The new method turns methane gas into liquid methanol. A team of researchers successfully converted methane into methanol using light and diffuse transition metals such as copper in a process known as photooxidation. According to a study published in the journal Chemical communications
The term bar as a unit of pressure comes from the Greek word for weight (baros). One bar equals 100,000 Pa (100 kPa), which is close to standard atmospheric pressure at sea level (101,325 Pa).
The results of the study are an important step towards making natural gas available as an energy source for the production of fuels, alternatives to gasoline and diesel. Although natural gas is a fossil fuel, its conversion to methanol produces less carbon dioxide (CO2) than other liquid fuels in the same category.
Methanol is vital in the production of biodiesel and the chemical industry in Brazil, where it is used to synthesize various products.
In addition, capturing methane from the atmosphere is critical to mitigating the negative effects of climate change, as this gas has 25 times the potential to contribute to global warming than CO2, for example.
“There is a great debate in the scientific community about the size of the methane reserves on the planet. According to some estimates, they may have twice the energy potential of all other fossil fuels combined. In the transition to renewable energy sources, we will have to use up all this methane at some point,” Marcos da Silva, the first author of the paper, told FAPESP. Silva is a Ph.D. candidate at the Department of Physics, Federal University of San Carlos (UFSCar).
The research was supported by FAPESP, the Higher Research Council (CAPES, an agency of the Ministry of Education) and the National Council for Scientific and Technological Development (CNPq, a division of the Ministry of Science, Technology and Innovation).
The photocatalyst used in the study was a key innovation, according to Yves Freitas Teixeira, a UFSCar professor, Silva's thesis advisor and the last author of the paper. “Our group has made a significant innovation by oxidizing methane in one step,” he said. “In the chemical industry, this conversion takes place through the production of hydrogen and CO2, in at least two steps and under conditions of very high temperature and pressure. Our success in producing methanol under mild conditions while using less energy is an important step forward.”
According to Teixeira, the findings pave the way for future research into using solar energy for this conversion process, potentially further reducing its environmental impact.
Photocatalysts
In the laboratory, scientists have synthesized crystalline carbon nitride in the form of polyheptazinimide (PHI) using non-noble or earth-common transition metals, especially copper, to produce active visible light photocatalysts.
They then used the photocatalysts in methane oxidation reactions with hydrogen peroxide as an initiator. The copper-PHI catalyst produced a large volume of oxygenated liquid products, especially methanol (2900 micromoles per gram of material, or μmol.g-1 in four hours).
“We discovered a better catalyst and other conditions needed for the chemical reaction, such as using a lot of water and only a small amount of hydrogen peroxide, which is an oxidizing agent,” Teixeira said. “Next steps include a greater understanding of the active copper sites in the material and their role in the reaction. We also plan to use oxygen directly to produce hydrogen peroxide in the reaction itself. If successful, this should make the process even safer and more economically viable.”
Another point the group will continue to investigate concerns copper. “We work with dispersed copper. When we wrote the paper, we did not know whether we were dealing with isolated atoms or clusters. Now we know that these are clusters,” he explained.
In the study, the scientists used pure methane, but in the future they will extract the gas from renewable energy sources such as biomass.
Since the pre-industrial era, methane has been responsible for about 30% of global warming, according to the United Nations. Human-caused methane emissions could be cut by 45% over the next decade, avoiding a temperature rise of almost 0.3°C by 2045.
The strategy of converting methane into liquid fuel using a photocatalyst is new and not commercially available, but its near-term potential is significant. “We started our research more than four years ago. We now have much better results than Professor Hutchings and his group in 2017, which motivated our own research,” said Teixeira, referring to the study published in the journal. Science researchers associated with universities in the United States and Great Britain, led by Professor Graham Hutchings Cardiff University in Wales.
List of references:
“Selective Photooxidation of Methane to Methanol under Mild Conditions Facilitated by Highly Dispersed Cu Atoms on Crystalline Carbon Nitrides” Marcos AR. By Kave Ribeira and Yves F. Teixeira, May 31, 2022. Chemical communications
DOI: 10.1039/D2CC01757A
“Aqueous Au-Pd Colloids Catalyze Selective CH oxidation to CH OH with O under mild conditions” Nishtha Agarwal, Simon J. Frickley, Rebecca W. McVicker, Sultan M. Altaban, Nikolaos Dimitratos, Tian He, David J. Morgan, Robert L. Jenkins, David J. Wheelock, Stuart H. Taylor, Christopher J. Kiley and Graham J. Hutchings, 7 September 2017. Science
DOI: 10.1126/science.aan6515
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