(631d) Comparison of Explicit and Implicit Representations of Coverage Dependence on the Microkinetics of Catalytic Reactions

Surface science experiments and density functional theory calculations face a common challenge in connecting to catalytic reality. In both cases, model systems are examined at conditions that differ from that of catalytic reality, in particular in terms of the pressures of the reacting species. In DFT calculations, that pressure gap manifests itself as adsorbate coverages that differ from computational models to reaction conditions. Those coverage gaps will impact absolute rates, rate orders, and rate controlling steps and may well influence the relative performance of different materials for a particular reaction. In this work, we illustrate the effects of adsorbate coverage within a simplified two-step reaction network inspired by ammonia synthesis and NO oxidation. We examine how rates, rate orders, apparent activation energies, and Sabatier plots respond to increasing inclusion of explicit lateral adsorbate interactions using a lattice-based kinetic Monte Carlo(kMC) framework. We subsequently formulate and solve the same kinetic system within a coverage-explicit mean field model. We highlight the performance of conventional parameterization schemes relative to the kMC results and identify opportunities for improving upon those mean-field parameterizations to yield rates and rate sensitivities more faithful to the underlying adsorbate interactions.