Liquid platinum and gallium combine for catalysis

When combined with liquid gallium, the amounts of platinum required are small enough to significantly extend the Earth’s reserves of platinum, while potentially offering more sustainable solutions for CO2 reduction, ammonia synthesis in fertiliser production, and green fuel cell creation, together with numerous possible applications in chemical industries. 

The results are published in Nature Chemistry.

Platinum is a very effective catalyst but is not widely used at industrial scale due to cost. Most catalysis systems involving platinum also have high ongoing energy costs to operate.

The melting point for platinum is 1,700°C and when it’s used in a solid state for industrial purposes, there needs to be around 10 per cent platinum in a carbon-based catalytic system.

Consequently, it is not an affordable ratio when trying to manufacture components and products for commercial sale.

Now, scientists at UNSW Sydney and RMIT University have found a way to use small amounts of platinum to create powerful reactions without expensive energy costs.

The team, including members of the ARC Centre of Excellence in Exciton Science and the ARC Centre of Excellence in Future Low Energy Technologies, combined the platinum with liquid gallium, which has a melting point of 29.8°C. When combined with gallium, the platinum becomes soluble.

For this mechanism, processing at an elevated temperature (300°C for an hour or two) is only required at the initial stage, when platinum is dissolved in gallium to create the catalysis system.

To create an effective catalyst, the researchers needed to use a ratio of less than 0.0001 platinum to gallium. The resulting system is said to have been over 1,000 times more efficient than its solid-state rival that requires around 10 per cent platinum to work.

In a statement, Dr Md. Arifur Rahim, the lead author from UNSW Sydney, said: “From 2011, scientists were able to miniaturise catalyst systems down to the atomic level of the active metals. To keep the single atoms separated from each other, the conventional systems require solid matrices to stabilise them. I thought, why not using a liquid matrix instead and see what happens.

“The catalytic atoms anchored onto a solid matrix are immobile. We have added mobility to the catalytic atoms at low temperature by using a liquid gallium matrix”.

The mechanism is also reportedly versatile enough to perform oxidation and reduction reactions.

Using advanced computational chemistry and modelling, RMIT scientists led by Professor Salvy Russo identified that the platinum never becomes solid, right down to the level of individual atoms.

“What we found is the two platinum atoms never came into contact with each other,” said Exciton Science Research Fellow Dr Nastaran Meftahi. “They were always separated by gallium atoms. There is no solid platinum forming in this system. It’s always atomically dispersed within the gallium. That’s really cool and it’s what we found with the modelling, which is very difficult to observe directly through experiments.”

“The platinum is actually a little bit below the surface and it’s activating the gallium atoms around it,” added Exciton Science Associate Investigator Dr Andrew Christofferson of RMIT. “So the magic is happening on the gallium under the influence of platinum.

“But without the platinum there, it doesn’t happen. This is completely different from any other catalysis anyone has shown, that I’m aware of. And this is something that can only have been shown through the modelling.”