The 'inert' material everyone ignored just became the key to efficient CO2 fuel

Every industrial catalyst has a dirty secret: most of the metal atoms inside the particles aren't doing any work. They're along for the ride while reactions happen only at the surface. A team from ETH Zurich has turned that limitation into an opportunity with a new catalyst design that uses individual indium atoms on hafnium oxide to convert CO2 into methanol more efficiently than the nanoparticles that have dominated the field for a decade.

The work, published in Nature Nanotechnology, challenges a long-standing assumption in catalysis research. For years, scientists believed single indium atoms were less active than clusters of indium atoms for methanol synthesis. The ETH team shows the opposite is true when you pair isolated atoms with the right support material.

"Indium has already been used in this catalyst for over a decade," said Javier Pérez-Ramírez, professor of catalysis engineering at ETH Zurich, who has been working on CO2-to-methanol since 2010, according to ETH Zurich's news release. "In our study, we show that isolated indium atoms on hafnium oxide allow more efficient CO2-based methanol synthesis than indium in the form of nanoparticles containing large numbers of atoms."

The support material turned out to be the key. Hafnium oxide—widely used in electronics and ferroelectrics because of its wide bandgap—was presumed catalytically inert. The ETH team transferred a concept from electronics and showed that a dielectric material long considered chemically inactive can actively participate in interfacial catalysis, enabling efficient reactant activation and facilitating intermediate hydrogenation around the isolated indium sites.

The catalyst is produced through flame spray pyrolysis, where starting materials are combusted at temperatures between 2,000 and 3,000 degrees Celsius and then rapidly cooled. Under these conditions, indium atoms remain on the surface and become stably incorporated into the heat-resistant hafnium oxide support. The resulting material can withstand the demanding conditions required for methanol synthesis: temperatures up to 300 degrees Celsius and pressures up to 50 times normal atmospheric pressure.

The old nanoparticle catalysts were also a black box for researchers. While reactions occurred only at surface atoms, measurement signals came from atoms throughout the particle, many of which didn't participate in the reaction at all. With single-atom catalysts, the researchers can analyze reaction mechanisms with far fewer interfering signals—opening the door to more deliberate, rational catalyst design rather than trial-and-error optimization, as described in a behind-the-paper blog post on the research.

The implications extend beyond indium. The researchers demonstrated that hafnium oxide as a support also enhances the CO2 hydrogenation performance of zinc and gallium single atoms by more than two orders of magnitude. "These results show the broad application of HfO2, justifying its role as an efficient and robust support for advancing sustainable chemical transformation and single-atom catalysis," the team writes.

Pérez-Ramírez collaborates closely with industry and holds several patents in this area. If the hydrogen and energy used in the process come from renewable sources, methanol production using this catalyst could become climate neutral—capturing CO2 from the atmosphere and converting it into a versatile raw material for fuels and chemicals.

Methanol has been called "the Swiss army knife of chemistry": a precursor for plastics, fuels, and a wide range of chemical products. The ability to produce it more efficiently from captured CO2 could accelerate the shift toward sustainable chemical manufacturing and provide a scalable route to store renewable energy in liquid form.

The research team included scientists from multiple Swiss institutions, reflecting what Pérez-Ramírez called a critical network of interdisciplinary expertise in catalysis research that has emerged in Switzerland over recent years.