Researchers strike gold with improved catalyst

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For the first time, researchers, including those from the University of Tokyo, discovered a way to improve the durability of a gold catalyst by creating a protective layer of metal oxide groups.

Advanced gold catalysts can withstand a greater range of physical environments than unprotected equivalent materials. This can expand the range of their potential applications and in some situations reduce energy consumption and costs.

These catalysts are widely used in all industrial settings including chemical synthesis and production of drugs. These industries could benefit from better gold catalysts.

Gold nanoparticle in scope.  The atomic resolution image of the researchers' novel nanoparticle was created using a technique called annular dark-field scanning transmission electron microscopy.

Gold nanoparticle in scope. The atomic resolution image of the researchers’ novel nanoparticle was created using a technique called annular dark-field scanning transmission electron microscopy. Image credit: Suzuki et al. CC BY ND

Everyone loves gold: athletes, pirates, bankers – everyone. It has historically been an attractive metal for making things like medals, jewellery, coins etc. The reason gold looks so shiny and attractive to us is because it is chemically resilient to physical conditions that would otherwise damage other materials, such as heat, pressure, oxidation, and other damages.

Paradoxically, however, at the nanoscopic scale, small gold particles reverse this trend and become very reactive, so much so that it has now long been necessary to realize them with a variety of catalysts, mediators that Accelerate or in some way enable a chemical reaction to occur. In other words, they are useful or necessary to transform one substance into another, hence their wide use in synthesis and manufacturing.

“Gold is a wonderful metal and is rightly appreciated in society and especially in science,” said Kosuke Suzuki, associate professor in the Department of Applied Chemistry at the University of Tokyo.

“It is great for catalysts and can help us synthesize many things, including medicines. This is because gold has a low tendency to absorb molecules and is highly selective about what it combines with, so it allows very precise control of chemical synthesis processes. Gold catalysts often operate at lower temperatures and pressures than conventional catalysts, requiring less energy and having less environmental impact.

However, as good as gold is, it also has some drawbacks. The smaller particles it forms become more reactive, and there comes a point when the catalyst made of gold may begin to suffer negatively from heat, pressure, corrosion, oxidation, and other conditions. Suzuki and his team thought they could improve this situation and designed a new protective agent that could allow a gold catalyst to retain its useful functions but in a larger range of physical conditions than would normally be possible. Inhibits or destroys a specific gold catalyst.

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

“We are currently investigating novel structures and applications of polyoxometalates. This time we applied polyoxometalates to gold nanoparticles and observed that polyoxometalates improve the stability of the nanoparticles. The real challenge was to apply a wide range of analytical techniques to test and verify all this.

The team used a variety of techniques collectively known as spectroscopy. It used at least six spectroscopic methods, which differ in the type of information they reveal about a material and its behavior. But generally speaking, they do this by shining some kind of light on a substance and measuring with special sensors how that light changes in some way. Suzuki and his team spent months testing their experimental material and running different configurations until they got what they were looking for.

Comparison of gold nanoparticles.  Thiol and organic polymer protection are two existing methods of adding flexibility to gold nanoparticles.  On the right is a representation of the researchers' new method using polyoxometalate. Comparison of gold nanoparticles.  Thiol and organic polymer protection are two existing methods of adding flexibility to gold nanoparticles.  On the right is a representation of the researchers' new method using polyoxometalate.

Comparison of gold nanoparticles. Thiol and organic polymer protection are two existing methods of adding flexibility to gold nanoparticles. On the right is a representation of the researchers’ new method using polyoxometalate. Image credit: Suzuki et al. CC BY ND

“We are not motivated just by trying to improve some methods of chemical synthesis. Our advanced gold nanoparticles have many applications that can be used to benefit society,” Suzuki said.

“Catalysts to break down pollution (many gasoline cars already have a familiar catalytic converter), less impactful pesticides, green chemicals for renewable energy, medical interventions, sensors for foodborne pathogens, the list goes on. But we also want to go ahead. Our next step will be to improve the range of physical conditions for which we can make gold nanoparticles more flexible, and also look at how we can add some durability to other useful catalytic metals like ruthenium, rhodium, rhenium and of course Some people also give awards. Higher than gold: platinum.”

Source: University of Tokyo


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