Making natural gas engines less leaky

As well as releasing CO₂ in the atmosphere, natural gas engines leak unburned methane as they’re powering up.

This potent greenhouse gas leakage makes natural-gas based engines in vehicles, compressors in hot water systems, and other combustors significant polluters.

But a team of US researchers has found a way to strip this excess methane out, using a catalyst made from the precious metal palladium.

They’ve published their findings in Nature Catalysis.

“There’s a big drive towards using natural gas, but when you use it for combustion engines, there will always be unburnt natural gas from the exhaust, and you have to find a way to remove that. If not, you cause more severe global warming,” says paper co-author Dr Frank Abild-Pedersen, a researcher at Stanford University.

“If you can remove 90% of the methane from the exhaust and keep the reaction stable, that’s tremendous.”

The catalyst is made from individual palladium atoms resting on a support made from cerium oxide.

The researchers found these atoms could remove methane at both low temperatures, when an engine was starting up, and higher temperatures once it was running.

It did this in different ways. When temperatures were low, the catalyst used trace amounts of carbon monoxide that appear in engines to bring palladium atoms together in small clusters where they could break methane molecules apart.

As temperatures rose, the clusters of palladium atoms separated and acted on their own, continuing to trap methane.

“It’s almost a self-modulating process which miraculously overcomes the challenges that people have been fighting – low temperature inactivity and high temperature instability,” says Professor Yong Wang, a researcher at Washington State University.