Scientists at ETH Zürich and oil and gas company Total have developed a new catalyst that efficiently converts CO₂ and hydrogen directly into methanol. Offering realistic market potential, the technology paves the way for the sustainable production of fuels and chemicals.

ETH Zürich and Total have jointly filed a patent for the technology. Total now plans to scale up the approach and potentially implement the technology in a demonstration unit over the next few years. An open-access paper on the work is published in Nature Communications.

The global economy still relies on the fossil carbon sources of petroleum, natural gas and coal, not just to produce fuel, but also as a raw material used by the chemical industry to manufacture plastics and countless other chemical compounds. Although efforts have been made for some time to find ways of manufacturing liquid fuels and chemical products from alternative, sustainable resources, these have not yet progressed beyond niche applications.

Methanol is regarded as a commodity or bulk chemical. It is possible to convert it into fuels and a wide variety of chemical products, including those that today are mainly based on fossil resources. Moreover, methanol itself has the potential to be utilized as a propellant, in methanol fuel cells, for example.

The core of the new approach is a chemical catalyst based on indium oxide, which was developed by Javier Pérez-Ramírez, Professor of Catalysis Engineering at ETH Zürich, and his team. Just a few years ago, the team successfully demonstrated in experiments that indium oxide (In₂O₃) was capable of catalyzing the necessary chemical reaction. Even at the time, it was encouraging that doing so generated virtually only methanol and almost no by-products other than water. The catalyst also proved to be highly stable. However, indium oxide was not sufficiently active as a catalyst; the large quantities needed prevent it from being a commercially viable option.

The team of scientists have now succeeded in boosting the activity of the catalyst significantly, without affecting its selectivity or stability. They achieved this by treating the indium oxide with a small quantity of palladium.

Recently, In₂O₃ was discovered as a highly selective and stable catalyst for green methanol production from CO₂. Activity boosting by promotion with palladium, an efficient H₂-splitter, was partially successful since palladium nanoparticles mediate the parasitic reverse water–gas shift reaction, reducing selectivity, and sinter or alloy with indium, limiting metal utilization and robustness.

Here, we show that the precise palladium atoms architecture reached by controlled co-precipitation eliminates these limitations. Palladium atoms replacing indium atoms in the active In₃O₅ ensemble attract additional palladium atoms deposited onto the surface forming low-nuclearity clusters, which foster H₂ activation and remain unaltered, enabling record productivities for 500 h.

—Frei et al.

Pérez-Ramírez points out that, with the aid of advanced analytical and theoretical methods, catalysis may now be considered nanotechnology, and in fact, the project clearly shows this to be the case.

The CO₂ may be extracted from the atmosphere or—more simply and efficiently—from the exhaust discharged by combustion power plants. Even if fuels are synthesized from the methanol and subsequently combusted, the CO₂ is recycled and thus the carbon cycle is closed.

Producing the second raw material, hydrogen, requires electricity. However, the scientists point out that if this electricity comes from renewable sources such as wind, solar or hydropower energy, it can be used to make sustainable methanol and thus sustainable chemicals and fuels.

Compared to other methods that are currently being applied to produce green fuels, Pérez-Ramírez says, this technology has the great advantage that it is almost ready for the market.

Resources

• Frei MS, Mondelli C, Garcia-Muelas R, Kley KS, Puértolas B, López N, Safonova O, Stewart JA, Curulla Ferré D, Pérez-Ramírez J (2019) “Atomic-scale engineering of indium oxide promotion by palladium for methanol production via CO₂ hydrogenation.” Nature Communications, doi: 10.1038/s41467-019-11349-9