RSC Advances
Paper
removed and the H form of the zeolite was obtained. The
HZSM-5@silicalite-1 core–shell composite molecular sieves
with densely packed silicalite-1 shells were prepared through
a surfactant-directed sol–gel coating process. In a typical
synthesis of HZSM-5@silicalite-1 composites with a shell
thickness of approximately 200 nm, a HZSM-5 zeolite (Si/Al ¼
75) water suspension containing zeolite particles (3.0 g) was
dispersed in a mixture containing TPAOH (1.22 g) and water
(30 g) under ultrasonic treatment for 30 min. Next, TEOS
Conclusions
Shape-selective methylation of toluene with methyl bromide
was studied over HZSM-5@silicalite-1 composite catalyst.
HZSM-5 crystals with different crystal sizes were chosen as
representative zeolite cores and coated with an ordered
silicalite-1 shell according to a facile base-catalyzed sol–gel
coating strategy using TEOS as silica source and TPAOH as
template. The silicalite-1 shell extends the diffusion path length
for xylenes and fully covers the acid sites on the external surface
of HZSM-5, improving catalyst stability as well as para-selectivity
in the methylation of toluene as a result.
ꢁ
(2.14 g) was added dropwise and stirred for 3 h at 80 C. The
mixture was heated in an autoclave at 180 ꢁC under static
condition for 48 h. Aerwards the as-generated core–shell
composites were collected by centrifugation and washed with
water, and dried overnight at 110 ꢁC. Finally, the organic
Acknowledgements
ꢁ
templates were removed by calcination at 550 C for 5 h.
This project was nancially supported by National Natural
Science Foundation of China (grant nos 21273067 and
U1162109). C.T. Au thanks the Hunan University for an adjunct
professorship.
Catalyst characterizations
Powder X-ray diffraction (XRD) experiment was conducted on a
Bruker D8 Advance diffractometer using Cu Kaꢂr1adiation. The
data were recorded at a scan rate of 0.02ꢁ (2q) s in the 5–60ꢁ
range. The surface area of catalyst was measured by the Bru-
nauer–Emmett–Teller (BET) method on a Tristar 3000 instru-
ment; before each measurement, the sample was heated to
Notes and references
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ꢁ
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microscope at an accelerating voltage of 200 kV.
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37300 | RSC Adv., 2014, 4, 37296–37301
This journal is © The Royal Society of Chemistry 2014