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利用量子化学理论研究了ZSM-5分子筛中骨架Al的分布,计算采用11T簇模型[(HSiO)_3 SiO(H)M(OSiH)_2OSi(OSiH)_3](M=Si,Al,Ga),和B3LYP/6-31G(d)的计算方法,得到了T1,T2,T12位置上的Al/Si,(Al,H)/Si替代能,结果表明11T簇模型中骨架Al优先取代于ZSM-5分子筛中的T12位。采用MP2/6-311++G(3df,2p),计算得到Al/ZSM-5、Ga/ZSM-5分子筛的质子亲和势分别是316.6 kcal/mol,319.4 kcal/mol;B3LYP/6-31G(d)的方法计算吡啶在分子筛及改性分子筛上的吸附能分别是-25.35 kcal/mol和-23.02 kcal/mol。研究结果表明Ga改性ZSM-5分子筛降低了其酸性强度。
The distribution of Al matrix in ZSM-5 molecular sieve was studied by using quantum chemistry theory. The 11T cluster model [(HSiO) 3SiO (H) M (OSiH) 2OSi (OSiH) 3] (M = Si, Al, Ga) (Al, H) / Si at T1, T2, and T12 positions were calculated by the method of B3LYP / 6-31G (d) 5 molecular sieve T12 position. The proton affinities of Al / ZSM-5 and Ga / ZSM-5 zeolites were 316.6 kcal / mol and 319.4 kcal / mol, respectively, using MP2 / 6-311 ++ G (3df, 2p) The calculated adsorption energies of pyridine on molecular sieves and modified molecular sieves were -25.35 kcal / mol and -23.02 kcal / mol, respectively, using the method of 31G (d). The results show that Ga modified ZSM-5 zeolite reduces its acid strength.