The “cool” catalyst for a sustainable revolution in industrial chemistry

Beads of liquid gallium and platinum close-up. Credit: Dr. Md. Arifur Rahim, UNSW Sydney.

Australian researchers have been able to use traces of liquid platinum to create cheap and highly efficient low-temperature chemical reactions, paving the way for dramatic emission reductions in crucial industries.

When combined with liquid gallium, the amounts of platinum needed are low enough to dramatically increase the earth’s reserves of this precious metal, while potentially providing more sustainable solutions for CO2 the reduction, synthesis of ammonia in the production of fertilizers and the creation of green fuel cells, as well as many other possible applications in the chemical industries.

These discoveries, which focus on platinum, are just a drop in the ocean of liquid metals when it comes to the potential of these catalysis systems. By developing this method, there could be over 1,000 possible combinations of elements for over 1,000 different reactions.

The results will be published in the journal natural chemistry Monday, June 6.

Platinum is very effective as a catalyst (the trigger for chemical reactions) but is not widely used on an industrial scale because it is expensive. Most catalysis systems involving platinum also have high energy costs to operate.

Normally, the melting point of platinum is 1700°C. And when used in the solid state for industrial purposes, there should be about 10% platinum in a carbon-based catalyst system.

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

That may change in the future, however, after scientists from UNSW Sydney and RMIT University found a way to use tiny amounts of platinum to create powerful reactions, and without high energy costs.

Platinum liquid at room temperature

An atomic view of the catalytic system in which silver spheres represent gallium atoms and red spheres represent platinum atoms. The small green spheres are reactants and the blue ones are products – highlighting catalytic reactions. Credit: Dr. Md. Arifur Rahim, UNSW Sydney.

The team, including members of the ARC Center of Excellence in Exciton Science and the ARC Center of Excellence in Future Low Energy Technologies, combined platinum with liquid gallium, which has a melting point of just 29, 8°C – this is room temperature on a hot day. When combined with gallium, platinum becomes soluble. In other words, it melts, and without lighting an extremely powerful industrial furnace.

For this mechanism, high temperature treatment is only required at the initial stage, when platinum is dissolved in gallium to create the catalysis system. And even then, it’s only about 300°C for an hour or two, a far cry from the continuous high temperatures often required in industrial-scale chemical engineering.

Contributing author Dr. Jianbo Tang of UNSW likened it to a blacksmith using a hot forge to craft equipment that will last for years.

“If you work with iron and steel, you have to heat it to make a tool, but you have the tool and you never have to heat it again,” he said.

“Other people have tried this approach, but they have to run their catalyst systems at very high temperatures all the time.”

To create an effective catalyst, the researchers needed to use a ratio of less than 0.0001 platinum to gallium. And most remarkable of all, the resulting system was found to be over 1,000 times more efficient than its solid-state rival (the one that had to be about 10% expensive platinum to work)

The benefits don’t stop there — because it’s a liquid-based system, it’s also more reliable. Solid-state catalytic systems eventually clog up and stop working. That’s not a problem here. Like a water feature with a built-in fountain, the liquid mechanism constantly refreshes itself, self-regulating its efficiency over a long period of time and avoiding the catalytic equivalent of pond scum that collects on the surface.

Dr. Maryland Arifur Rahim, lead author from UNSW Sydney, said: “As of 2011, scientists have been able to miniaturize catalytic systems down to the atomic level of active metals. To keep the individual atoms separated from each other, conventional systems require strong matrices (such as graphene or metal oxide) to stabilize them. I thought, why not use a liquid matrix instead and see what happens.

Platinum liquid at room temperature

Liquid gallium and three solid beads of platinum, demonstrating the process of dissolving platinum into gallium described in the research paper. Credit: Dr. Md. Arifur Rahim, UNSW Sydney.

“Catalytic atoms anchored to a solid matrix are immobile. We added mobility to catalytic atoms at low temperatures using a liquid gallium matrix.”

The mechanism is also versatile enough to perform both oxidation and reduction reactions, in which oxygen is supplied or removed from a substance respectively.

UNSW experimenters had to solve a few mysteries to understand these impressive results. Using advanced computational chemistry and modeling, their colleagues at RMIT, led by Professor Salvy Russo, were able to identify that platinum never becomes solid, down to the level of individual atoms.

Exciton Research Scientist Dr. Nastaran Meftahi revealed the importance of his RMIT team’s modeling work.

“What we found was that the two platinum atoms never came into contact with each other,” she said.

“They’ve always been separated by gallium atoms. There’s no solid platinum formation in this system. It’s always atomically dispersed in gallium. That’s really cool and that’s what we found with modeling, which is very difficult to observe directly through experiments.”

Surprisingly, it is actually the gallium that does the job of driving the desired chemical reaction, acting under the influence of nearby platinum atoms.

Exciton Science associate researcher Dr. Andrew Christofferson of RMIT explained how novel these findings are: “The platinum is actually a little below the surface and it’s activating the gallium atoms around it. So the magic is happening on the gallium under the influence of platinum.

“But without the platinum there, that doesn’t happen. It’s completely unlike any other catalysis that anyone has shown, that I know of. And that’s something that can only have been shown by the modelization.”

The “double decoration” improves the industrial catalyst

More information:
Arifur Rahim, low temperature liquid platinum catalyst, natural chemistry (2022). DOI: 10.1038/s41557-022-00965-6.

Provided by the ARC Center of Excellence in Excitation Science

Quote: Liquid Platinum at room temperature: The ‘cool’ catalyst for a sustainable revolution in industrial chemistry (June 6, 2022) retrieved June 7, 2022 from temperature-cool.html

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