Researchers have developed a catalyst capable of producing ethanol from hydrogen and CO2. This has the potential to transform CO2 into a valuable industrial resource. Researchers are now focusing on making the catalyst more affordable and proving that it is effective on a larger scale.
Most people recognise that CO2 accelerates climate change: humans emit huge quantities of CO2 that profoundly affect the climate, nature and the planet.
In recent years, both politicians and researchers have proposed solutions to address this, with most aiming to reducing CO2 emissions.
However, emitted CO2 can be captured and converted into useful products rather than reducing emissions. Researchers have achieved this in a new study by developing a catalyst that converts CO2 and hydrogen into ethanol.
The research has been published in two articles in the Journal of the American Chemical Society and Angewandte Chemie.
“Ethanol is desirable because it can be used in many industries, such as producing fuel and the pharmaceutical industry. The ethanol used today comes from crops that are grown and harvested and is expensive. This is an opportunity to turn CO2 into a valuable resource, which can hopefully be an incentive for industry not to emit CO2 but to capture it, transform it and make money from it,” explains a researcher behind the study, Matteo Cargnello, Associate Professor, Department of Chemical Engineering, Stanford University, Palo Alto, California, United States.
Simplifying revenue-generating opportunities for industry
Matteo Cargnello and colleagues are not the first to explore capturing and converting CO2 into industrially useful substances. Previous research has also delved into this.
However, a common challenge is that the chemical processes involved in converting CO2 are often not very selective. As a result, the output is frequently a mixture of various substances that must be separated before they can be used in industry. This separation process is both difficult and costly, making it less appealing to CO2-emitting industries.
Thus, a different approach is needed that enables the selective conversion of CO2 into a pure product that can be either used or sold.
“We aim to close the CO2 cycle so that we do not produce more but instead circulate the CO2 that is already out there,” says Matteo Cargnello.
Developing a special catalyst
Mixing CO2 and hydrogen to produce ethanol is not as simple as combining them in a flask and shaking it. The process requires a catalyst to initiate the chemical reaction. A catalyst facilitates a reaction between two other substances.
The researchers therefore sought catalysts that could make the CO2 and hydrogen mixture react to form primarily ethanol rather than a mixture of various substances.
They found that they needed a catalyst capable of producing both methane and methanol, which could then react to form ethanol.
This led to identifying ruthenium and indium as highly effective catalysts for converting CO2 into methane and methanol, respectively. They therefore designed a nanoscale ruthenium-indium-oxide catalyst.
“We have worked in this field for a long time and on converting CO2 into other types of industrially useful chemicals, but ethanol is particularly valuable, and the effect on CO2 emissions could be massive,” says Matteo Cargnello.
Producing 70% ethanol
In the next phase of their research, the team tested whether their new catalyst, a fine powder, could produce ethanol from CO2 and hydrogen. They used a closed metal cylinder, applying pressure (600 kPa) and heat (225°C) to accelerate the chemical process.
They then analysed the gas emitted from the cylinder. Initially, the experiments only produced methanol. However, as the researchers refined the catalyst, it began to produce more ethanol. Eventually, the reaction resulted in gas that was 70% ethanol.
“This is our great discovery. With our catalyst, we directed the chemical process and achieved the desired result,” notes Matteo Cargnello, adding that the ethanol must be separated from water vapour, but this is easy. As a result, the yield can increase to 95% ethanol, which aligns with distillation standards.
Reducing costs and scaling up
Although the researchers demonstrated that their catalyst can convert CO2 into ethanol, their work is far from complete.
Ruthenium and indium are rare and expensive metals, so using the developed catalyst is not a profitable venture.
The next step for the researchers is to determine how to create a catalyst with similar properties using more readily available and cost-effective transition metals.
In addition, the researchers aim to develop a system that can be integrated into chimneys, capturing CO2 directly at the emission source, converting it and capturing it as ethanol.
Matteo Cargnello hopes to have a prototype ready in about five years.
“We hypothesise that we can achieve this using less expensive metals and can scale up the process. Our goal is that the discovery will be not only academically relevant but also scalable and applicable to industry,” he concludes.
