Watching catalysis

Using a state-of-the-art spectroscopy system, scientists from the US Department of Energy’s Lawrence Berkeley National Laboratory have watched, for the first time, as nanoparticles composed of two catalytic metals changed their composition in the presence of different reactants.

Prof Gabor Somorjai, a surface science and catalysis expert, conducted the research with Prof Miquel Salmeron, a pioneer in a field of spectroscopy.

‘By watching catalysts change in real time, we can possibly design smart catalysts that optimally change as a reaction evolves,’ Prof Somorjai said.

Until now, nanoscale catalysts could only be observed before and after a reaction. How a catalyst behaved during a reaction remained the stuff of guesswork.

‘It’s difficult to tune a catalyst to do exactly what you want unless you know how it adapts during a reaction,’ added Prof Salmeron. ‘With our work, we can for the first time see what the catalyst is doing during the reaction, not before and after.’

Using techniques developed in his lab, Somorjai first synthesised nanoscale particles composed of common catalytic metals. Some particles were made of rhodium and palladium, while others were made of platinum and palladium.

Next, to see how these bimetallic catalysts change in the presence of reactants, they turned to one of the few spectroscopy instruments in the world that enables scientists to study catalytic and biological phenomena in their natural environment.

The instrument itself was developed by Salmeron and his colleagues. Like all spectroscopy systems, it identifies elements by detecting their unique spectral signals. But unlike most, the ambient pressure photoelectron spectroscopy system works under similar pressures and environments faced by everyday phenomena, instead of requiring a carefully controlled vacuum.

Using this system, the scientists watched, in real time, as the bimetallic nanoparticles restructured themselves when exposed to different gases, such as nitrogen oxide, carbon monoxide, and hydrogen. In the presence of some reactants, rhodium rose to a particle’s surface. While in the presence of other reactants, palladium rose to the surface.

With this information, scientists could be able to develop nanoparticle catalysts and reactants that are tailored more efficiently. For example, researchers can engineer bimetallic nanoparticle catalysts in which one metal rises to the surface during an initial stage of a reaction, and a different metal rises to the surface in a latter stage. The goal is to ensure that the most active metal is on the catalyst’s surface precisely when it’s needed most.

Prof Somorjai and Prof Salmeron now hope to observe how catalysts change shape during a reaction, which could be as equally important as compositional change in driving chemical reactions.

Berkeley Lab's Prof Miquel Salmeron and Prof Gabor Somorjai discuss how a ringside seat to fundamental chemistry could lead to more efficient catalysts, on YouTube here: http://uk.youtube.com/watch?v=OcPWWsdLcvs