Rhodium nanoparticles exposed to ultraviolet (UV) light catalyze the conversion of carbon dioxide almost exclusively to methane, report researchers at Duke University, Durham, N.C. Such plasmonic photocatalysis may offer high selectivity in other important reactions, they add.
“Effectively, plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently,” explains Henry Everitt, an adjunct professor of physics at Duke. “We discovered that when we shine light on rhodium nanostructures, we can force the chemical reaction to go in one direction more than another. So we get to choose how the reaction goes with light in a way that we can’t do with heat.”
Figure 1. Laboratory reactor uses UV light to make methane with very high selectivity. Source: Duke University.
“The fact that you can use light to influence a specific reaction pathway is very exciting,” comments Jie Liu, a professor of chemistry at Duke. “This discovery will really advance the understanding of catalysis.”
The UV-light-driven catalysis of CO2 boasts 98% selectivity to methane, in contrast to conventional catalytic processes that yield methane with about equal amounts of carbon monoxide and other side products, the researchers note.
More details appear in a recent article in Nature Communications.
[callToAction ]
The researchers now are giving highest priority to optimizing the UV-light-driven CO2 reaction, but also hope to use sunlight for that conversion, says Everitt. “We can use simulated sunlight soon, but using actual sunlight is a longer-term goal. We would be happy to partner with anyone interested in pursuing this.” They also are investigating other rhodium-catalyzed reactions driven by heat. “We are looking at other reactions and other catalysts, too, since different reactions require different catalysts,” Everitt adds.
“Our greatest remaining challenge is to ascertain how best to exploit the advantages of illuminated rhodium catalysts. We’ve shown that light highly selects methane over carbon monoxide, but we don’t yet know how much faster the reaction can go and how this advantage can be adapted for large-scale production. Designing the right reactor that can incorporate light is another challenge,” he explains. “We need help to design a reactor that can incorporate light sources and can also be used at high temperature.”
“Rarity of the catalyst notwithstanding, photocatalysis has always been challenging to implement on industrial scales because of the limited penetration depth of light within the catalyst. Our approach has the same limitations, but we believe the selectivity and superlinear dependence on light intensity provided by the rhodium plasmonic photocatalyst will be quite compelling to industry,” he concludes.