Copper clusters capture and convert carbon dioxide to make fuel

August 7, 2015 by Payal Marathe, Argonne National Laboratory
A copper tetramer catalyst created by researchers at Argonne National Laboratory may help capture and convert carbon dioxide in a way that ultimately saves energy. It consists of small clusters of four copper atoms each, supported on a thin film of aluminum oxide. These catalysts work by binding to carbon dioxide molecules, orienting them in a way that is ideal for chemical reactions. The structure of the copper tetramer is such that most of its binding sites are open, which means it can attach more strongly to carbon dioxide and can better accelerate the conversion. Credit: Larry Curtiss, Argonne National Laboratory

Capture and convert—this is the motto of carbon dioxide reduction, a process that stops the greenhouse gas before it escapes from chimneys and power plants into the atmosphere and instead turns it into a useful product.

One possible end product is methanol, a liquid fuel and the focus of a recent study conducted at the U.S. Department of Energy's (DOE) Argonne National Laboratory. The chemical reactions that make methanol from carbon dioxide rely on a to speed up the conversion, and Argonne scientists identified a new material that could fill this role. With its unique structure, this catalyst can capture and convert carbon dioxide in a way that ultimately saves energy.

They call it a copper tetramer.

It consists of small clusters of four each, supported on a thin film of aluminum oxide. These catalysts work by binding to carbon dioxide molecules, orienting them in a way that is ideal for . The structure of the copper tetramer is such that most of its binding sites are open, which means it can attach more strongly to carbon dioxide and can better accelerate the conversion.

The current industrial process to reduce carbon dioxide to methanol uses a catalyst of copper, zinc oxide and . A number of its binding sites are occupied merely in holding the compound together, which limits how many atoms can catch and hold carbon dioxide.

"With our catalyst, there is no inside," said Stefan Vajda, senior chemist at Argonne and the Institute for Molecular Engineering and co-author on the paper. "All four copper atoms are participating because with only a few of them in the cluster, they are all exposed and able to bind."

To compensate for a catalyst with fewer binding sites, the current method of reduction creates high-pressure conditions to facilitate stronger bonds with carbon dioxide molecules. But compressing gas into a high-pressure mixture takes a lot of energy.

The benefit of enhanced binding is that the new catalyst requires lower pressure and less energy to produce the same amount of methanol.

Carbon dioxide emissions are an ongoing environmental problem, and according to the authors, it's important that research identifies optimal ways to deal with the waste.

"We're interested in finding new catalytic reactions that will be more efficient than the current catalysts, especially in terms of saving energy," said Larry Curtiss, an Argonne Distinguished Fellow who co-authored this paper.

Copper tetramers could allow us to capture and convert carbon dioxide on a larger scale—reducing an environmental threat and creating a useful product like methanol that can be transported and burned for fuel.

Of course the catalyst still has a long journey ahead from the lab to industry.

Potential obstacles include instability and figuring out how to manufacture mass quantities. There's a chance that copper tetramers may decompose when put to use in an industrial setting, so ensuring long-term durability is a critical step for future research, Curtiss said. And while the scientists needed only nanograms of the material for this study, that number would have to be multiplied dramatically for industrial purposes.

Meanwhile, the researchers are interested in searching for other catalysts that might even outperform their copper tetramer.

These catalysts can be varied in size, composition and support material, which results in a list of more than 2,000 potential combinations, Vajda said.

But the scientists don't have to run thousands of different experiments, said Peter Zapol, an Argonne physicist and co-author of this paper. Instead, they will use advanced calculations to make predictions, and then test the catalysts that seem most promising.

"We haven't yet found a catalyst better than the copper tetramer, but we hope to," Vajda said. "With global warming becoming a bigger burden, it's pressing that we keep trying to turn emissions back into something useful."

For this research, the team used the Center for Nanoscale Materials as well as beamline 12-ID-C of the Advanced Photon Source, both DOE Office of Science User Facilities.

Curtiss said the Advanced Photon Source allowed the scientists to observe ultralow loadings of their small clusters, down to a few nanograms, which was a critical piece of this investigation.

Explore further: Researchers find less expensive way to convert carbon dioxide

More information: The study, "Carbon dioxide conversion to methanol over size-selected Cu4 clusters at low pressures," was published in the Journal of the American Chemical Society. pubs.acs.org/doi/full/10.1021/jacs.5b03668

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baudrunner
not rated yet Aug 07, 2015
Tying up compounds to keep them from breaking up is an interesting concept. Carbon nano-meshes offer the opportunity to trap and isolate such compounds as these copper tetramers while still perhaps permitting their functionality as catalyst to manufacture methanol.
NoTennisNow
4 / 5 (4) Aug 08, 2015
This might be technically sweet but does nothing to reduce CO2 emissions. Take CO2 that would otherwise be emitted to the atmosphere, turn the CO2 into a fuel by adding hydrogen and oxygen to it and burn that fuel and then emit the CO2 from that process to the atmosphere. This is simply ridiculous! Do the material and energy balances (this comment is from a retired chemical engineer with an energy background)
shavera
5 / 5 (4) Aug 08, 2015
Tennis: the point is to provide an alternative to digging up *new* carbon and putting it into the air. At least reusing the carbon already in the air helps slow the rate at which it's added.
KelDude
1 / 5 (1) Aug 08, 2015
what crap! Capture the CO2 so its "not in the air", then convert it to methane and burn it "so it IS IN THE AIR"! Making physical products like plastic or ?? is the way to keep it out of the air. Turning it into another "fuel" simply delays the pollution for one cycle. Still contributing to global warming. We need to move on to removing the CO2 from the air, not just from chimneys on factories. We're doomed with dumb ideas like this one.
docile
Aug 08, 2015
This comment has been removed by a moderator.
NoTennisNow
3 / 5 (2) Aug 08, 2015
Yes, let's get thermodynamics into the equation. Also, what makes anyone think (seriously that is) that the atmosphere can be artifically mined for CO2? Look at the energy requirements to accomplish this (just talking about need for fans to compress the air). Going further, consider the capital cost for balance of plant plus the size size of the plant and economic costs to finance the plants. Mining the atmosphere is unrealistic to the nth degree.

BTW, I have nothing against basic research. My thesis was on the kinetics involved in the liquifaction hydrodesulfurization of coal.

What I seriously object to is unrealistic claims about the use of the resulting research to distill moonbeamss.
FainAvis
not rated yet Aug 09, 2015
So specifically, where does the energy for this conversion come from?
NoTennisNow
5 / 5 (2) Aug 09, 2015
If we are talking just about chemicals from coal, coal gasification with the water shift reaction is already used to make SYN gas (CO and H2). Liquid fuels have also been made from coal liquifaction.

in all of the discussions we must remember these two rules: (1) there is no free lunch, and, (2) see rule 1.
NoTennisNow
not rated yet Aug 09, 2015
The Southern Company had a coal gasification project with hot gas cleanup to make a gas suitable for a turbine. The Southern Company process would result in a more concentrated gas stream and to minimize "tar'. A lot has been done in the coal gasification arena. I worked on a project a few years ago for a feasibility study using coal gasification in lieu of a coal fired electric steam generator. See also Southern Company TRIG gasifier with carbon sequestration.
docile
Aug 09, 2015
This comment has been removed by a moderator.
NoTennisNow
5 / 5 (1) Aug 09, 2015
The carbon as a fuel and a suitable replacement is sn almost intractable issue. Wind, solar, tideal, all have their niches. For pure energy density and reliability requires an integrated system that requires nukes in the mix.
NoTennisNow
5 / 5 (1) Aug 09, 2015
This discussion is great. Sorta like kick'n over a fire ant hill ain't it?
NoTennisNow
5 / 5 (1) Aug 09, 2015
Remember, in a brainstorming session, the first and only rule is that there are no stupid ideas. After the session is over, some might be real howler, but everybody participated and, therefore, moved the process forward.

No discussion is a much, much (add a few more muches here) worse situation to be in than keeping your mouth shut (or otherwise commenting).
docile
Aug 09, 2015
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