Adsorption of gases in multimolecular layers
Adsorption of gases in multimolecular layers
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DOI：
10.1021/ja01269a023
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发表时间：
1938-01-01
影响因子：
15
通讯作者：
Teller, E
中科院分区：
文献类型：
--
作者：
Brunauer, S;Emmett, PH;Teller, E
在离气体冷凝点不远的温度下，大多数吸附剂的吸附等温线有两个区域：在低压下，等温线是凹的;在高压下，等温线向压力轴凸出。高压凸起部分已经被各种解释。有些人认为这是由于吸附剂毛细管中的冷凝作用造成的，因为在分子尺度的毛细管中，冷凝作用可以在远低于液体蒸气压的压力下发生。另一些人则认为这种等温线表明形成了多分子吸附层。DeBoer和Zwicker 1解释了非极性分子在离子吸附剂上的吸附，假设吸附剂的最上层在第一层吸附分子中诱导偶极，这反过来又在下一层诱导偶极，依此类推，直到建立几层。他们和后来的布拉德利根据这种极化理论导出的等温线方程实际上是迄今为止提出来解释多分子吸附的唯一定量表达式。然而，正如我们将在本文的第一部分中表明的，第一层吸附气体对第二层吸附气体的极化已经太小，不足以构成两个吸附层之间结合能的主要部分，至少在那些气体分子不具有相当大的永久偶极矩的情况下是这样。在我们看来，产生凝结的力是造成凝结的主要原因。多分子吸附的结合能。在此假设下，在本文的第二部分，我们将进行推导的等温线方程的多分子吸附的方法，是一个推广的Langmuir的处理单分子层。在本文的第三部分中，我们将把等温线方程应用于由他人和我们在许多催化剂、催化剂载体和其他吸附剂上获得的各种实验温度。
The adsorption isotherms of gases at tempera-tures not far removed from their condensation points show two regions for most adsorbents: at low pressures the isotherms are concave, at higher pressures convex toward the pressure axis. The higher pressure convex portion has been variously interpreted. By some it has been attributed to condensation in the capillaries of the adsorbent on the assumption that in capil-laries of molecular dimensions condensation can occur at pressures far below the vapor pressure of the liquid. By others such isotherms are believed to indicate the formation of multimolecular adsorbed layers. DeBoer and Zwicker1 explained the adsorption of non-polar molecules on ionic adsorbents by assuming that the uppermost layer of the adsorbent induces dipoles in the first layer of adsorbedmolecules, which in turn induce dipoles in the next layer and so on until several layers are built up. The isotherm equation which they, and later Bradley, 2 derived on the basis of this polarization theory is practically the only quantitative expression that has been so far pro-posed to account for multimolecular adsorption. However, as we shall show in the first part of this paper, thepolarization of the second layer of adsorbed gas by the first layer is already much too small to constitute the major portion of the binding energy between the two adsorbed layers, at least in those instances in which the gas molecules do not possess considerable permanent dipole moments.It seems to us that the same forces that produce condensation are chiefly responsible for the bind-ing energy of multimolecular adsorption. On this assumption, in the second part of this paper we shall carry out a derivation of the isotherm equation for multimolecular adsorption by a method that is a generalization of Langmuir’s treatment of the unimolecular layer. In the third part of the paper we shall then apply the isotherm equation to a variety of experimentalisotherms obtained by others and by us on a number of catalysts, catalyst supports and other adsorbents.