Preparation Of Co₃O₄ Based Nanocomposite Catalysts And Its Catalytic Oxidation For Low Concentration Methane

China has abundant coal resources and coal mine gas resources,which means that China will not change its coal-based energy structure in the short term.In the process of coal resource exploitation,the extremely low gas content in the coal mines that have been evacuated in large quantities has not only caused a strong greenhouse effect,but also accompanied by huge waste of energy.How to develop and utilize the wasted coal mine gas and mitigate the greenhouse effect has always been a very important research topic.At present,the utilization methods of coal mine exhausted gas mainly include combustion-supported air combustion,chemical cycle combustion,(catalytic)countercurrent reactor thermal energy utilization,and concentrator methane enrichment,etc.In the above utilization schemes,catalysts play an important role.In the field of methane catalytic combustion,Pd,Pt,Au and other noble metal catalysts have been studied earlier.However,due to the problems of volatilization,sintering,poor thermal stability and high price of active components at high temperature,they have been restricted in use.Transition metal oxides have been studied more widely because of their relatively low price and high catalytic activity.Among all the transition metal oxides,Co3O4 has become a research hotspot because of its highest catalytic activity.The main content of this paper is to explore the promotion mechanism of Mn and Ce on the catalytic activity of Co3O4 and its application in the carrier type(SiO2,Al2O3)catalyst.The characterization methods mainly include XRD,SEM,EDS,BET,FT-IR,TG,TEM,XPS.(1)Co3O4 based nanocatalysts were successfully prepared by thermal adsorption combined with template method,in which the formation mechanism of the catalyst was related to the rapid oxidation of CNTs.In the doping process of Mn and Ce,the Co(0.9)/Mn3O4 and Ce(0.05)/Co3O4 catalysts prepared by molar ratio Co:Mn=0.9:0.5 and Co:Ce=0.9:0.05 showed the highest catalytic activity,nearly 400℃ achieved complete oxidation of methane.Regarding the research on the mechanism of Mn and Ce ion promotion,Mn ions mainly increase the number of Vo’ in the way of promoting the lattice distortion of Co3O4.Ce ions promote the Vo’ of Co3O4 due to the reduction oxidation of Co ions by OI.Vo’ are the production of reactive oxygen species,which is the main catalytically active center,so the catalytic activity of the catalyst will increase.(2)Based on the promotion mechanism of Mn and Ce ions,the core-shell structure of Co3O4/SiO2 catalyst was successfully prepared by hydrothermal method and introduction of spherical SiO2 carrier with small particle size.The two-dimensional structure of Co3O4 nanosheets is an important factor for the high reactivity of Co3O4/SiO2 based catalysts.In the experiments of adjusting the molar concentration ratio(Co:Mn and Co:Ce),Mn(1.0)/Co/SiO2 and Ce(0.08)/Co/SiO2 had the highest catalytic activity,and the complete oxidation of methane was achieved at 400℃.Compared with Co3O4-based nanocomposite catalysts,the thermal stability of this type of catalyst is improved.(3)Referring to the hydrothermal preparation process and parameters of the spherical nanocatalyst,the monolithic columnar support Al2O3 was introduced,and the carrier mass(0.1→1g)was increased,and the concentration of cobalt nitrate(3 mmol→0.1-0.9 mmol)was also reduced.Both Mn/Co(0.5)/Al2O3and Ce/Co(0.7)/Al2O3 catalysts achieve higher catalytic activity with lower catalyst loading,complete oxidation of methane at around 650℃,and thermal stability higher than that of Co3O4-based nanocatalysts and Co3O4/SiO2 based catalyst.Catalytic tests have also shown that higher catalyst loading does not significantly increase the catalytic activity of the catalyst.The excessive release of cobalt nitrate causes unnecessary waste of resources.In short,this low-load,low-cost monolithic columnar Co3O4/Al2O3 based catalysts are more suitable for catalytic industrial applications.