Reactions occurring at different surface sites on the same nanocatalyst can “communicate” with each other in ways that are very similar to catalytic allostery in enzymes. The new result will help researchers better understand nanoscale catalysis and ultimately develop improved catalysts in the future.
Enzymes are naturally efficient nanoscale catalysts and one of their characteristic features is so-called allostery. Here, reactions at one site affect reactions at another site, typically a few nanometres away, without the reactants directly interacting with each other. Enzymes are not the only nanoscale catalysts, however, and nanoparticles of various materials such as metals or metal oxides, which are the same size as enzymes, can catalyse many chemical transformations on their surfaces. The active sites on these surfaces can be structurally or electronically coupled too.
Researchers led by Peng Chen of Cornell University in the US recently developed a new way to map catalytic reactions on a single catalyst. “For every reaction occurring on a catalyst particle, we now know where it happened and when it happened,” he explains. “I wanted to take this work a step further and find out whether reactions at different places on the same catalyst could ‘talk’ to each other.”
Holes “carry” information
Using spatially and temporally resolved fluorescence imaging of individual catalytic reactions within single nanoscale catalysts (in this case nanoparticles of gold and palladium), Chen and colleagues found that this was indeed the case. They observed that the particles likely “communicate” with each other through the movement of positive charge carriers (holes) over distances of around 102 nm and over times of between 10 to 102 seconds. The researchers also saw that reactions on separate gold nanocatalysts affect each other over even longer distances of many microns. Here the mechanism occurs through diffusion of negatively charged reaction products.
“The inter-particle communication is analogous to the ‘spillover’ effect in heterogeneous catalysis,” says Chen. “Both of the intra-particle and inter-particle effects we saw represent first-of-their kind observations involving individual nanocatalysts and our results provide a new sort of conceptual framework for understanding how a nanoscale catalyst particle works.”
The team, reporting its work in Nature Chemistry doi:10.1038/s41557-018-0022-y, says that it is now busy studying this cooperative communication behaviour in more detail.