About the Use of Rhodium Nanoparticles in Hydrogenation and Hydroformylation Reactions

Even if rhodium is one of the rarest and the most costly metals, this noble metal has found many catalytic applications, particularly in hydrogenation and hydroformylation reactions owing to its specific catalytic properties. Tremendous research activities are thus carried out by the scientific community for the development of novel rhodium-based catalysts. This interest for rhodium catalysts concerns also the modern "nanocatalysis" area, situated at the frontier between heterogeneous and homogeneous ones, nanoparticles soluble in a liquid phase being considered as "pseudo homogeneous" systems. A high number of papers describe the preparation of diverse rhodium nanoparticles in suspension for their application as catalysts in hydrogenation of various substrates (mainly olefins and aromatic derivatives) in various catalytic conditions (mainly organic or biphasic phases). Concerning hydroformylation catalysis, it appears that only a few papers deal with rhodium metal nanoparticles for investigation in this reaction, although rhodium is well-known as highly active metal in hydroformylation reaction in homogeneous conditions. In this review, rhodium nanoparticle systems that have been prepared for investigation as nanocatalysts in liquid phase hydrogenation and hydroformylation reactions are described. This work is not comprehensive but provides an overview of the main methods used to synthesize rhodium nanoparticles for these selected catalytic applications. The objective of this review is to give to the readership an outlook of the recent advances in this field, as well as of the great potential of rhodium-based nanocatalysts for hydrogenation and hydroformylation reactions, two reactions of importance in organic synthesis.