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Alkaline-earth-doped mixed oxides obtained from LDH nanocomposites as highly basic catalysts

Abstract:

The anionic exchange of the nitrate compensating anions in host Mg/Al LDH by negatively charged [M(Edta)]2- (M = Ca2+, Sr 2+, Ba2+) guest entities has been performed. The increase from 0.83 nm to 1.5 nm of the d0 0 3 interlayer distance shows that intercalation has taken place leading to well ordered lamellar materials with 3-9 wt.% of alkaline-earth (AE) cations loading. The basic properties of the M/ Mg(Al)O mixed oxides catalysts obtained by thermal decomposition of the [M(Edta)]-Mg/Al LDH precursors have been investigated by TPD of CO2, FTIR spectroscopy of adsorbed CDCl3 and catalytic test reaction of 2-methyl-3-butyn-2-ol (MBOH). The AE-containing mixed oxides exhibit higher basicity than Mg(Al)O with, particularly, a large increase of the densities of sites of medium and high strength. Remarkably, the nature of the AE cations allows to finely tune the basicity. All the AE-containing mixed oxides are able to perform the isomerization reaction of 2,3-dimethyl-1-butene (DB-1) into 2,3- dimethyl-2-butene (DB-2), the Ca-containing sample being the most active according to its larger content of strong basic sites. © 2009 Elsevier B.V. All rights reserved.