Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Chemistry for Greenhouse Gases

16.12.2010
If fossil fuels burn completely, the end products are carbon dioxide and water. Today, the carbon dioxide is a waste product, one that goes into the air — adding to global warming; or the oceans — acidifying them; or underground — with as yet unknown consequences.

But it’s not impossible, says Liviu M. Mirica, PhD, assistant professor of chemistry in Arts & Sciences at Washington University in St. Louis, to drive things the other way, turning carbon dioxide into fuels such as methanol or hydrocarbons.

Until now, reversing combustion has been a loser’s game because making carbon dioxide into a fuel uses up more energy than combustion releases and produces more carbon dioxide than it reclaims.

But Mirica thinks catalysts might change everything. Catalysts might provide alternative reaction pathways with lower energy barriers. The reactants then could be bumped over those lower barriers with carbonless energy sources such as sunlight.

Instead of being a polluting one-way street, hydrocarbon chemistry could circle back on itself and become a clean carbon-neutral cycle, although one that still consumed energy.

In the Journal of the American Chemical Society, Mirica describes a new metal complex that can combine methyl groups (CH3) in the presence of oxygen to produce ethane (CH3-CH3).

This is the second step in the conversation of methane (CH4), the main component of natural gas, into a longer-chain hydrocarbon, or liquid fuel.

Mirica’s team is currently tweaking the complex so that it will perform the first step in the methane-to-ethane conversion as well.

The energy problem

Fossil fuels are useful because they pack energy in their chemical bonds and release that energy when they are burned. So they’re essentially convenient little energy suitcases.

Reactions that release energy, however, are reluctant to reverse themselves and the more energy they release, the more reluctant they are to back up.

There’s no way around this problem; if a reaction released energy both going forward and going backward, it could fuel a perpetual motion machine, which, of course, is an impossibility.

Still, it is possible to make hydrocarbon combustion reactions run backward — either by brute force or by finesse.

The brute force way is to pump in energy. That’s how the Nazis turned coal into oil during World War II. Saddled with an abundance of coal but short on oil, Germany solved the problem by transmuting coal to oil by chemical means.

But Nazi synthetic oil plants worked only at high temperatures and pressures and much more energy was used to drive the reactions than was ultimately stored in synthetic oil they produced. (See caption in Image 2: The brute force method.)

The finesse is to devise a chemical compound, a catalyst, that takes the reactants up an alternative, lower energy pathway to the reaction products. In effect, instead of going straight up the energy hill, the reaction takes a more manageable — ideally the minimal-energy — series of switchbacks to the top.

Like a ball in a glove

Last year, Mirica’s group was working with a palladium compound that they hoped could catalyze the splitting of water. “The catalyst we made for that reaction worked,” Mirica says. “But not as well as we hoped. But we noticed it was easily oxidized, even by the oxygen in air.

“This was our first hint that this might be an interesting system. So then we asked, what else could we use it for?

“One of our ideas was to use it to turn methane into ethane,” Mirica says. Methane, the main component of natural gas, is released in large amounts when an oil well is tapped. Currently the methane from the oil fields is wasted; it is flared off on site, releasing even more carbon dioxide into the atmosphere.

Turning methane to ethane, Mirica says, could be the first step in a process of building longer-chain hydrocarbons such as butane and octane, which would be liquid at normal temperatures and pressures and so could easily be transported to distant users.

Mirica’s metal complex solves half the problem of methane-to-ethane conversion. It takes two methyl groups (CH3) and, in the presence of oxygen and light, binds the carbon atoms to one another to form ethane.

The complex consists of an organic molecule that binds a central palladium atom through four nitrogen atoms, holding it like a ball in a glove.

The organic molecule is key to the metal complex’s function, because it stabilizes it in the unusual “+3” oxidation state (it has given up three electrons), which is responsible for its unprecedented chemical activity.

Once in the glove, the palladium atom still has two docking spots that can be occupied by chemical species whose reaction it might catalyze.

In the reported work, these sites are occupied by methyl groups, which the palladium atom joins to produce ethane. But, Mirica emphasizes, the sites could easily be occupied by other chemical species. What’s more, the reactions could be reducing ones (where electrons are donated to reactants) rather than the oxidizing ones (where electrons are removed from reactants) like the methyl-to-ethane conversion.

In short, the complex opens up a whole new area of palladium chemistry.

The to-do list

Mirica’s lab is currently trying to tweak the metal complex so that it can perform the entire methane-to-ethane reaction.

The first part of that reaction is pulling methyl groups off methane molecules. That’s a bit tricky, says Mirica, because it is hard to break one C-H bond of the methane molecule, which has four C-H bonds, without breaking all four.

“The reaction wants to run straight down the energy hill all the way to the bottom (CO2),” Mirica says. “Our goal is to design a catalyst that stops the reaction part of the way down the hill (when only one hydrogen has been removed).

His lab also is testing the metal complex’s ability to perform a reduction reaction, the conversion of CO2 into methanol (CH3OH).

“Carbon dioxide is an exceptionally stable molecule, so anything you do with it is going to require energy,” Mirica says. “We’re just trying to use the metal complex to minimize the energy input.”

Both the ethane and methanol reactions take greenhouse gases and transform them to liquid or easily liquefied compounds that could then be reused as fuels. If the energy penalty turns out to be low enough, the carbon could be recycled in this way many times.

Chemistry for the greenhouse

Ultimately, Mirica’s goal is a recycling carbon chemistry that requires so little energy that it can run off sunlight.

“If we’re going to keep using these carbon-containing fuels that make CO2, we should be trying to make combustion carbon-neutral by using catalysts and the sun’s energy to convert CO2 back into fuel,” he says.

Diana Lutz | Newswise Science News
Further information:
http://www.wustl.edu

More articles from Life Sciences:

nachricht Scientists unlock ability to generate new sensory hair cells
22.02.2017 | Brigham and Women's Hospital

nachricht New insights into the information processing of motor neurons
22.02.2017 | Max Planck Florida Institute for Neuroscience

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Microhotplates for a smart gas sensor

22.02.2017 | Power and Electrical Engineering

Scientists unlock ability to generate new sensory hair cells

22.02.2017 | Life Sciences

Prediction: More gas-giants will be found orbiting Sun-like stars

22.02.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>