Using Light, Rare Element Converts Carbon Dioxide to Fuel
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A metal made inside of a star billions of years ago may help feed a growing population here on Earth, while helping to slow or reverse climate change in the process! And it’s all kind of by accident.
Rhodium is one of many metals often used as a catalyst, meaning that it helps encourage chemical reactions - like a molecular wingman.
Dr. Henry Everitt, an adjunct professor of physics at Duke University, is co-author of a paper recently published in Nature Communications detailing their discovery that rhodium’s ability to use light instead of heat in catalysis allows for the manipulation of the chemical reaction.
The specific reaction that we happened to choose takes carbon dioxide, mixes it with hydrogen, and if you use heat you get about an equal mixture of carbon monoxide and methane.
Carbon monoxide is a poisonous gas, but...
...we discovered that when we add light to rhodium, rather than heat, we make only methane. That’s exciting because methane is a fuel.
In theory, this could help limit carbon dioxide output by recycling it. Imagine CO2 is captured at a power plant, converted to fuel, and used in your car.
This process uses nanotechnology; technology at the atomic scale.
We took rhodium, which is a very rare element, and turned it into nano-particles. Typically these nanoparticles are 10, 20, 30 nanometers across. [This] is 20, 40 maybe 60 atoms across, so they’re very small particles.
The nanoparticles act kind of like an antenna for the light, allowing the reaction to be manipulated.
Rhodium is rare, but the nanoparticle-antennas can be reused. Still, the team is actively seeking alternatives that will allow industries to scale up production using this method. They are also working toward some groundbreaking chemical reactions.
This represents a new form of catalytic chemistry; an emerging field that my colleagues and I have been working on called plasmonic photocatalysis. It takes advantage of the optical properties of these nano-structured metals and uses them to drive more and more interesting chemical reactions.
One of the ones that I think is most exciting - a holy grail for the catalytic community - is a reaction called the Haber-Bosch process.
A German chemist named Fritz Haber developed a process that converts atmospheric nitrogen into fertilizer…
...because there’s not enough nitrogen on Earth to fertilize food for everyone...
...so most people’s food comes as a result of this Haber-Bosch process.
It uses something like 5% of the world’s energy and is quite an expensive process, because it requires high temperatures, and it requires high pressures. Our hope is that we would be able to do the same reaction at room temperature using sunlight. If we could do that it would have transformative societal impact for the ability to feed the planet as we continue to grow in population.
This work shows that funding research is so important because it often leads to huge unintended benefits to society.
Our original experiments were never designed to address fuels, or carbon dioxide remediation. We did this purely for scientific purposes. We chose this reaction because it was convenient and well understood. So, we’re thrilled that it has this practical application toward carbon dioxide remediation, and converting that carbon dioxide into a fuel.
Our work began when we started beginning to study these antennas in the ultraviolet and discovered that every molecule we put near the antenna would be destroyed. We got frustrated, and we finally said you know what? If we’re destroying it, then maybe we should take that to an advantage, and instead of being disappointed when our molecules are being destroyed, let's actually try and do catalysis with it and use the destroyed molecules as the fragments from which we would build the products that we wanted. So we built a team of chemists and physicists, experimentalists and theorists, professors and students, and all of us working together were able to pull this concept together to get this surprising and exciting result.