Synthesis of metal nanoparticles inside a porous support in fluidized bed: application to elaboration of supported catalysts

摘要

The elaboration of composite materials by dry impregnation of porous supports can be carried out in a fluidized bed. This technique permits to obtain, in only one apparatus, composite materials which, by the traditional way, must successively undergo the stages of impregnation, filtration, drying and calcination/activation. This paper describes examples of composite materials containing metal nanoparticles prepared by the deposit of metals on a porous support such as a silica gel, in a fluidized bed. Three different types of precursors have been used as metal source: inorganic and organometallic complexes and also colloidal solutions containing preformed nanoparticles. The principle of this technique consists in the spraying of a solution containing a metallic precursor into a hot fluidized bed of porous fine particles as chosen support. After the impregnation step, the decomposition of metallic precursor and metal activation can be operated in the same reactor. For organometallic complexes, the decomposition/activation is achieved at low temperature (T<80°C) under a reactive atmosphere (H2/N2 mixture), while in the case of inorganic solution calcination is operated at high temperature (T approx =450°C) under air. The results show that in operating conditions the deposit efficiency is close to 100%, the deposit is quasi uniform inside the particles and nanoparticles size is controlled by pore diameter. Finally, some of the presented composite materials have been tested as catalysts: iron based materials were used in carbon nanotubes synthesis, while Pd and Rh composite materials have been investigated in hydrogenation reactions.