This paper summarizes the findings of several technical articles on diesel NOx catalytic converter technology. Simplified theoretical reactions for NOx removal are discussed. Currently, development of catalytic NOx control technology for diesel engines is focused on systems that incorporate fuel hydrocarbons as the chemical reducing agent. Copper-and zeolite-based catalysts have been the predominant systems studied to date, but now catalysts containing precious metals are being investigated. Observed NOx reduction efficiencies typically ranged from 10 to 30 percent on actual engine exhaust systems when exhaust hydrocarbon enrichment strategies were used. Effects of carbon monoxide, sulfur dioxide, and water on NOx reduction efficiencies are reviewed. Recommendations for future research include attempts to broaden the temperature range of efficient NOx reduction, improving hydrocarbon selectivity toward the NOx reduction reaction, and the development of a supplementary reductant delivery system suitable for transient diesel engine operation.

Issue Section:
Internal Combustion Engines
Topics:
Catalytic converters, Diesel, Nitrogen oxides, Catalysts, Diesel engines, Exhaust systems, Carbon, Control systems, Copper, Engines, Fuels, Metals, Sulfur, Temperature, Transients (Dynamics), Water
1.
“Request for Proposals” (RFP) entitled “Demonstration of a Non-additive Lean NOx, Catalytic Converter for Heavy-Duty Diesel Vehicles,” State of California Air Resources Board, RFP No. 92–7, Sept. 14, 1992.
2.
Heimrich, M. J., “Air Injection to an Electrically-Heated Catalyst for Reducing Cold-Start Benzene Emissions From Gasoline Vehicles,” SAE Paper No. 902115, 1990.
3.
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,
Koradia
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4.
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5.
Held, W., Konig, A., Richter, T., and Puppe, L., “Catalytic NOx Reduction in Net Oxidizing Exhaust Gas,” SAE Paper No. 900496, 1990.
6.
Iwamoto, M., Yahiro, H., Tanda, K., Mizuno, N., Mine, T., and Kagawa, S., “Removal of Nitrogen Monoxide Through a Novel Catalytic Process. 1. Decomposition of Excessively Copper Ion Exchanged ZSM-5 Zeolites,” The Journal of Physical Chemistry, Vol. 95, No. 9, American Chemical Society, 1991.
7.
Truex, T. J., “NOx, Reduction Under Lean-Burn Conditions,” Johnson Matthey Technology Centre.
8.
Iwamoto, M., and Mizuno, N., “NOx Emission Control in Oxygen-Rich Exhaust Through Selective Catalytic Reduction by Hydrocarbon,” submitted to the Journal of Automobile Engineering, Part D of the Proceedings of the Institution of Mechanical Engineers, 1992.
9.
Heimrich, M. J., Jones, K. B., and Bykowski, B. B., “Preparation and Evaluation of Lean NOx Catalysts,” ASME Paper No. 93-ICE-30, 1993.
10.
Heimrich, M. J., and Deviney, M. L., “Lean NOx Catalyst Evaluation and Characterization,” SAE Paper No. 930736, 1993.
11.
Engler, B. H., Leyrer, J., Lox, E. S., and Ostgathe, K., “Catalytic Reduction of NOx With Hydrocarbons Under Lean Diesel Exhaust Gas Conditions,” SAE Paper No. 930735, 1993.
12.
Herzog, P. L., Burgler, L., Winklhofer, E., Zelenka, P., and Cartellieri, W., “NOx Reduction Strategies for DI Diesel Engines,” SAE Paper No. 920470, 1992.
13.
Sumiya, S., Muramatsu, G., Matsumura, N., Yoshida, K., and Schenck, R., “Catalytic Reduction of NOx in Diesel Exhaust,” SAE Paper No. 920853, 1992.
14.
Inui, T., Kojo, S., Shibata, M., Yoshida, T., and Iwamoto, M., “NO Decomposition on Cu-Incorporated A-Zeolites Under the Reaction Condition of Excess Oxygen With a Small Amount of Hydrocarbons,” Zeolite Chemistry and Catalysis, 1991, p. 355.
15.
Sata, S., Hirabayashi, H., Yihiro, H., Mizuno, N., and Iwamoto, M., “Iron Ion-Exchanged Zeolite: The Most Active Catalyst at 473 K for Selective Reduction of Nitrogen Monoxide by Ethane in Oxidizing Atmosphere,” Catal. Letters, Vol. 12, No. 193, 1992.
16.
Hama, H., Kintaichi, Y., Sasaki, M., Ito, T., and Yoshinari, T., “High Efficiency of Alumina and H-Zeolite Catalysts for Selective Reduction of Nitrogen Monoxide by Methanol in the Presence of Oxygen and Water Vapor,” Appl. Catal. A: General, Vol. 88, Nos. L1–L7, 1992.
17.
Sato, S., Yu-u, Y., Yahiro, H., Mizuno, N., and Iwamoto, M., “Cu-ZSM-5 Zeolite as Highly Active Catalyst for Removal of Nitrogen Monoxide From Emissions of Diesel Engines,” Appl. Catal., Vol. 70, Nos. L1–L5, 1991.
18.
Konno, M., Chikahisa, T., Murayama, T., and Iwamoto, M., “Catalytic Reduction of NOx in Actual Diesel Engine Exhaust,” SAE Paper No. 920091, 1992.
19.
Monroe, D. R., DiMaggio, C. L., Beck D. D., and Matekunas, F. A., “Evaluation of a Cu/Zeolite Catalyst to Remove NOx From Lean Exhaust,” SAE Paper No. 930737, 1993.
20.
Heimrich, M. J., “Demonstration of a Non-additive Lean NOx Catalytic Converter for Heavy-Duty Diesel Vehicles,” Task 2 Interim Report to the State of California Air Resources Board, Contract No. 92-310, SwRI Project 08-5744, June 1, 1994.
21.
Khair, M. K., and Bykowski, B. B., “Design and Development of Catalytic Converters for Diesels,” SAE Paper No. 921677, 1992.
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