含氮ZSM-5分子筛骨架中氮取代位置的密度泛函计算

运用Gaussian 98程序包, 采用密度泛函理论B3LYP方法, 基于ZSM-5分子筛的8T模型, 分别通过6-31G, 6-31G(d)和6-311G(d,p)基组计算了ZSM-5分子筛中氮原子取代前后各O原子和各N原子的能量, 从而得到各O原子与各N原子在骨架中的稳定性及其对氮化取代反应的影响. 计算结果表明, N原子在骨架中的稳定性对氮取代反应的影响较大. ZSM-5分子筛晶体结构中与B酸位处于同一个四面体的O11位置, 为氮原子的最佳取代位置, 因此氮化后分子筛表面的B酸强度得到较大程度的减弱.

Density Functional Theory Studies on the Substitutional Site of Nitrogen in the Nitrogen-Incorporated ZSM-5 Zeolite

Density Functional Theory study was performed to predict the nitrogen substitutional site in the framework of nitrogen-incorporated ZSM-5 zeolite. All the calculations were performed on 8T clusters of ZSM-5 by Gaussian 98 program at B3LYP/6-31G, B3LYP/6-31G(d) and B3LYP/6-311G(d,p) levels, respectively. The calculations on energies of O atoms and N atoms show that the stability of N atoms in the framework has bigger effect on the reaction of substitution than the stability of O atoms. The O11 site, which is in the same tetrahedron with Brnsted acid, is the most preferred site for nitrogen substitution in the framework of ZSM-5 zeolite. So the Br nsted acidity on the surface of zeolite after nitridation is decreased.