Magnetic nanomaterials in catalysis: advanced catalysts for magnetic separation and beyond

While magnetic separation techniques have long been in use, intensive research into superparamagnetic nanomaterials has accelerated the development of magnetically recoverable catalysts. Preparation techniques are currently undergoing rapid development and magnetic separation has been studied to facilitate the handling and recovery of enzyme, organo-, metal complex-, and nanoparticle-catalysts. In this article, we emphasize the preparation of support materials, because the choice of the correct support and the immobilization strategy are of primary importance in the development of high-quality magnetically recoverable catalysts. We summarize the representative methods for the synthesis of well-defined uncoated and coated magnetic nanomaterials. Recent scientific progress on the preparation of surface-modified magnetic nanomaterials and the most common synthetic approaches to attach or immobilize non-magnetic catalytic active phases onto magnetic nanomaterials were discussed. Moreover, better control and understanding of the magnetic properties is now an essential tool not only in selecting the best preparation route for recoverable catalysts, but also for designing reactors (e.g., magnetic fluidized-bed reactors) and for developing magnetic field-driven technologies (e.g., changes in the catalytic output operating under an applied magnetic field).