No abstract

Spherical, micrometer‐sized particles with a layered structure were obtained by precipitation of a Silicalite‐1 zeolite nanoslab suspension upon addition of cetyltrimethylammonium bromide (CTMABr) and subsequent calcination. The material had a specific micropore volume of 0.69 cm3 g–1, distributed over super‐ and ultra‐micropores. The formation process of this peculiar microporous solid was studied using X‐ray diffraction (XRD), 29Si MAS NMR spectroscopy, thermogravimetry (TG), and nitrogen adsorption. In the precipitate, the Silicalite‐1 nanoslabs were laterally fused into nanoplates and stapled into layers with intercalated surfactant molecules. Removal of the surfactant through calcination caused facial fusion, besides additional lateral fusion, of the nanoplates. Empty spaces left lying laterally between individual nanoplates were responsible for the super‐microporosity. The ultra‐micropores were zeolitic channels inside the fused nanoplates. The potential of these Silicalite‐1 zeogrids as molecular sieves was demonstrated with pulse gas‐chromatographic separation of alkane mixtures. The mass‐transfer resistance of a packed bed of zeogrid particles was considerably lower than of compacted zeolite powder.

No abstract

NaY has been dealuminated in highly controlled conditions by SiC1,. The materials thus obtained, after subsequent washing and ammonium exchange, were characterized by chemical analysis, thermogravimetry, X-ray diffraction, infrared spectroscopy of the framework and surface hydroxyl groups and 29Si nuclear magnetic resonance spectroscopy.In order to obtain highly crystalline materials in a reproducible way, a very specific dealumination and washing procedure has to be followed. The mechanism of the dealumination is complex and always combines direct isomorphic substitution with acid leaching of aluminium. The materials obtained have continuously varying properties as far as unit-cell dimensions and framework vibrations are concerned. In contrast, the amount of extra-lattice aluminium retained in the zeolite reaches a maximum at intermediate degrees of dealumination.

No abstract