Catalytic Oxidation Of Toluene Over Manganese-supported Platinum Catalysts:Study On Performance And Reaction Mechanism

Since 2013,China’s ambient air quality has continued to improve,but the situation of regional compound air pollution characterized by ozone and fine particles is still grim.Volatile organic compounds（VOCs）,as important precursors of PM_2.5 and O₃,seriously affect the quality of atmospheric environment and people’s health.Catalytic oxidation technology has the advantages of degradation efficiency and less secondary pollution,which is considered to be one of the most effective and economically feasible technologies.In this paper,Pt/Mn₃O₄catalysts with different synthesis methods and different carriers were prepared to make certain the best synthesis method.Then the cause of best performance of the catalysts were explored.The reaction mechanism of catalytic oxidation of toluene was deeply studied,and the roles of different reaction factors were studied.The main contents and conclusions are as follows:（1）Three kinds of Pt/Mn₃O₄ catalysts were prepared by sodium borohydride reduction method,platinum particle adsorption method and impregnation method.Compared with the catalysts prepared by the other two methods,Pt/Mn₃O₄-S catalyst prepared by sodium borohydride reduction method showed the best catalytic activity for toluene oxidation,achiening 90%toluene conversion at 191℃.The best low-temperature reduction performance and the highest proportion of adsorbed oxygen species on the surface are probably the reasons for the excellent catalytic performance of the catalyst.（2）Taking Mn₃O₄-R synthesized by a simple two-step reduction method and commercial Mn₃O₄-C as supports,and Pt/Mn₃O₄-R and Pt/Mn₃O₄-C catalysts were prepared by sodium borohydride reduction method.The influence of the support effect on the performance of the Pt/Mn₃O₄ catalyst was studied.A series of characterization results indicate that the properties of the support can affect the Pt dispersion,low-temperature reduction performance and surface oxygen vacancies of the Pt/Mn₃O₄ catalyst,thereby affecting the catalytic performance of the catalyst for toluene oxidation.The results of TOF（turn over frequency）show that the surface oxygen vacancy is the main active site in the oxidation of toluene catalyzed over Pt/Mn₃O₄,rather than the Pt exposed on the catalyst surface.（3）The results of toluene-temperature programmed desorption,toluene-temperature programmed surface reaction and diffuse reflectance infrared Fourier transform spectrometry（in-situ DRIFTS）show that the oxidation of toluene on Pt/Mn₃O₄-R catalyst follows the Mars-van Krevelen（MVK）mechanism,and the oxidation path of toluene may be toluene→benzoic acid→carbamate→CO₂.In addition,through a series of in-situ DRIFTS experiments,we speculate that the decomposition of carbonates at 180-190℃is the rate controlling step of toluene oxidation on Pt/Mn₃O₄-R catalyst.