engleski

Unusual Pathway of Crystallization of Zeolite ZSM-5 in a Heterogeneous System: Phenomenology and Starting Considerations

Crystallization of zeolite ZSM-5 from a diluted heterogeneous system (12.5Na2O-Al2O3-8TPABr-60SiO2-4000H2O) was investigated by various experimental methods such as, X-ray diffraction (XRD), electron diffraction (ED), infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning-electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermo-gravimetric analysis (TG-DTG), particle size analysis (PSA) and Inductive Coupling Plasma (ICP) Emission Spectrometry. The crystallization process is characterized by a very long “induction period” (95 % of the entire reaction time) and very fast transformation (5 % of the entire reaction time) of amorphous to crystalline phase (zeolite ZSM-5) at the end of crystallization process. Analysis of the obtained results have shown that the crystallization process takes place by a chain of processes: (i) formation of “primary” amorphous aluminosilicate precursor (gel) at room temperature, (ii) formation of “secondary” amorphous aluminosilicate precursor (“worm-like” particles – WLPs), (iii) formation of “tertiary” amorphous aluminosilicate precursor (condensed aggregates – CAs) by aggregation of the WLPs and densification (condensation) of aggregates and (iv) formation of nuclei and their growth in the matrixes of CAs ; these processes result in the formation of fully crystalline zeolite ZSM-5 in the form of polycrystalline aggregates.

Zeolte ZSM-5 ; Unusual crystallization pathway ; “Worm-like” particles ; Condensed aggregates ; Polycrystalline aggregates ; Heterogeneous system

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