催化学报

催化学报 ›› 2010, Vol. 31 ›› Issue (8): 972-978.DOI: 10.1016/S1872-2067(10)60103-9

• 研究论文 • 上一篇    下一篇

Langmuir-Hinshelwood 动力学的有效实验条件

王德峥   

  1. 清华大学化学工程系北京市绿色反应工程与工艺重点实验室, 北京 100084
  • 收稿日期:2010-05-31 出版日期:2010-08-30 发布日期:2013-12-26
  • 通讯作者: 王德峥

Experimental Conditions for Valid Langmuir-Hinshelwood Kinetics

WANG Dezheng*   

  1. Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
  • Received:2010-05-31 Online:2010-08-30 Published:2013-12-26

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摘要： 使用 Langmuir-Hinshelwood (L-H) 动力学的学者大部分未注意到该动力学包含了所有吸附物种采用拟稳态假设的隐含条件, 因而他们通常忽视了确认实验条件是否允许采用拟稳态假设. 然而, 对于大部分气固催化反应, 拟稳态假设的成立需基于催化活性位浓度很小的前提. 对于催化活性位浓度高的反应体系, 其覆盖度较高的吸附物种不满足拟稳态假设. 因此, 在这种情况下通过实验测定的动力学常数没有物理意义, 而仅为该实验条件下的数学回归参数. 本文将活性位浓度小于最高反应气浓度的十分之一视为拟稳态假设成立的充分条件, 通过估算发现许多催化剂并不满足该条件.

关键词: 朗格缪尔吸附等温线, Langmuir-Hinshelwood 动力学, 吸附物种, 拟稳态假设, 速控步骤, 微观动力学

Abstract: Users of Langmuir-Hinshelwood kinetics often neglect that it invokes the pseudo-steady state hypothesis (PSSH) for all adsorbed species, and they do not check that the PSSH is validly used. However, with solid catalyzed reactions, the validity of the PSSH must often be based on the concentration of active sites being very small. With a high site concentration catalyst, the PSSH would be incorrect for adsorbates with significant coverages, which would make the deduced kinetic parameters lose their physical meaning and be only the parameters of curve fitting. It is estimated that many catalysts do not meet the criterion for their site concentration to be less than one-tenth the highest reactant concentration.

Key words: Langmuir adsorption isotherm, Langmuir-Hinshelwood kinetics, adsorbed species, pseudo-steady state hypothesis, rate-determining step, microkinetics