Published: 2005
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The research conducted in this program significantly increased the knowledge and understanding in the fields of plasma physics and chemistry in diesel exhaust, the performance and characteristics of multifunctional catalysts in diesel exhaust, and the complexities of controlling a combination of such systems to remove NOx. Initially this program was designed to use an in-line plasma system (know as a plasma assisted catalyst system or PAC) to convert NO --> NO2, a more catalytically active form of nitrogen oxides, and to crack hydrocarbons (diesel fuel in particular) into active species. The NO2 and the cracked hydrocarbons were then flowed over an in-line ceramic NOx catalyst that removed NO2 from the diesel exhaust. Even though the PAC system performed well technically and was able to remove over 95% of NOx from diesel exhaust the plasma component proved not to be practical or commercially feasible. The lack of practical and commercial viability was due to high unit costs and lack of robustness. The plasma system and its function was replaced in the NOx removal process by a cracking reforming catalyst that converted diesel fuel to a highly active reductant for NOx over a downstream ceramic NOx catalyst. This system was designated the ceramic catalyst system (CCS). It was also determined that NO conversion to NO2 was not required to achieve high levels of NOx reduction over ceramic NOx catalyst if that catalyst was properly formulated and the cracking reforming produced a reductant optimized for that NOx catalyst formulation. This system has demonstrated 92% NOx reduction in a diesel exhaust slipstream and 65% NOx reduction from the full exhaust of a 165 hp diesel engine using the FTP cycle. Although this system needs additional development to be commercial, it is simple, cost effective (does not use precious metals), sulfur tolerant, operates at high space velocities, does not require a second fluid be supplied as a reductant, has low parasitic loss of 2-3% and achieves high levels of NOx reduction. This project benefits the public by providing a simple low-cost technology to remove NOx pollutants from the exhaust of almost any combustion source. The reduction of NOx emissions emitted into the troposphere provides well documented improvement in health for the majority of United States citizens. The emissions reduction produced by this technology helps remove the environmental constraints to economic growth.
