Preparation And DeNO_x Performance Of MOF-74 In Low-temperature SCR Process

As one of the main atmospheric pollutants, Nitrogen oxides(NO_x) have caused serious impact on environment and human health. The denitrification(deNO_x) in power plants is very important since the emission of NO_x from power plants takes majority in China. Selective catalytic reduction(SCR) in the presence of NH3 is widely used for the deNO_x process in power plants as the most effective method. Metal organic framework(MOF) has many unique properties, such as large specific surface areas, regular pores with no dead volume, high porosity, stable framework, highly dispersed and absolutely exposed metal sites. Therefore, it has been proposed as the potential catalysts for the low-temperature SCR reaction. In this thesis, M-MOF-74(M = Mn, Co) with coordinatively unsaturated metal sites(CUSs) were synthesized and its low-temperature SCR catalytic performance were systematically investigated using experimental and computational methods.First of all, the preparation methods of M-MOF-74(M = Mn, Co) were investigated. It was found that Co-MOF-74 with perfect crystal structures could be synthesized at the hydrothermal reaction temperatures of 100, 120, 135 and 150?. The products prepared at 100? exhibited the largest specific surface area and pore volume. Mn-MOF-74 prepared at 135?exhibited perfect crystal structures. Stability tests showed that the above-mentioned MOF materials could maintain their structures in the process of low-temperature SCR reaction.In this thesis, the special catalytic nature of the CUSs in M-MOF-74(M = Mn, Co) were investigated and their influences on the low-temperature SCR mechanisms were explored. The results showed that the metal ions in MOF-74 exhibited distinctly different performances from conventional metal oxides: the capacities of NO adsorption and activation of Mn in Mn-MOF-74 were much stronger than those in Mn3O4 and MnO2, which affects the key step of the SCR process, namely, the adsorption and activation of NO. This could make the change of the low-temperature SCR mechanism from E-R to L-H. The performances of M-MOF-74(M = Mn, Co) were varied with different metal ions, and the adsorption and activation abilities for NO and NH3, especially for NO, in Mn-MOF-74 were stronger than those in Co-MOF-74, which led to the higher catalytic activities of Mn-MOF-74: 99% NO conversion and close to 100% N2 selectivity.In addition, by virtue of the advantages of MOF, MnO_x were prepared by the calcination of Mn-MOF-74. It was found that the MnO_x prepared at 700? under N2 atmosphere exhibited the largest specific surface area: 89.1 m2/g, and highest deNO_x activities: 98% NO conversion and close to 100% N2 selectivity.