospheric pressure.The effects of supporter change,active material loading,the ratio of Cu/Mn,calcination condition to the copper-manganese catalysts were analysised.The reaction kinetics parameters change of benzene rised by catalyst structure was analyzed and the following conclusions were drawn.?The main reason for the change of oxidation activity of CuMn catalysts with different supports for low concentration benzene is the change of dispersion of active substances.However,the surface of catalysts with relatively small pore size is not conductive to mass transfer of reactants and will aggravate the deactivation of coke deposits.The conversion of benzene below 1200 mg/m³ at atmospheric pressure over 10wt.%CuMn₂ catalyst follows:CuMn₂/Zeolite>CuMn₂/SiO₂>CuMn₂/?-Al₂O₃>CuMn₂/TiO₂.Both zeolite and silicon dioxide bimetallic copper-manganese catalysts could guarantee the complete decomposition of benzene about 300?,while benzene conversion rate over CuMn₂/zeolite during the 60h operation at 290?is much lower than that of CuMn₂/SiO₂.?Excessive or low loading will affect the growth of copper-manganese lattice,and the active substance dispersion is poor.Larger or smaller molar ratio between copper and manganese is not conducive to the interaction among different valence states of copper and manganese.Higher calcination temperature makes more holes on the catalyst surface open and the lattice structure formed more uniform,increasing the specific surface area of the sample and the transfer resistance for the surface reactants but not beneficial to the oxidation of benzene.Cu₃Mn₉/SiO₂ with calcination temperature of 300?,molar ratio for Cu and Mn of 3:9 and total load mass for Cu and Mn of 11%demonstrates the best catalytic performance.And the mixture containing benzene which was lower than 2000mg/m3could be completely decomposed over it at265?at 20000ml/?g.h?air speed.?The activity variation of Cu₃Mn₉/SiO₂ is mainly caused by the change of structure of copper-manganese composite oxides,which is less affected by the change of surface geometry structure.The aggregation of copper element on SiO₂ surface is easier than that of manganese element,and the secondary redistribution of elements with relatively weak binding to carriers occurs at high temperature and long time,which will change the structure of the original active substance.The catalytic activity of Cu₃Mn₉/SiO₂ for benzene decreased less than 5%within 24 hours at 260?,and the physical structure of the samples before and after treatment changed relatively little.