Dry-gel synthesis of zeolites [A1]EU-1 and [Ga]EU-1

The dry-gel conversion method using hexamethonium bromide (HMBr) as template allows to prepare zeolites [AI]EU-1 and [Ga]EU-1 (framework type EUO) with n(si)/n(Al) ratios of 18-142 and n(si)/n(Ga) ratios of 12-86, respectively. The most critical parameters of the dry-gel synthesis of zeolites EU-1 are the amount of water present in the autoclave during the crystallization process and the contents of sodium cations and template molecules in the dry gel. Zeolites EU-1 with a high crystallinity were obtained with a water content in the autoclave of mH(2)O /m(gel) greater than or equal to 0.67 and in the presence of a liquid water phase in the pores of the solid material during the conversion process occurring at T = 453 K. For a typical dry gel with an n(si)/n(Al) ratio of 41, contents of sodium cations n(Na)/n(si) and template molecules n(HMBr)/n(si) of 0.3 and >0.11, respectively, are necessary to obtain zeolite [Al]EU-1 without impurities such as zeolite EU-2, amorphous phases, or a-quartz. The concentration of Brphinsted acid sites as determined by H-1 MAS NMR spectroscopy of dehydrated zeolites H-EU-1 shows a linear dependence on the contents of aluminum or gallium. The strength of the Brphinsted acid sites in the obtained zeolites H-EU-1 was investigated by adsorption of C-13-2-acetone as probe molecule and application of C-13 MAS NMR spectroscopy. The experimentally obtained chemical shifts of C-13-2-acetone adsorbed on zeolites H-[Al]EU-1 and H-[Ga]EU-1 of 214.9 and 213.3 ppm, respectively, indicate a higher acid strength of the alummum-containing zeolite in comparison with the gallium-containing material. (C) 2003 Elsevier Inc. All rights reserved.