Liquid platinum catalyst 1000 times more effective

Platinum drew a lot of attention over the weekend as a marker for the Queen’s 70sth Anniversary. Its rarity makes it an extremely expensive metal, but platinum also has some very valuable chemical properties.

Platinum is a powerful catalyst – it can speed up a wide range of chemical reactions, from making medicines to capturing CO2 from the air. But it’s usually too expensive to use widely, and it often requires very high temperatures to work.

A team of Australian researchers have found a way to use a very small amount of platinum as a catalyst – at near room temperature. This discovery could eventually make platinum an affordable way to improve carbon capture, green hydrogen electrolysis, ammonia production for fertilizers, and a host of other industrial processes.

The trick, described in an article in natural chemistry, revolves around mixing platinum with another, less expensive metal – gallium – and turning it into a liquid.

The lead author Dr. Md Arifur Rahim, a post-doctoral fellow at the University of New South Wales’ School of Chemical Engineering, says the group has been working on liquid gallium “for a very long time”.

“Gallium is interesting because it’s a near-room temperature liquid, just like mercury,” says Rahim. Gallium melts at 30°C – in the palm of your hand.

“Because they are liquid, we can think of them as solvents.”

This means that, like water-soluble salt, gallium can dissolve other metals that are usually solid at much higher temperatures. For example, platinum typically has a melting point of 1700°C, but can dissolve in gallium after heating to 300°C for several hours.

Three solid platinum beads on liquid gallium. Photo credit: Dr. Md. Arifur Rahim, UNSW Sydney

And once in this liquid format, the platinum becomes a very efficient catalyst.

In fact, a mixture in which just 0.0001% of the atoms were platinum was able to catalyze several different types of test reactions that the researchers tried. This catalyst was over 1000 times more efficient than a conventional 10% platinum solid catalyst and operated between 40 °C and 70 °C, which are very low temperatures on an industrial scale.

The researchers’ computer modeling suggests a possible reason for this: It has to do with the way the platinum atoms are distributed in the gallium mixture.

“Platinum never aggregates, and this [platinum] Atoms don’t form a cluster,” says Rahim.

Instead, the platinum atoms stimulate the gallium atoms that completely surround them to also act as catalysts.

“The platinum also activates the gallium for catalysis,” summarizes Rahim.

co-author dr. Andrew Christofferson, a researcher at RMIT, says: “The magic happens on the gallium under the influence of platinum.

Ball of red and silver balls, more silver than red, none of the red balls touching
A representation of the system at the atomic level: red balls are platinum, silver is gallium. Photo credit: Dr. Md. Arifur Rahim, UNSW Sydney

“But without the platinum there, it doesn’t work. This is totally unlike any other catalysis I know of that anyone has shown. And that can only have been shown by the modelling.”

This substance is not only more efficient, but also more practical than its solid counterparts. Liquid catalysts are generally easier to refresh and last longer in chemical reactions.

Rahim says the team is now studying whether gallium has this effect on other precious metals (things like silver, gold, and ruthenium) — all expensive and powerful catalysts in their own right.

“We see there are some similarities, but I still can’t [yet] saying there’s a rationalization we can do,” says Rahim.

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