Platinum got a lot of attention over the weekend as a marker for the Queen’s 70e Jubilee. Its rarity is what makes it an extremely expensive metal, but platinum also has some very valuable chemical properties.
Platinum is a powerful catalyst – it can enhance a wide variety of chemical reactions, from manufacturing pharmaceuticals to capturing CO2 from the air. But it is generally too expensive to be used on a large scale and often requires very high temperatures to operate.
A team of Australian researchers has found a way to use a very small amount of platinum as a catalyst – at a temperature close to 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 by natural chemistry, involves mixing platinum with another cheaper metal – gallium – and turning it into a liquid.
Lead author Dr Md Arifur Rahim, a postdoctoral researcher 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 liquid near room temperature, just like mercury,” says Rahim. Gallium melts at 30°C – in the palm of your hand.
“Being liquids, we can think of them as a solvent.”
This means that, like water-soluble salt, gallium can dissolve other metals that are usually solid at much higher temperatures. Platinum, for example, usually has a melting point of 1700°C, but it can be dissolved in gallium after being heated at 300°C for a few hours.
And once in this liquid form, platinum becomes a very effective catalyst.
In fact, a mixture where only 0.0001% of the atoms were platinum was able to catalyze several different types of test reactions that the researchers tried. This catalyst was more than 1000 times more efficient than a conventional 10% platinum solid catalyst and it 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 how the platinum atoms are dispersed in the gallium mixture.
“Platinum never aggregates, and the [platinum] atoms do not form a cluster,” Rahim explains.
Instead, the platinum atoms induce the gallium atoms that completely surround them to function as catalysts as well.
“Platinum also activates gallium towards catalysis,” summarizes Rahim.
Co-author Dr. Andrew Christofferson, researcher at RMIT, says: “Magic happens on gallium under the influence of platinum.
“But without the platinum there, that’s not happening. It’s completely unlike any other catalysis anyone has shown that I know of. And that’s something that could only be shown through modeling.
In addition to being more effective, this substance is more convenient than its solid counterparts. Liquid catalysts are generally easier to cool and last longer in chemical reactions.
Rahim says the team is now investigating whether gallium has this effect on other noble metals (like silver, gold and ruthenium) – all expensive and powerful catalysts in their own right.
“We see there are similarities, but I still can’t [yet] say there’s a rationalization we can do,” Rahim says.