Interpretation of the kinetic compensation effect in heterogeneous reactions: thermochemical approach

Abstract

The kinetic compensation effect (KCE), unexplained by the Arrhenius activation model, is interpreted in the framework of the novel thermochemical approach to kinetics of heterogeneous reactions. Unlike the activation model, this theory includes the process of congruent dissociative vaporisation of solids described by the Langmuir quasi-equilibrium equations and consideration of the two different reaction regimes: equimolar and isobaric (with the external pressure of gaseous product, respectively, below and above its equilibrium pressure). Change of regimes is shown to be the reason for the mutual variations of the Arrhenius parameters in the equation: ln A = a + bE. This theoretical interpretation of the KCE is quantitatively supported by experimental observations for the following different types of heterogeneous reactions: high temperature atomisation of metal oxides, low-temperature solid-state decompositions, NiO reduction by H₂ and catalytic oxidations of CO and of H₂ on PtO₂. Fundamental reasons for the shortcomings of the activation model in the interpretation of mechanisms and kinetics of heterogeneous reactions are identified.

Keywords:

• heterogeneous reactions
• kinetic compensation effect
• thermochemical approach
• activation model shortcomings
• mechanism of catalytic reactions

Acknowledgements

We thank the Editor of IRPC, Professor J.M. Hutson FRS, and the (anonymous) Referee for their careful consideration of our work, including valuable comments which have greatly helped us in the presentation of this manuscript.