Catalytic Combustion Of Propane Based On Mn-based Catalyst

The rapid economic development has greatly improved people’s living standards,at the same time it has brought about more and more serious environmental problems.At present,air pollution is one of the serious environmental problems in China.There are many types of air pollutants,their typical representatives are volatile organic compounds(VOCs).VOCs are carbon-based chemical substances,which are directly related to air pollution phenomena such as photochemical smog and haze,which seriously affect human health.Therefore,effective control of VOCs emissions is of great significance for improving the atmospheric environment,the development of related emission reduction and elimination technologies has become a focus of attention in the environmental field.Catalytic combustion method has been extensively studied due to the advantages of low cost,simple operation,high purification efficiency.Based on this,the development of efficient and stable catalytic combustion catalysts is of great significance.Transition metal oxides have the advantages of easy availability of raw materials and long service life.They are widely used in the catalytic combustion of VOCs.Although some progress has been made in this area,the low-temperature activity and thermal stability of the catalyst need to be improved,the research on the oxidation mechanism is not clear enough.Based on this,we adjusted the surface oxygen vacancy concentration and surface lattice oxygen activity of the Mn-based catalyst through the surface defect structure and surface loading strategy.The dual purpose of improving the low-temperature activity and thermal stability of Mn-based catalysts was achieved,the reaction mechanism of catalytic combustion of propane molecules on Mn-based catalysts was investigated.The main research contents are as follows:1.For VOCs catalytic combustion reaction,oxygen vacancies can not only provide adsorption active sites for reactant molecules,but also promote the activation of reactants on the catalyst surface to accelerate the reaction.α-MnO2 has abundant reserves and variable valence.Based on this,we have constructed α-MnO2-70,α-MnO2-130,α-MnO2-180 with different oxygen vacancy concentrations by changing the hydrothermal temperature,which are used for propane catalytic combustion.EPR and XPS confirm that the lower hydrothermal temperature led to the higher of oxygen vacancy concentration.The increase of oxygen vacancy concentration improves the catalytic activity of α-MnO2,α-MnO2-70 has the best catalytic performance,its T90 is 260℃,which is about 80℃ lower than α-MnO2-180.Stability experiments show that α-MnO2-70 is continuously reacted for 24 hours at T50,the conversion rate is maintained about 50%;α-MnO2-70 cyclically reacts 3 times,the third catalytic performance is still maintained at the first level,which shows that α-MnO2-70 has good low-temperature thermal stability and cycle thermal stability.The results of H2-TPR and O2-TPD show that after increasing the oxygen vacancy concentration,the reducing ability of the catalyst is improved,and the migration and release ability of surface lattice oxygen and chemically adsorbed oxygen is enhanced.Finally,through in situ DRIFTS of propane catalytic combustion,the possible reaction mechanism of α-MnO2-70 and α-MnO2-180 catalytic combustion of propane was proposed.2.The deactivation of manganese oxide catalyst at high temperature is the main reason that limits its practical application.In order to build a Mn-based catalyst that can maintain stability at high temperature,we select mullite(SmMn2Os)and prepare different loaded Co3O4/SmMn2O5 for propane catalytic combustion reaction.Activity experiments show that 30%Co3O4/SmMn2O5(the mass ratio of Co to SmMn2O5 is 30%)has the best catalytic performance.Its T90 is 215℃,which is about 75℃ lower than carrier mullite,Stability experiments show that 30%Co3O4/Smn2O5 not only remains stable at low temperatures,but also reacts continuously at 800℃ for 24 hours,the original structure can still be maintained.XRD and Raman confirmed that Co element exists in the form of Co3O4.TEM and XPS show that there is a strong interaction between Co3O4 and SmMn2O5.H2-TPR and O2-TPD show that the interaction between Co3O4 and SmMn2O5 enhances the reduction ability of the catalyst,and enhances the activity of chemisorption oxygen and surface lattice oxygen.Finally,through in situ DRIFTS of propane catalytic combustion,the possible reaction mechanism of SmMn2O5 and 30%Co3O4/SmMn2O5 catalytic combustion of propane was proposed.