Erschienen in:
Zeitschrift für anorganische und allgemeine Chemie, 637 (2011) 1, Seite 75-82
Sprache:
Englisch
DOI:
10.1002/zaac.201000273
ISSN:
1521-3749;
0044-2313
Entstehung:
Anmerkungen:
Beschreibung:
AbstractZeolites of type USY (ultra‐stable Y) were obtained by steaming of NH4NaY modification. Samples were modified by subsequent alkaline treatment in KOH solution. USY and USY‐KOH were characterised by chemical element analysis, XRD, IR, 29Al and 29Si MAS NMR spectroscopic measurements. Correct silicon to aluminium ratios (Si/Al) were determined by XRD and IR (double ring vibration wDR) data whereas values calculated according to data of 29Si MAS NMR and IR spectroscopy (asymmetrical TOT valence vibration wTOT) appeared to be too high., In the latter case, the signals of the zeolite framework were strongly superimposed by that of extra‐framework silica gel (EFSi) formed during steaming. It was found that alkaline leaching induces desilication of silicon‐rich area of the zeolite framework and partial dissolution of EFSi. Silicate ions of both react with likewise dissolved extra‐framework aluminium (EFAl) to form X‐ray amorphous aluminosilicate. Consequently, the superposition of the 29Si MAS NMR signals of the zeolite framework by silica gel was reduced for Q4(0Al) but increased for Q4 (2Al) and Q4(3Al) structure units. A reinsertion of EFAl into the zeolite framework has not been observed.