Researchers boost resilience of gold catalysts

Japanese researchers have discovered a way to improve the durability of gold catalysts by creating a protective layer of metal oxide clusters, which could benefit industries including chemical synthesis and medicine production. The work has been described in the journal Nature Communications.

Gold is chemically resilient to physical conditions that might otherwise tarnish other materials, such as heat, pressure, oxidation and other detriments. However, at nanoscopic scales, tiny particles of gold reverse this trend and become very reactive, making them essential to realising different kinds of catalysts — intermediary substances which accelerate or in some way enable a chemical reaction to take place.

“Gold is a wonderful metal and is rightly praised in society, and especially in science,” said Associate Professor Kosuke Suzuki from The University of Tokyo. “It’s great for catalysts and can help us synthesise a range of things, including medicines. The reasons for this are that gold has a low affinity for absorbing molecules and is also highly selective about what it binds with, so it allows for very precise control of chemical synthesis processes. Gold catalysts often operate at lower temperatures and pressures compared to traditional catalysts, requiring less energy and reducing environmental impact.”

As good as gold is, though, it does have some drawbacks. It becomes more reactive the smaller particles are made of it, and there is a point at which a catalyst made with gold can begin to suffer negatively from heat, pressure, corrosion, oxidation and other conditions. Suzuki and his team thought they could improve upon this situation and devised a novel protective agent that could allow a gold catalyst to maintain its useful functions but across a greater range of physical conditions that usually hinder or destroy a typical gold catalyst.

“Current gold nanoparticles used in catalysts have some level of protection, thanks to agents such as dodecanethiols and organic polymers,” Suzuki said. “But our new one is based on a cluster of metal oxides called polyoxometalates and it offers far superior results, especially in regard to oxidative stress.

“We are currently investigating the novel structures and applications of polyoxometalates. This time we applied the polyoxometalates to gold nanoparticles and ascertained the polyoxometalates improve the nanoparticles’ durability. The real challenge was applying a wide range of analytical techniques to test and verify all this.”

The team employed no less than six spectroscopic methods, which work by casting some kind of light onto a substance and measuring how that light changes in some way with specialised sensors. They spent months running various tests and different configurations of their experimental material, until they were able to confirm that their enhanced gold catalysts could withstand a greater range of physical environments compared to unprotected equivalent materials.

“There are many applications of our enhanced gold nanoparticles that could be used to benefit society,” Suzuki said. “Catalysts to break down pollution … less impactful pesticides, green chemistry for renewable energy, medical interventions, sensors for foodborne pathogens, the list goes on.

“Our next steps will be to improve the range of physical conditions we can make gold nanoparticles more resilient to, and also see how we can add some durability to other useful catalytic metals like ruthenium, rhodium, rhenium and, of course, something people prize even more highly than gold: platinum.”

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