MIT Chemists Design New Light-Powered Catalysts That Could Help Manufacturing

 
MIT chemists have developed a novel photoredox catalyst that may make it easier to incorporate light-driven reactions into continuous flow manufacturing processes. As depicted in this digital artwork, polymer catalysts could be used to coat tubing and perform chemical transformations on reactants as they flow through the tube. Photographer: Richard Liu
MIT chemists have developed a novel photoredox catalyst that may make it easier to incorporate light-driven reactions into continuous flow manufacturing processes. As depicted in this digital artwork, polymer catalysts could be used to coat tubing and perform chemical transformations on reactants as they flow through the tube. Credit:Richard Liu

Catalysts could act on chemicals flowing through plastic tubing, assisting in the synthesis of drugs and other compounds.

MIT chemists have developed a new type of photoredox catalyst that may make it easier to incorporate light-driven reactions into continuous flow manufacturing processes. The key is their insolubility, which allows them to be reused repeatedly.


Light-driven chemical reactions are a valuable tool for chemists working on novel methods of producing pharmaceuticals and other important molecules. Photoredox catalysts, which absorb light and transfer the energy to a chemical reaction, are required to harness this light energy.

MIT chemists have developed a new photoredox catalyst that may make it easier to incorporate light-driven reactions into manufacturing processes. Unlike most existing photoredox catalysts, the new class of materials is insoluble, allowing them to be reused. Catalysts of this type could be used to coat tubing and perform chemical transformations on reactants as they pass through it.

"One of the most difficult challenges to overcome in order to use photoredox catalysis in manufacturing is the ability to recycle the catalyst." "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 one of the study's co-lead authors.


The new catalysts, which can be tailored to perform a wide range of reactions, could also be incorporated into other materials such as textiles or particles.

A catalyst is a substance that increases the rate of a chemical reaction. Catalysis is the use of a catalyst to speed up a reaction. Photoredox catalysts work by absorbing photons and then converting the light energy into chemical energy.

Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT, is the paper's senior author, and it was published in the journal Nature Communications on May 27, 2022. The paper is also co-authored by Sheng Guo, an MIT research scientist, and Shao-Xiong Lennon Luo, an MIT graduate student.

Hybrid Materials

Photoredox catalysts work by absorbing photons and then converting that light energy into chemical energy, similar to how chlorophyll in plant cells absorbs solar energy and uses it to build sugar molecules.


Chemists have created two main types of photoredox catalysts: homogeneous and heterogeneous catalysts. Organic dyes or light-absorbing metal complexes are commonly used in homogeneous catalysts. These catalysts are simple to tune to perform a specific reaction, but they dissolve in the solution where the reaction occurs. This means that they cannot be easily removed and reused.

In contrast, heterogeneous catalysts are solid minerals or crystalline materials that form sheets or 3D structures. Because these materials do not dissolve, they can be reused. These catalysts, however, are more difficult to tune to achieve the desired reaction.


The researchers decided to embed the dyes that make up homogeneous catalysts into a solid polymer to combine the benefits of both types of catalysts. The researchers adapted a plastic-like polymer with tiny pores that they had previously developed for gas separations for this application. The researchers demonstrated that they could incorporate approximately a dozen different homogeneous catalysts into their new hybrid material in this study, but they believe it could work with many more.


"These hybrid catalysts have the recyclability and durability of heterogeneous catalysts as well as the precise tunability of homogeneous catalysts," says Liu. "You can incorporate the dye without losing its chemical activity, so you can pick and choose from the tens of thousands of known photoredox reactions to get an insoluble equivalent of the catalyst you need."


The researchers discovered that incorporating the catalysts into polymers made them more efficient. One reason for this is that reactant molecules can be held in the pores of the polymer, ready to react. Furthermore, light energy can easily travel along the polymer to find the reactants that are waiting.

Swager explains, "The new polymers bind molecules from solution and effectively preconcentrate them for reaction." "The excited states can also move quickly throughout the polymer." The combination of excited state mobility and reactant partitioning in the polymer allows for faster and more efficient reactions than are possible in pure solution processes."

Higher Efficiency

The researchers also demonstrated that depending on the application, they could tune the physical properties of the polymer backbone, such as thickness and porosity.

Swager explains, "The new polymers bind molecules from solution and effectively preconcentrate them for reaction." "The excited states can also move quickly throughout the polymer." The combination of excited state mobility and reactant partitioning in the polymer allows for faster and more efficient reactions than are possible in pure solution processes."


The researchers also demonstrated that depending on the application, they could tune the physical properties of the polymer backbone, such as thickness and porosity.


"The idea is to coat a tube with the catalyst so that you can flow your reaction through the tube while the catalyst remains in place." "You never get the catalyst in the product that way, and you can also get a lot higher efficiency," Liu says.


Catalysts could also be used to coat magnetic beads, making them easier to remove from a solution once the reaction is complete or to coat reaction vials or textiles. The researchers are now working on incorporating a wider range of catalysts into their polymers, as well as engineering the polymers to optimize them for various applications.

Source :

Richard Y. Liu, Sheng Guo, Shao-Xiong Lennon Luo, and Timothy M. Swager, "Solution-processable microporous polymer platform for heterogenization of diverse photoredox catalysts," Nature Communications, 27 May 2022.

DOI: 10.1038/s41467-022-29811-6

The National Science Foundation and the KAUST Sensor Initiative funded the study.

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