Mechanism discrimination in heterogeneous catalytic reactions: Fractal analysis
Mechanism discrimination in heterogeneous catalytic reactions: Fractal analysis
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DOI：
10.1021/ie970341u
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发表时间：
1998-02-01
影响因子：
4.2
通讯作者：
Kazemeini, M
中科院分区：
文献类型：
--
作者：
Khorasheh, F;Radmanesh, R;Kazemeini, M
在催化表面上的反应可以由Langmuir-Hinshelwood（LH）机理表示，并且取决于该机理，反应速率对表面活性位点的总浓度具有某种依赖性。这些位点的浓度与催化剂的表面积成比例。催化剂的不规则表面可以被建模为分形，因此？总的可用表面积取决于反应物的尺寸。在本文中，分形几何的概念已被扩展到帮助区分机制的反应，一个同系分形催化表面。在过去，同系反应物速率的差异归因于诸如电感应和空间效应的因素。这些因素可能确实很重要;然而，将表面建模为分形可以解释反应速率的变化，这种变化可能仅由反应物尺寸的变化引起。在这方面的分形分析的使用检查与烷基芳烃化合物的催化加氢脱烷基化的数据参考。在该分析中使用的简单图（log初始速率对log反应物横截面积）可用于区分可能的催化机制。为了验证反应物的尺寸对反应速率的影响，使用不同尺寸的反应物对分形表面上的催化反应进行了二维计算机模拟。使用LH机制，其中表面反应是速率控制。模拟是基于蒙特卡罗方法，并考虑反应物的扩散到分形催化剂表面，吸附和解吸从表面，和表面反应。
Reactions on catalytic surfaces can be represented by Langmuir-Hinshelwood (LH) mechanisms and, depending on the mechanism, the reaction rate has some dependence on the total concentration of surface active sites. The concentration of these sites is proportional to the surface area of the catalyst. The irregular surface of a catalyst can be modeled as a fractal and, as such? the total available surface area depends on the size of the reactant. In this paper the concept of fractal geometry has been extended to help discriminate between mechanisms for reactions of a homologous series on fractal catalytic surfaces. In the past, differences in rates for homologous reactants have been attributed to factors such as electronuclear induction and steric effects. These factors may indeed be important; however, modeling the surface as a fractal would explain the variations in reaction rate that could arise from changes in the reactant-size alone. The use of fractal analysis in this context is examined with reference to data on catalytic hydrodealkylation of alkylaromatic compounds. Simple plots used in this analysis (log initial rate versus log reactant cross-sectional area) are useful in discriminating amongst possible catalytic mechanisms. To verify the effect of reactant size on the reaction rate, a two-dimensional computer simulation is performed for catalytic reactions on fractal surfaces using reactants of different sizes. A LH mechanism is utilized where the surface reaction is rate controlling. The simulation is based on a Monte Carlo approach and considers the diffusion of reactants to a fractal catalyst surface, adsorption to and desorption from the surface, and surface reaction.