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Protector against air pollution is vulnerable to air

Catalyst research aims to make gasoline less polluting. It turns out that during experiments it is actually necessary to protect catalysts from air itself. Publication in The Journal of Physical Chemistry C on August 26.

We owe it to catalysts that nowadays gasoline is much less polluting than earlier. Crude oil contains the harmful substance sulfur, which refineries filter out in the process of turning oil into gasoline. They add hydrogen and for example the catalyst NiMoS2. The hydrogen removes a sulfur component of NiMoS2, giving the catalyst room to collect the sulfur from the oil.

Clean sample

To further improve the process, scientists research substances like NiMoS2. A small adaptation in the chemical composition could make it a more efficient catalyst. In such experiments it is important to know how to keep the studied sample free from external influences.

Harmful air

A group of physicists led by Joost Frenken (Leiden University) and Patricia Kooyman (University of Cape Town) together with TU Eindhoven have now shown that exposure to air is very harmful. ‘Oxygen molecules from the air oxidize the NiMoS2 catalyst particles, so that further studying the sample essentially produces no relevant information,’ says first author Marien Bremmer. ‘We noticed that the oxidation occurred extremely fast at first, but slowed down in the long-term. This indicates the formation of a shielding oxide ring.’


The research group used a high-resolution transmission electron microscope (HRTEM) to see that after 24 hours already twenty percent of each NiMoS2 particle is covered with oxygen. They describe the study in The Journal of Physical Chemistry C.


After 24 hours, a clean NiMoS2 particle (yellow-red) is already 20% covered with oxygen (blue spheres). In the subsequent period this process settles down, but a month later the coverage still has significantly increased.​



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