B. Xue et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 384–391
385
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molecular size, such as triethyl borate, as the precursor of B O3 to
The scanning range was from 1700 to 1400 cm and the resolution
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1
prepare oxide modified zeolite shape-selective catalysts. Results
confirmed that a high shape-selectivity along with a high catalytic
activity was obtained in the production of p-DEB by alkyltaion of
EB with diethyl carbonate (DEC) over the boron oxide modified
HZSM-5 catalysts. This method is effective and innovative for the
preparation of shape-selective catalysts developed to date. In the
present study, boron oxide modified HZSM-5 shape-selective cat-
alysts were prepared by selecting a series of borate with different
molecular size and the catalytic performances of these catalysts
for para-alkylation of EB with DEC were investigated in detail.
was 4 cm . The sample powder was pressed into a self-supporting
wafer. Prior to each experiment, the catalysts were evacuated (1 Pa)
at 653 K for 3 h, and then cooled at 303 K for 2 h, and then exposed
to 4 kPa of pyridine or 2,4-DMQ solubilized in CH Cl2 (30 mol
for 1 mL solvent) for 5 min, and finally evacuated for 1 h at 303 K.
After adsorption of pyridine the samples were heated to 473 K at
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1
10 K min and the spectra were recorded.
Cracking of 1,3,5-triisopropylbenzene (1,3,5-TIPB) and cumene
(IPB) was carried out using a fix bed reactor at 723 K under N flow
with a WHSV (weight hourly space velocity) of 1 h . The cata-
lysts were tested for 1 h on stream. The products were analyzed by
gas chromatography (GC-2010, SHIMADZU) using a FFAP capillary
column and flame ionization detector (FID).
2
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1
2
. Experimental
2.1. Catalyst preparation
2.3. Alkylation of EB with DEC
ZSM-5 zeolite (Si/Al = 50) was synthesized by hydrothermal
Alkylation of EB with DEC was carried out in a fixed bed con-
tinuous down-flow reactor. About 3 g of the catalyst (as pellets of
0–40 mesh) was packed in the middle of the reactor and calcined
crystallization according to an established procedure [25]. The
NH4+ form of the as synthesized ZSM-5 zeolites was obtained by
ion-exchange with aqueous NH NO solution, and then calcined at
2
4
3
in a dry nitrogen flow for about 1 h at 653 K before reaction. The
reaction mixture of EB with DEC was introduced at the top of the
reactor by means of an infusion pump. The products were collected
in a water-cooled condenser attached to the end of the reactor and
analyzed by gas chromatography (GC-2010, SHIMADZU) using a
FFAP capillary column and flame ionization detector.
8
23 K for 3 h. The boron oxide modified HZSM-5 catalysts was pre-
pared as follows. The borate, including trimethyl borate and triethyl
borate, was dissolved in dehydrated alcohol. HZSM-5 was impreg-
nated with an ethanol solution containing borate. The mixture was
stirred for 1 h and allowed to stand overnight. Afterwards, the mix-
ture was evaporated in a constant temperature bath at 353 K for 6 h
and then dried in an oven at 383 K for 6 h. Then, the resulting mate-
rials were calcined at 823 K for 5 h in an air stream. The obtained
catalyst was denoted as x% B O /HZSM-5(M) or B O /HZSM-5 (E),
3. Results and discussion
2
3
2
3
where the x represented the mass percentage of B O based on
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3
3.1. Catalytic performances of B O /ZSM-5 catalysts
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3
the supports. The M and E represent the precursor of B O in the
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3
catalysts is from trimethyl borate or triethyl borate, respectively.
In contrast, boric acid was also used as the precursor of B O to
The catalytic performances of B O /ZSM-5(E), B O /ZSM-5(M)
2
3
2
3
2
3
and B O /ZSM-5(H) catalysts in the synthesis of p-DEB by alkyl-
2 3
prepare B O /ZSM-5 catalysts, and the catalysts were denoted as
2
3
ation of EB with DEC were presented in Tables 1–3, respectively. As
shown in Table 1, HZSM-5 exhibited the highest conversion of EB
among the investigated catalysts. However, the selectivity for p-
DEB over HZSM-5 was poor. After modification with triethyl borate,
x% B O /ZSM-5 (H).
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3
2.2. Catalyst characterization
the conversion of EB over B O /ZSM-5(E) catalysts decreased grad-
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3
ually from 48.2% to 31.3% with increasing the amount of B O3
2
X-ray diffraction (XRD) measurements were conducted using a
to 18%. Notably, a relatively high conversion of EB was retained
even for 18% B2O3/ZSM-5(E) catalyst. Meanwhile, the selectivity
for p-DEB over B2O3/ZSM-5(E) catalysts increased obviously with
increasing the amount of B O . The highest selectivity for p-DEB,
Rigaku D/max2500PC diffractometer with Cu K␣ (ꢀ = 1.54 A˚ ) radia-
◦
tion. The diffractograms were recorded in 2ꢁ range 5–50 in steps
of 0.02 with a count time of 15 s.
◦
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3
N2 adsorption/desorption analyses were obtained at 77 K
using a physical adsorption instrument (Micromeritics ASAP
about 97.6%, was observed over 18% B O /ZSM-5(E) catalyst. The
2
3
catalytic performances of B O /ZSM-5(M) and B O /ZSM-5(H)
2
3
2
3
2
5
020, USA). Before measurement, the samples were degassed at
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3
catalysts in alkylation of EB with DEC differed from those of
23 K under vacuum until a final pressure of 1 × 10 kPa was
B O /ZSM-5(E) catalysts. Although the selectivity for p-DEB over
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3
reached. The specific surface area was calculated according to the
Brunauer–Emmett–Teller (BET) isothermal equation.
B O /ZSM-5(M) or B O /ZSM-5(H) catalysts was also significantly
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3
2
3
improved with increasing the amount of B O , the catalytic activ-
2
3
Sample acidity was measured by NH3 temperature-
ities decreased severely, as shown in Tables 2 and 3. As for 15%
B O /ZSM-5 catalysts, the conversion of EB over B O /ZSM-5(E)
programmed desorption (NH -TPD) using
a
Quantachrome
3
2
3
2
3
CHEMBET-3000 instrument. A 200 mg sample was pre-treated at
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catalyst was markedly higher than those over B2O3/ZSM-5(M) and
B O /ZSM-5(H) catalysts. In particular, only a 2.3% conversion of
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3
23 K for 1 h in dry helium (flowing at 50 mL min ), cooled to
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93 K, then exposed to 10% v/v NH /He mixture for 0.5 h. After
3
EB was acquired over 15% B O /ZSM-5(H) catalyst.
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3
purging the catalyst with He for 0.5 h, the TPD plot was obtained
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1
at a heating rate of 10 K min
from 393 to 823 K. The thermal
conductivity detector (TCD) signal and temperature corresponding
3.2. Catalysts characterizations
to NH desorption were recorded simultaneously. The amount and
3
temperature of the desorbed NH3 corresponded qualitatively to
the amount and strength of the acid sites.
Fig. 1 shows the XRD patterns of HZSM-5 and B O /HZSM-5(E)
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3
catalysts with different B O3 loadings. Compared with HZSM-5,
2
FT-IR spectra of the samples were recorded using a Bruker FT-IR
spectrometer (TENSOR 27) with the KBr pellet technique. Spectra
no obvious changes in the position of peaks belonging to HZSM-5
zeolite were detected in the XRD patterns of the B O /HZSM-
5(E) catalysts. This indicated that the structure of HZSM-5 zeolite
was retained without any significant changes after modification
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were recorded in the range 4000–400 cm
.
FT-IR spectra with pyridine and 2,4-dimethylquinoline (2,4-
DMQ) adsorption was carried out using a Bruker FT-IR spectrometer
with triethyl borate. The peaks due to B O3 were not observed
2
(
TENSOR 27) together with a high temperature vacuum chamber.
even for 15% B O /HZSM-5(E) catalyst. The XRD patterns of 15%
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