Leaching in metal nanoparticle catalysis.

Since the discovery of catalysis, the identification of the different species in the mechanism involved in the reaction has been a challenge. When nanocatalysis entered the scene, the detection of material that came out from solutions attracted the attention and raised several questions: was this solid part of the nanocatalyst? was it the precursor of the nanocatalysts (the so-called precatalyst)? or was it the nanocatalyst itself? The discussion focuses on whether the catalysis is determined by the species that exist in solution or if it is generated from the support and hence the catalytic reaction is carried out with these soluble species. Furthermore, it appears that leaching is a phenomenon which occurs mainly in palladium- catalyzed reactions and that involves palladium nanoparticles (NPs). The research, findings and patents in the leaching process in catalytic reactions are reviewed in the present paper.