Bifunctional Tandem Catalysis on Multilamellar Organic–Inorganic Hybrid Zeolites
journal contributionposted on 05.09.2014, 00:00 by Le Xu, Chen-geng Li, Kun Zhang, Peng Wu
Tandem catalysis has been realized on the multilayered zeolites with organic-structure-directing agent (OSDA) molecules occluded within micropores. A combination of mild acid treatment and ion-exchange with ammonia solution was carried out on as-synthesized multilamellar MFI aluminosilicate, giving rise to an acid–base bifunctional catalyst. Containing tripropyl head groups, the Gemini-type quaternary ammonium OSDAs were firmly immobilized in the intersection of straight and sinusoidal 10-membered ring channels, with the other one exposed to the layer surface of the nanosheets. The resulting organic–inorganic materials possessed simultaneously the acid sites related to the framework Al and the base sites derived from coexisting OSDAs. In particular, two types of base sites were present, that is, the Lewis base sites due to the SiO– species and Brønsted base sites due to the OH– counteranion of exposed quaternary ammonium cations. The rigid materials were highly active and reusable in the one-pot reaction of tandem deacetalization–Knoevenagel condensation. Supporting palladium nanoparticles (Pd NPs) on the organic–inorganic hybrid zeolite led to bifunctional catalysts, which catalyzed effectively one-pot synthesis of benzylidene malononitrile from benzyl alcohol under soluble-base-free conditions, in which the benzyl alcohol was first aerobic oxidized to intermediate benzaldehyde followed by Knoevenagel condensation with malononitrile.