3. Results and discussion
3.1. Structural identity and framework dealumination
The powder XRD patterns of all three samples were
found to be almost identical, except a slight decrease in
the intensity of peaks after the severe acid treatment,
indicating that the dealumination conducted even under
severe acid treatment conditions caused no drastic
changes such as framework collapsing of mordenite,
and the structure of mordenite was protected during
the acid treatment. However, 27Al NMR of both the
acid treated samples exhibited the presence of octahedral
alumina (Aloct) and the occurrence of framework
dealumination due to acid treatment, and that may be
the reason for a slight decrease in the intensity of
XRD peaks of ATHM-3. XRD is a bulk characterizationtechnique and it is thus likely that the local modifications
of the micropore structure of H-MOR upon
dealumination cannot be detected by this method. However,
the Si/Al ratios of parent and acid treated mordenite
samples, measured by XRF (Table 1) were increased
from 18 of HM to 25 and 39 of ATHM-1 and ATHM-3,
respectively, and confirms the occurrence of dealumination
by acid treatment.