Effect of hydration temperature on the structure reconstruction of MgAlY layered materials

• Published in: Comptes rendus. Chimie Vol. 21; no. 3-4; pp. 318 - 326
• Main Authors: Zăvoianu, Rodica, Bîrjega, Ruxandra, Angelescu, Emilian, Pavel, Octavian D.
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 01.03.2018
• Subjects: Base catalysts; Cyanoethylation; Hydrotalcite; Layered double hydroxides; Memory effect; Yttrium; Cyanoethylation; Hydrotalcite; Yttrium; Memory effect; Base catalysts; Layered double hydroxides
• ISSN: 1631-0748; 1878-1543; 1878-1543
• DOI: 10.1016/j.crci.2017.07.002

This contribution investigates the obtaining of layered double hydroxides (LDHs) modified with different concentrations of yttrium and the effect of the yttrium concentration and temperature during the rehydration of the mixed oxides derived from these solids. Mg3Al(1−x)Yx-LDH (where x = 0.04–0.6) have been prepared using the standard coprecipitation method under low supersaturation conditions. After the calcination of these solids (460 °C, 18 h), the corresponding mixed oxides were obtained. The reconstruction of the layered structure was attempted by rehydration of the mixed oxides under two different conditions: (1) at 25 °C and (2) at 70 °C. All the aforementioned solids have been characterized by chemical analysis, X-ray diffraction, DRIFTS spectra, N2 adsorption–desorption isotherms, and determination of base sites. Their catalytic activity was tested in cyanoethylation of ethanol with acrylonitrile. The results obtained after the characterization and the catalytic activity tests were compared with those obtained for a standard hydrotalcite Mg3Al. Cette contribution étudie l'obtention d'hydroxydes doubles en couches (LDH) modifiés avec différentes concentrations d'yttrium et l'effet de la concentration d'yttrium et de la température pendant l'hydratation des oxydes mixtes dérivés de ces solides. Des composés de formule Mg3Al(1−x)Yx-LDH (x=0.04–0.6) ont été préparés par la méthode de coprécipitation standard à faible sursaturation. Après calcination de ces solides (460 °C, 18 h), on obtient les oxydes mixtes correspondants. La reconstitution de la structure stratifiée a été tentée par hydratation des oxydes mixtes dans deux conditions différentes : (i) à 25 °C, (ii) à 70 °C. Tous les solides mentionnés ci-dessus ont été caractérisés par analyse chimique, XRD, DRIFTS, BET et détermination des sites basiques. Leur activité catalytique a été testée dans la cyanoéthylation de l'éthanol avec l'acrylonitrile. Les résultats obtenus après la caractérisation et les essais d'activité catalytique ont été comparés à ceux obtenus pour une hydrotalcite standard Mg3Al. [Display omitted] •The driving force for the inclusion of Y in the brucite-type layer is its presence in a molar amount exceeding aluminum.•At 70 °C the amount of OH− groups embedded is more pronounced than at 25 °C.•The increase in basicity is closely linked to the presence of yttrium due to its lower electronegativity.•For all catalysts, the selectivity of β-ethoxyproprionitrile is >99% and there was no polymerization of acrylonitrile.•The most active catalyst Mg3Al0.4Y0.6-MO was stable for more than five cycles.