Abstract
A highly efficient solid-base catalyst for aldol condensation reaction was synthesized by grafting site-isolated secondary amines onto the channel walls of mesoporous silica, MCM-41, in a polar-protic solvent. These site-isolated organoamines pair up with the neighboring residual surface silanol (weak acid) groups to form optimized acid and base groups, which cooperatively catalyze the aldol condensation reaction with high TON (turn over number) and selectivity (alcohol products over alkene products). The organoamine samples grafted in a polar-protic solvent, isopropanol, showed higher catalytic efficiency toward aldol reaction than those grafted in a non-polar solvent, toluene, because the former gave a sample with less dense loading of grafted organoamines (or more silanols present in it). To elucidate the role of surface silanols as acidic sites and their ability to activate the substrates in aldol condensation, control experiment with diethylamine as a homogeneous catalyst in the presence of MCM-41, silica microspheres, methyl-capped MCM-41 or methyl-capped catalyst was carried out. MCM-41 resulted in significant enhancement of catalytic activity compared to the corresponding reactions conducted in the absence of MCM-41, or in the presence of methyl-capped catalysts or silica spheres. By testing materials with different grafted organoamine groups as catalysts, we also found that secondary amine functionalized sample produced the best acid and base pairs and most efficient catalytic activity in aldol reaction. This was followed by primary amines, while the tertiary amine functionalized samples showed negligible catalytic property.
| Original language | English |
|---|---|
| Pages (from-to) | 131-140 |
| Number of pages | 10 |
| Journal | Journal of Catalysis |
| Volume | 265 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Jul 25 2009 |
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Keywords
- Aldol condensation
- Aldol reaction
- Catalysis
- Heterogeneous catalyst
- MCM-41
- Mesoporous catalyst
- Organoamine grafting
- Site-isolated catalyst
ASJC Scopus subject areas
- Catalysis
- Physical and Theoretical Chemistry
Cite this
Efficient solid-base catalysts for aldol reaction by optimizing the density and type of organoamine groups on nanoporous silica. / Xie, Youwei; Sharma, Krishna K.; Anan, Abhishek; Wang, Gang; Biradar, Ankush V.; Asefa, Teddy.
In: Journal of Catalysis, Vol. 265, No. 2, 25.07.2009, p. 131-140.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Efficient solid-base catalysts for aldol reaction by optimizing the density and type of organoamine groups on nanoporous silica
AU - Xie, Youwei
AU - Sharma, Krishna K.
AU - Anan, Abhishek
AU - Wang, Gang
AU - Biradar, Ankush V.
AU - Asefa, Teddy
PY - 2009/7/25
Y1 - 2009/7/25
N2 - A highly efficient solid-base catalyst for aldol condensation reaction was synthesized by grafting site-isolated secondary amines onto the channel walls of mesoporous silica, MCM-41, in a polar-protic solvent. These site-isolated organoamines pair up with the neighboring residual surface silanol (weak acid) groups to form optimized acid and base groups, which cooperatively catalyze the aldol condensation reaction with high TON (turn over number) and selectivity (alcohol products over alkene products). The organoamine samples grafted in a polar-protic solvent, isopropanol, showed higher catalytic efficiency toward aldol reaction than those grafted in a non-polar solvent, toluene, because the former gave a sample with less dense loading of grafted organoamines (or more silanols present in it). To elucidate the role of surface silanols as acidic sites and their ability to activate the substrates in aldol condensation, control experiment with diethylamine as a homogeneous catalyst in the presence of MCM-41, silica microspheres, methyl-capped MCM-41 or methyl-capped catalyst was carried out. MCM-41 resulted in significant enhancement of catalytic activity compared to the corresponding reactions conducted in the absence of MCM-41, or in the presence of methyl-capped catalysts or silica spheres. By testing materials with different grafted organoamine groups as catalysts, we also found that secondary amine functionalized sample produced the best acid and base pairs and most efficient catalytic activity in aldol reaction. This was followed by primary amines, while the tertiary amine functionalized samples showed negligible catalytic property.
AB - A highly efficient solid-base catalyst for aldol condensation reaction was synthesized by grafting site-isolated secondary amines onto the channel walls of mesoporous silica, MCM-41, in a polar-protic solvent. These site-isolated organoamines pair up with the neighboring residual surface silanol (weak acid) groups to form optimized acid and base groups, which cooperatively catalyze the aldol condensation reaction with high TON (turn over number) and selectivity (alcohol products over alkene products). The organoamine samples grafted in a polar-protic solvent, isopropanol, showed higher catalytic efficiency toward aldol reaction than those grafted in a non-polar solvent, toluene, because the former gave a sample with less dense loading of grafted organoamines (or more silanols present in it). To elucidate the role of surface silanols as acidic sites and their ability to activate the substrates in aldol condensation, control experiment with diethylamine as a homogeneous catalyst in the presence of MCM-41, silica microspheres, methyl-capped MCM-41 or methyl-capped catalyst was carried out. MCM-41 resulted in significant enhancement of catalytic activity compared to the corresponding reactions conducted in the absence of MCM-41, or in the presence of methyl-capped catalysts or silica spheres. By testing materials with different grafted organoamine groups as catalysts, we also found that secondary amine functionalized sample produced the best acid and base pairs and most efficient catalytic activity in aldol reaction. This was followed by primary amines, while the tertiary amine functionalized samples showed negligible catalytic property.
KW - Aldol condensation
KW - Aldol reaction
KW - Catalysis
KW - Heterogeneous catalyst
KW - MCM-41
KW - Mesoporous catalyst
KW - Organoamine grafting
KW - Site-isolated catalyst
UR - http://www.scopus.com/inward/record.url?scp=67649158688&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=67649158688&partnerID=8YFLogxK
U2 - 10.1016/j.jcat.2009.04.018
DO - 10.1016/j.jcat.2009.04.018
M3 - Article
VL - 265
SP - 131
EP - 140
JO - Journal of Catalysis
JF - Journal of Catalysis
SN - 0021-9517
IS - 2
ER -