3. Results and discussion
3.1. Characterization of catalyst
The XRD patterns of H-Mor and H-M-Mor samples exhibit well resolved
diffraction peaks (Fig. 1), which are characteristic for the MOR
framework structure. The peak intensity of H-M-Mor had no obvious
change compared with that of H-Mor, indicating that the crystal structure
of mordenite was remained well after acidic and alkali treatment
under the given condition. N2 sorption experiments exhibited a type
IV N2 adsorption–desorption isotherm for H-M-Mor (Fig. 2), which is
typical for mesoporous materials, with a capillary condensation step
at a relative pressure of 0.4bP/Pob0.6. A narrow mesopore distribution
centered at 3.8 nm by the Barrett–Joyner–Halenda (BJH) model was observed
for H-M-Mor (Fig. 2 inset). In comparison, H-Mor gave a type I
isotherm which is typical for microporous materials. The sorption data
(Table 1) showed that H-M-Mor had a higher BET surface area
(393 m2
/g) than that of H-Mor (360 m2
/g). The microporous volume
of H-M-Mor (0.16 cm3
/g) is slightly lower than that of H-Mor
(0.17 cm3
/g), suggesting that microporosity in mordenite was largely
preserved after the post treatment. These results suggested that at
first the acid leaching resulted in the extraction of partial Al species in
the framework of mordenite and then the base treatment removed
the partial silica species possibly on the corresponding extraction position
of Al species. Therefore, after the whole post treatment, the microporosity
could be well maintained. However, the surface area was
increased because the porosity of the sample was improved. Notably,
H-M-Mor possessed a much higher mesopore volume than that of
H-Mor. The value for H-M-Mor (0.06 cm3
/g) is six times as that of
H-Mor (0.01 cm3
/g). That means that the ability of mass transfer for
H-M-Mor should be greatly enhanced in catalytic reactions. This fact
has been proved by the benzylation of benzene with benzyl alcohol
over both samples. The result showed that H-M-Mor had a much higher
catalytic activity than H-Mor.