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4000 cmÀ1, and the KBr pellet tech-
nique was used. UV/vis spectra
were obtained by using a Jasco
UV-550 spectrometer from 190–
500 nm, and pure BaSO4 was used
as a reference. Argon physisorp-
tion measurements were per-
formed at liquid argon tempera-
ture by using a Quantachrome Au-
tosorb iQ2 physical sorption appa-
ratus. The total surface area and
pore volume were calculated ac-
cording to the BET and t-plot
methods, respectively. The appear-
ances of the crystals were deter-
mined by using a Hitachi S-4800
scanning electron microscope. X-
ray photoelectron spectra (XPS)
were acquired by using a Thermo
VG ESCALAB250 instrument using
AlKa radiation operated at a con-
stant power of 260 W. The ob-
tained spectra were analyzed by
Figure 12. SEM images of the sample prepared with 0.5 wt% of seeds treated for different times.
using
a
curve-fitting program
XPSPEAK, which was helpful to
find the best fitting results. A PerkinElmer OPTIMA 2000DV optical
emission spectrometer was used to provide the bulk element com-
position.
Experimental Section
Synthesis of TS-1
TS-1 with different crystal sizes was synthesized in a TPABr/ethyla-
mine (EA) hydrothermal system using colloidal silica and titanium
tetrachloride as Si and Ti sources, respectively. TPABr was the tem-
plate, and ethylamine was the base. The molar composition of the
gel was: n(SiO2)/n(TiO2)/n(TPABr)/n(EA)/n(H2O)=1:0.025:0.15:1.0:16.
A suspension that contained nano-sized silicalite-1 was adopted as
seed. The amount of seed was calculated by the weight ratio of
the solid in the suspension to the SiO2 in the colloidal silica, and
was varied from 0 to 0.12 to adjust the crystal size of TS-1. For ex-
ample, the addition of 6 wt% seed means the weight ratio of the
solid in the suspension to the SiO2 in the colloidal silica was 0.06.
The suspension was prepared by mixing tetraethyl orthosilicate,
TPAOH, and water in a glass flask equipped with a condenser and
heated at 808C for 72 h. The molar ratio of the mixture was:
n(SiO2)/n(TPAOH)/n(H2O)=1:0.3:20. The obtained light milky sus-
pension was used as seeds directly without any other treatment.
Epoxidation of propene
The epoxidation of propene was performed in a 400 mL stainless-
steel reactor. First, H2O2/methanol solution (1.4 molLÀ1, 34 mL) and
TS-1 powder (0.2 g) were fed into the reactor. Propene was then
charged to the reactor to reach 0.4 MPa. The reaction was finished
after heating the mixture at 408C for 1 h. The residual H2O2 was
checked by iodometric titration. The products were analyzed by
using a Tianmei 7890F gas chromatograph equipped with a flame
ionization detector (FID) and a PEG-20m capillary column (30 m
0.25 m 0.4 mm). PO is the target product, and propene glycol
(PG) and its monomethyl ethers (MME) are byproducts. X(H2O2),
S(PO), and U(H2O2) were calculated as follows [Eqs. (2)–(4)]:
XðH2O2Þ ¼ 1ÀnðH2O2Þ=n0ðH2O2Þ
ð2Þ
ð3Þ
ð4Þ
The synthesis procedure was as follows: titanium tetrachloride was
added dropwise into isopropyl alcohol, and the obtained solution
was added to colloidal silica. Finally, TPABr, EA, seed, and water
were added to the colloidal silica gradually. The mixture was stirred
for 30 min, then transferred to a Teflon-lined autoclave and crystal-
lized at 1708C for 6–72 h. The obtained suspension was centri-
fuged, and the solid was washed by centrifugation twice, dried at
1008C overnight, and calcined at 5408C for 6 h to remove the tem-
plate. The synthesized samples were denoted as TS-1-a-t, in which
a and t stand for the content of seed and crystallization time, re-
spectively. For example, TS-1-6-72 was prepared by the addition of
6 wt% seed and crystallized for 72 h.
SðPOÞ ¼ nðPOÞ=ðnðPOÞþnðMMEÞþnðPGÞÞ
UðH2O2Þ ¼ ðnðPOÞþnðMMEÞþnðPGÞÞ=ðn0ðH2O2ÞXðH2O2ÞÞ
in which n0(H2O2) and n(H2O2) are the initial and final molar con-
tents of H2O2, respectively, and n(PO), n(MME), and n(PG) represent
the molar contents of PO, MME, and PG, respectively.
Treatment of the seed
Synthetic sources were added in the same way as with the normal
synthesis procedure, but without the addition of colloidal silica
and titanium tetrachloride (cf. Synthesis of TS-1). Amounts of 9 or
0.5 wt% of seed were used to observe the changes of the seed in
the simulated crystallization conditions. The mixture was heated at
1708C for 1–8 h in a Teflon-lined autoclave. The obtained suspen-
sion was separated, and the solid was dried and calcined at 5408C
for 6 h. The remaining solid was treated silicalite-1, which was char-
acterized by XRD and SEM.
Characterization of TS-1
XRD patterns were recorded by using a Rigaku Corporation Smar-
tLab 9 X-ray diffractometer using CuKa radiation. FTIR spectra were
collected by using a Bruker EQUINOX55 spectrometer from 400–
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