ZSM-5 precursors assembled to a mesoporous structure and its subsequent transformation into a zeolitic phase - from low to high catalytic activity

Mesoporous materials were synthesized from solutions containing ZSM-5 precursors in the presence of a micellar template (CTACl). The effect of different parameters like aluminum content, aging conditions and hydrothermal treatment conditions on the properties of the final materials was investigated by dynamic light scattering (DLS), N-2 physisorption, XRD, Al-27 MAS-NMR, TEM and IR. In addition two catalytic test reactions (cracking of isopropyl benzene and 1,3,5-triisopropylbenzene) and acidity measurements via pyridine adsorption were carried out. We observed a transition of the initially formed mesoporous structure containing protozeolitic seeds to a zeolitic phase during hydrothermal treatment. The rate of zeolitization strongly depended on the conditions of the aging period and on the composition of the synthesis solution: the more protozeolitic seeds were formed during the aging procedure the faster the zeolitization. Catalytic test reactions and acidity measurements showed that the XRD amorphous materials with protozeolitic seeds in the mesoporous structure are more active and more acidic than mesoporous materials prepared without ZSM-5 precursors, but far less active and acidic than zeolites. A combination of high activity and accessibility of most active sites was found for samples containing small zeolite crystals. (c) 2005 Elsevier Inc. All rights reserved.