Sunlight turns carbon dioxide to methane

March 05, 2009

Dual catalysts may be the key to efficiently turning carbon dioxide and water vapor into methane and other hydrocarbons using titania nanotubes and solar power, according to Penn State researchers.

Burning fossil fuels like oil, gas and coal release large amounts of carbon dioxide, a greenhouse gas, into the atmosphere. Rather than contribute to global climate change, producers could convert carbon dioxide to a wide variety of hydrocarbons, but this makes sense to do only when using solar energy.

"Recycling of carbon dioxide via conversion into a high energy-content fuel, suitable for use in the existing hydrocarbon-based energy infrastructure, is an attractive option, however the process is energy intense and useful only if a renewable energy source can be used for the purpose," the researchers note in a recent issue of Nano Letters.

Craig A. Grimes, professor of electrical engineering and his team used titanium dioxide nanotubes doped with nitrogen and coated with a thin layer of both copper and platinum to convert a mixture of carbon dioxide and water vapor to methane. Using outdoor, visible light, they reported a 20-times higher yield of methane than previously published attempts conducted in laboratory conditions using intense ultraviolet exposures.

The chemical conversion of water and carbon dioxide to methane is simple on paper -- one carbon dioxide molecule and two water molecules become one methane molecule and two oxygen molecules. However, for the reaction to occur, at least eight photons are required for each molecule.

"Converting carbon dioxide and water to methane using photocatalysis is an appealing idea, but historically, attempts have had very low conversion rates," said Grimes who is also a member of Penn State's Materials Research Institute. "To get significant hydrocarbon reaction yields requires an efficient photocatalyst that uses the maximum energy available in sunlight."

The team, which also included Oomman K. Varghese and Maggie Paulose, Materials Research Institute research scientists and Thomas J. LaTempa, graduate student in electrical engineering, used natural sunlight to test their nanotubes in a chamber containing a mix of water vapor and carbon dioxide. They exposed the co-catalyst sensitized nanotubes to sunlight for 2.5 to 3.5 hours when the sun produced between 102 and 75 milliwatts for each square centimeter exposed.

The researchers found that nanotubes annealed at 600 degrees Celsius and coated with copper yielded the highest amounts of hydrocarbons and that the same nanotubes coated with platinum actually yielded more hydrogen, while the copper coated nanotubes produced more carbon monoxide. Both hydrogen and carbon monoxide are normal intermediate steps in the process and as the building blocks of syngas, can be used to make liquid hydrocarbon fuels.

When the team used a nanotube array with about half the surface coated in copper and the other half in platinum, they enhanced the hydrocarbon production and eliminated carbon monoxide. The yield for these dual catalyst nanotubes was 163 parts per million hydrocarbons an hour for each square centimeter. The yield from titania nanotubes without either copper or platinum catalysts is only about 10 parts per million.

"If we uniformly coated the surface of the nanotube arrays with copper oxide, I think we could greatly improve the yield," said Grimes.

Grimes also found that lengthening the titanium dioxide tubes, which for other applications increases yield, does not improve results.

"We think that distribution of the sputtered catalyst nanoparticles is at the top surface of the nanotubes and not inside and that is why increased length does not improve the reaction," says Grimes.

Although all these experiments were done with nitrogen-doped titanium dioxide nanotubes, the researchers conclude that the nitrogen did not enhance the conversion of carbon dioxide to hydrocarbons. The catalysts, however, did shift the reaction from one that used only the energy in ultraviolet light to one that used other wavelengths of visible light and therefore more of the sun's energy.

The researchers are now working on converting their batch reactor into a continuous flow-through design that they believe will significantly increase yields.

The researchers have filed a provisional patent on this work.

Penn State

---

---

	Carbon Dioxide Recovery and Utilization by M. Aresta (Editor) Carbon Dioxide Recovery and Utilization is a complete and informative resource on the carbon dioxide sources and market at the European Union level, with reference to the world situation. The book covers the following themes: - Sources of carbon dioxide and their purity, - Market of carbon dioxide and its uses, - Separation techniques of carbon dioxide from flue gases, - Analysis of the potential of each technique and application, - Basic science and technology of supercritical CO2, - Reactions in supercritical CO2 and its use as reactive solvent, - Utilization of CO2 in the synthesis of chemicals with low energy input, - Conversion of CO2 into fuels: existing techniques, - Dry reforming of methane, - Assessment of the use of carbon dioxide for the synthesis of methanol. This...
	Carbon Dioxide as Chemical Feedstock by Michele Aresta (Editor) Filling the need for an up-to-date handbook, this ready reference closely investigates the use of CO2 for ureas, enzymes, carbamates, and isocyanates, as well as its use as a solvent, in electrochemistry, biomass utilization and much more. Edited by an internationally renowned and experienced researcher, this is a comprehensive source for every synthetic chemist in academia and industry.
	Dense Phase Carbon Dioxide: Food and Pharmaceutical Applications by Murat O. Balaban (Editor), Dr. Giovanna Ferrentino (Editor) Dense phase carbon dioxide (DPCD) is a non-thermal method for food and pharmaceutical processing that can ensure safe products with minimal nutrient loss and better preserved quality attributes. Its application is quite different than, for example, supercritical extraction with CO 2 where the typical solubility of materials in CO 2 is in the order of 1% and therefore requires large volumes of CO 2. In contrast, processing with DPCD requires much less CO 2 (between 5 to 8% CO 2 by weight) and the pressures used are at least one order of magnitude less than those typically used in ultra high pressure (UHP) processing. There is no noticeable temperature increase due to pressurization, and typical process temperatures are around 40°C.DPCD temporarily reduces the pH of liquid foods and...
	Carbon Capture and Storage by Steve Rackley (Author) Carbon dioxide capture and storage (CCS) is a technology aimed at reducing greenhouse gas emissions from burning fossil fuels during industrial and energy-related processes. CCS involves the capture, transport and long-term storage of carbon dioxide, usually in geological reservoirs deep underground that would otherwise be released to the atmosphere. Carbon dioxide capture and storage offers important possibilities for making further use of fossil fuels more compatible with climate change mitigation policies. The largest volumes of CO2 could be captured from large point sources such as from power generation, which alone accounts for about 40 per cent of total anthropogenic CO2 emissions. The development of capture technologies in the power generation sector could be particularly important...
	How Bad Are Bananas?: The Carbon Footprint of Everything by Mike Berners-Lee (Author) Is it more environmentally friendly to ride the bus or drive a hybrid car? In a public washroom, should you dry your hands with paper towel or use the air dryer? And how bad is it really to eat bananas shipped from South America? Climate change is upon us whether we like it or not. Managing our carbon usage has become a part of everyday life and we have no choice but to live in a carbon-careful world. The seriousness of the challenge is getting stronger, demanding that we have a proper understanding of the carbon implications of our everyday lifestyle decisions. However most of us don't have sufficient understanding of carbon emissions to be able to engage in this intelligently. Part green-lifestyle guide, part popular science, How Bad Are Bananas? is the first book to...
	Hiding the bad gas.(capturing and storing carbon dioxide): An article from: E by Simon Birch (Author) This digital document is an article from E, published by Earth Action Network, Inc. on January 1, 2005. The length of the article is 476 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Hiding the bad gas.(capturing and storing carbon dioxide) Author: Simon Birch Publication: E (Magazine/Journal) Date: January 1, 2005 Publisher: Earth Action Network, Inc. Volume: 16 Issue: 1 Page: 12(1) Distributed by Thomson...
	Carbon dioxide an often overlooked natural resource.(Energy & Utilities): An article from: Mississippi Business Journal by George McNeill (Author) This digital document is an article from Mississippi Business Journal, published by Venture Publications on May 3, 2004. The length of the article is 876 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Carbon dioxide an often overlooked natural resource.(Energy & Utilities) Author: George McNeill Publication: Mississippi Business Journal (Magazine/Journal) Date: May 3, 2004 Publisher: Venture Publications Volume: 26 Issue: 18 Page: 27(1) Distributed by Thomson...
	High fluxes but different patterns of nitrous oxide and carbon dioxide emissions from soil in a cattle overwintering area [An article from: Agriculture, Ecosystems and Environment] by J. Hynst (Author), M. Simek (Author), P. Brucek (Author), S.O. Petersen (Author) This digital document is a journal article from Agriculture, Ecosystems and Environment, published by Elsevier in 2007. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser. Description: Cattle overwintering areas common in central Europe may represent significant point sources of the important greenhouse gases, nitrous oxide (N"2O) and carbon dioxide (CO"2). A 2-year field study was carried out in order to estimate the emissions of N"2O and CO"2 from soil in a cattle overwintering area located in the southwest of the Czech Republic. The measurements were performed at three sampling locations along a gradient of animal impact (severe, moderate, slight) to test the hypothesis...
	Luminescence lifetime-based carbon dioxide optical sensor for clinical applications [An article from: Analytica Chimica Acta] by M. Cajlakovic (Author), A. Bizzarri (Author), V. Ribitsch (Author) This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser. Description: The development of both an optical planar and capillary based carbon dioxide sensor, which final aim is pCO"2 monitoring in adipose tissue of critically ill patients, is reported. The sensor is based on the measuring principle of phase fluorometry using a dual luminophore referencing scheme (DLR) to convert the CO"2 dependent intensity signal into phase domain. The CO"2 sensors have been prepared by incorporating two appropriate luminophores and a phase transfer agent in a same hydrophobic polymer as matrix....
	Possible role for dust or other northern forcing of ice-age carbon dioxide changes [An article from: Quaternary Science Reviews] by T.C. Johnston (Author), R.B. Alley (Author) This digital document is a journal article from Quaternary Science Reviews, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser. Description: A simple impulse-decay model driven by the history of atmospheric dust loading from Greenland can match the history of glacial-interglacial changes in atmospheric carbon dioxide concentration rather accurately, if model parameters are tuned within physically possible ranges; forcing with the Greenland temperature record produces a similarly good match. Calculations using southern forcing do not match as accurately. These results leave open the possibility of northern control of glacial-interglacial carbon...