Study On The Catalytic Performance Of Three-dimensional Ordered Macroporous Cerium-based Ompound Oxide Catalyst For Toluene Combustion

In recent years,with the acceleration of China’s industrialization,the environmental problems are becoming more and more prominent,especially the atmospheric environment problems.Although China has also introduced a series of policies,such as the National Action Plan for the Prevention and Control of Air Pollution,and the air quality has generally improved year by year,the air environment in China is still not optimistic.Among them,volatile organic pollutants（VOCs）is one of the main sources of air pollution,in a strong oxidizing environment,VOCs can be converted to particulate matter,such as PM2.5,the main component of haze,can also react with nitrogen oxides to generate ozone,will cause adverse effects on the atmospheric environment and human life.Catalytic combustion is a highly efficient VOCs treatment technology with low energy consumption and no secondary pollution.The key of catalytic combustion technology is to prepare economical and efficient catalysts.Cerium oxide catalyst has become the focus of many researchers because of its excellent oxygen storage performance and redox performance.However,pure cerium oxide has poor thermal stability and unstable catalytic performance.In some cases,some transition metals,such as zirconium,manganese,copper or cobalt,can be doped into cerium oxide to improve the activity of the catalyst.At present,the research focuses on the preparation of cerium-based composite oxides catalysts,and there are few studies on the three-dimensional ordered monolithic cerium-based composite oxides.In this paper,PMMA hard template-excess impregnation method was used to prepare 3DOM Ce-Mn（6:4,4:6,2:8）catalysts with different Ce-Mn ratios and Ce O₂ and Mn O_x catalysts.The effects of different Ce-Mn ratios on the integrity of three-dimensional ordered macroporous structures and catalytic combustion activity were discussed.The selected catalysts were loaded onto cordierite.Based on the optimized preparation conditions,such as the loading method,the loading amount and the roasting temperature of the catalyst,the influence of catalytic combustion performance of toluene was discussed.The results show that the pore structure and catalytic effect of the catalysts prepared with different Ce/Mn ratios are very different.When Ce--Mn is 6:At 4℃,3DOM Ce-Mn（6:4）showed a high-quality three-dimensional ordered macroporous structure,with a specific surface area of 57.83 m²·g^-1,complete pore wall and a macropore diameter of 170-200 nm.The concentration of oxygen and Mn⁴⁺adsorbed on the catalyst surface was high,which was conducive to the adsorption and catalytic oxidation of toluene on the catalyst surface.When the intake concentration of the catalyst in toluene is 300±50mg·m^-3 and the space velocity is15,000 h^-1,T_50%and T_90%are 100℃and 153℃,respectively.Compared with the centrifugal deposition method,the active components of the integrated catalyst prepared by the deposition and solidification method are evenly distributed on the surface of the support.Although the large pore of the catalyst formed cannot be arranged in an orderly manner,it can form a complete pore structure,which is conducive to the material exchange in the catalytic combustion process and is not easy to cause blockage.For the investigation of load,three kinds of load,10%,15%and 20%,were selected for investigation.Among them,the mono catalyst with 10%loading capacity can form a complete pore structure,and the catalyst has the best performance in reducing performance（low temperature peak at 276℃）,specific surface area(26.13m²·g^-1),adsorbed oxygen concentration,Mn⁴⁺concentration and catalytic combustion performance(T_50%=158℃,T_90%=230℃).3DOM Ce-Mn（6:4）/cordierite catalysts were prepared at three different calcining temperatures of 550℃,650℃and 750℃.The results showed that the 3DOM Ce-Mn（6:4）/cordierite catalyst calcasted at 550℃with 10%loading capacity exhibited good surface area(26.13m²·g^-1),reduction performance（low temperature peak at 276℃）,surface adsorption oxygen concentration and Mn⁴⁺concentration.The catalytic combustion performance of the catalyst(T_50%=158℃,T_90%=230℃)is the best.Finally,the performance and stability of 3DOM Ce-Mn（6:4）/cordierite catalyst with10%loading capacity and calcining temperature at 550℃were tested.The results show that3DOM Ce-Mn（6:4）/cordierite catalyst has good catalytic combustion stability.The removal efficiency of toluene remains at about 82%in the 40-hour dynamic continuous test,which can meet the VOCs purification requirements in general industrial production.The catalyst is suitable for the removal of VOCs at concentrations below 2000mg/m³ in industrial production,and the catalytic combustion efficiency of toluene removal is the highest at lower concentrations,T_50%and T_90%are 158℃and 230℃(300mg·m^-3),respectively.