Nanostructured catalyst enables carbon dioxide and methane to be converted into fuels
Direct conversion of carbon and hydrocarbon molecules into useful fuels has been an area of significant activity in recent years, as researchers look for ways of limiting CO2 emissions, or methods of turning them into something more useful to the energy industry.
Ethanol has been one area of particular focus. Indeed, last year a team at the US Department of Energy’s (DoE) Oak Ridge National Laboratory (ORNL) discovered a nanostructured catalyst made of carbon, copper and nitrogen capable of turning carbon dioxide (CO2) and water (H2O) directly into ethanol (C2H6O) with the application of a voltage. The team described it as “essentially [reversing] the combustion process.”
A new process with similar results was published by a team from the UK’s University of Liverpool in September. In a paper published in chemistry journal Angewandte Chemie, the group reported a plasma synthesis process which allowed for the direct, one-step activation of CO2 and methane (CH4) into other “higher value” fuels and chemicals, including acetic acid, methanol, ethanol and formaldehyde. Moreover, the process could be performed at room temperature and atmospheric pressure.
This catalysis is markedly different from the typical systems for synthetic gas (syngas) production which traditionally require high additional energy inputs and/or pressure controls.
According to the researchers’ paper, non-thermal plasmas (NPT) – any plasma in which there is a net flow of energy – has been used for removing gas pollutants, but not in direct chemical conversion applications. In NPTs, the gas temperature remains low while the electrons are highly energetic – enough to activate inert molecules such as CO2 and CH4 and produce new reactive chemicals.
According to their reported results, acetic acid is the largest product created, but also acetone, methanol, ethanol and formaldehyde. The products and volume created can be adjusted through the alteration of the ratio of CH4 and CO2, as well as the type of catalyst.
What makes the system advantageous, they argue, is that these systems can be scaled up and down, and the steady rate of catalysis means production can be turned on and off quickly and with little additional energy inputs, meaning the system could be used easily on-demand. This “offers 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,” the University says.
In addition to renewables, it could also be used to convert excess CH4 into usable fuels, avoiding the need for flaring at oil and gas wells.
“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,” commented co-author Dr. Xin Tu of the University’s Department of Electrical Engineering and Electronics.