(498d) Development and Implementation of Experimental Protocol for Steady-State and Transient SCR Kinetics

Authors: 
Toops, T. J., Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory
Strots, V., Navistar, Inc.
Pihl, J. A., Oak Ridge National Laboratory
Parker, G., Michigan Technological University
Johnson, J., Mississippi State University


Control of NOx emissions from diesel or lean burn gasoline engines is a technical barrier that must be overcome if the fuel efficiency advantages of these engines are to be fully realized. Ammonia-based Selective Catalytic Reduction (SCR) catalysts are a promising solution for minimizing NOx emissions while maintaining high overall vehicle efficiency. Aftertreatment systems based on these catalysts are starting to see commercial application, but it is difficult to develop a well-defined control strategy for these systems due to the frequency that catalyst manufacturers change their formulation. One of the key features that must be captured in a SCR model is the temperature dependence and the capacity of the catalyst to capture and store NH3, and once this reductant is stored its relative reactivity to oxidation versus NO reduction. This relies on both steady-state and transient chemistry and the accuracy of a model in capturing these features will dictate the NH3 and NO concentrations that are emitted to the atmosphere. The goal of this study is to define and implement an experimental protocol to capture the key rate parameters that will allow the development of an effective control strategy model.

A core from a commercial-intent zeolite-based SCR catalyst was used in this study in conjunction with a bench-scale flow reactor. The developed protocol was implemented between 150 and 600°C with space velocities ranging from 60,000 to 120,000 h-1. The protocol measures NH3 storage capacity under inert and oxidizing conditions, NH3 oxidation, NO SCR while varying the NH3/NO ratio from 0.8 to 1.2 and the NO2/NOx ratio from 0.0-1.0, NO oxidation, and temperature-programmed-oxidation of the stored NH3.