Metal nanoparticles: challenges on the preparation, stabilization and activation for catalysis

Abstract

Catalysis is one of the oldest nanotechnological applications if one consider that heterogeneous catalysts are composed of metal particles in a wide range of sizes, sometimes including objects in the nanometer range. The developments of nanoscience brought great advances in the characterization of catalysts, both ex situ and in situ, allowing the identification of nanoobjects, but also contributed for the development of new preparation techniques, allowing designing catalysts with particle sizes in the range of interest. One of the main advantages of employing metal nanoparticles in catalysis is the growing number of metal centers and thus potential active sites, as the size decreases; however this is not the only and often not even the most important property. Metallic nanoparticles are able to develop reactivities not seen in the corresponding bulk materials and high selectivities in catalytic reactions. However, much remains to be discovered regarding the influence of nanoparticle size on catalytic activity. In this context, nanoparticles studies are of interest or relevant only if their synthesis is reproducible with well-defined, or adjustable, area specific as with classical molecular homogeneous catalysts. Thus, parallel to the choice of a stabilizing agent, which is essential to stabilize the size of the nanoparticles, it is important to choose the metal and synthetic strategy precursor (metal salts or organometallic compounds) which must be performed according to the reaction medium (aqueous or organic medium) and to the desired catalytic application. Moreover, the ligands used as nanoparticles stabilizers have a direct action on the catalytic activity of the material, and they can act as activator or inhibitor of the reactivity. Very little has been studied so far on the role of stabilizers chosen in the synthesis of nanoparticles for applications in catalysis. In this research project, we study strategies for the synthesis of metal nanoparticles, their use as components for the preparation of heterogeneous catalysts and activation and deactivation processes involving the ligands used as stabilizers or purposely added to the reaction medium or support for stimulate new reactivity and selectivity in reactions of industrial interest, such as hydrogenation, oxidation and hydroformylation. (AU)