Amine-Functionalized Nanoporous Silica Monoliths for Heterogeneous Catalysis of the Knoevenagel Condensation in Flow.
Journal
ACS omega
ISSN: 2470-1343
Titre abrégé: ACS Omega
Pays: United States
ID NLM: 101691658
Informations de publication
Date de publication:
12 Jan 2021
12 Jan 2021
Historique:
received:
05
10
2020
accepted:
07
12
2020
entrez:
18
1
2021
pubmed:
19
1
2021
medline:
19
1
2021
Statut:
epublish
Résumé
Porous carrier materials functionalized with organocatalysts offer substantial advantages compared to homogeneous catalysts, e.g., easy separation of the catalyst, scalability, and an improved implementation in continuous operations. Here, we report the immobilization of (3-aminopropyl)trimethoxysilane (APTMS) onto self-prepared silica monoliths and its application as a heterogeneous catalyst in the Knoevenagel condensation between cyano ethylacetate and various aromatic aldehydes under continuous-flow conditions. The meso-macroporous silica monoliths (6-7 cm in length) were optimized to be used in flow taking advantage of their hierarchical meso- and macroporosity. The monoliths were cladded with a poly(ether ether ketone) (PEEK) tube by a refined procedure to guarantee tight connection between the carrier material and PEEK. Functionalization of the bare silica monoliths consisting of APTMS can be efficiently performed in flow in ethanol and toluene. While a large grafting gradient is obtained for toluene, the grafting in ethanol proceeds homogenously throughout the monolith, as evidenced by elemental analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The silica monoliths exhibit high conversion up to 95% with concurrent low back pressures, which is of importance in flow catalysis. By connecting two monoliths, high conversions can be maintained for several flow rates. Two types of monoliths were synthesized, possessing different mesopore sizes. The monolith bearing the larger mesopore size showed an enhanced turnover frequency (TOF), while the monolith with the smaller mesopores allowed for larger quantities of the product to be synthesized, due to the higher surface area. A long-term stability test showed that the functionalized monoliths were still active after 66 h of continuous usage, while the overall yield decreased over time.
Identifiants
pubmed: 33458494
doi: 10.1021/acsomega.0c04857
pmc: PMC7807742
doi:
Types de publication
Journal Article
Langues
eng
Pagination
425-437Informations de copyright
© 2020 American Chemical Society.
Déclaration de conflit d'intérêts
The authors declare no competing financial interest.
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