Preparation Of Cobalt-manganese And Cobalt-copper Composite Oxides Monolithic Catalysts And Their Performance For VOCs Catalytic Oxidation

Volatile organic compounds（VOCs）are one of the important components of air pollution.Catalytic combustion is one of the most widely used technologies in the treatment of VOCs,and the key is the choice of catalyst.Monolithic catalysts have been widely concerned because they overcome the disadvantages of traditional granular catalysts in industrial application.In this paper,low price and abundant transition metal Co,Mn,Cu were used as the active component and supported on cordierite honeycomb ceramics by simple ultrasonic impregnation method to prepare CoMn and CoCu composite oxides monolithic catalysts.The effects of different Co/Mn and Co/Cu molar ratios on the catalytic performance of toluene and ethyl acetate and the relationship between the performance and the structure of the catalysts were investigated.The main work and results are as follows:（1）Composite metal oxide monolithic catalysts with different molar ratios of Co/Mn were prepared by ultrasonic impregnation method using acetate precursor.Through characterization analysis,it was found that Mn species can entered the crystal lattice of Co₃O₄spinel.When the Mn/Co molar ratio is less than 1,Mn doping can cause lattice distortion and bring lattice defects,while the excessive amount of Mn species would lead to the destruction of Co₃O₄ spinel structure and the formation of new crystalline structures.Co_0.67Mn_0.33O_xmonolithic catalyst formed a kind of solid solution with spinel structure which showed the largest lattice distortion,and its surface Mn³⁺,Co³⁺species and surface chemisorbed oxygen content were higher than other catalysts,so it had the best catalytic oxidation performance.In the activity tests（WHSV=45000 m L/（g·h）and pollutant concentration=500 ppm）,the T₉₀（the temperature at which 90%VOCs are degraded）of toluene and ethyl acetate were 217^oC and172^oC,respectively.The catalyst showed good adaptability in different reaction conditions including the mixed pollutants of toluene and ethyl acetate,toluene concentration from 500ppm to 1000 ppm and WHSV from 45000 to 78000 m L/（g·h）.Meanwhile,the catalyst had no catalytic activity decrease or deactivation in the reaction stability test,so it has practical application value.（2）Composite metal oxide monolithic catalysts with different molar ratios of Co/Cu were prepared by ultrasonic impregnation method using nitrate precursor.It can be seen that Cu²⁺can replace the Co²⁺at the A position of Co₃O₄ spinel to form Cu_xCo_3-xO₄ spinel.When the molar ratio of Co/Cu was equal to 2,Cu²⁺has the best replacement effect for Co²⁺,and Cu_xCo_3-xO₄ became the main structure of Co_0.67Cu_0.33O_x which had the smaller crystalline size and obvious lattice distortion.Compared with other catalysts,Co_0.67Cu_0.33O_x monolithic catalyst had better redox ability and higher ratio of Cu²⁺,Co³⁺and surface chemisorbed oxygen,so it had the best catalytic performance for toluene and ethyl acetate catalytic oxidation which the T₉₀ of two pollutants were 210^oC and 172^oC respectively（WHSV=45000m L/（g·h）and pollutant concentration=500 ppm）.The Co_0.67Cu_0.33O_x monolithic catalyst also maintained good adaptability in the tests under different reaction conditions.And it showed good reaction stability in the seven cycles test and 24 h,but reversible decline of catalytic performance which meant the activity could be restored after the removal of water occurred in the water resistance stability test.Moreover,the prepared monolithic catalysts had good mechanical stability.And compared with the monolithic catalysts in other literatures,the catalysts prepared in this paper have obvious advantages in terms of catalytic activity of toluene and ethyl acetate,which further demonstrates their excellent catalytic oxidation ability.