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Acid–base cooperativity in condensation reactions with functionalized mesoporous silica catalysts

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Abstract.
The Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate was used to test the acid–base
cooperativity of SBA-15 mesoporous silica co-condensed with aminopropyl groups as well as silica cocondensed
with dihydroimidazole groups. Surface silanols were capped with trimethylsilyl groups using
hexamethyldisilazane to determine the effects of the silanol groups on catalytic activity. The activities of
the mesoporous silicas with or without capped silanols were compared to the activity of propylamine
free in solution. Silylation resulted in a significant loss of activity, where turnover frequencies dropped
nearly to those of the homogeneous base. The same behavior was also observed with dihydroimidazolefunctionalized SBA-15, which catalyzes the Knoevenagel condensation by a different mechanism. Not only did these results indicate cooperative effects in heterogeneous systems, but cooperativity between
a homogeneous base and silanols on unfunctionalized SBA-15 was also observed to a lesser extent.
These results demonstrated that acid–base cooperativity seen in well-defined single sites can also be
demonstrated on an extended catalytic domain on the surface of mesoporous silica where the active
sites are not rigorously isolated.

Keywords:
Mesoporous silica
Co-condensation
Acid–base cooperativity
Knoevenagel condensation
Silylation

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2009

Deskripsi Fisik

Journal of Catalysis 263 (2009) 181–188

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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