Ockham's razor for paring microkinetic mechanisms: Electrical analogy vs.Campbell's degree of rate control

Abstract

Elucidation of the key molecular steps and pathways in an overall reaction is of central importance in developing a better understanding of catalysis. Campbell's degree of rate control (DRC) is the leading methodology currently available for identifying the germane steps and key intermediates in a catalytic mechanism. We contrast Campbell's DRC to our alternate new approach involving an analysis and comparison of the “resistance” and de Donder “affinity,” that is, the driving force, of the various steps and pathways in a mechanism, in a direct analogy to electrical networks. We show that our approach is as just rigorous and more insightful than Campbell's DRC. It clearly illuminates the bottleneck steps within a pathway and allows one to readily discriminate among competing pathways. The example used for a comparison of these two methodologies is a DFT study of the water–gas shift reaction on Pt–Re catalyst published recently. © 2015 American Institute of Chemical EngineersAIChE J, 61: 4332–4346, 2015