Base-catalyzed condensation of citral and acetone at low temperature using modified hydrotalcite catalysts

Abstract

A study on the catalytic properties of properly activated hydrotalcite (HT) with special attention to the nature and amount of active sites present in this solid base catalyst has been undertaken. Only a small fraction (5%) of the available basic sites in the rehydrated calcined HT is active in liquid-phase aldol condensations. These sites exhibit high catalytic activity and are most likely localized at the edges of the HT-platelets. Besides a high activity, these modified HTs also show a high selectivity. No further condensation products other than diacetone alcohol (DAA) in the acetone self-condensation could be observed. Initial results with the citral-acetone condensation show that even at 273 K this reaction is catalyzed by modified HTs with a conversion of 65% and a selectivity of 90%, when the citral concentration is not too high (∼1 wt.%). At higher citral concentrations, no reaction is observed indicating a negative order in citral concentration.

A hydrotalcite-based catalyst system for the single-stage liquid-phase synthesis of MIBK

“…After heat treatment of HT as the surface area as well as the pore volume increased significantly. Only with HT heat micropores were observed, caused by the evolution of water and CO 2 during heat treatment of HT as [25,32,36,37]. After rehydration of the mixed oxide (HT re ) a BET surface area similar to that of HT as was found, whereas Pd/HT re exhibited a relatively low surface area.…”

“…To an aqueous solution (70 ml) containing 0. 35 To activate HT as [32,33] it was heated in a nitrogen flow to 723 K (10 K min À1 ) for 8 h and allowed to cool down to room temperature (HT heat ). HT heat was rehydrated by suspending it in decarbonated water under N 2 atmosphere for 1 h. Next, the sample was filtered under N 2 atmosphere and dried in N 2 flow at 293 K. The sample is further denoted as HT re .…”

“…X-ray diffraction patterns of HT as , HT heat , HT re and 1 wt% Pd/HT re . [32,33,[37][38][39][40]. This low amount of accessible basic sites is best explained by further agglomeration of the HT platelets as could already be observed with activated HTs [33,37,38,41,42], induced by the additional heat treatment and rehydration procedure.…”

Selective oxidation of rhodinol to citral using H2O2-platinum black system under microwave irradiation

“…These similarities make rhodinol inseparable into individual geraniol and citronellol by normal distillation processes [10][11]. The oxidation product of rhodinol known as citral, has a wide range of valuable applications such as ingredient in fragrances and precursors for the synthesis of vitamin A, makes it highly demanded in the market [12][13]. Therefore, a chemical process which can selectively convert rhodinol to citral is desired.…”

Single-stage liquid-phase synthesis of methyl isobutyl ketone under mild conditions

“…In these studies, the actual condensation catalyst is a mixed oxide obtained by calcination of the hydrotalcite. Recently, extending the pioneering work of Tichit and co-workers [21][22][23][24] our group developed a highly active catalyst for the liquid-phase condensation of acetone at low temperatures, i.e., activated Mg-Al hydrotalcite (HT) [25,26]. Furthermore, this catalyst showed dehydration functionality of DAA to MO already at room temperature [2,26].…”