Novel catalysis scheme is sustainable, affordable and recordable

Researchers at the University of Bonn have developed a novel catalysis scheme that enables chemical reactions that were previously virtually impossible, without the need for rare or precious metals. The researchers recorded the exact course of the catalysis in a kind of high-speed film, while their results have been published in the journal Angewandte Chemie.

In order for many chemical reactions to proceed, you first have to supply them with enough energy. A catalyst reduces the amount of energy required, meaning the reaction is easier and faster. As noted by Bonn’s Prof Dr Andreas Gansäuer, “Some reactions are even only made possible by the use of catalysts.”

Gansäuer has been working for years on how to simplify the production of certain carbon compounds. The use of catalysts is usually required here; the problem is that the ‘reaction accelerators’ often consist of rare and precious metals such as platinum, palladium or iridium.

“We usually use titanium compounds instead,” Gansäuer said. “This is because titanium is one of the most abundant elements in the Earth’s crust and is also completely non-toxic.”

However, titanium-based catalysts often still need a companion to be able to accelerate chemical reactions. Most often, this is also a metal. It activates the catalyst, is consumed in the reaction and generates by-products as waste.

“This is both costly and not very sustainable,” said Gansäuer’s colleague Prof Dr Peter Vöhringer. “However, there have been attempts for some time to achieve this activation in a different way: by irradiating the catalyst with light. We have now implemented this idea. At the same time we filmed, in a sense, the processes that occur during activation and catalysis.”

The ‘high-speed camera’ used by the researchers was a spectrometer — a complex instrument that can be used to determine what a molecule looks like at a certain point in time. For this to work, you also need a flash. To do this, the researchers use a laser that switches on and off continuously. The bright moments each last only a few hundred femtoseconds (a millionth of a billionth of a second); the catalysis process is thus broken down into a sequence of individual images.

“This allows us to visualise ultrafast processes,” said Vöhringer, who is a specialist in this method.

Not all molecules can be filmed easily, so the scientists had to make some modifications to the titanium catalyst they usually use. Their experiments show that the compound can be activated by light and is then able to catalyse a specific form of redox reactions. In redox reactions, electrons are passed from one reactant to the other.

“This process is facilitated by the activated catalyst,” Gansäuer said. “This allows us, for example, to produce compounds that serve as starting materials for many important drugs.”

Jonas Schmidt, who is doing his doctorate in Vöhringer’s research group, explained exactly what happens during light activation: “Electrons resemble a compass needle that points in a certain direction; this spin changes as a result of irradiation.” Figuratively speaking, the titanium compound thus becomes ‘greedier’ to accept an electron. When it does, it starts the redox reaction.

The method is already enabling the researchers to carry out chemical reactions that were hardly feasible before, but thanks to the insights they have gained, they can now further optimise the catalyst. It also highlights the fruits that can come from collaboration between two research groups with completely different methodological backgrounds — organic chemistry on the one hand, and laser and molecular physics on the other.

Image caption: Pictured at the experimental set-up is Prof Dr Peter Vöhringer, Dr Luis Domenianni, Jonas Schmidt and Prof Dr Andreas Gansäuer. Photo ©Volker Lannert/University of Bonn.