IR AND SI-29 NMR INVESTIGATION OF THE INFLUENCE OF ALKALINE MODIFICATION ON THE STRUCTURE OF HYDROTHERMALLY DEALUMINATED Y-ZEOLITES .1. MODERATELY DEALUMINATED ZEOLITES

The change in the structure of NH4NaY zeolite (53 % NH4+, Si/Al = 2.37 ) after hydrothermal treatment at 873 K followed by modification with aqueous KOH solution at 353 K was studied by IR and Si-29 NMR spectros copy. It has been shown that hydrolytic cleavage of the Al-O bond of t he deammoniated zeolite sites by hydrothermal treatment predominates i n the framework groups Si(OAl)(n)(OSi)(4-n), n = 2, 3. Molecular water adsorbed on such a sample exists as hydrogen-bonded associates with h ydrogen bonds of various strengths reaching that in ice-like structure s (the band at 2468 cm(-1)). Treatment with an alkali results in parti al regeneration of the normal bridge bonds. The exchange of the proton s of the terminal silanol groups with the alkaline cation prevents tho se groups from participating in the regeneration process.