On the Structure of Activated Hydrotalcites as Solid Base Catalysts for Liquid-Phase Aldol Condensation

Roelofs, Jules C. A. A.; Lensveld, Dennis J.; Dillen, A.J. van; Jong, Krijn P. de

doi:10.1006/jcat.2001.3295

Cited by 195 publications

(165 citation statements)

References 38 publications

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“…Other investigations reported in literature showed that the actual active basic sites in activated HTs are situated at the edges of the platelets and that the number of these sites can be varied by changing the lateral platelet size [38,40,41,45,46]. A linear correlation between the number of active sites and the activity in the condensation of acetone at 273 K was found [38,40,46].…”

Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 67%

“…[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. This is supported by considering the density of sites, which is in both types of samples 2.6-2.8 mmol m À2 .…”

Section: Catalyst Characterizationmentioning

confidence: 99%

“…A linear correlation between the number of active sites and the activity in the condensation of acetone at 273 K was found [38,40,46]. We investigated whether a similar structure-activity relationship could be derived for the dehydration reaction as the dehydration reaction is also catalyzed by basic sites [1].…”

Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 99%

“…We investigated whether a similar structure-activity relationship could be derived for the dehydration reaction as the dehydration reaction is also catalyzed by basic sites [1]. To this end we have prepared HTs with increasing platelet size by increasing the synthesis temperature, 333, 373, 423 and 473 K [38,47]. TEM-and SEM-analyses of these samples showed that HT prepared at 473 K consisted of large platelets of about 400-500 nm, whereas the smallest platelets ($60-90 nm) were found for HT prepared at 333 K (data not shown).…”

Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 99%

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

Winter

Wolters

Dillen

et al. 2006

Applied Catalysis A: General

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A comparative study was performed between Pd supported on activated hydrotalcites bi-functional catalysts and physical mixtures of activated hydrotalcites with Pd supported on carbon nanofibers for the single-stage liquid-phase synthesis of methyl isobutyl ketone from acetone and H 2 . Since it was found earlier that the dehydration reaction of diacetone alcohol over activated hydrotalcites is the rate-determining step in this process, Mg-Al hydrotalcites were investigated in the condensation of acetone to diacetone alcohol and its dehydration to mesityl oxide to enhance the activity. A correlation between the number of active base sites, as determined by volumetric CO 2 adsorption measurements at low pressures, and the activity in the dehydration reaction could be derived. A dependency on the Pd-loading (0-1 wt%) of Pd supported on activated hydrotalcites catalysts was found in the single-stage synthesis of methyl isobutyl ketone, whereas no such an effect was found when using physical mixtures of activated hydrotalcites with Pd on carbon nanofibers. Results from TEM, CO 2 chemisorption and N 2 physisorption as well as catalytic experiments in the hydrogenation of mesityl oxide and of cyclohexene indicate that this dependency is largely accounted for by entrapment of Pd particles in the agglomerates of the irregular stacks of hydrotalcite platelets, making these sites inaccessible for the reactants. #

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Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 67%

Section: Catalyst Characterizationmentioning

confidence: 99%

Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 99%

Section: Condensation and Dehydration Over Activated Htsmentioning

confidence: 99%

See 2 more Smart Citations

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

Winter

Wolters

Dillen

et al. 2006

Applied Catalysis A: General

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“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Winter

Dillen

Jong

2004

Journal of Molecular Catalysis A: Chemical

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In this study, a catalyst mixture of activated Mg/Al hydrotalcite as solid base and Pd on carbon nanofibers was investigated for the single-stage liquid-phase synthesis of methyl isobutyl ketone (MIBK) from acetone and H 2 at 313 K and H 2 pressures of 1-20 bar. With this catalyst system acetone and H 2 are selectively converted into MIBK in a single reactor, even at 1.2 bar H 2 . Although the hydrogenation of one of the intermediates, mesityl oxide (MO), at 1.2 bar suffers from severe mass transfer limitations in H 2 , the catalytic activity in the single-stage synthesis is stable over several hours if the steady-state concentration of MO is kept low. Under the presented conditions the dehydration reaction of diacetone alcohol to MO is rate limiting in the production of MIBK.

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The Thermal Decomposition of Mg-Al Hydrotalcites: Effects of Interlayer Anions and Characteristics of the Final Structure

et al. 2002

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The thermal decomposition of hydrotalcites (HTs) with different interlayer anions in the 298–523 K region has been investigated by using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and IR, 27Al MAS‐NMR and X‐ray absorption near‐edge structure (XANES) spectroscopy. The thermal stability of the HT with interlayer oxalate was remarkably higher than that of HTs with interlayer carbonate; the onset temperatures for decomposition were 523 K and 473 K, respectively. It is proposed that the basicity of the interlayer anion is the key factor in the onset of dehydroxylation of the brucite‐like layers: the lower the basicity, the more thermally stable the HT compound. After heat treatment at 723 K, small Mg(Al)O domains (≈5 nm) within the HT crystallites cause broadening of the XRD reflections. The electron diffraction pattern consists of spots and rings, due to nonrandomly oriented crystalline material. Formation of disordered bonds, caused by nonideal packing between the decomposing adjacent cation layers in the (1 1 1) direction, could explain the expanded d value in the resulting MgO‐like phase observed with XRD and electron diffraction. The orientation of the Mg(Al)O domains in the heat‐treated material may be crucial for the so‐called “memory effect” of HTs.

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On the Structure of Activated Hydrotalcites as Solid Base Catalysts for Liquid-Phase Aldol Condensation

Cited by 195 publications

References 38 publications

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

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

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

The Thermal Decomposition of Mg-Al Hydrotalcites: Effects of Interlayer Anions and Characteristics of the Final Structure

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