Catalysts, which are used in 95% of industrial processes, can eliminate pollution from gases emitted by vehicles with combustion engines. They are substances that speed up chemical reactions and the human body has hundreds of them in the form of enzymes. From the point of view of energy, the role of a catalyst is to reduce the amount of energy required to trigger these reactions.

A team of researchers from the University of Barcelona (UB), the Universitat Politècnica de Catalunya (UPC) and the ALBA Synchrotron has just discovered that atoms react differently depending on the characteristics of the catalyst that is used. The study is a very important step forward in the design of new catalysts with applications in the field of energy and the elimination of pollutant gases.

The study was published on the 31st October, in the journal Science. The paper is signed by the researcher Inma Angurell, from the Department of Inorganic Chemistry of UB; Jordi Llorca, leader to the study and researcher at the Centre for Research in NanoEngineering (CRnE) and the Institute of Energy Technologies (INTE) —both centres belong to the UPC—; Núria J. Divins, PhD student at UPC, and researchers Carlos Escudero and Virginia Pérez Dieste, from the ALBA Synchrotron Light Source.

Custom-made catalysts

The catalyst chosen by researchers contained metal (rhodium and palladium) nanoparticles prepared by the Dendrimers and Molecular Polygons Group at the UB. The nanoparticles were fixed to a ceria support. This catalyst is very effective at producing hydrogen, a product that could replace fossil fuels before they are depleted and allow the current energy model to be changed in favour of a more sustainable and environmentally friendly one.

In this sense, the results of the study pave the way for obtaining hydrogen in the most efficient possible way, that is, from water and ethanol, the latter of which is a renewable, inexpensive resource that is easily obtained from forestry and agricultural waste. A metaphor for understanding this more efficient process would be finding the best way to cross a mountain: the shortest route is to climb up one side and then down the other, but this option is the one that requires the greatest amount of energy. If we find a better way to cross the mountain, although it may seem longer it will require less energy and therefore we will get across the mountain faster.

One step in finding the way is to learn how atoms and nanoparticles really behave in a catalyst and whether they always behave in the same way. For this experiment, researchers used the CIRCE beamline of the ALBA synchrotron, specifically near ambient pressure photoemission (NAPP). The ALBA synchrotron became operational in September 2013 and this was its first experiment.

To date, researchers had been able to ascertain what happens when the ethanol and water molecules are heated to 550 degrees Celsius, in the X-ray photoelectron spectroscopy chamber at CRnE-UPC. Thanks to the ALBA Synchrotron, however, researchers were able to pinpoint more accurately the movement of atoms in the nanoparticles during chemical reactions; they found that these nanoparticles behave differently depending on the characteristics of the catalytic support, which can affect their composition, form and nanostructure.

This discovery paves the way for custom-made catalysts that are more efficient because they can be developed or adapted according to the process for which they are required.

In the case of hydrogen, the research team discovered that to produce it the atoms in the catalyst need to be in certain positions. These positions allow electrons to be exchanged between the metal nanoparticles and the ceria support appropriately when they break and form new chemical bonds to produce hydrogen.

Concerning vehicles that use combustion engines (cars, motorcycles, planes, ships, etc.) with ceria-supported catalysts, new nanostructures could be designed or existing ones adapted to make them more energy efficient.

Reference article:
N. J. Divins; I. Angurell, C. Escudero, V. Pérez Dieste, J. Llorca. “Influence of the support on surface rearrangements of bimetallic nanoparticles in real catalysts”. Science, 31 October 2014. DOI: 10.1126/science.1258106

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