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

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

Hydrotalcites (HTs) of different, well-defined platelet sizes were hydrothermally synthesized. Activation via calcination and rehydration resulted in highly active catalysts. Their activities in the self-condensation of acetone at 273 K showed a linear increase with the amount of accessible Brønsted...

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Bibliographic Details
Published in:Journal of catalysis Vol. 203; no. 1; pp. 184 - 191
Main Authors: Roelofs, J.C.A.A., Lensveld, D.J., van Dillen, A.J., de Jong, K.P.
Format: Journal Article
Language:English
Published: Amsterdam Elsevier Inc 01-10-2001
Elsevier
Subjects:
aldol condensation
calcination/rehydration
Catalysis
Catalysts: preparations and properties
Chemistry
Exact sciences and technology
General and physical chemistry
hydrotalcite
layered double hydroxide
solid base catalysts
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
aldol condensation
solid base catalysts
layered double hydroxide
calcination/rehydration
hydrotalcite
Aluminium Hydroxides
Base catalysis
Hydroxides
Lamellar compound
Liquid phase
X ray diffraction
Mesoporosity
Aldol condensation
Calcining
Heterogeneous catalysis
Pore size
Hydrotalcite
Transmission electron microscopy
Magnesium Hydroxides
Rehydration
Structure
Catalyst
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Summary:Hydrotalcites (HTs) of different, well-defined platelet sizes were hydrothermally synthesized. Activation via calcination and rehydration resulted in highly active catalysts. Their activities in the self-condensation of acetone at 273 K showed a linear increase with the amount of accessible Brønsted basic sites as determined by CO2 adsorption. The number of accessible sites, based on the CO2/Al ratio, was below 5%. Both results support our model in which only basic sites near edges of HT platelets are partaking in aldol condensations. Besides incorporation of interlayer OH− upon rehydration, the hexagonal morphology changed as a result of activation into a more irregular but still layered structure containing mesopores (<10 nm). In contrast to this, HTs with interlayer OH− prepared via ion exchange preserved their original hexagonal structure, but they lacked the high catalytic activity. The results show an enhanced activity of interlayer OH− close to disordered edges, obtained via rehydration, in contrast to interlayer OH− in a regular HT structure.
ISSN:0021-9517
1090-2694
DOI:10.1006/jcat.2001.3295