New catalyst can reduce pollution from diesel vehicles

Scientists have developed a catalyst that can curb emissions of nitrogen oxides from diesel-powered vehicles, an advance that may help reduce air pollution and smog.
Nitrogen oxides (NOx) is a priority air pollutant that is a key ingredient in smog.
"Diesel engines power virtually all heavy-duty trucks, and NOx emissions control remains one of the key challenges facing manufacturers and operators," researchers said.
The team focused on copper-exchanged zeolites, a particular class of catalysts used to promote the conversion of NOx into environmentally benign nitrogen gas.
These catalysts begin functioning at temperatures too high to capture a large fraction of the NOx produced, researchers said.

They discovered the key chemical step that limits the performance of these catalysts at low temperature.

"We knew that copper ions trapped in the zeolite pores were responsible for the catalytic reaction, but we did not know what caused the chemical reaction to slow to such an extent at lower temperatures," said William Schneider from University of Notre Dame in the US.
The team tracked the movement of the copper ions within the zeolite pores. They discovered that the ions were much more mobile than anyone had appreciated, so much so that they were able to swim through the zeolite pores and pair up.

"We hypothesised that this pairing was key to the low- temperature performance," said Schneider.
Researchers proved that this pairing was indeed happening during one step in the overall catalytic process.
They were able to combine the experiments and computations to quantify the pairing and its influence on NOx removal.
"This information paves the way to developing catalysts that outperform current formations at lower temperatures, allowing diesel engines to meet stringent emissions regulations," said Schneider.
"Further, we think we can take advantage of the pairing process for other catalytic reactions beyond NOx removal," he added.
The study was published in the journal Science.