A group of researchers has succeeded in converting methane into methanol using light and dispersed transition metals such as copper in a process known as photo oxidation. The reaction was the best achieved so far for the conversion of methane gas into liquid fuel under temperature and pressure conditions (25 °C and 1 bar respectively).
The word bar as a unit of pressure is derived from the Greek word for weight (baros). One bar is equal to 100,000 Pascals (100 kPa), which is very close to normal atmospheric pressure at sea level (101,325 Pa).
The results of the research are an important step in making natural gas available as an energy source for the production of alternative energy to gasoline and diesel. Although natural gas is considered a fossil fuel, its conversion to methanol emits less carbon dioxide (CO2) than other liquid fuels in the same category.
In Brazil, methanol plays an important role in the production of biodiesel and in the chemical industry, which uses it to synthesize many products.
Furthermore, capturing methane from the atmosphere is important to reduce the negative effects of climate change, as the gas has 25 times the potential of CO2, for example, to contribute to global warming.
“There’s a lot of debate in the scientific community about the size of the planet’s methane reserves. According to some estimates, they could have twice the energy potential of all other fuels combined. In the recycling transition, we’re going to have to tap into all of this methane at some point, ” Marcos da Silva, first author of the article, told Agência FAPESP. Silva is a PhD candidate at the Department of Physics of the Federal University of São Carlos (UFSCar).
According to Ivo Freitas Teixeira, professor at UFSCar, Silva’s thesis advisor and final author of the article, the photostimulator used in the study was an important innovation. “Our group made a big breakthrough by adding methane oxide in one step,” he said. “In the chemical industry, this conversion occurs through the production of hydrogen and CO2 in at least two steps and under conditions of very high temperature and pressure. Our success in obtaining methanol under mild conditions, while also using less energy, is a big step ahead.
According to Teixeira, the results pave the way for future research in the use of solar energy for this conversion process, the possibility of reducing its environmental impact even more.
Photocatalysts
In the laboratory, scientists combined crystalline carbon nitride through polyheptazine imide (PHI), using non-precious or abundant earth metals, especially copper, to produce visible-light photocatalysts.
They then used photocatalysts in the oxidation reactions of methane with hydrogen peroxide as the initiator. The copper-PHI catalyst produced large amounts of oxygenated liquid products, mainly methanol (2,900 micromoles per gram of material, or µmol.g-1 in four hours).
“We discovered the best catalyst and other conditions necessary for the chemical reaction, such as using a large amount of water and 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 the reaction. We also plan to use oxygen directly to produce hydrogen peroxide in the reaction itself. If successful, this should make the process safer and more 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 did not know if we were dealing with isolated atoms or clusters. Now we know they are clusters,” he explained.
In the study, the scientists used pure methane, but in the future they will produce the gas from alternative materials such as biomass. According to the United Nations, methane has so far caused about 30% of global warming since the pre-industrial era. Methane emissions from human activities can be reduced by 45% in the next decade, avoiding a rise of about 0.3°C by 2045.
The strategy to convert methane into liquid fuel using a photocatalyst is new and not commercially available, but its potential in the short term is significant. “We started our research more than four years ago. Now we have better results than those of Professor Hutchings and his group in 2017, which inspired our own research,” Teixeira said, referring to the study published in the journal. Science and researchers collaborating with universities in the United States and England, and led by Graham Hutchings, a professor at Cardiff University in Wales.