Aldol condensation of acetone and butyraldehyde over alkali supported hydrotalcite catalysts

Abstract

Thermally treated hydrotalcite prepared at different temperatures (HT400, HT600 and HT 800) and alkali metal (Li, K and Cs) incorporated on HT400 catalysts have been studied for their surface properties and catalytic activity/selectivity in the continuous gas phase aldol condensation reaction between acetone and butyraldehyde. The synthesized catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and temperature-programmed desorption of carbon dioxide (CO₂-TPD). The catalytic activity of the thermally treated hydrotalcite increases in the following order: HT400 < HT600 < HT800. The cross- and self-aldol condensation reactions give a mixture of multiple condensation products. In the aldol condensation reaction between acetone and butyraldehyde using HT600 catalyst, the self-aldol reaction of butyraldehyde to form C8 products proceeded much faster than the cross-aldol reaction to form C7 products. After incorporation of lithium (1 mol%) with HT400 by impregnation, such catalyst can increase the catalytic activity. However, the lithium species may agglomerate to form relatively larger clusters upon increasing metal loading (5 and 10 mol%) leading to the lower conversion. Regarding the effect of metal, the catalytic activity of the alkali incorporated HT400 (10 mol%) decreases in the following order: 10Li/HT400 > 10Cs/HT400 > 10K/HT400. It suggests that the formation of the different metal species and cluster size can influence the catalytic activity, stability and selectivity of catalyst in aldol condensation reaction.