Novel zeolite nanosheets

15 September 2009 - Catalysis

Zeolites are microporous aluminosilicate minerals that can be used as catalysts. A substrate diffuses through the microchannel system with size and shape selection based on channel dimensions and catalysis takes place at specific acidic sites. Ideally, surface to mass ratio is optimized for maximum exposure but the production of very thin slices of zeolite is difficult due to interference of Ostwald ripening , the well-known process in which the larger crystals always grow at the expense of the smaller ones.

Choi et al have (DOI) presented a new way to synthesise nanosheet zeolites using a special bis-ammonium surfactant in a mix with the regular components for so-called ZSM-5 zeolite: tetraethyl orthosilicate and aluminium sulfate. After mixing and a lot of heating the crystals form as 20-40 nm wide sheets composed of alternating layers of zeolite (pentasil) with embedded ammonium salts units and aliphatic tail layers.

The surface area of the new material is found to be higher than that of conventional zeolites ( BET area 520 m2/g ). It's catalytic properties have been tested in methanol to gasoline conversion (see methanol economy): catalyst deactivation is slowed down and attributed to slower coke (degraded hydrocarbon) formation.