Engineering news
Researchers at the Massachusetts Institute of Technology have developed a a new type of catalyst called a photoredox catalyst, that can speed up chemical reactions in the pharmaceutical industry and others.
Unlike existing photoredox catalysts, this new class of materials is insoluble, so it can be used over and over again. It could be used to coat tubing and perform chemical transformations on substances as they pass through the tube.
“Being able to recycle the catalyst is one of the biggest challenges to overcome in terms of being able to use photoredox catalysis in manufacturing. We hope that by being able to do flow chemistry with an immobilized catalyst, we can provide a new way to do photoredox catalysis on larger scales,” says Richard Liu, an MIT postdoc and the joint lead author of the new study.
Photoredox catalysts absorb photons and then use that energy to power a chemical reaction, in a similar way to how chlorophyll in plant cells absorbs energy from the sun and uses it to build sugar molecules.
Chemists have developed two main classes of photoredox catalysts, which are known as homogeneous and heterogeneous catalysts. Homogeneous catalysts usually consist of organic dyes or light-absorbing metal complexes. These catalysts are easy to tune to perform a specific reaction, but the downside is that they dissolve in the solution where the reaction takes place. This means they can’t be easily removed and used again.
Heterogeneous catalysts, on the other hand, are solid minerals or crystalline materials that form sheets or 3D structures. These materials do not dissolve, so they can be used more than once. However, these catalysts are more difficult to tune to achieve a desired reaction.
The MIT researchers wanted to get the benefits of both types of catalysts, and so decided to try to embed the dyes that make up homogeneous catalysts into a solid polymer.
“These hybrid catalysts have the recyclability and durability of heterogeneous catalysts, but also the precise tunability of homogeneous catalysts,” Liu says. “You can incorporate the dye without losing its chemical activity, so, you can more or less pick from the tens of thousands of photoredox reactions that are already known and get an insoluble equivalent of the catalyst you need.”
The new catalysts could be tuned to perform many different types of reactions, and could also be incorporated into textiles or particles. In one example, the researchers showed they could make fluorinated polymers that would stick to fluorinated tubing, which is used for continuous flow manufacturing, where chemical reactants flow through a series of tubes while new ingredients are added.
It's currently difficult to incorporate photoredox reactions into these systems because catalysts get used up too quickly. Incorporating the new MIT-designed catalysts into the tubing used for this kind of manufacturing could allow photoredox reactions to be performed during continuous flow. The tubing is clear, allowing light from an LED to reach the catalysts and activate them.
“The idea is to have the catalyst coating a tube, so you can flow your reaction through the tube while the catalyst stays put. In that way, you never get the catalyst ending up in the product, and you can also get a lot higher efficiency,” Liu says.
The catalysts could also be used to coat magnetic beads, making them easier to pull out of a solution once the reaction is finished, or to coat reaction vials or textiles. The researchers are now working on incorporating a wider variety of catalysts into their polymers, and on engineering the polymers to optimise them for different possible applications.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.