A group of Brazilian researchers managed to convert methane into methanol using light and dispersed transition metals, such as copper, in a photo-oxidation process. The work was published in the scientific journal Chemical Communications and, according to the article, was the best performance reported so far for the conversion of gas to liquid fuel at ambient temperature and pressure conditions – 25 °C and 1 bar, respectively.
The bar, from the Greek barys (meaning “heavy”), is a unit of pressure equivalent to 100,000 pascals (105 Pa) – a value very close to the standard atmospheric pressure (101,325 Pa).
The result of the work is an important step in the use of natural gas, which can make this energy source viable for the production of fuels in the future, becoming an alternative to gasoline and diesel. Despite being considered fossil, the conversion of natural gas into methanol generates less carbon dioxide (CO2) when compared to other types of liquid fuels in this category.
In the Brazilian market, methanol plays a crucial role in the production of biodiesel and for the chemical industry, being used as an input to synthesize numerous chemical products.
In addition, capturing methane from the atmosphere plays a relevant role in mitigating the effects of climate change, as this gas has 25 times more potential to contribute to global warming than CO2, for example.
“There is a great debate in the scientific community about the amount of methane reserves in the world. It is estimated that they have twice the energy potential of all other existing fossil fuels. In the transition to renewable energies, we will have to count on methane at some point”, explains to Agência Fapesp the doctoral student Marcos da Silva, from the Department of Chemistry at UFSCar (Federal University of São Carlos), first author of the article.
The study received support from Fapesp through two projects (20/14741-6 and 21/11162-8) and also from Capes (Coordination for the Improvement of Higher Education Personnel) and CNPq (National Council for Scientific and Technological Development) .
For UFSCar professor Ivo Freitas Teixeira, Silva’s advisor and corresponding author of the article, one of the novelties of the research was the photocaliper. “The great innovation obtained by our group was to oxidize methane in a single step. In the chemical industry, this transformation occurs through the production of hydrogen and CO2 carried out in at least two steps and with very high temperature and pressure conditions. this in milder conditions, using less energy and obtaining methanol is an advance”, says Teixeira.
According to the professor, the results pave the way for new research to seek to adopt solar energy as the promoter of this process, further reducing the environmental impact.
Step by step
In the laboratory, the scientists synthesized crystalline carbon nitrides (PHI) with non-noble or abundant transition metals, mainly copper, generating active visible light photocatalysts.
These photocatalysts were employed in methane oxidation reactions using hydrogen peroxide as an initiator. The copper-PHI catalyst generated large amounts of oxygenated liquid products, especially methanol (2,900 µmol.g-1, unit of measurement called micromole per gram of material), in a period of four hours.
“We discovered the best catalyst and other essential conditions for the chemical reaction, such as using a lot of water and just a little hydrogen peroxide, which is an oxidizing agent. Now, for the next steps, we need to understand a little more about the sites copper actives in the material and their role in the reaction. And we also intend to use oxygen directly to, in theory, produce hydrogen peroxide in the reaction itself, making the process even safer and economically viable”, adds Teixeira.
According to the professor, another point that the group will continue to research is related to copper. “We worked with dispersed copper. When we finished the article, we still didn’t know if they were isolated atoms or clusters. Today we know that they are clusters”, he says.
In the study, the scientists worked with pure methane. However, they intend in the future to use renewable sources, such as gas extracted from biomass.
According to the UN (United Nations), methane has been responsible for about 30% of global warming since pre-industrial times. For the UN, human-caused methane emissions could be reduced by up to 45% over the next decade, avoiding nearly 0.3°C of global warming by 2045.
The researchers point out that this type of strategy for converting gas into liquid fuel using a photocatalyst is still new, not yet commercially available, but with great potential in the coming years. “We started our work more than four years ago. Now we have obtained a much better result than the one registered by Professor Hutchings’ group in 2017, which motivated our work”, says Teixeira.
He refers to the study published by a group of scientists from universities in the United States and Britain in the journal Science, led by Professor Graham Hutchings, from Cardiff University.
