Study On The Catalytic Oxidation Of Toluene And Propane By Cobalt Cerium Composite Oxides

Volatile organic compounds?VOCs?,as one of the common air pollutants,not only have a bad impact on the environment,but also have great harm to human health.Therefore,it is urgent to control VOCs pollution.As one of the main VOCs control technologies,catalytic oxidation technology has been widely used in recent ten years.Catalyst materials are the key problem of the catalytic oxidation technology.Therefore,it is necessary to develop catalysts with higher catalytic activity and better thermal stability.In this paper,the effect of small organic acids on cobalt cerium composite oxide catalysts prepared by sol-gel method was studied.In addition,we found that cobalt content played an important role in the preparation of cobalt cerium composite oxide catalysts using MOFs?metal-organic frameworks?template method.Furthermore,the influence of different methods on the catalytic performance of cobalt cerium composite oxide catalysts was also investigated.The phase structure,specific surface area and pore volume,redox performance and surface atomic state of the catalysts were characterized by TG-DSC,XRD,N₂ adsorption and desorption,SEM-EDS,TEM,Raman,XPS,H₂-TPR and O₂-TPD,respectively.The VOCs catalytic performance of the catalysts was investigated and the structure-activity relationship of the catalysts was also clarified.Firstly,four kinds of natural small organic acids?SOAs?,such as malic acid?MA?,citric acid?CA?,glycolic acid?GA?and tartaric acid?TA?,were investigated to prepare cobalt cerium composite oxides?CoCe-X,where X stands for the abbreviation of the SOA used?as chelating agents.The effect of organic acids on the composition,structure,morphology and catalytic performance of metal oxides has been discussed in details.Characterization results showed that the type of organic acids influenced the hydrolysis,condensation as well as calcination processes,and then strongly affected the textural and physicochemical properties of the metal oxides synthesized.The best catalytic activity was obtained with the CoCe-MA catalyst,and the toluene conversion reached 90%at 242?.The superior catalytic performance of the CoCe-MA catalyst could be related to its textural,redox properties and unique surface compositions and oxidation states.In addition,the CoCe-MA catalyst also showed excellent stability in long-time activity test.Secondly,using MOFs as template,Co_aCe_1-a-BTC-MOFs precursors were prepared by hydrothermal method,Co_aCe_1-aO_x?a=0-1?catalysts with specific morphology and structure were obtained,and investigated for the catalytic oxidation of toluene and propane.The results showed that cobalt cerium composite catalysts exhibited excellent catalytic performance for oxidation of toluene and propane,and the Co_0.30Ce_0.70O_x catalyst was the most active catalyst obtained,which reached 90%of the toluene and propane conversion rate at 238 and 256?,respectively.The effect of cobalt amount on the physicochemical properties of Co_aCe_1-aO_x catalysts synthesized have been discussed in details.Among them,S_BET,lattice defects,Ce³⁺ions,redox properties and surface oxygen vacancies play an important role in enhancing the catalytic performance of Co_a Ce_1-a-a O_x catalysts.Finally,the co-precipitation method?CP?,sol-gel method?SG?and MOFs template method?MOF?were selected to prepare cobalt cerium oxide catalysts?marked as CoCeO_x-Y,where Y stands for the the preparation method used?,and its catalytic performance for toluene and propane oxidation were studied.If T₉₀ was used as the activity standard,the order of activity of CoCeO_x-Y catalyst were:CoCeO_x-MOF>CoCeO_x-SG>CoCeO_x-CP.The T₉₀ of CoCeO_x-MOF catalyst for toluene and propane was 238 and 256?,respectively.The characterization results revealed that S_BET and lattice defects,as well as surface Ce³⁺ions and oxygen vacancies played an important role in improving the catalytic activity of CoCeO_x-MOF catalysts.