Abstract: In this study，the effect of pore structure on diffusion of two C7 hydrocarbons，n-heptane and toluene，which have the same number of carbon atoms and different diameters of molecular dynamics and structures，in nano-ZSM-5 materials were investigated using the zero-length column （ZLC） method. Furthermore，the corresponding MFI zeolite sample was also investigated using the same technique. The effective diffusion time constants of these two sorbates on ZSM-5 materials were evaluated by the Crank model，and the diffusion activation energies were estimated. The values of activation energy of diffusion of toluene were about 1.5 times higher than those of n-heptane，whereas the effective diffusion time constants of toluene were much smaller than those of heptane，which could be attributed to more complex structure and larger kinetic diameter of toluene. Diffusion rates of heptane and toluene depended on particle size of the nano-ZSM-5 crystal. Diffusion time constants of heptane and toluene in nano-ZSM-5 zeolite were found about 2 times higher in comparison to the corresponding MFI zeolite sample. However，diffusion activation energies for both C7 hydrocarbons in the MFI zeolite were about 2 times higher than those in the corresponding nano-ZSM-5 zeolite sample，which suggested that decrease of the diffusion path length within the microporous crystals by reducing the particle size could promote the process of diffusion.

Key words: zeolite ZSM-5, kinetics, nanoparticles, diffusion, activation energy, zero-length column

摘要： 实验选取了碳原子数相同、结构和分子动力学直径不同的正庚烷和甲苯作为探针分子，通过零长柱法（zero-length column，ZLC）考察了纳米级介孔ZSM-5沸石的孔结构对探针分子扩散性能的影响。采用Crank扩散模型计算了有效扩散时间常数，并估算了扩散活化能。实验结果表明，由于甲苯比庚烷分子结构复杂、分子动力学直径大，因此甲苯在ZSM-5样品中的扩散活化能约为庚烷的1.5倍，有效扩散时间常数远小于庚烷。庚烷和甲苯在纳米级介孔ZSM-5沸石中的扩散速率取决于粒径的大小，两者在纳米级介孔ZSM-5中的有效扩散时间常数是微米级纯微孔ZSM-5的两倍，然而两者在微米级纯微孔ZSM-5中的活化能为纳米级介孔ZSM-5中的两倍，说明对于纳米级介孔ZSM-5，微粒粒径减小、扩散路径缩短，对扩散起到了极大的促进作用。

关键词: 沸石ZSM-5, 动力学, 纳米粒子, 扩散, 活化能, 零长柱法（ZLC）