Rungsirisakun Ratana, Nanok Tanin, Probst Michael, Limtrakul Jumras
Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand.
J Mol Graph Model. 2006 Mar;24(5):373-82. doi: 10.1016/j.jmgm.2005.10.003. Epub 2005 Nov 9.
Molecular dynamics (MD) simulations of benzene in siliceous zeolites (FAU, ZSM-5, and MCM-22) were performed at loadings of 1, 2, 4, 8, and 16 molecules per supercell. The potential energy functions for these simulations were constructed in a semi-empirical way from existing potentials and experimental energetic data. The MD simulations were employed to analyze the dynamic properties of the benzene-zeolite systems. The adsorption energies of benzene/siliceous zeolite complexes increase with increasing loading number, due to the intermolecular attraction between benzene molecules. The self-diffusion coefficient of benzene in siliceous zeolites decreases with increasing loading due to the steric hindrance between the sorbates passing each other. From the zeolite-benzene radial distribution functions it was found that the benzene molecules are relatively far from each other, about 5.2A for siliceous FAU, 5.2A for siliceous ZSM-5, and 4.8A for siliceous MCM-22. In the case of FAU, the benzene molecules prefer to be adsorbed parallel to the surface of the sodalite cage above the six-membered-ring. In ZSM-5, we found a T-structure of the benzene molecules at loadings 2, 4, and 8 molecules per supercell. At loadings of 16 molecules per supercell, the molecules are lined up along the straight channel and their movement is highly correlated. For MCM-22 we found adjacent benzene molecules at a loading of 4 molecules with an orientation similar to the stacked conformation of benzene dimer in the gas phase.
在每个超晶胞中分别加载1、2、4、8和16个分子的情况下，对硅质沸石（FAU、ZSM - 5和MCM - 22）中的苯进行了分子动力学（MD）模拟。这些模拟的势能函数是根据现有势能和实验能量数据以半经验方式构建的。分子动力学模拟用于分析苯 - 沸石体系的动态性质。由于苯分子之间的分子间吸引力，苯/硅质沸石络合物的吸附能随着负载量的增加而增加。由于相互通过的吸附质之间的空间位阻，硅质沸石中苯的自扩散系数随着负载量的增加而降低。从沸石 - 苯径向分布函数发现，苯分子彼此相对较远，对于硅质FAU约为5.2埃，对于硅质ZSM - 5约为5.2埃，对于硅质MCM - 22约为4.8埃。在FAU的情况下，苯分子倾向于平行吸附在六元环上方的方钠石笼表面。在ZSM - 5中，我们发现每个超晶胞加载2、4和8个分子时苯分子呈T形结构。在每个超晶胞加载16个分子时，分子沿直通道排列，它们的运动高度相关。对于MCM - 22，我们发现在加载4个分子时相邻苯分子的取向类似于气相中苯二聚体的堆积构象。
