(58d) Kinetic Consequences of Adsorbate Coverage

Nick Delgass has been a leader in advocating for making deep, quantitative connections between microscopic mechanisms, like those accessible through density functional theory models, and observed macroscopic catalytic activity. While Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics can satisfactorily capture the observed kinetics of many reactions, the relationship between empirically inferred rate parameters and underlying microscopic reaction rates is not always clear. One of the features that complicates this relationship is the strong influence of adsorbate coverage on adsorption and activation energies at a metal surface. Metal-catalyzed reactions like water-gas shift on Pd and Pt, NO and CO oxidation on Pt, and many others occur at high coverages that have a strong influence on kinetics. Here we summarize recent work to construct coverage-dependent kinetic models from first principles. We take advantage of cluster expansion techniques to quantitatively describe adsorbate-adsorbate interactions and their influence on surface adsorption and reaction. We show how these techniques can be applied to low-symmetry adsorption situations, in which multiple adsorption sites become occupied at increasing coverage. We report coverage-explicit kinetic models for NO oxidation and WGS based on these results, and illustrate the relationship between the coverage-dependent models and the mean-field LHHW models.