Theoretical Study On The Reaction Mechanism Of The Direct Catalysis Decomposition For N₂O Over Metal-Organic Frameworks

N2O is a greenhouse gas, which can cause the ozone depletion. Furthermore, it is also responsible for the generation of photo-chemical smog, acid rain formation and particulate pollutant. How to effectively control and eliminate N2O has became a hotspot and key problem in the field of atmospheric pollution and environmental catalysis. Metal-organic frameworks (MOFs) coordinated with unsaturated metal ions, can be used as Lewis acid catalyst for N2O direct decomposition. Based on the synthesized M-BTC (M=Cr, Fe, Ni, Cu, Zn, Mo) in the experiment, using density functional theory (DFT) and cluster model to study N2O direct decomposition and the microscopic reaction mechanism over MOFs, which has the same topological structure with different metal ions centers. Accordingly, the main contents can be divided into the following parts:(1)At B3LYP/LANL2DZ level, the adsorption energy of N2O adsorbed on Ni-BTC is higher than that of on Fe-BTC. In the present work Ni-BTC and Fe-BTC are used to explore the N2O decomposition processes and the microscopic reaction mechanism.(2)At B3LYP/LANL2DZ level, the activation energy and O2 desorption energy of O2 formation mechanism are close to that of NO formation mechanism. The activation energy of NO2 formation is higher than that of NO formation, so there are two possible mechanisms of N2O decomposition over Fe-BTC, which are O2 formation mechanism and NO formation mechanism. For N2O decomposition over Ni-BTC, the activation energy of NO formation mechanism is lower than that of O2 formation mechanism and the desorption energy of NO is also lower than O2 desorption energy. Therefore, the product of N2O decomposition over Ni-BTC is NO. The adsorption energy of N2O adsorbed on Ni-BTC is higher than that of on Fe-BTC, but the activation energy of the first N2O decomposition over Ni-BTC is higher than that of decomposition over Fe-BTC, so the catalytic activity of Ni-BTC is lower than that of Fe-BTC. In the present work, the adsorption energy can not become the only criterion to judge the catalytic activity.(3)At the B3LYP/6-31g(d,p) and ROB3LYP/6-31g(d,p) level, the broken-spatial-symmetry(BS) approach was used to study the N2O decomposition over Cu-BTC with antiferromagnetic secondary building unit. The calculated result shows that the mechanism of N2O decomposition over Cu-BTC is O2 formation mechanism. Under the levels of B3LYP and ROB3LYP the energy barrier is different, but the overall trend of the same reaction.