Of all the chemicals emitted in diesel engine exhaust, it's the ones you can't see, the nitrogen oxides (NOx ), that cause the most public health concern. Nitrogen oxides form when fuel is burned at high temperatures. The primary manmade sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. NOx also forms through certain natural processes, such as bacterial processes, lightning, and naturally occurring wildfires.

According to the U.S. Environmental Protection Agency, NOx contributes to the formation of ground-level ozone, which can trigger serious respiratory problems; the formation of acid rain; nutrient overload that deteriorates water quality; formation of atmospheric particles that cause visibility impairment; and global warming. In addition, NOx reacts to form nitrate particles, acid aerosols, toxic chemicals, and NO2 , which can cause respiratory problems.

A series of state and federal programs and regulations aimed at reducing NOx emissions began taking effect in 2004, and increasingly stringent rules will be implemented throughout the decade. In order to comply with these new regulations, vehicle engine manufacturers seek new NOx emission-reduction technologies.

Argonne's Research

equipment used to test the Cu-ZSM-5 catalyst

Argonne post-doctoral associate Sundar Krishnan (left), and researchers Steve Ciatti (center) and Chris Marshall (foreground, right) working with the equipment that will be used to engine-test the Cu-ZSM-5 catalyst. Marshall is holding a beaker of the catalyst material.

Researchers in Argonne's Chemical Engineering Division have developed a zeolite-based catalyst that may help diesel truck manufacturers eliminate harmful NOx emissions from diesel exhausts. Ceramic catalytic reactors containing the Argonne catalyst placed into vehicle exhaust pipes could convert NOx emissions into nitrogen.

Argonne's catalyst is Cu-ZSM-5 with an external coating of cerium oxide. Cu-ZSM-5 is a zeolite with copper ions attached within its micropore structure. Although Cu-ZSM-5 and similar catalysts have traditionally performed poorly for removing NOx from diesel exhaust due to insufficient heat and the presence of water vapor, Argonne researchers have developed an additive that allows Cu-ZSM-5 and similar catalysts to overcome these difficulties. When this cerium-oxide additive is combined with Cu-ZSM-5, the resulting catalyst works at normal exhaust temperatures and is actually more effective in the presence of water vapor than without it. With a lean fuel-air mixture, it removes as much as 95–100 percent of NOx emissions.

The Argonne catalyst has performed well in the laboratory with a number of diesel and diesel-type fuels, including standard diesel, synthetic diesel, bio-diesel, and JP8, which is a jet fuel preferred by the military. The catalyst will next undergo engine testing at Argonne's Diesel Engine Test Facility .

The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy funded the initial research on the cerium-oxide catalyst. The catalyst was further developed for chemical plant emissions under a joint research agreement with BP. Research plans call for expanded work aimed at both diesel and natural gas engines and coal-fired power plants.

Update

July 1, 2008: Integrated Fuel Technologies gets worldwide license for Argonne-developed Diesel DeNOx Catalyst. Read more.

September 2007