Preparation Of Carbon-based Catalyst And Supported MnO_x Catalyst And Their Application In NO Catalytic Oxidation

Air pollution has always been a global issue of widespread concern to society.Nitrogen oxides,as the main air pollutants,are extremely harmful to the human body and the ecological environment.Therefore,the emission of nitrogen oxides must be reduced.In this thesis,a series of nitrogen-doped activated carbon catalysts and supported MnOx catalysts were prepared,and their catalytic oxidation denitrification performance in medium and low temperature flue gas was studied.Firstly,a series of nitrogen-doped activated carbon catalysts were prepared by using dicyandiamide solution to do nitrogen-doping modification on commercially available coconut shell activated carbon by impregnation method.Results showed that after activated carbon was impregnated in 0.5 mol/L dicyandiamide solution and calcined at 600℃,the prepared N(0.5)-AC-600 had relatively best catalytic activity.When the NO inlet concentration was 500 ppm and the reaction temperature was 40℃,the maximum NO conversion rate on the N(0.5)-AC-600 catalyst could reach 67.2%.Studies found that active components,such as pyridine nitrogen(N-6)and graphitic nitrogen(N-Q)groups,could be generated on activated carbon by nitrogen doping modification.The activity of nitrogen-doped activated carbon catalyst increased with the increase of nitrogen content,but it was limited by the specific surface area of activated carbon.The reaction mechanism of NO on nitrogen-doped activated carbon catalyst:NO and O2 are adsorbed on the active site of the catalyst together,and then NO is oxidized to NO2 and then desorbed.Secondly,this thesis used Mn(NO3)2 solution and KMnO4 solution as Mn source,ZSM-5 zeolite or γ-Al2O3 as carrier,through the deposition-precipitation method,successfully synthesized ZSM-5 zeolite or γ-Al2O3 supported MnOx catalysts.Experimental results showed that when the concentration of Mn(NO3)2 solution and KMnO4 solution were both 0.09 mol/L,the experimentallγ-prepared Mn(0.09)-ZSM-5 catalyst had relatively best catalytic activity.Under the conditions of a NO inlet concentration of 500 ppm and a reaction temperature of 260℃,the NO conversion rate on the Mn(0.09)-ZSM-5 catalyst could reach up to 89%.Studies found that the MnOx crystal form generated on the support by the catalyst preparation method in this paper was mainly γ-MnO2.The activity of the supported MnOx catalyst increased with the increase of the MnOx loading,but it was limited by the specific surface area of the catalyst and the thermodynamics of the chemical reaction.ZSM-5 molecular sieve was more conducive to the generation,loading and dispersion of Mn4+ on the surface of the carrier than γ-Al2O3.The reaction mechanism of NO on the supported MnOx catalyst:NO is first chemically adsorbed,coordinated on the active site of MnOx in the form of nitrosyl,and then oxidized to nitrate by the active lattice oxygen.Subsequently,nitrates decompose to generate and desorb No2,and the consumed lattice oxygen is replenished by O2.In addition,the deactivation of the two catalysts caused by H2O was reversible,while the deactivation caused by SO2 was irreversible.