Nanoseeding Effect in ZSM-5 Crystallization Process

Abstract

ZSM-5 zeolites were hydrothermally synthesized in three di®erent seeding pathways under the direction of tetrapropylammonium bromide (TPABr) template. In order to investigate the seeding e®ect in ZSM-5 crystallization process, ZSM-5 crystals and pre-fabricated MFI-type nanoseeds were added into the original self-induction system, respectively. The¯nal ZSM-5 zeolites were systematically investigated based on XRD (X-ray di®raction), SEM (scanning electron micrograph), TEM (transmission electron micrograph), nitrogen adsorption characterizations and NH 3 -TPD (ammonia-temperature programmed desorption). The self-induction system produced ca. 20 m ZSM-5 zeolite displaying hexagonally uniform prisms. After the addition of ZSM-5 crystal seeds, the crystal sizes were decreased greatly to ca. 5 m. When MFItype nanoseeds were adopted, irregular aggregate particles consisting of 20À50 nm primary particles were rapidly synthesized. The varied hydrothermal crystallization kinetics of the three synthesis system was also explored. Adjusting the seed agents alone, ZSM-5 crystals with diverse structural, morphological, textural and hydrothermal behaviors could be fabricated conveniently. The three ZSM-5 zeolites loaded by 0.05 wt.% Pt were assessed for the xylene isomerization reaction to investigate the particle size e®ect on the catalytic properties.

Effect of ZSM-5 zeolite morphology on the catalytic performance of the alkylation of toluene with methanol

“…Figure 4 illustrates the argon adsorption-desorption isotherms of different extruded ZSM-5 sample at 87 K. The argon adsorption-desorption isotherms of ZSM-5 samples are of type IV with distinct hysteresis loop, which is typical for a porous material with mesoporous structure. The nonmicropore volume could be formed by piling up of the particles [32]. All the samples yield prominent peaks in their respective pore-size distributions at approximately 0.52 nm, a value that agrees very well with the dimension of the MFI nanopores.…”

“…The addition of ZSM-5 crystal seeds speeded up the nucleation and growth of ZSM-5. The acceleration could be largely attributed to the external surface areas of the crystal seeds and uniform distribution of the particles within the amorphous gel system [31,32]. The ZSM-5-C sample synthesized in the presence of added NaCl displays as 20 µm spherical aggregate with 3 µm cubic particles on the surface of the sphere.…”

Seed-assisted OSDA-free synthesis of ZSM-5 zeolite and its application in dehydrogenation of propane

“…Effect of seeding step in ZSM-5 crystallization process was examined by introducing ZSM-5 crystals and pre-fabricated silicalite-1 nanoseeds into the original self-induction system [12]. Adoption of silicalite-1 nanoseeds had much more prominent effect which led to the formation of relatively small particles with promoted catalytic performance in benzene alkylation and xylene isomerization.…”