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Publisher Summary This chapter discusses the effects on the acidity of postsynthesis treatments on HY-type zeolites using ammonia (NH3) adsorption calorimetry and silicon 29(Si) and aluminium 27(Al) nuclear magnetic resonance (NMR). The reaction of aqueous (NH4)2SiF6 solutions with NHaY can yield HY crystals with a Si-enriched framework free from measurable nonframework Al species in which T(3Si, IA1)/T(4Si,0A1) > 1.0. LZ-210 type crystals with Si/A1=3.1–4.4 have greater acid-site density and contain more acid sites with strength > 100 kJ/mol than the reference LZY-82. Steam aging causes a drastic decrease in acid sites density. However, in the temperature range (760–815°C) investigated, the strength of the strongest acid sites in the reference LZY-82 remains practically unaffected after hydrothermal treatment. |
