A novel organic-inorganic layered titanosilicate consisting of Ti-containing MWW-type nanosheets and piperidine ligands was constructed. It exhibited an unprecedented high catalytic activity and recyclability in alkene epoxidation.
Organic-inorganic hybrid zeolites with the MFI-type lamellar structure serve as efficient solid Lewis base catalysts for solvent-free synthesis of a variety of cyclic carbonates from corresponding epoxides and carbon dioxide. The ion-exchange with iodide, in particular, renders these materials an excellent catalytic activity and good recyclability.
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.
A hierarchical titanosilicate, with epitaxially grown MFI nanosheets on microsized TS-1 crystals, has been prepared through a desilication-recrystallization method using a diammonium surfactant as the secondary structure-directing agent (SDA). This core/shell material features multiple mesoporosities, significantly improved epoxidation activity as well as easy separation in synthesis and catalytic reactions.
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