Modern Alchemy Makes "Chameleon Metal" Behave Like Precious Catalysts

A cheap and thin layer of aluminum has been made to act like powerful catalysts - not only tungsten, but others far more expensive. Image Credit: Dauenhauer Group/University of Minnessota

Nuclear reactions can make the alchemists' dream of turning one metal into another a reality, albeit at a huge expense. Scientists think they've found how to do something almost as good – making a cheap metal behave like more expensive ones – with far lower investment. If they're right, it will transform energy storage and chemical manufacturing.

Catalysts speed up chemical reactions, in some cases by factors of millions, without being consumed themselves. Unfortunately, for the most important reactions for which they are needed, the most effective catalysts are exceptionally rare and precious.

To produce hydrogen from water, for example, we can use either immensely expensive platinum or nickel-iron alloys that are cheap but much slower. Other reactions, such as the breaking down of pollutants from car engines, rely on even more obscure metals like rhodium and palladium.

In the Journal of the American Chemical Society Au, a team from the University of Minnesota describes tuning an ultrathin layer of alumina over graphene to behave like other metals.

“The substantial ability to tune the catalytic and electronic properties of the catalyst exceeded our expectations." said study author Dr Tzia Ming Onn in a statement

Catalysts' effectiveness lies in the positions of their electrons and “holes”, marked by the absence of electrons. By their nature, it is only the surface layer of catalysts, where they interact with reacting chemicals, that matters.

Consequently, researchers made an active alumina surface layer 4 nanometers thick that can replicate the positions of atoms and holes in powerful catalysts. This was layered on top of graphene, which in turn sits on an insulating internal layer, before a suitable voltage was applied. The team refers to their product as a “catalytic condenser”.

The authors acknowledge the work builds on semiconductor design and the use of ultrathin zinc-oxide layers to control the rate of transfer of electrons to solutions. “However, to our knowledge, the use of capacitive charging to enhance thermocatalytic activity has not been reported,” the authors write.

The reaction catalyzed in this case – dehydrating the alcohol isopropanol – may not be world-changing, but the team considers this just a proof of concept for much bigger things.

“We view the catalytic condenser as a platform technology that can be implemented across a host of manufacturing applications,” study author Professor Dan Frisbie said. “The core design insights and novel components can be modified to almost any chemistry we can imagine.”

It's a big claim – but if it proves right, it will slash the cost of processes that currently rely on expensive catalysts. There will also be major environmental benefits: to get tiny scraps of precious metals, we dig vast amounts of ore from the Earth, often in sensitive locations. Replacing these with a thin layer of abundant alumina and a product of carbon could end all that.

Perhaps most importantly of all, hydrogen and ammonia represent some of the most promising options for storing energy from intermittent sources, but need better (or at least cheaper) catalysts to make them. The paper's authors are working on this, as well as ways to make more environmentally-friendly plastics and remove the most damaging pollutants in waste gasses.

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