Preparation Of Fe-MOFs And Mn-MOFs And Their NH₃-SCR Catalytic Properties

With the continuous development of China’s industrialization process, serious pollution problems such as acid rain and photochemical smog have appeared. Much attention has been devoted to elimination of nitrogen oxides (NOx), which is one of the root causes of such pollutions. Selective catalytic reduction of NOx with ammonia (NH3-SCR) is an effective process for NOx removal. Currently, the denitration catalyst of V2O5-WO3/TiO2has been widely used in industry, but the problems such as high operation temperature, narrow window and the toxic of active component still exist in actual operation. Therefore, seeking novel catalysts with high catalytic activity, high porosity and non-toxic has become a hot research in the field of denitrification. Metal-organic frameworks (MOFs) as a new class of porous materials have been successfully applied in the field of catalysis because of its high porosity, more active sites and high surface area. However, the application of MOFs as denitrification catalyst has yet not been reported. In this dissertation, Fe-MOFs and Mn-MIL-100were selected as NH3-SCR catalysts to study their denitrification activities. The structures and properties of synthesized materials were charactered, and the influences of different synthesis conditions on their denitrification activity were investigated in detail. The following research results were obtained:(1) MIL-100(Fe) and MIL-53(Fe) materials were prepared by solvothermal method and used as catalysts for NH3-SCR reactions. The results showed that MIL-100(Fe) possess a higher denitrification efficiency.(2) Different MIL-100(Fe) synthesis conditions have important effects on NH3-SCR catalytic activity. Firstly, MIL-100(Fe) materials were synthesized by different solvents (H2O and DMF) and their NH3-SCR catalytic activity was tested respectively. The results showed that MIL-100(Fe) with H2O as solvent exhibited high catalytic activity. Then, two materials were prepared with different organic ligands (H3BTC and NH2-H2BDC). The material with NH2-H2BDC ligand showed better catalytic activity than that with H3BTC. This is mainly because that the functional groups of NH2-H2BDC can provide more active sites for such reaction. Finally, the effects of activation temperature were investigated and the results showd that MIL-100(Fe) dried after200℃,12h in vacuum can reach95%NOx conversion at300℃. This is due to after the removal solvent molecules at high temperature vacuum, more FeⅢ catalytic active sites are present with remained inherent pore structure. Further, when the temperature rose to above150℃, the metal center of FeⅢ can effectively transfer into Fe" while the frame structure stay unchanged. The FeⅢ/FeⅡ mixed valence state in such framework would be more beneficial to NH3-SCR reaction.(3) Mn-MIL-100as NH3-SCR catalyst was synthesized by solvent-thermal method. The result showed that Mn-MIL-100was active at lower temperature, mainly due to the presence of unsaturated metal active site of Mn ions in the skeleton.(4) The material of MIL-100(Fe-Mn) was synthesized by hydrothermal method for NH3-SCR reaction. The experimental results illustrated that MIL-100(Fe-Mn) showed better NO conversion performance, achieving80%NO conversion at300℃.