possible to estimate the internal size of the spherical cavities of 1.13 and 1.36 nm for
the Zeolite 5A and FAU, respectively. In contrast, HK and SF methods provide
inferior cavity sizes. Another result worth to highlight is that the PSD obtained with
the HK (slit pores) method predicts cavity or channel sizes of 28 and 48% less than
the theoretical value for these samples. Thus, it is imperative to take into account the
most representative pore geometry for each sample.
In Fig. 15 is presented the comparison between the micropore size distribution
obtained by CY and non-local DFT (NLDFT) methods, using the argon adsorption
data at 87 K of Zeolite 5A. For NLDFT, the kernel used was “Ar-zeolite/silica
adsorption branch kernel at 87 K based on a spherical pore model (pore diameter
Fig. 12 Argon adsorption
isotherms of 5A and FAU at
87 K and ZSM-5 at 77 K.
Argon isotherms of 5A and
ZSM-5 adapted with
permission from Maglara
et al. [51]. Copyright (1994)
American Chemical Society
[54]
Fig. 13 Micropore size
distributions with HK, SF,
and CY methods for ZSM-5.
The structures shown in
each PSD correspond to
each zeolite, indicating the
sizes of channels (green)
Critical Overview of Textural Characterization of Zeolites by Gas Adsorption
49