Nanoparticles deposit location control on porous particles during dry impregnation in a fluidized bed

This work deals with the synthesis of composite materials, catalytic or not, by an innovating technique named dry impregnation in a fluidized bed. This process permits the obtainment, in only one apparatus, of composite materials which, by the traditional way, must successively undergo the stages of impregnation, filtration, drying and calcination/activation. Its principle consists in the spraying of a solution containing a metallic precursor into a hot fluidized bed of porous particles as a chosen support. After the impregnation step, the decomposition of metallic precursor and metal activation can be operated in the same reactor. It is found that the competition between two phenomena (drying and capillary) controls the deposit location.This paper presents experimental results obtained during the dry impregnation of coarse and fine porous particles using different types of precursors: inorganic precursors (metallic salts), metal organic complexes and a colloidal suspension containing preformed metallic nanoparticles (rhodium). The effect of drying parameters (solvent content in gas phase and temperature) on deposit distribution within the support grains at the local scale is examined.It appeared that a fast drying leads to a deposit located only at the external particle surface (similar to a surface coating), whereas a uniform deposit on the whole particle volume is obtained with slow drying conditions. It indicates that dry impregnation in fluidized beds is very flexible and, by a simple modification of the operating conditions, we can fix the deposit location.

A key parameter was identified: τs, solvent vapour saturation rate and a dimensional number, IM, was defined. An appropriate choice of the operating conditions permits the adjustment of the τs and IM values, thus controlling the deposit location during dry impregnation in fluidized bed whatever the precursor nature and for a large range of support particle sizes.Figure optionsDownload as PowerPoint slide