Selective Catalytic Reduction (SCR) Deactivation Kinetics Study for Aging, Control and OBD Applications, 03-R8048Printer Friendly Version
Inclusive Dates: 04/01/09 10/01/10
Background - Urea SCR is one of the prevailing technologies being used to reduce oxides of nitrogen (NOx) emissions from diesel engines down below U.S. 2010 and Euro-6 heavy-duty and Tier 2 light-duty emission limits. SwRI continues to perform research, development and testing work to support its clients and advance the understanding of this important technology. This project sought to provide data to feed into three key areas: refining model-based controls to include progressive deactivation, determining deactivation energies (Ed) for use in accelerated aging cycle protocols, and evaluating a proposed on-board diagnostic (OBD) methodology.
Approach - SwRI used its Universal Synthetic Gas Reactor®: (USGR®) to perform all of the aging and testing work.
The USGR has the ability to provide catalyst core samples with accurate mixtures of simulated exhaust gases under controlled conditions of concentration, flow rate and temperature. It is relatively cost-effective, less time-consuming to generate data, and more precise than engine-based approaches. Catalyst cores were aged at various temperatures for various times using a suitable aging gas mixture. Three test types were then performed at each aging point to obtain data relevant to each of the three key areas. Tests were performed on examples of the three main current SCR catalyst formulations: V/W/TiO2, Cu-zeolite and Fe-zeolite.
Accomplishments - The work successfully determined Ed values for all three SCR catalyst formulations. These values are already in use for the DAAAC-HD Consortium work. Ammonia storage capacity (Ω) values were measured, and algorithms derived that can be used in model-based controls to account for progressive thermal deactivation of the catalysts. And it was determined that the NOx transient response method for use as an OBD method demonstrated that it is a viable approach, but there are issues with the method that may limit its usefulness. The primary problem discovered was that the method requires the NH3 stored to be at equilibrium prior to running an OBD test. Equilibration times may be too long for practical application of the method. Overall, the project was successful at meeting all of its intended goals.