Aldol condensation of citral and acetone over mesoporous catalysts obtained by thermal and chemical activation of magnesium–aluminum hydrotalcite-like precursors

Abstract

Hydrotalcite-like materials containing a various amount of magnesium and aluminum cations in the brucite like sheets, and carbonate/nitrate anions in the interlayer space were synthesized by the coprecipitation method. The as-prepared samples were characterized with respect to structure (XRD), chemical composition (elemental analysis and XRF) and thermal stability (evolved gas analysis by mass spectrometry). The thermal treatment of the hydrotalcite-like compounds at an elevated temperature (450–600 °C) resulted in a structural transformation of the layer structure into mixed Mg–Al oxides. The textural and acid–base properties of such materials were examined by low-temperature sorption of N 2 and temperature-programmed desorption of NH 3 and CO 2, respectively. An influence of chemical composition and pre-treatment conditions on the catalytic activity and selectivity of the hydrotalcite-derived oxides in the self-condensation of acetone and the cross-condensation of citral and acetone was discussed. The pseudoionone yield was significantly enhanced by rehydration of the hydrotalcite-derived catalysts. The rehydrated samples showed a higher catalytic activity than Ba(OH) 2, which was tested as a standard catalyst of aldol condensation process.