Motivation -- Lean-burn engines have been identified by U.S. automakers as the next major technological step in combustion engine design and fuel economy. By using more air during combustion, lean-burn engines yield better mileage and produce less carbon monoxide and unburned hydrocarbon pollutants than conventional gasoline engines. However, destruction of NOx pollutants, which are produced by all engines, is more difficult in a lean-burn engine. Catalytic converters that were developed for conventional engines cannot be used for lean-burn engines. If a lean-burn engine is to become commercially viable, novel catalyst technologies are needed. Similar catalysts may also find application for compression ignition, direct injection (CIDI or diesel) engines, where highly oxidizing conditions in the exhaust stream demand similar advances in catalyst technology.
Accomplishment Our initial goal was to develop hydrous metal oxide (HMO)-based catalysts to mitigate NOx emissions in lean-burn engine exhaust. The flexibility of the HMO process chemistry allowed a wide variety of catalysts to be screened for activity in the selective catalytic reduction of NOx via hydrocarbon reaction using materials in bulk powder form. We fabricated and tested promising catalyst compositions on small-scale cordierite monoliths using HMO coating and ion exchange techniques. The best HMO-supported catalyst systems were evaluated by scaling up the HMO-coating and ion-exchange processes to a full developmental size (110 cubic inch) catalytic converter (Fig. 1). Tests of these prototype converters on a lean-burn engine dynamometer at Lockheed Martin Energy Systems Y-12 Plant showed that NOx reduction activity rivaled a commercial benchmark catalytic converter. Total time from initial bulk screening to developmental size catalytic converter fabrication was less than 2 years.
With the new Environmental Protection Agency (EPA) Tier II emission standards scheduled to be in place starting in 2004, we are now addressing new and potentially more efficient NOx reduction options for lean-burn exhaust aftertreatment. We are investigating catalysts for use in the selective catalytic reduction of NOx by urea (or NH3). We are also engaged in more studies related to determining the mechanism of the selective catalytic reduction of NOx over different catalyst materials with various reductants, and are conducting mixed catalyst and support studies designed to optimize lean-burn NOx catalysts.
Significance This effort involves a unique project team of multiple national laboratories, automakers, and catalyst suppliers. The overall program, which is sponsored by the DOE Office of Transportation Technologies, is facilitated by separate CRADAs between three national laboratories, Los Alamos, Oak Ridge, and Sandia National Laboratories, and the Low Emission Technologies Research and Development Partnership (LEP), which consists of General Motors, Ford, and DaimlerChrysler. The CRADA efforts are focused on the development and evaluation of new catalyst materials for reducing NOx emissions.
This project received the 1996 Partnership for a New Generation of Vehicles Award for Technical Accomplishment. The Sandia project team also was awarded the 1999 National Laboratory CIDI R&D Award in recognition of outstanding achievement in R&D of lean NOx catalysts for CIDI engine exhaust emission control. Two U.S. patents have been awarded for NOx reduction by hydrocarbon technologies developed by Sandia.
Sponsors for this work: DOE Office of Transportation Technologies
Contacts: Eric Coker, (505) 272-7593, encoker@sandia.gov
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