Energy

Reversing the combustion process to convert CO2 into ethanol

Reversing the combustion proce...
A photomicrograph of the ORNL catalyst showing the carbon nanospikes that can convert carbon dioxide into ethanol
A photomicrograph of the ORNL catalyst showing the carbon nanospikes that can convert carbon dioxide into ethanol
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A photomicrograph of the ORNL catalyst showing the carbon nanospikes that can convert carbon dioxide into ethanol
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A photomicrograph of the ORNL catalyst showing the carbon nanospikes that can convert carbon dioxide into ethanol
The ORNL researchers involved in the CO2-to-ethanol conversion research: Yang Song (seated), Dale Hensley (standing left) and Adam Rondinone
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The ORNL researchers involved in the CO2-to-ethanol conversion research: Yang Song (seated), Dale Hensley (standing left) and Adam Rondinone

The danger of the ever-increasing levels of carbon dioxide (CO2) in Earth's atmosphere has become one of the most pressing issues of our age. As such, much research has been conducted to find ways not only to reduce it, but also in ways to remove it. This has led to many schemes that simply sequester CO2 underground, or store it in volcanic rocks. More ambitious schemes even aim to not only remove this gas, but to usefully employ it to create usable products, such as plastics and foam, or even to produce hydrocarbon fuels. Now scientists from the Oak Ridge National Laboratory (ORNL) claim to have produced one of the most usable of all chemicals – ethanol – in a process that is not only cheap, efficient, and scalable, but also conducted at room temperature.

Employing a catalyst made of copper nanoparticles embedded in spikes of carbon, the team found that electricity applied at just 1.2 volts was sufficient to convert CO2 suspended in water into ethanol. In effect, the team were able to produce a complicated chemical reaction, essentially reversing the combustion process, with relative ease and an initial conversion rate of some 63 percent. This was a surprise to the researchers, as this type of electrochemical reaction often produces many different chemicals, including methane, ethylene, and carbon monoxide.

"We're taking carbon dioxide, a waste product of combustion, and we're pushing that combustion reaction backwards with very high selectivity to a useful fuel," says Dr Adam Rondinone, of ORNL. "Ethanol was a surprise – it's extremely difficult to go straight from carbon dioxide to ethanol with a single catalyst. We discovered somewhat by accident that this material worked, we were trying to study the first step of a proposed reaction when we realized that the catalyst was doing the entire reaction on its own."

The ORNL researchers involved in the CO2-to-ethanol conversion research: Yang Song (seated), Dale Hensley (standing left) and Adam Rondinone
The ORNL researchers involved in the CO2-to-ethanol conversion research: Yang Song (seated), Dale Hensley (standing left) and Adam Rondinone

Whilst many of the metals used in other such studies into converting CO2 into a useful fuel, such as titanium dioxide used in the University of Texas' experiments converting CO2 to liquid hydrocarbons, are often rare or expensive, the ORNL work uses inexpensive copper combined in a novel way with carbon to form fields of nanospikes on an inert silicon substrate. It is this particular arrangement that provides an abundance of reactive sites within the material to so effectively and efficiently produce ethanol.

"By using common materials, but arranging them with nanotechnology, we figured out how to limit the side reactions and end up with the one thing that we want," said Dr Rondinone. "They are like 50-nanometer lightning rods that concentrate electrochemical reactivity at the tip of the spike".

In detail, the dense nanotextured carbon film created by the ORNL team contains randomly-positioned nanospikes approximately 50–80 nm in length, each of which consists of layers of wrinkled carbon ending in a tip about 2 nm wide. The film was grown using a comparatively simple chemical vapor deposition technique employing acetylene and ammonia as the reagents (the substances used to initiate the chemical reaction).

Acting as one of a pair of electrodes, this film of nanospikes had an electrical current run through it and the electrochemical reaction produced by this combination saw a large proportion of the CO2 electrons dimerized (a chemical reaction where two molecular subunits are joined) into ethanol.

The researchers believe that their technique's use of inexpensive substances and ability to produce ethanol could easily be up-scaled to commercial levels, and even in alternative energy-storage systems where excess electricity generated by wind and solar could readily be turned into liquid fuel.

"A process like this would allow you to consume extra electricity when it's available to make and store as ethanol," said Dr Rondinone. "This could help to balance a grid supplied by intermittent renewable sources."

Plans are in train by the ORNL researchers to better improve their methods in an aim to increase ethanol production rates and to better determine the full mechanism of selective chemical production of the copper/carbon catalyst.

The results of this research were recently published in the journal Chemistry Select.

The video below shows the ORNL team demonstrating and explaining their technique.

Source: Oak Ridge National Laboratory

Nano-spike catalysts convert carbon dioxide directly into ethanol

19 comments
Peter Kelly
Clearly, this is an astonishing discovery, but until there is a vast surplus of 'clean' electricity then it certainly won't address CO2 issues. If it is to be of even minor use, though, depends upon how ethanol is normally created and the energy that production consumes. If it's less energy efficient than this then we could see a saving within ethanol production, but that is surely just a tiny contributor to the CO2 problem.
Rick3
Would reduce CO2, but it's not entirely "green" as the use of the ethanol will generate further CO2 - unless you can capture that as well... ?
JamieFrew
Excellent results but, this seems a bit too good to be true. This seems like a major discovery yet it has been published in an almost unknown journal. Surely this would be worthy of a Nature publication. I suspect that these findings are more complicated than the article suggests
Nik
As CO2 is not a significant greenhouse gas, and never has been, during human existence, extracting it from the air is pointless, and potentially dangerous. There is far more CO2 stored in the oceans, which would make a more effective source of supply. However, growing forests in desert areas, and using the wood as a source of energy would be far more beneficial, as this would increase oxygen output, and help cool the atmosphere simultaneously.
Science and Econ
The current level of CO2 in our atmosphere is around 400 ppm, which is far too low for excellent plant growth. 5,000 ppm would be a better level for all plants and animals to enjoy. Even 1,000 ppm would be worthy of celebration but is far away from the "CO2 starvation" levels of today.
VincentWolf
Boy is Nik misinformed and a misinformant. CO2 is the most significant green house gas in the atmosphere and is responsible for runaway heating on every planet in the Universe. Just go visit Venus if you don't believe that. As a Chemist I note you are so far off reality you might as well be from a different Universe entirely.
slarmas
400ppm is hardly a Co2 disaster. Wake me up when it gets to 1700ppm and I might yawn and roll over.
Robert in Vancouver
CO2 levels are near their lowest levels in 150 million years, and if we reduce CO2 by 20% there won't be enough for vegetation to survive. It's time to stop and think about trying to reduce CO2 without considering all of the consequences. Don't worry about questioning the man-made global warming religion, Al Gore and his partners at Goldman Sachs have already made billions from selling phony CO2 credits, so they'll be OK.
qwerrk
Talk about click-bait for a chemist! :D This is could be YUGE! Have to expect that development of practical applications will take many moons but if they can scale the technology to the point where it could capture and process all or most of the CO2 coming from fossil fuel power plants while maintaining a profitable energy balance, that is, consume only a small fraction of the electricity being produced, you got a winner, in effect, coal to electricity + ethanol.
ThierryLombry
Sorry but ethanol is not better for the health than CO2, read "Effects of ethanol (E85) versus gasoline vehicles on cancer and mortality in the United States" at http://www.ncbi.nlm.nih.gov/pubmed/17612204