Tuning the acidic–basic properties by Zn-substitution in Mg–Al hydrotalcites as optimal catalysts for the aldol condensation reaction

Hernández, Willinton Y.; Aliç, Funda; Verberckmoes, An; Voort, Pascal Van Der

doi:10.1007/s10853-016-0360-3

Cited by 38 publications

(29 citation statements)

References 44 publications

(63 reference statements)

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“…The strength of basic sites can be tuned by changing the Mg/Al ratio and the calcination temperature. It was reported that the presence of less basic cations than Mg 2+ , such as Al 3+ , could decrease the basic strength of LDH samples . In our experiment, the increase in Mg/Al ratio enables to increase the amount of basic sites of calcined samples due to the decrease in Lewis acidic sites.…”

Section: Resultsmentioning

confidence: 99%

Isomerization Kinetics of Glucose to Fructose in Aqueous Solution with Magnesium‐Aluminum Hydrotalcites

Wang

Zhang

et al. 2020

ChemistrySelect

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Mg−Al hydrotalcites for catalyzing glucose isomerization to fructose are prepared. Effects of atom ratios of Mg/Al ranging from 1 to 4 and calcination temperatures from 250–650 °C on catalytic performance were examined systematically. It was found that the hydrotalcite (Mg2Al1LDH) calcined at 450 °C with an atom ratio of Mg/Al=2 is an excellent catalyst for glucose isomerization. Characterizations by SEM, EDS, TEM, XRD, FTIR, TG and BET demonstrated that the formed oxide condensed phase as well as the interaction with the alumina helps promote glucose isomerization reaction due to their appropriate basic sites at high calcination temperature. With Mg2Al1‐450 as the catalyst, kinetic model analysis confirmed that the reaction of glucose isomerization to fructose was an exothermal reversible reaction; both the forward and reverse reactions are quasi‐first‐order reactions with activation energies of 71.82 kJ/mol and 48.15 kJ/mol, respectively, while the side reaction is a zero‐order reaction with an activation energy of 94.22 kJ/mol. Therefore, high isomerization reaction temperature is not beneficial to enhance the yield and selectivity of fructose.

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Section: Resultsmentioning

confidence: 99%

Isomerization Kinetics of Glucose to Fructose in Aqueous Solution with Magnesium‐Aluminum Hydrotalcites

Wang

Zhang

et al. 2020

ChemistrySelect

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“…The strength and density of the acid sites were determined using ammonia temperature-programmed desorption (NH 3 -TPD) analysis (Figure 4b). The NH 3 -TPD profile has two overlapping curves, where the first peak at around 110 • C could be due to the desorption of residual NH 3 weakly bonded to the surface of the catalyst, and could be attributed to the existence of Brønsted acid sites on the surface of catalysts, created by the existence of OHgroups [28]; and the second peak at around 190 • C, might be caused by further desorption of stronger bonded NH 3 species from the Lewis acid sites ascribed to the presence of Al 3+ − O 2− − Mg 2+ species in the structure of the mixed oxides and containing the Al 3+ cations mainly in octahedral sites [28,29].…”

Section: Catalyst Characterizationmentioning

confidence: 99%

Solvent-Free Synthesis of Jasminaldehyde in a Fixed-Bed Flow Reactor over Mg-Al Mixed Oxide

et al. 2020

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In spite of the rapid developments in synthesis methodologies in different fields, the traditional methods are still used for the synthesis of organic compounds, and regardless of the type of chemistry, these reactions are typically performed in standardized glassware. The high-throughput chemical synthesis of organic compounds such as fragrant molecules, with more economic benefits, is of interest to investigate and develop a process that is more economical and industrially favorable. In this research, the catalytic activity of Mg-Al catalyst derived from hydrotalcite-like precursors with the Mg/Al molar ratio of 3 was investigated for the solvent-free synthesis of jasminaldehyde via aldol condensation of benzaldehyde and heptanal. The reaction was carried out in a fixed-bed flow reactor, at 1 MPa, and at different temperatures. Both Brønsted and Lewis (O2− anions) base sites, and Lewis acid sites exist on the surface of the Mg-Al catalyst, which can improve the catalytic performance. Increasing the reaction temperature from 100 °C to 140 °C enhanced both heptanal conversion and selectivity to jasminaldehyde. After 78 h of reaction at 140 °C, the selectivity to jasminaldehyde reached 41% at the heptanal conversion 36%. Self-condensation of heptanal also resulted in the formation of 2-n-pentyl-2-n-nonenal. The presence of weak Lewis acid sites creates a positive charge on the carbonyl group of benzaldehyde, and makes it more prone to attack by the carbanion of heptanal. Heptanal, is an aliphatic aldehyde, with higher activity than benzaldehyde. Therefore, the possibility of activated heptanal reacting with other heptanal molecules is higher than its reaction with the positively charged benzaldehyde molecule, especially at a low molar ratio of benzaldehyde to heptanal.

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“…Aldol condensation of aldehydes can be catalyzed by acid, base or acid-base bifunctional catalysts [19] [20]. In aldol condensation catalyzed by base (Scheme 1), an enolate is formed by the abstraction of the α-hydrogen of the carbonyl compound with the help of a base.…”

Section: Mechanism Of Aldol Condensationmentioning

confidence: 99%

“…Strong bases are usually used for condensation of ketone with large steric hindrance. Acid catalysts are often used in aldol condensation reactions [19] [20]. Commonly used acid catalysts include (VO 2 P 2 O 7 , VOHPO 4 ), niobate and MFI zeolite.…”

Section: Mechanism Of Aldol Condensationmentioning

confidence: 99%

Upgrading of Biomass-Derived Feedstocks to Liquid Transportation Fuel Precursors by Aldol Condensation

Jiang¹

2020

OALib

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The upgrading of biomass-derived feedstocks to liquid transportation fuels is complex because of the chemical differences between biomass-derived chemicals and conventional fuels. Aldol condensation may play an important role in converting biomass-derive components to fuels because it allows smaller species to be converted to larger species that are more similar to conventional fuels. This review covers recent progress in aldol condensation of biomass-derived 5-hydroxymethylfurfural, acetone, methyl ketones, acetoin, levulinic acid, furfural, cyclopentanone and levulinic acid. The corresponding catalytic mechanisms and future research directions in these areas are also discussed.

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Tuning the acidic–basic properties by Zn-substitution in Mg–Al hydrotalcites as optimal catalysts for the aldol condensation reaction

Cited by 38 publications

References 44 publications

Isomerization Kinetics of Glucose to Fructose in Aqueous Solution with Magnesium‐Aluminum Hydrotalcites

Isomerization Kinetics of Glucose to Fructose in Aqueous Solution with Magnesium‐Aluminum Hydrotalcites

Solvent-Free Synthesis of Jasminaldehyde in a Fixed-Bed Flow Reactor over Mg-Al Mixed Oxide

Upgrading of Biomass-Derived Feedstocks to Liquid Transportation Fuel Precursors by Aldol Condensation

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