Kinetic description and study of heterogeneous catalytic reactions

Abstract

The kinetic assessment of catalytic reactions is essential to the design and application of chemical processes useful in petrochemical synthesis, energy conversion, and environmental remediation. Here, we exploit and develop methods for the kinetic description of heterogeneously-catalyzed reactions in generality and in the context of methane dehydroaromatization (DHA)—a direct, non-oxidative route for C1 valorization. CH4 DHA is hindered by strong, apolor C-H bonds which confer onerous thermodynamic barriers to selective CH4 conversion and, in so doing, complicate rigorous appraisal of candidate catalysts. We synthesize learnings from disciplines of mass transport, thermodynamics, and reaction kinetics to clarify mechanistic observations and ascertain the identity of molecular events, species, and catalytic moieties which determine the activity of benchmark DHA catalysts. Foundations established in these experimental efforts are leveraged to formulate a mathematical framework which resolves long-standing questions in the fields of thermochemical and electrochemical kinetics. In particular, we demonstrate that the ubiquitously used Langmuir–Hinshelwood formalism is incomplete and fails to correctly describe even simple catalytic reactions (e.g., A + A → A2). We develop an analytical method which, in essence, expands the spatial scope of the Langmuir-Hinshelwood framework to explicitly describe the dynamics of ensembles of any shape and size. The presented formalism captures site-ensemble dynamics with the same fidelity as stochastic-computational kinetic Monte Carlo simulation and is robust to inclusion of (i) multiple types of sites, (ii) lateral adsorbate interactions, (iii) surface diffusion events, and (iv) electron transfer steps.