The aspect of increase or decrease in volume of the
three types of micropores can be quantitatively measured
from the data generated based on the H–K differential
pore volume plot, given in Table 1. Firstly, the volume
in pores of < 6A ˚ in HM, ATHM-1 and ATHM-3 was
increased from 0.04850 cm3/g to 0.07221 cm3/g and
0.09280 cm3/g, clearly indicating that acid leaching
caused a significant increase in the volume in a side
pockets and this increase was further progressed with
dealumination severity. Secondly, the volume in the
pores corresponding to mordenite main channels with
pore sizes between 6 and 7A ˚ was decreased from
0.01940 cm3/g of HM to 0.01148 cm3/g and 0.00900
cm3/g of ATHM-1 and ATHM-3, respectively. This
can be understood by recollecting structural changes in
the zeolite framework; acid treatment expels alumina
from the framework of mordenite and an increase in pore
volume of small micro pores can be understood by opening
of more and more side pockets of mordenite during
framework dealumination. Out of the total extra-framework
alumina (EFAL) formed by dealumination, the
major amount EFAL can be removed from the mordenite
pores by acid leaching. However, the small amount
of EFAL that remains intact after acid leaching can
occupy the 12-membered mordenite pore channels, or
can be located at the entrance of the pores which can
affect the volume in the 12-membered channels, due to
the volume occupied by EFAL debris. 27Al NMR indeed
supported the presence of Aloct (octahedral alumina) in
the samples (ATHM-1 and ATHM-3) after acid treatment
and hence supports the possible presence of EFAL
material in the mordenite main channels. The third type
of micropores are secondary micropores (7–20 A ˚ ), wherethe increase in volume can be observed from 0.0384 cm3/
g (HM) to 0.0412 cm3/g and 0.0417 cm3/g (ATHM-1 and
ATHM-3, respectively) after acid leaching, suggesting
the formation of larger micropores also in mordenite
after acid leaching.