An Overview of Palladium Nanocatalysts: Surface and Molecular Reactivity

The use of metallic nanoparticles in catalysis under homogeneous conditions leads to a discussion of their catalytic nature: whether the catalyst behaves as a molecular species or, on the contrary, the metallic surface is directly involved in the reactivity. This dilemma is intrinsically associated to the kinetic stability of the nanoclusters, favouring their agglomeration, and also to the formation of molecular species by reaction of the atoms placed at low‐coordination positions at the metallic surface. In particular, for palladium‐catalyzed processes, a large number of contributions have been reported in the last decade involving nanoparticles, but few of them analyze the mechanistic aspects. The present review aims to collect the more relevant research carried out in catalysis involving palladium nanoparticles in the liquid phase and addressing the nature of the catalytically active species. This kind of work is mainly focused on hydrogenation and C–C coupling processes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) From a mechanistic point of view, the use of nanoparticles as catalysts requires analysis of the catalytically active species in terms of their agglomeration and the leaching of the molecular species. This aspectbecomes crucial for work under “wet” catalytic conditions. The present review focuses on the nature of palladium nanoparticle catalysts that are either preformed or generated in situ.