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Researchers at the University of Liverpool claim they have made a "significant breakthrough" in the direct conversion of carbon dioxide (CO2) and methane (CH4) into liquid fuels and chemicals, which could help industry to reduce greenhouse gas (GHG) emissions.

In their paper, entitled 'One-step reforming of CO2 and CH4 into high-value liquid chemicals and fuels at room temperature by plasma-driven catalysis', the researchers report a "very unique" plasma synthesis process for the direct, one-step activation of carbon dioxide and methane into higher-value liquid fuels and chemicals (e.g. acetic acid, methanol, ethanol and formaldehyde).

The one-step, room-temperature synthesis of liquid fuels and chemicals from the direct reforming of CO2 with CH4 was achieved by using a novel atmospheric-pressure, non-thermal plasma reactor with a water electrode and a low-energy input.

It is the first time this process has been shown; it is a significant challenge to directly convert these two stable and inert molecules into liquid fuels or chemicals using any single-step conventional (e.g. catalysis) processes that bypass a high-temperature, energy-intensive syngas production process and high-pressure syngas processing for chemical synthesis.

Dr. Xin Tu, from Liverpool University's Department of Electrical Engineering and Electronics, said: "These results clearly show that non-thermal plasmas offer a promising solution to overcome the thermodynamic barrier for the direct transformation of CH4 and CO2 into a range of strategically important platform chemicals and synthetic fuels at ambient conditions. Introducing a catalyst into the plasma chemical process, known as plasma catalysis, could tune the selectivity of target chemicals.

"This is a major breakthrough technology that has great potential to deliver a step-change in future methane activation, CO2 conversion and utilisation and chemical energy storage, which is also of huge relevance to the energy and chemical industry and could help to tackle the challenges of global warming and greenhouse gas effect."

Methane and carbon dioxide emissions are considered GHGs that contribute to global warming and climate change. The largest source of CO2 emissions is from burning fossil fuels for electricity, heat, and transportation, while methane is mainly emitted during the production, processing, transportation and storage of natural gas and crude oils.

CO2 emissions and methane leakage have been described extensively before on this site as areas of great concern for both shipping and bunkering.

Plasma

According to the researchers, plasma - the fourth state of matter and an electrically charged gas mixture - offers a promising and attractive alternative for the synthesis of fuels and chemicals, providing a unique way to enable thermodynamically unfavourable reactions to take place at ambient conditions.

In non-thermal plasmas, the gas temperature remains low (as low as room temperature), while the electrons are highly energetic with a typical electron temperature of 1-10 eV, which is sufficient to activate inert molecules (e.g. CO2 and CH4) present and produce a variety of chemically reactive species including radicals, excited atoms, molecules and ions.

These energetic species, which are produced at a relatively low temperature, are capable of initiating a variety of different reactions. Plasma systems have the flexibility to be scaled up and down. In addition, a high reaction rate and fast attainment of steady state in a plasma process allows rapid start-up and shutdown of the plasma process compared to other thermal processes, which significantly reduces the overall energy cost and is said to offer a promising route for the plasma process powered by renewable energy (e.g. wind and solar power) to act as an efficient chemical energy storage localised or distributed system.

Image: Victoria Building, Liverpool University. Credit: Rept0n1x / Wikimedia Commons.