Abstract
Modified zeolite ZSM-5 samples were prepared by synthesis in the presence of the organics acting as mesoporogens: cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) and cationic polymer, polydiallyldimethylammonium chloride (PDADMAC), as well as by alkali etching of the parent zeolite. Properties of modified zeolites were compared to the parent ZSM-5 zeolite. X-ray diffractograms demonstrate that the obtained modified zeolite ZSM-5 samples in all cases have preserved parent crystalline zeolite framework of the MFI-type. However, scanning electron micrographs of the same samples show morphology variations of the modified samples as compared to the starting zeolite. Thermogravimetric analyses show distinct weight loss curves of the samples. Differences have been also noted in the hydroxyl stretching range of the infrared spectra, and in the results of positron annihilation lifetime spectroscopy (PALS) measurements, which indicated dissimilarities by probing free volume in parent and modified zeolite ZSM-5 samples. In that way, PALS as scarcely used technique in zeolite studies, proved its applicability in structural investigation of this kind.
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