A new cerium-oxide catalyst developed by researchers at the Department of Energy’s Argonne National Laboratory is showing promise for the efficient reduction of NOx emissions in diesel engine exhaust.
The technology has been under development for a number of years and has a patent pending. A number of companies have expressed interest in licensing the technology and working with Argonne researchers to scale it up and bring it to market. Argonne researcher Christopher Marshall, one of the technology’s developers, believes there could be a commercially available product within two to three years.
The most promising catalyst is Cu-ZSM-5—a zeolite with copper ions attached within its micropore structure—with an external coating of cerium oxide.
Those working previously with Cu-ZSM-5 and similar catalysts in the past found that they performed poorly at removing NOx from diesel exhaust, according to Marshall. Those catalysts require temperatures higher than normal diesel exhaust temperatures and don’t work well in the presence of water vapor, which is almost always found in engine exhausts.
With the help of the Advanced Photon Source at Argonne to analyze the structure and performance of various catalysts, Marshall’s group at Argonne developed an additive that allows Cu-ZSM-5 and similar catalysts to overcome these difficulties.
Our new cerium-oxide additive is the breakthrough that makes it work. When it’s combined with Cu-ZSM-5, the resulting catalyst works at normal exhaust temperatures and is actually more effective with water vapor than without it. With a lean fuel-air mixture, it removes as much as 95-100 percent of NOx emissions.—Christopher Marshall
The new Argonne catalyst uses the on-board diesel fuel as the reductant; there is no requirement for a separate urea tank for ammonia-selective catalytic reduction. Unlike NOx traps that are platinum-based, the Argonne catalyst contains no platinum and is affected far less by any fuel-borne sulfur.
Marshall says the Argonne catalyst has been tested and performed well with a number of diesel and diesel-type fuels, including standard diesel, synthetic diesel, biodiesel and JP-8. Having performed well in these tests, the next step is to subject the catalyst to engine testing, which will soon take place soon at Argonne's Diesel Engine Test Facility.
Marshall expects these tests will show that in addition to its other advantages, the Argonne catalyst has a greater life expectancy than other catalysts currently on the market.
Marshall and his colleagues are also working with the Chemical Engineering Division’s fuel cell research group. Using a reformer developed by this group could provide better fuel for the catalyst, said Marshall.
Our catalyst already works well, but it would work even better with the smaller hydrocarbons produced by a reformer.—Christopher Marshall
Initial research on the cerium-oxide catalyst was funded by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy. The catalyst was 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.