Chapter 5: Metal Nanoparticles and Cyclodextrins for Catalytic Applications

This chapter has highlighted several historical roles of the cyclodextrin in catalysis using metal nanoparticles as active phase; whatever the nature of the catalyst, it means solvent-dispersed nanoparticles or nanoparticles immobilized on a support. Indeed, cyclodextrin as stabilizing agent of metal nanocatalyst has been widely studied since the first study of Komiyama and Hirai in 1983. The stability, the catalytic activity, and the recyclability of the resulting nanoparticles have been improved by using more complex cyclodextrin-based protective agents. From the first studies using native cyclodextrins to cyclodextrin-based polymers or rotaxanes, native and functionalized cyclodextrins have proven their ability to protect metal nanoparticles against agglomeration via different stabilizing properties (electrostatic, steric, and electrosteric). Most of the examples reported in this chapter clearly showed that
cyclodextrin-based systems have improved both the average size decrease and the dispersion of the metal nanoparticles in comparison to their free cyclodextrin controls leading to the enhancement of their catalytic activity. According to several studies, cyclodextrins could be also used as reducing agents of metal precursor by their sugar-like reducing properties.
Due to a dynamic organization at the surface of metal nanoparticles, the classical mass transfer property of cyclodextrins has also been exploited with solvent-dispersed nanoparticles or nanoparticles immobilized on a support. The catalytic activity is generally improved thanks to the inclusion complex formed between the substrate and the cyclodextrin via hydrophobic interactions. This inclusion complex could also, in some cases, improve the selectivity of the reaction by inhibiting some side reactions. Cyclodextrins could also serve as agent to get confining catalytic systems by forming supramolecular hydrogels where the metal nanoparticles can be embedded. This confinement could improve the selectivity of the reaction, the catalytic activity by enhancing the proximity between the substrate and the metal particles, and also the stability leading to longer lifetime which is very important from an economical point of view.
The combination of cyclodextrin and polymer in a physical mixture and as cyclodextrin-based
polymer where the cyclodextrin is directly incorporated into the polymer structure has recently proven to be very promising both in the use of nanoparticles dispersed into a solvent or immobilized on cyclodextrin polymer where it could play the role of stabilizing agent and also the role of support.

Noël, S., Ponchel, A., Sadjadi, S., Monflier, E., Léger, B. (2020) Metal Nanoparticles and Cyclodextrins for Catalytic Applications. In: Crini, G., Forurmentin, S., Lichtfouse, E. (eds.) The History of Cyclodextrins. Springer, New York. pp. 219-279. https://www.springer.com/gp/book/9783030493073