Abstract
The self-condensation reaction of acetone, producing diacetone alcohol (DAA), is of great industrial importance. It was used to study the catalytic activity of Mg-Al catalysts synthesized by the coprecipitation method. For this purpose, we synthesized Mg-Al based hydrotalcite with a molar ratio of 3, obtained either after conventional heating or after microwave irradiation with of 100 W for three minutes. Structural and chemical properties of the obtained catalysts were characterized, using different techniques: X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscope (SEM), equipped with energy dispersive X-ray (EDX), and specific surface area of the catalysts were determined by the methylene blue (MB) adsorption method. Also, these catalysts were tested in the self-condensation reaction of acetone at 273 K in the liquid phase without solvent, a reaction which requires very high catalytic activity. The microwave treatment improves the catalyst activity, and the conversion of acetone to diacetone alcohol increases from 13.2 to 18.3% after 8 h of reaction. Moreover, the microwave-treated hydrotalcite catalyst, calcined at 723 K and rehydrated under a flow of N2, is the most active and gives conversion of acetone of 52% under the same reaction conditions.
Highlights
IntroductionSeveral important industrial reactions such as condensation, hydrogenation, dehydrogenating reactions, oxidation, alkylation, and addition are carried out in the homogeneous phase by the liquid bases, for instance, KOH, NaOH, and Na2CO3
Hydrotalcites (HT), which are layered double hydroxides (LDHs) family, are well-known as heterogeneous base catalysts for various reactions. ey need layered structures containing anions and H2O molecules between charged metal hydroxides with the chemical formula:
All the diffraction peaks are in good agreement with the characteristics of the hexagonal phase as the (003), (006), and (012) peaks and indicate the formation of the compounds with a good crystallinity and no impurities (Figure 1) [9]. e building block parameters were calculated assuming a 3R stacking sequence, that is, a 2d110 and c 3d003
Summary
Several important industrial reactions such as condensation, hydrogenation, dehydrogenating reactions, oxidation, alkylation, and addition are carried out in the homogeneous phase by the liquid bases, for instance, KOH, NaOH, and Na2CO3. Hydrotalcites (HT), which are layered double hydroxides (LDHs) family, are well-known as heterogeneous base catalysts for various reactions. Ey need layered structures containing anions and H2O molecules between charged metal hydroxides with the chemical formula: M21+−. E structure of hydrotalcite Mg6Al2(OH)16CO3.4H2O resembles that of brucite Mg(OH). E structure of hydrotalcite Mg6Al2(OH)16CO3.4H2O resembles that of brucite Mg(OH)2 Within the latter structure, the magnesium cations are octahedrally coordinated by hydroxyl ions, leading to the stacks of edgeshared layers of the octahedral. For the HT structure, a part of the Mg2+ ions is replaced by Al3+ ions leading to positive charge layers, whose charge is compensated by interlayer anions, essentially the carbonate ions. To create catalytic activity in aldol condensation reactions, HT should undergo a selected treatment. For gas-phase condensation reactions at a hot temperature, calcination at 723 K is sufficient [5]. For gas-phase condensation reactions at a hot temperature, calcination at 723 K is sufficient [5]. e resulting Mg-Al-(O)x mixed
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