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The EU industrial sector consumes around 70 billion cubic metres of natural gas every year. Around 15 % of this is used as chemical feedstock, to make everything from fertilisers to flavourings, through a process known as heterogenous catalysis.
“People tend not to think about it, but we are hugely dependent on this technology,” notes CATACOAT project coordinator Jeremy Scott Luterbacher from the Swiss Federal Institute of Technology Lausanne.
“There is not a single molecule of petrol, nor a single molecule of plastic, that has not at some point interacted with a heterogenous catalyst (usually a metal oxide). If we were to stop heterogenous catalysis, society would stop functioning extremely quickly.”
Protecting catalysts for renewable feedstock
While fossil fuels are the feedstock for many industrial chemicals, there have been concerted efforts to move towards using renewable sources of carbon, such as plants. However, undesirable reactions between the heterogenous catalysts and these replacement feedstocks can make them troublesome to use. Heterogeneous catalysts tend to be sensitive to water, often found in plant-based feedstocks, and contain metals that leach into this water during processing.
The aim of the CATACOAT project, supported by the European Research Council, was to address this challenge by coating catalytic molecules in a protective layer, to make them usable in oxygen-rich, watery compounds. “The basic idea was relatively simple,” says Luterbacher. “We wanted to take conventional catalytic materials that are fairly sensitive to renewable feedstock conditions, and make them more resistant.”
A key challenge was that while these catalytic molecules required protection from the feedstock, they still needed to be in close contact with it to work. This meant that the protective layer needed to be porous and incredibly thin – a layer of 5 to 50 atoms thick. To achieve this, the team developed and trialled new techniques to deposit thin layers of metal oxides.
“We were able to show that we could provide armour for these catalysts, and that these could then be used to process renewable carbon feedstock from plants,” adds Luterbacher. “Conventional catalysts would normally have been destroyed under these conditions.”
Control of catalysts at the atomic level
While succeeding in this primary objective, the project team also made some unexpected discoveries. “A lot of our focus was on trying to control the layering of the coating,” says Luterbacher. “In doing so, we developed a very interesting approach.”
As the team was building a protective layer, atom by atom, they discovered that they could grow these layers from a single ‘anchor’ on the surface of the target molecule, to create a sort of atomic cluster, or island. While this work is still in its infancy, the technique could give scientists greater control of molecules at the atomic level, enabling them to shape better, more effective catalysts.
“We think this could be a generalisable tool, with many industrial applications,” remarks Luterbacher. “Some of these applications might work, some won’t. We can’t say right now, but this is an exciting development.”
Perfumes, plastics and more potential uses
The CATACOAT project has fed into a commercial venture, established previously by Luterbacher’s lab, to bring their cutting-edge research to market. “This spin-off is about finding ways of making renewable chemicals from plants, and substituting chemicals based on fossil fuels,” he explains. “Potential end uses include flavours and fragrances, as well as biomaterials and bioplastics.”
Luterbacher also believes that the project has enabled his lab to build and combine expertise in both heterogenous catalysis and plant chemistry. In the long run, this will help industry to find ways of moving towards renewable chemicals. “This is why basic research like this is so important,” he adds. “We need to invest in ideas where the results might not necessarily be immediately usable, but could be critical later.”