The unit-cell parameter of the reference sample, Y, was found to be 2.426(1) nm. The
micropore volume, Vmp, obtained from the Dubinin transformation was 0.36 cm3(liq)/g.
These results agree well with data found in the literature [8,13,21]. The Langmuir-specific
area was 1.03 3 103 m2/g zeolite (Table 2).
The USY retained its crystallinity at 1000°C for several days. The powder X-ray diffraction
analyses of the samples generally confirmed that the zeolite unit cell parameter, a 5
2.426(1) nm, was unaffected by the heat treatment. Comparison of powder diffraction
patterns before and after heat treatment at 1000°C revealed a very slight broadening of the
reflections. According to the TG/DTA analysis no phase transition or change of weight was
observed, as shown in Figure 1. Heating the USY at 1200°C caused a collapse of the structure
within an hour. According to powder X-ray diffraction analysis the phase was completely
amorphous. No other phase had occurred after 10 days of heating. After 4 h at 1300°C,
recrystallization of the amorphous phase into cristobalite had begun. Based on these results,
1000°C was used as the sintering temperature for zeolite crystallites.