Nanoscale magnets separate catalysts

Scientists are using magnetic nanoparticles to separate and reuse catalysts from multi-step chemical reactions carried out in a single vessel.

By combining the new magnetic separation process with traditional gravity-driven separation, the technique could lead to more efficient production of specialty chemicals and a reduction in waste normally produced by separation processes.

"We have developed a way to do multiple reactions in a single vessel while being able to recover the catalysts in pure form for reuse," said Christopher W. Jones, an associate professor in the School of Chemical & Biomolecular Engineering at the Georgia Institute of Technology. "By doing the reactions in a single vessel, we can cut out two or three separation steps to provide both an economic advantage and an environmentally benign process."

Separations using magnetic catalysts have been limited by a tendency of the nanoparticles to clump together because of their magnetic attraction for one another. The clumping dramatically reduces their catalytic activity.

To overcome this problem, the Georgia Tech researchers used nanometre-scale magnetic particles that are so small (5 to 20 nanometres in diameter) that they no longer exhibit a net magnetic attraction. But these superparamagnetic nanoparticles, developed by the research group of Z. John Zhang in Georgia Tech's School of Chemistry and Biochemistry, are attracted to an external magnetic source, providing a mechanism for separating them in pure form from the reaction vessel.

"These magnetic nanoparticles work well as catalyst supports because they are very small and so have a high surface area that allows creation of many catalytic sites for high activity levels," Jones said. "Because they are superparamagnetic, they remain suspended in the reaction vessel and do not clump together until a magnetic source is brought near them."

The new technique would allow more than one catalyst to be recovered and reused at the end of the one-pot reactions. Jones envisions the new process being used in the specialty chemical and pharmaceutical industries which produce relatively small volumes of high-value chemicals. For the future, Jones and Zhang envision using multiple catalysts whose magnetic properties would be tuned for activation at different temperatures, allowing them to be separated independently.