Characterization studies calcination step

All the other characterization studies have been performed after the calcination step XRD experiments have shown that the material formed during the synthesis has the MFI structure Si and 27a1 MASNMR spectra indicated that this phase has a Si/Al ratio varying between 550 and 30 as a function of the sample prepared and also that no extra framework A1 is present. 

The decrease of the total adsorption capacity of steamed HY zeolites with respect to that of the parent zeolite is due to the obstruction of the secondary network by the aluminic species created during the extraction of the framework aluminium atoms. An acid leaching solubilizes the extraframework species and so on increases widely the adsorption capacity. Electronic microscopy and nitrogen adsorption are used to study quantitatively the formation of the secondary network and to characterize the relative extent of the steps of calcination and acid leaching (ref. 9). 

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