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Plasma Assisted Catalysis M. L. Balmer, R. Tonkyn, G. Maupin,(a) S. Barlow, S. Yoon,(b) and A. Kolwaite(b) Supported by DOE Energy Efficiency Office of Advanced Automotive Technology. (a) Environmental and Health Sciences Division. (b) Graduate Student. The objective of this work is to develop an aftertreatment system that will achieve 90% NOx reduction using less than 5% of the engine power on a compression ignition direct injection (CIDI) diesel-fueled engine. The program supports goals of the Partnership for the Next Generation of Vehicles (PNGV). A non-thermal plasma in conjunction with new catalytic materials is being developed to reduce NOx emissions with a secondary goal of oxidizing hydrocarbons and particulate. A partnership between PNNL and the Low Emissions Technologies Research and Development Partnership (LEP) consisting of Ford, General Motors, and Daimler-Chrysler has been established under a Cooperative Research and Development Agreement (CRADA). In addition, Oak Ridge National Laboratory (ORNL) is collaborating with PNNL and the LEP in the area of ceramic synthesis and engine testing. FY99 Accomplishments New catalysts have been discovered that can reduce NOx when placed in or down-stream from a plasma reactor. Bench tests with simulated diesel exhaust show that a plasma-catalyst system can reduce up to 70% of NOx emissions at temperatures typical of CIDI exhaust (150-370°C) and an equivalent fuel penalty of 1%. Tests on a slip-stream of diesel engine exhaust from a diesel generator show that 53% NOx reduction can be achieved at 200°C and an equivalent fuel penalty of 6%. SO2 in simulated mix does not degrade catalyst activity. A full-scale prototype plasma reactor/catalyst system has been fabricated and delivered for testing. Tests on a VW 1.9L TDI diesel engine are ongoing. Nitrogen balance has been obtained for the best catalysts. The role of NO2 over the best catalysts has been determined. Previous work on this program showed that plasma-catalyst systems can reduce NOx emissions in simulated diesel exhaust; however, improvements in the efficiency and design of the plasma reactor systems as well as in the efficiency of the catalysts are necessary for vehicle applications. Research in FY99 was aimed at improving catalyst and reactor efficiency as well as at understanding effects of real diesel exhausts on NOx reduction activity. Research in FY99 focused on three general areas: catalyst development, reaction mechanism identification, and prototype reactor development. Systematic studies of structure property relationships in catalysts resulted in the discovery of a new catalyst with improved activity over a range of temperatures. As shown in Figure 7.24, the new catalyst (designated catalyst B) maintains 67% NOx reduction activity up to 350°C, a 27% improvement over a catalyst developed last fiscal year (designated catalyst A). Figure 7.24. NOx reduction as a function of temperature for new (B) and old (A) catalysts. Because sulfur dioxide in the exhaust has been shown to rapidly poison many lean NOx catalysts, the NOx reduction activity of the new catalyst was tested in simulated exhaust with high sulfur dioxide content. As illustrated in Figure 7.25, this catalyst showed no degradation in activity after 30 hours of exposure to simulated diesel exhaust mix containing 50 ppm of SO2. Figure 7.25. Data from 6 hours of a 30-hour test of NOx reduction activity of Catalyst B as a function of time in simulated exhaust containing 50 ppm SO2. A complete nitrogen balance was obtained for catalyst B. As shown in Figure 7.26, some N2O is formed; however, N2 is favored at all temperatures. Bench-scale plasma-assisted catalyst reactor systems were scaled-up for slip-stream and full scale testing on exhaust from a diesel generator and from a VW TDI engine at ORNL. While more work is required to integrate a plasma device into a vehicle, this stand-alone device is the first device designed to treat the full exhaust stream from a diesel-fueled vehicle. Full scale testing at two predetermined test points is ongoing. Up to 53% NOx reduction at an equivalent fuel penalty of 6% was observed on a slip-stream of diesel generator exhaust as shown in Figure 7.27. Some improvement could be observed when hydrocarbon concentrations were increased by injecting propylene into the exhaust. Figure 7.26. Ratio of nitrogen to N2O formation as a function of temperature for new catalyst. Nitrogen is strongly favored at all temperatures. Figure 7.27. NOx conversion using plasma assisted catalysis on diesel generator exhaust with propylene injection. 53% reduction is observed at an equivalent fuel penalty of 6%. Plasma assisted catalyst systems can routinely reduce 70% NOx on simulated diesel exhaust; however, NOx reduction drops to 43-53% on real diesel exhaust from a diesel generator. In the last year a new catalyst with increased activity at high temperature and resistance to sulfur poisoning has been discovered. In addition a full-scale plasma-catalyst system has been designed, fabricated and delivered for testing on a VW TDI engine at ORNL. William R. Wiley Environmental Molecular Sciences Laboratory Feedback: webmaster@emsl.pnl.gov Revised: April 17, 2000 Security & Privacy PNNL-13147