Preparation Of 3DOM Ce-Co-Cu Catalyst And Its Degradition Characteristics For O-xylene

As one of the main pollutants of atmospheric environmental pollution,volatile organic compounds(VOCs)not only directly pollute the environment,but also form photochemical smog with sulfur oxides and nitrogen oxides in the atmosphere,resulting in secondary pollution.Seriously affect human life and physical and mental health.Catalytic combustion is a common technology in VOCs treatment.Catalytic combustion technology uses catalyst to burn organic matter to form CO2 and H2O at low temperature.High efficient and stable catalyst is the key of catalytic combustion technology.In this paper,polyethylene glycol and citric acid assisted sol-gel method was used as the preparation method,The template was polymethyl methacrylate(PMMA)with large specific surface area,well-arranged pore channels and uniform pore size distribution.Three dimensional ordered mesoporous(3DOM)Ce-Co-Cu catalyst was prepared by selecting transition metal Co-Cu and rare earth metal Ce as active components.Chemical agent The effects of different molar ratio and calcination temperature on the performance of the catalyst were studied.The surface structure and ionic concentration of the catalyst were characterized by a series of methods.The factors affecting the degradation of o-xylene by catalyst,including initial concentration,space velocity and relative humidity,were studied.The catalytic degradation mechanism of o-xylene was deduced from the product analysis.The main conclusions of this paper are as follows:(1)The PMMA template was prepared by a modified hard template method,and a 3DOM Ce-Co-Cu catalyst was prepared by a sol-gel method assisted by polyethylene glycol and citric acid.The activity of the catalysts with different metal components was studied.The results showed that the PMMA templates were arranged in order,the pores were neat and orderly,and the spheres were full.Ce-Co-M(M=Al,Mn,Fe,Cu)composite catalyst has the best degradation effect on o-xylene by Ce-Co-Cu composite catalyst,and its T50=260 ?,T90=280 ?.The removal rate of 3DOM Ce-Co-Cu(2:1:1)catalyst was maintained above 96%at 260 ?.(2)The preparation conditions were optimized by different molar ratios and different calcination temperatures,and The initial concentration of 600 ppm,space velocity 32000 h-1,and the calcination temperature of 500 ?prepared 3DOM Ce-Co-Cu(2:1:1)had the best catalytic effect,and its T50 and T90 were 237 ? and 250 ?.The addition of Cu in different molar ratios increases the catalytic effect of the 3DOM Ce-Co catalyst.The catalyst has a distinct three-dimensional mesoporous structure and the catalyst surface contains polycrystals.According to the results of BET,XRD and XPS analysis,the addition of Cu element increases the specific surface area of the catalyst,surface oxygen,reduces surface crystals,and causes the crystal size of CeO2 to decrease,resulting in an increase in the active site of the catalyst.Among them,the 3DOM Ce-Co-Cu(2:1:1)catalyst has the smallest crystal size and contains a large amount of surface oxygen and Cu2+ and Ce3+.According to the results of H2-TPR and FT-IR analysis,3DOM Ce-Co-Cu(2:1:1)catalyst has the most O-H and C=O,and has the strongest reduction performance.When the calcination temperature is too high,agglomeration occurs on the surface of the catalyst,resulting in a decrease in the solid solution in the catalyst,a decrease in the concentration of the active ion,and a decrease in the dispersibility of the catalyst.(3)The results of the influencing factors on the catalyst showed that the initial concentration was 600 ppm,the space velocity was 16000 h-1,50%O2,and 5%water vapor,The removal rate of o-xylene by 3DOM Ce-Co-Cu(2:1:1)catalyst was 98%at 260 ?.Under the condition of space velocity 32000 h-1,the removal rate of o-xylene decreased with the increase of initial concentration.At an initial concentration of 600 ppm,the removal rate of o-xylene decreased as the space velocity increased.Under the initial concentration of 600 ppm and airspeed of 32000 h-1,the removal rate of o-xylene increased with the increase of O2 content,and decreased with the increase of water vapor.Mixing 150 ppm of ethyl acetate in the gas stream can increase the conversion of o-xylene.(4)The catalysts before and after the reaction were characterized by BET,XRD,XPS and FT-IR.The results showed that the specific surface area and pore volume of the catalyst decreased,the crystallinity increased,and the sizes of CeO2,Co3O4 and CuO increased accordingly.The surface oxygen content was decreased,the lattice oxygen content was increased,and the catalyst storage oxygen capacity was weakened,resulting in a decrease in catalytic activity.The product after catalysis by GC-MS and GC showed that The catalytic temperature is below 240 ?,the catalytic oxidation of o-xylene produces a small amount of o-methylbenzaldehyde and o-methylbenzoic acid intermediates;the catalytic temperature is above 260 ?,and the catalyst does not produce intermediates and Complete degradation to CO2 and H2O.The catalyst reaction in o-xylene degradation involves the degradation principle of Mars Van Krevelen mechanism(MVK),o-xylene is oxidized to o-methylbenzaldehyde,and further oxidized to o-methylbenzoic acid to finally form CO2 and H20.