Researchers at the University of Illinois Urbana-Champaign have developed a groundbreaking method to recycle platinum catalysts used in the production of valuable silicone materials.
Homogenous catalysts made of valuable metals like platinum are commonly used in hydrosilylation – a key chemistry used in the production of silicones. Recycling these catalysts offers cost saving benefits, but doing so via traditional methods is costly and difficult due to the low concentration of platinum, the high viscosity and boiling point of hydrosilylation products, and the catalysts’ propensity for deactivation.
In a new study led by chemical and biomolecular engineering professor Xiao Su and published in JACS Au, engineers detail a method to recover these catalysts using specially designed molecular attachments and advanced electrochemical separation technologies.
“Most electrochemistry works for things that are very polar, things that are conductive – for example, aqueous solutions such as water,” Su said. “It was very challenging to move towards a real industrial process in which everything is apolar, like oils.”
Their first step was to preserve the activity in the catalyst after the reaction so that it could be used again. To achieve this, the team introduced a special molecule – an olefin ligand – to attach to the platinum atom. The ligand attachment prevents particle aggregation, a primary cause of deactivation, and preserves the catalyst’s effectiveness after use. Next, the team created a redox-active polymer to coat the electrodes used during the capture process. The coating is activated by electrochemistry and introduced into the reaction mixture, which can then bind the catalysts – even in non-conductive media – and release them into a separate solution from which they can be easily recovered.
“It's a little bit like a filter,” Su explained. “It binds the platinum catalyst, which is now stable, and then we bring it to another solution and release it so it can be used again. So we have this catch and release system that basically ‘catches’ the platinum from the product solution and then ‘releases’ it into a fresh reaction media. And this allows you to keep using the catalyst.”
Using this technique, the researchers were able to retain nearly 100 percent of the activity of the catalyst and achieve close to 90 percent release efficiency, even in the difficult hydrosilylation conditions.
Su and his colleagues collaborated on the project with Dow researchers Miao Wang and Evan Bergman through the Dow University Partnership Initiative. This partnership enabled them to develop their method using real-world industrial processes.
“We've demonstrated before that you can recycle catalysts from conductive solutions like water, but this is the first time where we're actually doing it with real industrial processes which have a lot of nonpolar solvents,” Su said. “We worked with Dow’s R&D teams – the industrial researchers that are actually working on the process for making the silicones – so we had a lot of real feedback on practical issues that industry faces.”
Recycling the catalysts offers more than just economic benefits: it reduces overall waste and eliminates the need to mine for new platinum, a process that is both costly and environmentally damaging. Su envisions this sustainable approach being useful for chemical manufacturing more broadly.
“I think it's an exciting new paradigm shift to really think about the whole process as a circularity problem: this element goes into waste, and then you can fish it out again and use it back in the process,” Su said. “Not only are you not having this metal in the waste, but you're bringing back value and saving the primary mining of these elements. So overall, your supply chain is more resilient.”
Illinois Ph.D. students Jemin Jeon and Ching-Hsiu Chung, and undergraduate Sean Roh contributed to this project. Su is also affiliated with civil and environmental engineering in The Grainger College of Engineering, chemistry in the College of Liberal Arts & Sciences and the Beckman Institute for Advanced Science and Technology at the U. of I.
Editor’s notes:
To reach Xiao Su: (217) 300-0134, x2su@illinois.edu
The paper, Olefin-Assisted Electrochemical Recycling of Homogeneous Hydrosilylation Catalysts in Nonpolar Media, is available online at pubs.acs.org/doi/10.1021/jacsau.4c01071