UV light-driven catalyst makes fuels from CO2

RHODIUM nanoparticles activated by UV light can convert CO₂ into methane with high selectivity, according to researchers at Duke University, US.  

Catalysts based on rhodium are used in various industrial processes, including making drugs, detergents and fertilisers, and in catalytic converters in cars. In most reactions, heat is used to add energy and accelerate the process, but can shorten the lifespan of the catalysts and create unwanted byproducts. When the metal catalysts are in nanoparticle form, light can be used to add energy instead – a research field known as plasmonics.

“Plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently and can do a number of things like generate strong electric fields. For the last few years there has been a recognition that this property might be applied to catalysis,” explained Henry Everitt, an adjunct professor of physics at Duke.

The Duke team has now proved this theory, and the researchers believe it is a very important step along the road to an efficient, cost-effective catalyst that can convert CO₂ to methane, CH₄, potentially offering an alternative option for fuel production.

Researcher Xiao Zhang synthesised rhodium nanocubes, measuring around 37 nm, which were then supported on aluminium oxide nanoparticles. The team used a fixed-bed reaction chamber with a quartz window. The catalysts were packed in to a depth of 4 mm to ensure complete light absorption. Zhang then passed a mixture of CO₂ and hydrogen over the catalyst, and either activated the catalyst with heat (275?C) or by illuminating it with UV light. All reactions were performed at atmospheric pressure.

When the catalyst was heated, CH₄ and CO were produced at a ratio of 60:40. When illuminated with UV light instead, the ratio of CH₄ to CO was 95:5, therefore showing very high selectivity towards CH₄. No other detectable products resulted from either reaction.

“The fact that you can use light to influence a specific reaction pathway is very exciting. This discovery will really advance the understanding of catalysis,” said Jie Liu, a Duke chemistry professor.

The researchers will now test the UV-driven technique with other processes that currently use heated rhodium catalysts. They will also experiment with different sizes of rhodium nanoparticles to develop a version of the catalyst which will work with sunlight.