CO2 can be turned into liquid hydrocarbons to make fuel for planes

Scientists have developed a method that can turn carbon dioxide into valuable liquid hydrocarbons, which are the main components of jet fuel. Developed by chemists from the National University of Singapore (NUS), the method in green fuel production uses a nickel-based material to catalyze the electrochemical reduction of carbon dioxide.

Researchers found that they could fine-tune the catalytic process as they introduced a small amount of fluoride ions into the nickel structure as well as by applying pulsed potential electrolysis.

These strategies allowed them to have unprecedented control over the types of hydrocarbons produced, especially in determining whether the molecules are straight chains or have branches, according to researchers.

Complementary expertise in catalyst synthesis

“This work brings together complementary expertise in catalyst synthesis, mechanistic investigation and computational modelling, which allows us to uncover new mechanisms and design strategies for carbon dioxide reduction to long-chain hydrocarbons,” said Associate Professor Boon Siang YEO from the Department of Chemistry at NUS.

“This work would not have been possible, if not for the intense collaboration between experimentalists and theoreticians.”

Schematic illustration of the key strategies employed in the study. These approaches allowed the researchers to guide the reaction toward making more branched and longer-chain molecules, which are sought after for advanced fuels. [Credit: Nature Catalysis]

Production of branched hydrocarbons

Researchers also highlighted that their study showcases new strategies to selectively promote the production of branched hydrocarbons.

By applying a technique called pulsed potential electrolysis, where the electrical bias is varied in periodic cycles, the team was able to markedly increase the branch-to-linear ratio of hydrocarbons with five or more carbon atoms, achieving an over 400% improvement compared to standard methods, according to a press release.

In addition, fluoride doping in the nickel catalyst helped maintain its oxidation state under reducing conditions, a key factor in promoting the formation of longer hydrocarbon chains.

“A key advancement of our work is that we were able to reveal why copper-based catalysts, despite being heavily studied by the community over the past ten years, are not able to form appreciable amounts of long-chain hydrocarbons, as compared to nickel catalysts,” said Dr Ou Yingqing, a Research Fellow of the team.

Researchers showed that nickel-based catalysts promote the removal of oxygen from reaction intermediates and favour asymmetric coupling between adsorbed carbon monoxide intermediates and unsaturated hydrocarbon species.

Researchers also revealed that by developing ways to precisely control the structure of hydrocarbons produced from carbon dioxide using electricity, this study opens new pathways for the development of on-demand, sustainable aviation fuels and chemical precursors. 

Published in the journal Nature, the study reveals that the Nickel-based materials can facilitate the electrocatalytic CO2 reduction (CO2R) reaction to generate hydrocarbons up to C6. The research shows that fluorine doping alters the nature of the Ni active sites, which proves instrumental in tuning the selectivity of the CO2R.

“We interrogate the CO2R reaction mechanism using intermediate surrogates, including aldehydes, alkyl iodides and acetylene. Aldehydes are electroreduced to alcohols and deoxygenated intermediates,” said researchers in the study.

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