(112c) Key Features of Pt-Catalyzed Nitric Oxide Oxidation Revealed by Coverage-Dependent Microkinetic Modeling

Pt-catalyzed NO oxidation is a key step in NOx removal from lean burn exhaust. Experimental evidence shows that high activity is associated with large Pt particles, but even those are prone to oxidative deactivation. To design new catalysts, we must first understand how Pt functions. In this work we use ab initio-based thermodynamic and microkinetic modeling to elucidate the key features of Pt-catalyzed NO oxidation under actual reaction conditions. We explore two pathways for O=O bond dissociation as functions of surface O coverage and solve for the reaction mechanism using the method of DeDonder relations, which makes no assumptions about the relative kinetics of intermediate steps. The results indicate independent O2 dissociative adsorption is rate limiting at the O coverages present under reaction conditions. In contrast, product NO2 dissociation is reversible and fast. This reaction controls the O coverage, O binding energy, and thus the kinetics on the surface. Catalyst design depends on moderating these effects, and future work in this area will be discussed.