MCM-22型分子筛中苯分子吸附行为的分子动力学模拟

Diffusion of Benzene in MCM-22 Zeolite: A Molecular Dynamics Study

用分子动力学方法研究了纯硅 ＭＣＭ－２２型分子筛（ＩＴＱ－１）中苯分子的吸附行为．计算结果 表明，模拟采用刚性骨架或柔性骨架对苯分子的扩散系数并没有大的差别，这表明在较低吸附值 的情况下，分子筛骨架的柔性对苯分子吸附和扩散并没有产生大的影响．从吸附质的分子运动轨 迹上看，苯分子的扩散和吸附主要发生在１２元环超笼内，而通过１０元环窗口从一个超笼扩散到 附近的超笼时则需要较高的激发能量．在吸附质的运动过程中，Ｓ１位点和Ｓ２位点附近成对苯分 子之间会产生较强的π－π堆积力，为了使体系在能量上处于最佳，吸附质之间在运动上会保持很 强的协同效应．

s Molecular dynamics has been performed to study the diffusion behaviors of benzene molecules in pure siliceous MCM-22 analog: ITQ-1. The diffusion coefficients of benzene do not show obvious differences using rigid zeolite framework or flexible zeolite framework, which means the flexibility of the zeolite framework does not introduce remarkable effects to the simulation results. From the trajectories of molecular dynamics, it can be found that the diffusion and migration of benzene mainly occured in 12-MW cavities, while high activtion energy must be needed when one sorbate molecule migrating from one 12-MW cavity to another nerarby 12-MW cavity through the 10-MW windows. Moreover, the diffusion characteristics of the benzene molecules indicates that a pair of benzene molecules in S1 and S2 sites will produce relatively strong π－π stacking force and the motions between two benzenes near S1 and S2 sites will keep very synergistic status in order to make the system remaining in the state of optimal energy.