用实验吸附等温线和计算机分子模拟表征中孔分子筛MCM-41  

Characterization of Mesoporous MCM-41 Adsorbents by Computer Simulation and Adsorption Isotherm

作　　者：张现仁[1] 汪文川[1] 

机构地区：[1]北京化工大学化学工程学院,北京100029

出　　处：《化学学报》2002年第9期1606-1612,共7页Acta Chimica Sinica

基　　金：国家重点基础研究发展规划项目 (G2 0 0 0 0 480 10 ) ;国家高性能计算基金 ( 99118);北京化工大学教育部超重力工程研究中心资助项目

摘　　要：首先比较了表征MCM 4 1的两个势模型对吸附等温线的影响 .发现在一维势模型中 ,低压部分的吸附应与选用的势模型的势阱深度有关 ,而毛细凝聚发生的位置与孔壁在离壁面较远处与流体分子的相互作用的强弱有关 .然后作者使用了一个“混合”的势模型 ,即采用作者提出的势函数表征孔壁中氧原子对MCM 4 1中流体分子的作用 ,而采用Tjatjopoulos等提出的势函数近似地表征MCM 4 1表面硅醇基团以及一些未知因子对流体分子的作用 .虽然这种势模型仍然是一维的 ,但这种势模型将孔壁内氧原子的作用和表面上非均匀性分开考虑 ,具有较明确的物理意义 .通过计算机模拟与实验数据的比较发现 ,这种势模型可以较好地拟合氮气在MCM 4 1中的吸附等温线 .In this paper, two potential models representing the interaction between the pore wall and the molecules inside the pore have been compared. One of the models is the potential function proposed by Tjatjopoulos for cylindrical surface, the other is proposed by our previous work for cylindrical pores with a wall thickness being not negligible. Grand Canonical Monte Carlo (GCMC) method has been used to obtain the adsorption isotherms of the nitrogen in MCM-41 by these two potential models, when both the models have the same well depths. It is interesting to find that the change in the potential energies nearby the pore center strongly affects the capillary condensation pressure. Then, a mixed potential model is proposed, which consists of two parts: the potential energies from the oxygen atoms inside the wall, which are represented by our previous proposed potential model and the potential energies from the silanol coverage and/or other unknown factors in the surface of the channels of MCM-41, which are represented by the potential function of Tjatjopoulos et al. To test the proposed mixed potential, we have carried out GCMC simulation of the nitrogen in the MCM-41 pore at 77 K, and compared the simulated adsorption isotherm with the experimental nitrogen isotherm. The simulated isotherm from our model is in good agreement with the experiment, which indicates that the method proposed in this work can be used for characterization of MCM-41 adsorbents.

关 键 词：实验吸附等温线 计算机分子模拟 表征 中孔分子筛 MCM-41 势函数 孔结构 吸附剂 催化剂 

分 类 号：O647.3[理学—物理化学]