Diesel NOx catalytic converter development: A review

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.