The catalytic intermediates and key characteristics of the mechanism of the conversion of carbon dioxide to methanol with a copper-based catalyst have been identified by researchers at the University of Tsukuba. Their discovery has the potential to enhance the efficiency of pre-existing decarbonisation systems.
With increasing carbon dioxide levels in the atmosphere causing global warming, efforts in the scientific community have been focused on removing this pollutant from the atmosphere and transforming it into a more useful resource. Some scientists have been studying methods to convert carbon dioxide into methanol, which is a usable fuel and raw material that may be used to synthesise adhesives and water bottles, among other things.
Using current technology, such conversions are catalysed by copper-based catalysts. However, the reaction mechanisms by which carbon dioxide is converted to methanol via the catalysts have not been properly understood, thus any further tweaks to improve the efficiency of this process are limited. To overcome this challenge, more studies will have to be conducted, either through experimentation or computer simulations to gain more insights into the reaction mechanism of the key reaction.
Fortunately, researchers from the University of Tsukuba and their collaborators have managed to observe and measure the hydrogenation of copper-adsorbed formate. The study, published in the Journal of the American Chemical Society, will help researchers better understand the catalytic mechanisms of the copper-based catalyst, such that key steps in the reaction may be streamlined to improve yields. “Hydrogenation of carbon dioxide into methanol is a potential key technology for producing fuel and chemical feedstocks, but optimising the reaction remains difficult,” explains Dr. Kotaro Takeyasu, senior author.
To study the intermediates in this reaction, the researchers utilised infrared reflection absorption spectroscopy and temperature-programmed desorption.
One of the key findings was that the adsorbed formate underwent hydrogenation at 200K. While the exact chemical nature of the product remains unknown, the hydrogenated formate decomposed back into the original adsorbed formate at 250K in a 96:4 ratio.
“On the basis of our experimental and computational work, the activation energy of the hydrogenation of adsorbed formate is approximately 121 kilojoules per mole,” states Dr. Takeyasu. “Our results are consistent with reported results of methanol synthesis studies.”
For this particular conversion of carbon dioxide, alloys made out of copper and zinc are frequently used in the construction of catalysts for this reaction. The team of researchers is also further studying how the activation energy of copper-zinc catalysts compares with other alloys with different compositions of metal using computational and experimental investigations.
The insights gained from this research will help the researchers design more efficient processes to gain better yields of methanol. This would valorise carbon dioxide, turning it from a waste product to more useful fuels or raw materials suitable for industrial use. In the future, if the hydrogenation step of the formate is made even more efficient, researchers might be on the way to developing a reliable alternate source of methanol.
Source: Takeyasu et al. (2022). Hydrogenation of Formate Species Using Atomic Hydrogen on a Cu (111) Model Catalyst. Journal of the American Chemical Society.