Scientists reveal method of converting methane gas into liquid methanol

A group of researchers have succeeded in converting methane to methanol using a light, dispersed transition metal such as copper in a process known as photooxidation. According to an article reporting on research published in Chemical Communications, the reaction is the best obtained to date for the conversion of methane gas to liquid fuel under ambient temperature and pressure conditions (25 °C and 1 bar, respectively).

The term bar as a unit of pressure comes from the Greek word for weight (baros). One bar is equivalent to 100,000 Pascals (100 kPa), which is very close to the standard atmospheric pressure at sea level (101,325 Pa).

The results of this study are an important step in making natural gas available as an energy source for the production of alternative fuels other than gasoline and diesel. Although natural gas is considered a fossil fuel, its conversion to methanol produces less carbon dioxide (CO2) than other liquid fuels in the same category.

In Brazil, methanol plays a key role in biodiesel production and the chemical industry, which uses it to synthesize many products.

In addition, capturing methane from the atmosphere is critical to mitigating the adverse effects of climate change, as the gas has a 25-fold potential for CO2, for example, to contribute to global warming.

“There is a huge debate within the scientific community about the size of the planet’s methane reserves. According to some estimates, they may have twice the energy potential of all other fossil fuels combined. In the transition to renewable energy, we will have to harness all this methane at some point,” Marcos da Silva, the first author of the article, told Agência FAPESP. Silva is a PhD candidate in the Department of Physics of the Federal University of São Carlos (UFSCar).

This study was supported by FAPESP through two projects (20/14741-6 and 21/11162-8), by the Higher Research Council (CAPES, an agency of the Ministry of Education), and by the National Council for Scientific and Technological Development (CNPq, an arm of the Ministry of Science, Technology and Innovation).

According to Ivo Freitas Teixeira, a professor at UFSCar, Silva’s thesis advisor and author of the final article, the photocatalyst used in this study was a key innovation. “Our group innovated significantly by oxidizing methane in one step,” he said. “In the chemical industry, this conversion occurs through the production of hydrogen and CO2 in at least two stages and under very high temperature and pressure conditions. Our success in obtaining methanol under mild conditions, while also consuming less energy, is a huge step forward.”

According to Teixeira, the results pave the way for future research into using solar energy for this conversion process, potentially reducing its environmental impact even further.

Photocatalyst

In the laboratory, scientists synthesize crystalline carbon nitride in the form of polyheptazine imide (PHI), using a base or abundant transition metal, primarily copper, to produce an active visible light photocatalyst.

They then used a photocatalyst in the methane oxidation reaction with hydrogen peroxide as the initiator. The copper-PHI catalyst yields a large amount of oxygenated liquid product, mainly methanol (2,900 micromoles per gram of material, or mol.g-1 in four hours).

“We found the best catalyst and other conditions that are important for chemical reactions, such as using a large amount of water and only a small amount of hydrogen peroxide, which is an oxidizing agent,” Teixeira said. “Next steps include understanding more about the active copper sites in the material and their role in reactions. We also plan to use oxygen directly to produce hydrogen peroxide in the reaction itself. If successful, this will make the process more secure and economically viable.”

Another thing the group will continue to investigate is related to copper. “We are working with dispersed copper. When we wrote the article, we didn’t know if we were dealing with isolated atoms or groups. We now know they are clusters,” he explained.

In the study, the scientists used pure methane, but in the future they will extract the gas from renewable energies such as biomass.

According to the United Nations, methane has so far caused about 30% of global warming since pre-industrial times. Methane emissions from human activities could be reduced by as much as 45% in the next decade, avoiding an increase of nearly 0.3°C by 2045.

The strategy of converting methane to liquid fuel using photocatalysts is new and not commercially available, but its potential in the near future 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 a study published in the journal Science by researchers affiliated with universities in the United States and Britain, and led by Graham Hutchings, a professor at Cardiff University in Wales.

About the São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by providing scholarships, scholarships and grants to researchers related to higher education and research institutions in the State of São Paulo, Brazil. FAPESP recognizes that the best research can only be done in collaboration with the best international researchers. Therefore, it has established partnerships with funding institutions, higher education, private companies, and research organizations in other countries known for the quality of their research and has encouraged grant-funded scientists to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit the FAPESP news agency at www.agencia.fapesp.br/en to stay up-to-date on the latest scientific breakthroughs that FAPESP is helping to achieve through various programs, awards and research center. You can also subscribe to the FAPESP news agency at https://agencia.fapesp.br/subscribe

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