New catalyst could cut pollution from millions of engines

Researchers demonstrate a way to remove the potent greenhouse gas from the exhaust of engines that burn natural gas.

Individual palladium atoms attached to the surface of a catalyst can remove 90% of unburned methane from natural-gas engine exhaust at low temperatures, scientists reported today in the journal Nature Catalysis

While more research needs to be done, they said, the advance in single atom catalysis has the potential to lower exhaust emissions of methane, one of the worst greenhouse gases, which traps heat at about 25 times the rate of carbon dioxide. 

Researchers from the Department of Energy’s SLAC National Accelerator Laboratory and Washington State University showed that the catalyst removed methane from engine exhaust at both the lower temperatures where engines start up ­­­and the higher temperatures where they operate most efficiently, but where catalysts often break down. 

“It’s almost a self-modulating process which miraculously overcomes the challenges that people have been fighting – low temperature inactivity and high temperature instability,” said Yong Wang, Regents Professor in WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering and one of four lead authors on the paper. 

A growing source of methane pollution 

Engines that run on natural gas power 30 million to 40 million vehicles worldwide and are popular in Europe and Asia. The natural gas industry also uses them to run compressors that pump gas to people’s homes. They are generally considered cleaner than gasoline or diesel engines, creating less carbon and particulate pollution.

However, when natural-gas engines start up, they emit unburnt, heat-trapping methane because their catalytic converters don’t work well at low temperatures. Today’s catalysts for methane removal are either inefficient at lower exhaust temperatures or they severely degrade at higher temperatures. 

“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,” said co-author Frank Abild-Pedersen, a SLAC staff scientist and co-director of the lab’s SUNCAT Center for Interface Science and Catalysis, which is run jointly with Stanford University. “If you can remove 90% of the methane from the exhaust and keep the reaction stable, that’s tremendous.”

A catalyst with single atoms of the chemically active metal dispersed on a support also uses every atom of the expensive and precious metal, Wang added. 

“If you can make them more reactive,” he said, “that’s the icing on the cake.”

Unexpected help from a fellow pollutant 

In their work, the researchers showed that their catalyst made from single palladium atoms on a cerium oxide support efficiently removed methane from engine exhaust, even when the engine was just starting. 

They also found that trace amounts of carbon monoxide that are always present in engine exhaust played a key role in dynamically forming active sites for the reaction at room temperature. The carbon monoxide helped the single atoms of palladium migrate to form two- or three-atom clusters that efficiently break apart the methane molecules at low temperatures. 

Then, as the exhaust temperatures rose, the clusters broke up into single atoms and redispersed, so that the catalyst was thermally stable. This reversible process enabled the catalyst to work effectively and used every palladium atom the entire time the engine was running – including when it started cold.

Read more on SLAC website

Synthesised a new catalyst with key properties to solve environmental issues

A research led by the ITQ-CSIC-UPV has discovered a new catalyst enabling hydrogenation of carbon dioxide to methane with advantages not seen until now. This new catalyst, whose structure and mechanism have been understood by synergistically exploiting different ALBA Synchrotron techniques, can be used for methane (natural syngas) production, that is considered as a promising energy carrier for hydrogen storage.

Linear economy has proven to be unsustainable in the long run due to its ineffective use of natural resources that leads to a huge amount of greenhouse gas emissions and waste generation. An alternative model, the so-called circular economy is based on an efficient production cycle that focuses on minimising waste and better recycling and seems to be key to find solutions for the climate crisis. One process that can be essential in this challenge is carbon dioxide (CO2) sequestration and usage, that is, transform atmospheric or produced carbon dioxide into energy carriers or platform molecules of the chemical industry.

An international collaboration between the Instituto de Tecnología Química – a join research center between Consejo Superior de Investigaciones Científicas and Universitat Politècnica de València (ITQ-CSIC-UPV), SOLEIL SynchrotronUniversidad de Cádiz, and ALBA Synchrotron permitted to synthesize a new catalyst able to hydrogenate carbon dioxide to methane with significant improvements in comparison to existing analogues. Its main advantage is that it possesses a much higher activity and so the reaction temperature can be lowered from usual 270-400ºC to only 180ºC, with an excellent long-term stability. Furthermore, this catalyst is able to operate under intermittent power supply conditions, which couples very well with electricity production systems based on renewable energies. Moreover, its synthetic procedure itself is ecofriendly, making it an even greater option in environmental issues.

This new catalyst can be used for methane (natural syngas) production, that is considered as a promising energy carrier for hydrogen storage.

The new solid catalyst was designed and synthesized in the ITQ (CSIC-UPV) by a mild, green hydrothermal synthesis procedure resulting in a material that contains interstitial carbon atoms doped in the ruthenium (Ru) oxide crystal lattice, enabling the stabilization of Ru cations in a low oxidation state with the formation of a none yet reported ruthenium oxy-carbonate phase.

Read more on ALBA website

Building better catalysts to close the carbon dioxide loop

The best way to stave off the worst effects of climate change is to reduce CO2 emissions around the world. And one way to do that, says Zhongwei Chen, a professor in the Department of Chemical Engineering at the University of Waterloo, is to capture the CO2 and convert it into other useful chemicals, such as methanol and methane for fuels. Stopping emissions at the source, and further reducing future ones by replacing CO2-producing fuels with cleaner ones “…is a way to close the circle,” Chen says.

In order to turn CO2 into methanol, you need a catalyst to jump-start the electrochemical reaction. Traditionally, these catalysts have either been made out of precious metals like gold or palladium, or base metals like copper or tin. However, they are expensive and break down easily, hindering large-scale implementation. “Right now we can’t meet industrial requirements,” says Chen, who holds a Canada Research Chair. “So we are trying to design catalysts with better activity, selectivity, and durability.”

Read more on the CLS website

Image: Chithra Karunakaran on the SM beamline at the Canadian Light Source

Credit: David Stobbe