简单气体在ITQ-3分子筛中扩散性质的分子动力学模拟

Molecular Dynamics Simulation on Diffusion Properties of Simple Gases in Zeolite ITQ-3

通过平衡分子动力学方法模拟了Ne,CH4和Ar在二维分子筛ITQ-3中的扩散,考察了两个不同方向上扩散系数与负载量之间的依赖关系.在窄孔径的Z方向上,扩散系数随负载量的增加先逐渐增大,而后逐渐减小;在宽孔径的Y轴方向,分子的扩散系数随负载量的增加而作单调减小.沿Z轴方向扩散势能曲线的计算,清晰地说明了出现这两种截然不同扩散模式的机理,即扩散系数随负载量的增加是通过降低扩散活化能实现的.模拟结果也说明了即便是同样一种空腔结构的分子筛,扩散也会因孔径和分子大小的不同而呈现出不同的对负载量的依赖关系.

The equilibrium molecular dynamics simulation was conducted to study the diffusion of Ne,CH4 and Ar in the two-dimensional zeolite ITQ-3,and the dependence of diffusion coefficients on adsorptions in two directions was explored.As the loading increasing,the diffusion coefficients increase to its maximum point and decrease afterwards along the narrow pore in Z direction.The diffusion coefficients along Y direction with relatively wider pores,however,decrease monotonically with respect to its loading.The two distinct diffusion mechanisms can be clearly explained by the calculation of potential energy profiles.The reduction of diffusion activation energy makes the diffusion coefficient an increasing function with respect to the loading.The simulations showed that,even for the zeolites with the same kind of cavities,the diffusion exhibited different relations with respect to the loadings according to different pores and different molecular size.