Preparation Of Cobalt-based Oxides And Their Catalytic Properties For Toluene Oxidation

VOCs（volatile organic compounds）exist in our production and life.It will not only increase ozone concentrations and PM2.5 concentrations,but also damage the human respiratory system,etc.Among the many elimination methods,catalytic oxidation method is considered to the most powerful technique to eliminate VOCs.The catalyst is the core of the technology.This paper used Co-based catalysts to eliminate VOCs.Based on the characteristics of Cu and Ce,binary metal oxide catalyst is constructed.The redox ability and surface species of catalysts were adjusted,to improve the catalytic performance of the catalysts.The relationship between structure of catalyst and catalytic activity was researched by various characterizations.A series of Co₃O₄,Cu_aCo_1-aO_x（a=0.1,0.2,0.4 and 0.6）and Ce_0.06CoO_x catalysts were synthesized by solvothermal method and their catalytic performance on toluene were investigated.A variety of characterization results show that the catalytic performance on toluene by Co₃O₄ catalysts with different morphologies is different.Among them,the Co₃O₄ catalyst with flower structure has better catalytic performance on toluene.However,it can be found that the low temperature catalytic activity and water resistance of Co₃O₄ catalysts need to be improved.To improve the low temperature performance of the Co₃O₄ catalyst and a series of Cu_aCo_1-aO_x（a=0.1,0.2,0.4 and 0.6）catalysts were synthesized.It is shown that the Cu_0.4Co_0.6O_x catalyst exhibits better catalytic performance on toluene at 120,000 m L·g^-1·h^-1(T₁₀₀=255 ^oC).Furthermore,a varies of characterization results indicated that the introduction of Cu can produce strong interaction between Cu and Co oxides(Co²⁺+Cu²⁺?Co³⁺+Cu⁺)and thus improve the redox ability of catalysts.Besides,the Cu_0.4Co_0.6O_x catalyst owns the more Co³⁺/(Co³⁺+Co²⁺)ratio and surface absorbed oxygen,which improves the oxidation performance of toluene by Cu_0.4Co_0.6O_x catalyst.However,the influence of water on the catalyst is great at low temperature.To improve the water resistance of the catalyst and a series of Ce_0.06CoO_x catalysts were prepared.The effect of water was investigated for toluene catalytic oxidation.As a result,the Ce_0.06CoO_x-P catalyst showed better activity performance and excellent water resistance.When 5vol%H₂O is injected in the feed,the temperature of 50%toluene conversion is 222 ^oC and 100%is230 ^oC.Through various characterization results,it can be concluded that the introduction of Ce can improve the surface structure and redox ability of catalysts.Meanwhile,a large number of Ce³⁺species can produce more oxygen vacancies and improving the oxygen migration ability,thus improving the catalytic performance on toluene.Besides,the adsorption of water becomes weak on the Ce_0.06CoO_x-P catalyst.These are the main reasons for the better catalytic oxidation and water resistance of Ce_0.06CoO_x-P catalysts.