T.-T. Li et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 38–44
43
2
−1
surface area of 92.8 m g , which is about 36% higher than that
the basic solutions also act as guests and are in situ coated onto
the newly formed mesopores. Hence, the fabrication and function-
alization of mesoporous ceria can be realized in one step, which
avoids the collapse of nonsiliceous mesoporous frameworks in
post-modification. Our materials also exhibit excellent basic cat-
alytic performance in the synthesis of DMC via transesterification.
The catalytic activity of NaMC sample is apparently better than that
over the samples derived from post-modification (Na/MC) and non-
mesoporous ceria (Na/CeO2). The present strategy might open up
a route for the synthesis of new mesoporous functional materials.
2
−1
of KMC (59.6 m g ). The second factor is the different strength
of basic sites. As disclosed by CO -TPD results (Fig. 6), the CO2
2
desorption peak corresponding to superbasic sites is centered at
◦ ◦
20 C in NaMC, whereas 750 C in KMC. It should be stated that
6
◦
the samples were activated at 700 C prior to reaction. This activa-
tion temperature is high enough to expose all active sites in NaMC,
but only a part of active sites in KMC can be exposed. In order to
expose all active sites in KMC, we tried to activate the sample a
◦
higher temperature of 750 C. Unfortunately, the obtained sample
exhibited even worse catalytic performance, and the yield of DMC is
lower than 5% at 4 h. Further characterization shows that the sam-
ple after activated at 750 C possesses a surface area of 3.1 m g .
Acknowledgements
◦
2
−1
Additionally, no diffraction lines can be observed in the low-angle
XRD pattern. It can be therefore inferred that the mesostructure of
KMC is destroyed at the activation temperature of 750 C.
To study the effect of sodium content in the samples on the cat-
alytic performance, two additional samples, namely NaMC (1 M)
and NaMC (3 M), derived from 1 and 3 M NaOH solution were
prepared. Their respective Na/Ce molar ratios are 0.22 and 0.84
The National Science Foundation of China (nos. 21006048 and
20976082), the Specialized Research Fund for the Doctoral Program
of Higher Education of China (no. 20093221120001), the Natural
Science Foundation of Jiangsu Province Colleges (no. 09KJB530004),
the Major Basic Research Project of Natural Science Foundation of
Jiangsu Province Colleges (no. 08KJA530001), China Postdoctoral
Science Foundation (no. 20110491406), and the Priority Academic
Program Development of Jiangsu Higher Education Institutions are
◦
(
Table S1). The synthesis of DMC catalyzed by NaMC (1 M) and
NaMC (3 M) was conducted and the results were shown in Fig. S3.
The yields of DMC are 24.3% and 47.5% at 4 h under the catalysis
of NaMC (1 M) and NaMC (3 M). Both yields are lower than that
over NaMC derived from 2 M NaOH solution (64.6%). The small
Appendix A. Supplementary data
−1
amount of basic sites (1.14 mmol g ) as well as weak base strength
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.09.030.
(
(
22.5) should be responsible for the low DMC yield over NaMC
1 M). The increase of sodium content leads to the improvement of
−1
both amount of basic sites (4.22 mmol g ) and base strength (27.0),
while the surface area decreases obviously due to the blockage of
pores by sodium species in NaMC (3 M) (Table 1). As a result, the
sample NaMC (3 M) exhibits worse catalytic activity as compared
with NaMC derived from 2 M NaOH solution.
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