As scientists look for ways to help remove excess carbon dioxide from the atmosphere, a number of experiments have focused on employing this gas to create usable fuels. Both hydrogen and methanol have resulted from such experiments, but the processes often involve a range of intricate steps and a variety of methods. Now researchers have demonstrated a one-step conversion of carbon dioxide and water directly into a simple and inexpensive liquid hydrocarbon fuel using a combination of high-intensity light, concentrated heat, and high pressure.
According to the researchers from the University of Texas at Arlington (UTA), this breakthrough sustainable fuels technology uses carbon dioxide from the atmosphere, with the added benefit of also producing oxygen as a byproduct, which should create a clear positive environmental impact.
"We are the first to use both light and heat to synthesize liquid hydrocarbons in a single stage reactor from carbon dioxide and water," said Brian Dennis, UTA professor of mechanical and aerospace engineering and co-principal investigator of the project. "Concentrated light drives the photochemical reaction, which generates high-energy intermediates and heat to drive thermochemical carbon-chain-forming reactions, thus producing hydrocarbons in a single-step process."
Known as solar photothermochemical alkane reverse combustion, the one-step conversion process turns carbon dioxide and water into oxygen and liquid hydrocarbons using a photothermochemical flow reactor operating at around 180° C to 200° C (356 to 392° F) and at pressures up to six atmospheres.
"Our process also has an important advantage over battery or gaseous-hydrogen powered vehicle technologies as many of the hydrocarbon products from our reaction are exactly what we use in cars, trucks and planes, so there would be no need to change the current fuel distribution system," said Frederick MacDonnell, UTA interim chair of chemistry and biochemistry and co-principal investigator of the project.
To initiate the hybrid photochemical and thermochemical reaction, a titanium dioxide (TiO2) photocatalyst was used. Titanium dioxide is very effective in the realm of hydrolysis – the breaking down of water into hydrogen and oxygen – and is a very effective catalyst under UV light, but it is not so efficient in ordinary visible light.
"Our next step is to develop a photo-catalyst better matched to the solar spectrum," MacDonnell said. "Then we could more effectively use the entire spectrum of incident light to work towards the overall goal of a sustainable solar liquid fuel."
According to the research, the team suggests that cobalt, ruthenium, or even iron may be considered as good candidates for a new catalyst, particularly as the TiO2 in the experiment was observed to drop in photoluminescent intensity at higher pressures.
In the future, the researchers imagine parabolic mirrors could also be used to concentrate sunlight onto the catalyst in the reactor, thereby providing both the required heating and photo-excitation for the reaction to occur without the need for other external power sources. The team also believes that any excess heat created in this way may be used to help power other aspects of a solar fuels facility, such as material separation and the purification of water.
The results of this research were published in the Proceedings of the National Academy of Sciences (PDF).
Source: University of Texas at Arlington
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