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New basic catalysts obtained from layered double hydroxides nanocomposites

Redouane Chebout 1,2,3Géraldine Layrac 1Didier Tichit 1Akila Barama 2Bernard Coq 1

1. Institut Charles Gerhardt, CC15, Place eugène Bataillon, Montpellier 34095, France
2. Université des sciences Houari Boumedienne (U.S.T.H.B), Bp N°9 El AliA Bab Ezzouar, Alger 16141, Algeria
3. Centre de Recherche Scientifique et Technique en Analyse Physico-Chimique (CRAPC), BP248, Alger RP. Alger 16004,Algerie, Alger 16004, Algeria

Abstract

Mixed oxides obtained from Layered Double Hydroxides (LDH) precursors exhibit basic properties giving rise to very efficient catalysts for syntheses of fine chemicals. Until now their properties have been mainly tailored through the activation temperature and the composition of the LDH. Alkaline, alkaline-earth or La3+ cations, particularly interesting to reach high basic levels, cannot be introduced in the brucite-like layers of LDHs. This work presents an original approach to avoid this drawback going through the nanocomposite route. Nanocomposites precursors have been prepared by intercalation of host Mg/Al LDH with negatively charged guest colloids. These latter are obtained by complexation of La3+ with strong complexing agents (citrate, edta). The intercalation degree, the composition of the colloids and the activation temperature allow to finely tune the basic properties of the mixed oxides catalysts. This has been put into evidence by physico-chemical characterizations and the reaction test of methylbutynol (MBOH) conversion. A correlation is found between the strength of the basic sites measured by microcalorimetric adsorption of CO2 and the average charge on the oxygens calculated from Sanderson’s theory of electronegativity. The basic character of the catalysts is confirmed by the catalytic conversion of MBOH, leading to acetone and acetylene. The performances of the catalysts obtained from the nanocomposite precursors, higher than those obtained with the mixture of Mg(Al)O and lanthanum oxide, resulting from the decomposition of coprecipitated Mg/Al/La LDHs, show that a synergy between the different cations is achieved using the new nanocomposite precursors. 

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium D, by Didier Tichit
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-07 15:39
Revised:   2009-06-07 00:48