Global Reaction Kinetics in Three-Way Catalysts-an Experimental and Modeling Study

摘要

Stronger emission legislation throughout the world has led to the need for con-stant and rapid improvement in the performance of catalytic converters,and mathe-matical modeling plays a prominent role in driving this improvement.In the present work,we present a combined experimental and modeling study on understanding the performance of a commercial three-way catalyst (TWC).We focus on the light-o behavior (otherwise called cold-start emissions) as most of the undesired emissions in TWCs occur during this time.Fundamentally,TWC converts carbon monoxide (CO),nitrogen oxides (NOx),and hydrocarbons (HC) into benign gases by simultaneous oxidation and reduction reactions in the presence of platinum group metals (PGMs).A thorough investiga-tion of the performance of TWCs therefore requires a detailed understanding of the heat and mass transfer in catalytic converter substrates 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 con-ditions,we leverage our in-house lab setup to isolate individual reactions.We then utilize the 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 avail-able exhaust aftertreatment model.We identify the important reactions a ecting the TWC performance and reactions that do not play a signi cant role in emissions.We also examine the e ect of oxygen storage in TWCs on reaction kinetics.