Shape controlled zeolite EU-1 (EUO) catalysts: Dry gel conversion type synthesis, characterization and formation mechanisms

摘要

Shape controlled zeolite EU-1 (EUO) catalysts were synthesized by a dry gel conversion (DGC) type synthesis. Silica extrudates as starting material were impregnated to the incipient wetness point and subjected to a hydrothermal treatment under water vapor. All-zeolite extrudates with the same size and shape as initial silica extrudates were obtained. Formation mechanisms were investigated by varying the initial extrudate water content. Hydrothermal treatment was carried out in the presence or in the absence of an external water source. Extrudate H2O/SiO2 molar ratios of at least 1.5 were required to obtain zeolite extrudates with high crystallinity. In the presence of an external water source, a non-uniform progression of zeolite crystallization from the outer to the inner extrudate surface was observed. On the contrary in the absence of an external water source, first crystals appeared throughout the extrudates. For both methods, mesopores of silica extrudates disappeared during impregnation processes and micro- and macropores were formed during crystallization. In a m-xylene isomerization reaction shape controlled zeolite EU-1 extrudates display an enhanced p-xylene selectivity.