Mario Padovan

Studies on the ZSM-5 zeolite formation

Abstract The crystallization of ZSM—5 zeolite, from a 3.6 Na2O, 6.6 TPA-Br, 1 Al2O3, 24.0 SiO2, 180 H2O system at 120°C, proceeds through various steps which have been followed by many techniques. The results suggest that a Silicalite-like zeolite initially crystallizes quickly and thereafter the aluminum enters the structure probably through dissolution of the crystal aggregates and formation of real ZSM—5 zeolite.

Effect of the aluminium content on the ZSM—5 zeolite crystallization in the presence of alkanolamine

Abstract The alkanolamines have been found to favour the crystallization of MFI structures only in the presence of Al (ZSM—5 zeolite), but not in its absence (silicalites) as the tetralkylammonium salts do. When the starting SiO 2 Al 2 O 3 molar ratios (R0) > 100 a mixture of ZSM—5 and a crystalline silicate (magadiite) is formed. The magadiite percentage increases with R0, until it becomes the single phase present when Al is practically absent in the sample. The structural Al content in the ZSM—5 phase, as determined for the various samples by three independent methods, never goes below two atoms per unit cell of 96 tetrahedral (T) atoms (Si + Al).

Comparison of different samples of HZSM-5 as catalysts for toluene disproportionation

Abstract Toluene disproportionation was performed at 300°–360°C in a fixed-bad reactor (carrier H 2 ) over samples of HZSM-5 differing in surface acidity, organic compound used for the synthesis, crystal size and procedure used for decationation. Xylene isomers in the product were in equilibrium ratios. The catalyst activity was found to be clearly dependent on surface acidity. An interpretation is given, in terms of a slow toluene disproportionation within the zeolite pores, followed by fast xylene isomerization on the external surface. Measurements of the reaction rate at 300°C over one of the catalysts confirmed a kinetic model as previously suggested.