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Hierarchical FAU‐ and LTA‐Type Zeolites by Post‐Synthetic Design: A New Generation of Highly Efficient Base Catalysts
Author(s) -
Verboekend Danny,
Keller Tobias C.,
Mitchell Sharon,
PérezRamírez Javier
Publication year - 2013
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201202320
Subject(s) - knoevenagel condensation , mesoporous material , malononitrile , catalysis , zeolite , materials science , benzaldehyde , ion exchange , base (topology) , chemical engineering , porosity , inorganic chemistry , ion , organic chemistry , chemistry , composite material , mathematical analysis , mathematics , engineering
Hierarchical FAU‐ and LTA‐type catalysts are prepared by post‐synthetic modifications and evaluated in the base‐catalyzed Knoevenagel condensation of benzaldehyde with malononitrile. A novel route to attain mesoporous Al‐rich zeolites (A and X) is demonstrated, while mesoporous Y and USY zeolites are prepared using recently developed methods. Base functionality is introduced by alkali ion exchange (Cs, Na) or by high‐temperature nitridation in ammonia. A thorough characterization of the zeolites' structure, composition, porosity, morphology, and basicity demonstrates that the presence of a secondary mesopore network enhances the ion‐exchange efficiency and the structural incorporation of nitrogen. The modified USY zeolites display twice the conversion, while the hierarchical A, X, and Y are up to 10 times more active based on the enhanced accessibility. These results demonstrate that the Knoevenagel condensation takes place predominately at the external surface, highlighting secondary porosity as a key criterion in the design of basic zeolite catalysts.