Researchers in Australia have found that a limited reaction environment created by copper atoms arranged in pyramidal structures can selectively convert carbon dioxide and carbon monoxide to ethylene glycol.1 The work not only identifies a new reaction mechanism for the production of a valuable diol with various industrial applications, but also shows the potential of designing reaction environments to increase catalyst selectivity and efficiency.
“The electrocatalytic conversion of carbon dioxide into chemicals and fuels was seen as a promising way to achieve the climate-neutral goal set in the Paris Agreement,” said Ling Chen of Adelaide University. “Successful implementation, however, depends on the development of highly selective and energy-efficient catalysts.” Carbon dioxide can be converted electrochemically into single and multi-carbon products. However, the production of alcohols is more difficult than the formation of hydrocarbons and the selective production of higher-valent C.2 Chemicals like ethylene glycol remain elusive. “To the best of our knowledge, no complete route for the electrosynthesis of diols from carbon monoxide and carbon dioxide has been described, either experimentally or theoretically,” says Chen.
Diols are industrially important intermediates and building blocks. Currently, the main technology for producing ethylene glycol on a scale is energy and cost intensive. A drive to address the increasing effects of greenhouse gases and develop more sustainable methods of making ethylene glycol inspired Chen and colleagues to explore the potential of tightly packed copper nanopyramids for the electrochemical production of ethylene glycol from carbon dioxide or carbon monoxide.
Previously, the researchers showed2 arithmetically, the formation of the copper catalyst as a pyramid would increase the electrocatalytic activity and selectivity for C2 Products. This was attributed to improved adsorption, the presence of preferential sites for CC coupling, and improved electron transfer. Building on this work, the team used density functional theory calculations to demonstrate that the environment created by neighboring copper nanopyramids enables the selective conversion of carbon dioxide and carbon monoxide to ethylene glycol.
The Adelaide researchers also discovered the reaction pathway that facilitates the direct electrosynthesis of ethylene glycol. This route is not favorable on a planar copper surface or less densely packed nanopyramids. Closely arranged copper nanopyramids allow the formation of an additional O-Cu bond between adsorbed COH-CO and copper on an adjacent pyramid. Such an atomic arrangement not only promotes CC coupling, but also protects oxygen atoms against dehydroxylation. The additional bond also improves the hydrogenation to ethylene glycol by lowering the formation barrier for the key intermediate COH-CHO and kinetically suppressing the usual dominant pathways.
“Spatial reactivity is essential for many biological processes in nature,” comments Reshma Rao from Imperial College London, Great Britain, who studies the electrochemical reactivity at interfaces. She says that the findings from this work “provide experimenters with a framework to rationally exploit nanoconfinement effects and to change the local reaction environment in order to produce high-quality products from carbon dioxide.”