SURFACE CURVATURE EFFECTS IN PHYSISORPTION AND CATALYSIS BY MICROPOROUS SOLIDS AND MOLECULAR-SIEVES
SURFACE CURVATURE EFFECTS IN PHYSISORPTION AND CATALYSIS BY MICROPOROUS SOLIDS AND MOLECULAR-SIEVES
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DOI：
10.1016/0021-9517(88)90297-7
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发表时间：
1988-03-01
影响因子：
7.3
通讯作者：
LUCAS, AA
中科院分区：
文献类型：
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作者：
DEROUANE, EG;ANDRE, JM;LUCAS, AA
分子筛，包括沸石，通过表面的曲率（内部孔和笼，以及外部“口袋”）将其自身与其它吸附剂和催化剂区分开，所述表面的曲率在进入分子到达催化活性位点的途中提供给进入分子。阐述了最近提出的一般概念“嵌套”，本文试图量化它的一个方面，即表面曲率的作用时，主机结构的大小和客体分子变得可比。主题和实例选自沸石的物理吸附和/或催化的文献。一个简单的货车德瓦尔斯模型的相互作用能和吸附力的分子住宿在一个孔是用来合理化半定量的一些公认的意见，例如，(i)沸石作为分子陷阱的作用;（ii）表面势垒的起源，假定调和晶内之间的巨大分歧（自扩散）和宏观测量（iii）分子在紧密配合的沸石孔中的快速扩散;（iv）观察到的C3-C14直链烷烃在毛沸石中扩散的“窗口效应”;（v）表观酸强度、裂化活性和分子“嵌套”之间的关系;和（vi）“约束指数”对温度的依赖性。特别是引入了两个新的概念：当分子的尺寸与通道壁的尺寸紧密匹配时获得超流动性的漂浮分子和分子沿通道壁沿着的蛇形或爬行运动。
Molecular sieves, including zeolites, distinguish themselves from other sorbents and catalysts by the curvature of the surface (internal pores and cages, and external “pockets”) which they offer to incoming molecules on their way to catalytically active sites. Elaborating on the recently proposed general concept of “nesting,” this paper attempts to quantify one of its aspects, namely the role of surface curvature when the size of the host structure and that of the guest molecule become comparable. Topics and examples are selected from the literature on physisorption and/or catalysis by zeolites. A simple van der Waals model for the interaction energy and the sticking force of a molecule lodging in a pore is used to rationalize semiquantitatively a number of well-accepted observations, e.g., (i) the role of zeolites as molecular traps; (ii) the origin of the surface barrier postulated to reconcile the large divergence between intracrystalline (self-diffusion) and macroscopically measured (nonequilibrium) diffusion coefficients; (iii) the rapid diffusion of molecules in tight-fitting zeolite pores; (iv) the “window effect” observed for the diffusion of C3C14linear chain paraffins in erionite; (v) the relationship among apparent acid strength, cracking activity, and molecular “nesting”; and (vi) the dependence of the “constraint index” on temperature. In particular, two new concepts are introduced: thefloatingmolecule which acquires supermobility when its dimension(s) matches closely that of the surrounding channel and the serpentine orcreepingmotion of the molecule along the channel walls.