From CO₂ to acetaldehyde: new copper catalyst offers green alternative to fossil fuel-based processes

Acetaldehyde is an important chemical used in the production of everything from perfume to plastics. Currently, its production relies primarily on the petrochemical ethylene. However, growing environmental concerns have pushed the chemical industry to reduce its dependence on fossil fuels, and scientists have been searching for more environmentally friendly ways to produce acetaldehyde.

Currently, acetaldehyde is produced through the so-called Wacker process, a chemical synthesis method that uses ethylene from petroleum and natural gas and other chemicals such as strong acids such as hydrochloric acid. Not only does the Wacker process have a large carbon footprint, it is also resource intensive and unsustainable in the long term.

A promising solution to this problem is the electrochemical reduction of carbon dioxide (CO2) to produce useful products. Since CO2 is a waste product that contributes to global warming, this approach simultaneously addresses two environmental issues: reducing CO2 emissions and producing valuable chemicals.

Innovative catalyst for increased efficiency

Copper-based catalysts have shown potential for this transformation, but have so far suffered from low selectivity, i.e., the formation of a mixture of products rather than the desired acetaldehyde.

Now, scientists from a public-private consortium led by Cedric David Coolen in a group that includes Andreas Süttel of EPFL, Jacques K. Pedersen of the University of Copenhagen, and Wen Luo of Shanghai University have found that selectively converts CO2 to acetaldehyde with high efficiency.

This breakthrough technology, published in Nature Synthesis, offers a greener and more sustainable way to produce acetaldehyde and could replace the Wacker process. Additionally, the catalyst is scalable and cost-effective, opening the door to industrial applications.

“The Wacker process has remained virtually unchanged for the past 60 years. It’s still based on the same basic chemistry. It’s ripe for a green breakthrough,” Coolen said.

“Fascinating chemistry”

The researchers started by synthesizing small clusters of copper particles, each about 1.6 nanometers in size, using a method called spark ablation. The technique involved evaporating copper electrodes in an inert gas environment, allowing scientists to precisely control particle size. The copper clusters were then immobilized on a carbon support to create a stable and reusable catalyst.

In the lab, the researchers tested the catalyst’s performance by having it perform a series of electrochemical reactions with CO2 in a controlled environment. Using a synchrotron, a large-scale facility that produces extremely bright light sources, the researchers confirmed that the copper clusters were actively converting CO2 into acetaldehyde using a technique called X-ray absorption spectroscopy.

The results were amazing. The copper cluster achieved 92% selectivity toward acetaldehyde at relatively low voltage. This is essential for energy efficiency. During the 30-hour stress test, the catalyst showed high stability and maintained its performance over multiple cycles. The researchers also found that the copper particles retained their metallic properties throughout the reaction, contributing to the longevity of the catalyst.

“What was really surprising to us was that even after the potential was removed and exposed to air, the copper remained a metal,” said co-lead author Wen Luo. “Normally copper, especially copper this small, oxidizes violently. But in our case, an oxide shell formed around the cluster, protecting the core from further oxidation. This is what makes the material recyclable. It’s an interesting chemistry.”

key to success

Why did the new catalyst work so well? Computer simulations show that the copper clusters bind and convert CO2 molecules in a way that favors the production of acetaldehyde over other products such as ethanol and methane. It has been shown to feature a specific atomic configuration that promotes

“The great thing about our process is the fact that it can be applied to other catalyst systems,” says co-lead author Jack K. Pedersen. “Our computational framework allows us to quickly screen clusters to find promising properties. For CO2 reduction and water electrolysis, spark ablation can be used to easily produce new materials. and can be tested directly in the lab. It’s much faster than the typical test-learn-repeat cycle.”

The new copper catalyst is an important step towards greener industrial chemistry. Once scaled up, it could replace the Wacker process, reducing the need for petrochemicals and reducing CO2 emissions. Because acetaldehyde is a building block of many other chemicals, this research has the potential to transform multiple industries, from pharmaceuticals to agriculture.