Hydrophobic properties of all-silica zeolite beta

By optimizing the crystallization time and various other parameters, a procedure for the synthesis of all-silica zeolite beta was developed allowing a scale-up in a 51 autoclave. H-1 MAS NMR investigations of this all-silica zeolite beta, zeolite beta with a silicon to aluminum ratio of n(Si)/n(Al) = 22 and a dealuminated zeolite beta (n(Si)/n(Al) = 620) confirms that the former zeolite exhibits a significantly smaller amount of defect OH groups than the other materials. The hydrophobicity index (HI), determined by competitive adsorption of water/toluene or water/methylcyclohexane vapor mixtures, was used as a quantitative measure of the hydrophobic surface properties. It is shown that the hydrophobicity of ail-silica zeolite beta is on the same order as that of activated carbon and twice to eight times higher than those of other siliceous 12-membered ring zeolites, such as dealuminated zeolites beta, Y or EMT. (C) 1998 Elsevier Science B.V. All rights reserved.