An international team of researchers has developed a homogeneous catalytic process that converts methanol, carbon dioxide and hydrogen into ethanol using inexpensive and stable catalyst precursors.
Published in Royal Society of Chemistry's Catalysis Science & Technology , the study addresses a key challenge in efforts to transform captured carbon dioxide into useful chemicals. While ethanol can be produced from carbon dioxide and hydrogen, many existing homogeneous catalytic systems rely on expensive or complex catalyst precursors that can be difficult to deploy at industrial scale.
In the study – a collaboration between researchers from The University of Manchester, the Institute of Chemistry, Chinese Academy of Sciences, the University of Chinese Academy of Sciences, Tianjin University of Science and Technology, and Fuzhou University - the team designed a homogeneous catalytic system using commercially available ruthenium chloride hydrate and cobalt chloride hexahydrate. After activation with carbon monoxide, the catalyst converted methanol, carbon dioxide and hydrogen into ethanol under relatively mild reaction conditions of 170°C.
Under optimised conditions, the catalyst achieved an ethanol selectivity of 64.9% and an ethanol space-time yield of 3.9 g L⁻¹ h⁻¹, which the authors report is higher than previous ruthenium-cobalt catalyst systems used for this type of reaction.
Dr Jie Li , co-author and Senior Lecturer in the Centre for Process Integration, based in the Department of Chemical Engineering at The University of Manchester explains:
"One of the challenges in this area is developing catalytic systems that combine strong performance with practical considerations such as cost, stability and ease of handling. Our study shows that readily available catalyst precursors can be activated to drive ethanol production efficiently, while also offering advantages for storage, recycling and potential scale-up."
Ethanol is one of the world's most widely used chemicals. It is used in fuels, solvents, disinfectants and as a feedstock for manufacturing. Finding new ways to produce ethanol from carbon-containing waste streams could help support broader efforts to make chemical production less dependent on fossil resources. The study focused on a process in which methanol acts as a starting material and carbon dioxide provides an additional carbon source.
The team also investigated how the catalyst works. Their experiments showed that carbon dioxide is first converted into carbon monoxide through a reverse water gas shift reaction. The carbon monoxide then acts as an intermediate in forming ethanol. The researchers found that ruthenium and cobalt perform complementary roles, with ruthenium helping drive hydrogenation steps and cobalt promoting the carbon-carbon bond formation needed to build the ethanol molecule.
Beyond performance, the researchers assessed characteristics important for industrial use. The activated catalyst remained stable during storage tests and retained good activity after five recycling cycles. The catalyst system also uses precursor materials that are easier to obtain and store than many alternatives previously reported for similar reactions.
The work has already progressed to preliminary scale-up studies. The authors report that the catalyst maintained high activity and ethanol selectivity in larger-scale reactor (3 L). Based on these findings, the team proposed a process flow for producing ethanol from methanol, carbon dioxide and hydrogen, with catalyst recycling and recovery of unreacted materials built into the design.
Dr Li adds: "There is still further work to do before a process such as this could be implemented commercially. However, these results demonstrate a promising route that combines accessible catalyst materials with recyclability and strong performance, which are all important considerations when developing practical carbon utilisation technologies."
This international collaboration was funded by the National Key Research and Development Program of China (Grant No. 2024YFE0206500) from MOST International S&T Cooperation Centre.
Journal: Catalysis Science & Technology
Full title: Synthesis of ethanol via methanol homologation with CO₂ and H₂ using an industrially relevant Ru–Co catalyst
DOI: 10.1039/D6CY00285D
URL: https://doi.org/10.1039/d6cy00285d
