Study On Catalytic Oxidation Of Formaldehyde Removal With Manganese Based Catalyst

Formaldehyde is a pollutant gas,which is "teratogenic,mutagenic,carcinogenic",and derived from building materials and textiles.In order to improve air quality and ensure people's health,this pollution problem must be solved.At present,formaldehyde concentration can be effectively reduced through degradation or adsorption.The main methods include photochemical degradation,catalytic oxidation,plasma treatment,physical,chemical adsorption and so on.Among them,the catalytic oxidation method has become a hot spot due to its high conversion efficiency and no secondary pollution.Considering the requirements of its application environment,the key problem of catalytic oxidation is to research and develop a catalyst that can efficiently catalyze and oxidize formaldehyde in a low temperature and humid environment(Temperature?room temperature,Humidity?50%).In this thesis,a series of manganese-based catalysts have been researched and developed,and the performance and mechanism of formaldehyde removal by catalytic oxidation have been thoroughly and systematically studied,and the high-efficiency low-temperature catalytic oxidation removal of formaldehyde has been realized.Due to the controllable pore size,large specific surface area and hydrophobicity of three-dimensional(3D)mesoporous manganese dioxide,it has a strong affinity for formaldehyde and can selectively adsorb formaldehyde molecules.In this thesis,3D mesoporous MnO2 was prepared by hard template method,and modified by Pt/K additives to explore a new method for formaldehyde removal efficiently at low temperature.3D mesoporous Pt/MnO2 and K-Pt/MnO2 catalyst were prepared,and their formaldehyde oxidation activity was studied in depth.The complete oxidation of 20 ppm formaldehyde was achieved by 3D mesoporous Pt/MnO2 catalyst at 9?,and achieved by 3D mesoporous K-Pt/MnO2 at 0? and the activity was much better than that of unmodified MnO2(130?).The mechanism was revealed:the strong carrier-metal interaction between Pt and MnO2,which changes the electronic state of Mn,increases the ratio of Mn3+/Mn4+and forms oxygen vacancy which promotes the production of surface active oxygen.And the K ion in K-Pt/MnO2 catalyst converts water into hydroxyl radicals(OH-)as a strong oxidant,weakening the Mn-O bond,and electron-rich K transfers the charge to O,increasing the electricity negativeness,promotes the dissociation of oxygen,increases the surface adsorbed oxygen,and improves the low-temperature reducibility of the catalyst.According to the research,the increase in the ratio of Mr3+/Mn4+plays an important role in the catalytic oxidation of formaldehyde.In this thesis,cerium with excellent performance and high reducing ability was selected to modify the manganese-based catalyst,and the composite transition metal oxide MnO2(x)-CeO2(x=Mn/Ce molar ratio)was prepared.Studies have shown that the modification of cerium can also increase the ratio of Mn3+/Mn,generate more oxygen vacancies,expose low-coordination cerium atoms to adsorb oxygen and chemically adsorb oxygen molecules on the surface,maintain surface electrostatic balance,promote active oxygen generation,and improve the oxidation activity of formaldehyde.It can completely remove formaldehyde at 60? and space velocity of 120 000 mL(gcat h)-1.It showed better activity than single MnO2(130?)and CeO2(170?)catalysts,and the mechanism of formaldehyde oxidation was proposed.The morphology and structure of the catalyst have an important influence on the catalytic performance.The morphology and structure of the manganese-based catalyst were further optimized,and a hollow spherical manganese-cerium catalyst with high specific surface area,low density and high gas permeability was prepared.The MnO2/CeO2 hollow sphere catalyst achieves 70%conversion of formaldehyde at 20?;and completely converts formaldehyde at about 47?,which is the best overall performance in this paper.Mechanism analysis shows that the hollow inner space and the penetrable shell can promote the transfer of gas molecules to the active site,so that there is sufficient contact between the active site and the reaction gas.In the preparation process,the carbon ball is used as a hard template.During the process of removing the carbon balls by high-temperature calcination,the cationic-OH groups are converted into metals oxide.The residual carbon in the MnO2/CeO2 hollow spheres forms a strong synergistic effect with MnO2/CeO2 through interface electron transfer,which improves the chemical stability of the catalyst and facilitates the formation of oxygen vacancies and active oxygen,thereby improving the formaldehyde oxidation activity of the catalyst.