中文摘要：

建立了一个基于过渡态理论的分子在ITQ-3窄孔道方向扩散的模型.该模型中,由于分子从空腔中的一个吸附位越过势垒到相邻的另一个空腔中的吸附位需要克服很大的势垒能,因而分子在势垒处可以简化处理为只存在排斥势,可得到扩散系数依赖温度和Lennard-Jones作用参数的解析关系.用分子动力学方法对CF4在ITQ-3上扩散进行了模拟并验证了解析关系的合理性.分子动力学模拟计算得到的扩散活化能、势垒能和吸附位势能与实际值相吻合.模拟结果也显示了扩散系数依赖于附载量,表现为先增大后减小的变化模式.扩散活化能的计算证实了这一变化机理,即当附载量增加时,由于处于空腔中的分子彼此抬高了势能,降低了扩散活化能,使得扩散系数随附载量的增加而增大,之后由于堵塞效应,扩散系数随附载量的增加而逐步减小.

英文摘要：

A model of molecular diffusion in the narrow pores of zeolite ITQ-3,which is based on transitionstate theory,is proposed. In this model,the movement of molecules is treated as hopping from one adsorption site to another in connected cavities and the potential barriers between them are thought to be large. This assumption could simplify the potential at the windows between the cavities as pure repulsive form,from which the formula for the dependence of diffusion upon temperature and Lennard-Jones parameters can be obtained analytically. The model is compared with molecular dynamics simulations of carbon tetrafluoride CF4 diffusing on ITQ-3. The diffusion activated energy,the barrier height,and the potential at adsorption sites given by simulations are in accordance with the actual values. This indicates that molecular diffusion behaves in the same way assumed in the model. The simulations also show that the diffusion coefficients first increase and then decrease in response to the loadings. The changes of the activated energy calculated at different loadings have explained this dependence behavior. The increasing of the loading will elevate the potential energy of molecules at cavities,namely lower the activated energy,and consequently give rise to the increasing of diffusion coefficients. Further increasing of the loadings would lead the decreasing trend of the diffusion owing to the blocking effect.