Scientists led by EPFL, the University of Copenhagen, and Shanghai University have developed a copper catalyst that can efficiently convert carbon dioxide into acetaldehyde, a key chemical used in manufacturing. The breakthrough offers a green alternative to fossil-fuel-based processes.

Acetaldehyde is a vital chemical used in making everything from perfumes to plastics. For automotive manufacturing, acetaldehyde is used in:

• Polymer Resins and Coatings. Acetaldehyde is a precursor in the production of pentaerythritol, which is used to make alkyd resins for paints and coatings. These resins are crucial for providing durable, corrosion-resistant finishes on automotive parts like body panels and chassis components.

• Adhesives and Sealants. It is used in the synthesis of polyvinyl acetate, which is a common polymer in adhesives. These adhesives are used in the assembly of automotive parts, providing strong bonding capabilities for both interior and exterior applications.

• Plasticizers. Acetaldehyde can be used in the manufacture of various plasticizers, which are essential in making flexible and durable plastics used in automotive interiors, such as dashboard panels or seat covers. The production of n-butyraldehyde from acetaldehyde, which is then used to make plasticizers, is particularly relevant.

• Synthetic Rubber and Plastics. Acetaldehyde serves as an intermediate in the production of synthetic rubber and other plastics, which are integral to many automotive parts due to their durability, elasticity, and resistance to wear.

• Fuel Additives. Although not directly, acetaldehyde can be part of processes leading to the production of certain fuel additives or components. Its role in the synthesis of acetic acid, which can be further used in fuel additives or in the production of biofuels, indirectly supports automotive manufacturing.

Today, acetaldehyde production largely relies on ethylene, a petrochemical. Increasing environmental concerns are pushing the chemical industry to reduce its reliance on fossil fuels, so scientists have been searching for greener ways to produce acetaldehyde.

Currently, acetaldehyde is produced through the Wacker process, a chemical synthesis method that uses ethylene from oil and natural gas with other chemicals such as strong acids, i.e. hydrochloric acid. The Wacker process not only has a large carbon footprint but is resource-heavy and is unsustainable in the long run.

A promising solution to this problem is the electrochemical reduction of carbon dioxide (CO₂) into useful products. As CO₂ is a waste product that contributes to global warming, this approach tackles two environmental issues at once: it reduces CO₂ emissions and creates valuable chemicals.

Copper-based catalysts have shown potential for this transformation, but so far, they’ve struggled with low selectivity. Now, scientists of a public-private consortium, led by Cedric David Koolen in the group of Andreas Züttel at EPFL, Jack K. Pedersen at the University of Copenhagen, and Wen Luo at Shanghai University have developed a novel copper-based catalyst that can selectively convert CO₂ into acetaldehyde with an efficiency of 92%.

The research, published in Nature Synthesis, provides a greener and more sustainable way to produce acetaldehyde, and could replace the Wacker process. Moreover, the catalyst is scalable and cost-effective, opening the door for industrial applications.

The researchers began by synthesizing tiny clusters of copper particles, each about 1.6 nanometers in size, using a method called spark ablation. This technique involves vaporizing copper electrodes in an inert gas environment, and allowed the scientists to precisely control particle sizes. The copper clusters were then immobilized on carbon supports to create a stable and reusable catalyst.

In the lab, the team tested the catalyst’s performance by running it through a series of electrochemical reactions with CO₂ in a controlled environment. Using a synchrotron—a large scale facility that generates a very bright light source—the team ensured that the copper clusters were actively converting CO₂ to acetaldehyde by a technique called X-ray absorption spectroscopy.

The results were remarkable. The copper clusters achieved 92% selectivity for acetaldehyde at a relatively low voltage, which is essential for energy efficiency. In a 30-hour stress test, the catalyst demonstrated high stability, maintaining its performance across multiple cycles. The researchers also found that the copper particles retained their metallic nature throughout the reaction, which contributes to the catalyst’s longevity.

What was really surprising to us was that the copper remained metallic, even after removal of the potential and exposure to air. Copper usually oxidizes like crazy, especially copper that small. But in our case, an oxide shell formed around the cluster protecting the core from further oxidation. And this explains the recyclability of the material. Fascinating chemistry.—co-lead author Wen Luo

Computational simulations showed that the copper clusters feature a specific configuration of atoms that promotes CO₂ molecules to bond and transform in a way that favors the production of acetaldehyde over other possible products, such as ethanol or methane.

The new copper catalyst is a significant step toward greener industrial chemistry. If scaled up, it could replace the Wacker process, reducing the need for petrochemicals and cutting down on CO₂ emissions. Since acetaldehyde is a building block for many other chemicals, this research has the potential to transform multiple industries, from pharmaceuticals to agriculture.

Resources

• Koolen, C. D., Pedersen, J. K., Zijlstra, B., Winzely, M., Zhang, J., Pfeiffer, T. V., Vrijburg, W., Li, M., Agarwal, A., Akbari, Z., Kuddusi, Y., Herranz, J., Safonova, O. V., Schmidt-Ott, A., Luo, W., Züttel, A. Scalable synthesis of Cu cluster catalysts via spark ablation for the highly selective electrochemical conversion of CO₂ to acetaldehyde. Nature Synthesis 03 January 2025.doi: 10.1038/s44160-024-00705-3