We present a formalism that describes the rate of the overall reaction in the form of an apparent rate-controlling step that is a sensitivity-weighted average of the elementary steps that comprise the overall reaction. Reaction parameters—apparent reaction orders, apparent enthalpy and entropy of activation—of the composite reaction network are determined within this framework by directly applying transition state theory to this apparent rate-controlling step. The derivation of this formalism via a Taylor series linearization of the rate function of the composite reaction will be presented with the objective of identifying sensitivity as the salient parameter in determining the rate determining characteristics of elementary steps within a reaction network. Additionally, we demonstrate the utility of this formalism control in the context of methane dehydroaromatization catalysis on Mo/ZSM-5 by reconciling (i) thermodynamic driving forces for reaction described by De Donder relations and (ii) kinetic driving forces for reaction quantified by the degree of rate control.

The apparent rate-controlling step of composite reactions: Insights from transition-state theory and degrees of rate control

ACS Fall 2021

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