Alongside hybrid cars that use fuel cells and specialized batteries to reduce auto emissions and increase fuel efficiency, so-called lean-burn engines have the potential to do the same, and become important components in the next generation of green car designs. Researchers at the Department of Energy’s Pacific Northwest National Laboratory have recently discovered a chemical process that may help clean up emissions in lean-burn engines, which is one of the biggest challenges they have to overcome.

Lean-burn engines are able to increase fuel efficiency and reduce emissions because they use more air during combustion, and produce less carbon monoxide than conventional engines. However, the biggest problem with lean-burn engines is destroying the NOx pollutants that they create.  Conventional catalytic converters are unable to sufficiently reduce the nitrogen oxides, carbon monoxide, hydrocarbons, and particulates from lean-burn engines, so the development of new exhaust cleanup technologies is seen as a critical next step. Specialized catalytic converters are being developed to deal with this problem, and most of the promising cleanup technologies involve complex chemical reactions between the gaseous exhaust particles and catalytic materials coated on ceramic substrates.

The Pacific Northwest National Lab researchers focused on the toxic nitrogen oxide (NOx) pollutant problem, and chemists recorded the first observations of how certain catalyst materials used in emission control devices are constructed. Alumina is seen as an inexpensive catalyst support material that can be used to clean up exhaust, so the researchers looked at the interactions of aluminum ions, oxygen ions, and barium oxide.

The lab’s scientists used the world’s first 900-MHz nuclear magnetic resonance spectrometer to reveal the anchoring behavior of aluminum ions as they bond with oxygen ions. Researchers found that, in the presence of water, aluminum ions on the surface of alumina bond to six oxygen ions. Heating removes the water and leaves some aluminum ions with only five oxygen ions. This creates a bonding site for the NOx-removing catalyst barium oxide.

“The discovery is encouraging because understanding catalysts in molecular and atomic detail can directly identify new ways to improve them,” said PNNL researcher Janos Szanyi. The manner in which barium oxide anchors onto alumina suggests the exact site where catalytic materials begin to form – and where they can be available to absorb NOx emissions.

The Department of Energy is funding a number of research projects targeting cleanup technologies for lean-burn engines, including software simulations that use physics and chemistry to reveal different approaches for formulating new catalytic materials.