How precipitation techniques can be useful for catalysts preparation ?
|Jean-Francois Hochepied , Alain Gaunand|
Laboratoire de Systemes Colloidaux dans le Processus Industriels (SCPI), Ecole des Mines de Paris, Paris F - 75272, France
Oxide particles can be obtained by various precipitation methods. The reaction of a metallic precursor with a base can be monitored by chemical, physico-chemical and process parameters, with variable impact on the nucleation/growth/agglomeration stages. Parametric studies are the experimental tools for developing kinetics models explaining the observed behaviors and allowing in some cases a fine control or tuning of size and monodispersity.
Some examples will be given. Thermal hydrolysis of acidic titanyle precursors leading to titanium dioxide (anatase) monodisperse particles, generally dense and small agglomerates of nanoparticles, was studied in a batch reactor and the effects of temperature, concentrations and seeding were analyzed to lead to a precipitation kinetics model. The coupling of complexation and template agents can allow a fine tuning of monodisperse nanostructured nickel hydroxide cylinders thanks to slow and homogenous precipitation by decomplexation; the particles can be calcined into NiO with size, morphology and nanostructure retention. The perturbation of a dissolution-reprecipitation phase transformation by external action (addition of a new compound, pH or temperature jump) may also lead to final particle size tuning as will be shown in the case of magnetite. The final objects may be dispersed submicronic or nanoparticles or, as mainly observed with homogenous precipitation, multi-scale objects. This multi-scale objects may result from the use of some agents as surfactants as illustrated by nickel hydroxide/oxide, but they may also result from agglomeration and/or oriented attachment without templates as in the case of thermohydrolysis of titanyl compounds. Hence such techniques can be used for the making of new architectures for catalysts.
Presentation: Invited oral at E-MRS Fall Meeting 2006, Symposium B, by Jean-Francois Hochepied
See On-line Journal of E-MRS Fall Meeting 2006
Submitted: 2006-05-15 17:24 Revised: 2009-06-07 00:44
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