(60g) Global Reaction Kinetics in Commercial Three-Way Catalysts (TWCs)– an Experimental and Modeling Study

Stronger emission legislation throughout the world has led to the need of constant and rapid improvement in the performance of catalytic converters, and mathematical modeling plays a prominent role in driving this improvement. In this work, we present a combined experimental and modeling study in understanding the performance of a commercial Three-Way Catalyst (TWC). We focus on the light-off behavior (otherwise called cold-start emissions) as most of the emissions in TWCs occur during this time.

Fundamentally, TWC converts carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC) into cleaner gases by simultaneous oxidation and reduction reactions in the presence of platinum group metals (PGMs). A thorough investigation of the performance of TWCs therefore requires a detailed understanding of the heat and mass transfer in catalyst substrate and washcoat, and most importantly the rates of chemical reactions occurring on the surface of the precious metals. Since many reactions occur simultaneously during real-life vehicle test conditions, we leverage our in-house lab setup to isolate individual reactions. We then utilize Langmuir-Hinshelwood mechanism to model the global reaction kinetics on the catalyst surface to obtain the pre-exponential factors and activation energies in the Arrhenius equation. We use Dakota, an open source code by Sandia national Labs, to optimize the reaction kinetics along with Axisuite, a commercially available exhaust aftertreatment model. We identify the important reactions affecting the TWC performance and reactions that do not play a significant role in emissions. We also examine the effect of oxygen storage in TWCs on reaction kinetics.