Got NOx?

March 18, 2005

Pacific Northwest National Laboratory researchers have developed a new cost effective and energy efficient method for reducing oxides of nitrogen, or NOx, in diesel engine emissions. Called the reformer assisted catalysis, the process is three-fold -- "syngas" production, reductant synthesis and catalytic reduction of NOx in emissions.

Though they are the dominant choice in commercial trucks and heavy equipment, diesel engines are burdened with significant NOx emissions, which can affect breathing, visibility, vegetation growth, metals, fabrics and dyes.

In the most recent data collected by the U.S. Bureau of Transportation, national NOx emissions in 2001 were more than 22 million tons. As regulatory requirements on exhaust emissions become more stringent, reduction of nasty pollutants has become a high priority in automotive and other commercial industries.

PNNL began to work on this problem more than 10 years ago. Researchers developed a plasma facilitated catalyst, but recognized that a more energy- and cost-efficient system could be built, leading to the development of the reformer assisted catalysis.

The process includes treating hydrocarbon in a reformer before being introduced into the exhaust; diesel is then extracted from the fuel tank and reformed into syngas, a mixture of hydrogen and carbon monoxide.

Next, the mixture is chemically converted to dimethyl ether, which has proved to be highly selective for NOx reduction, from the syngas stream.

In the final step, catalysis, the ether mixture is injected into the exhaust, enhancing the performance of certain catalysts that allow for significant NOx reduction. Researchers took advantage of the earlier plasma catalysis system that offered changing the chemistry of the fuel to generate a better catalysis. They changed the process slightly to retain the oxygenated fuel in the exhaust, making it more cost and energy efficient.

Researchers plan to test the process on a small engine late this year.

Source: PNNL