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M. Okamoto et al. / Applied Catalysis A: General 467 (2013) 55–60
autoclave was heated at 170 ◦C for 48 h under a static condition.
The solid product was separated by centrifugation, washed several
times with distilled water, dried overnight at 100 ◦C and calcined
in air at 550 ◦C for 7 h.
After recovery of the used catalyst, we reused the catalyst for the
reaction.
2.3. Catalyst characterization
2.1.2. Synthesis of triethoxysilyl-terminated PDMS
Powdered X-ray diffraction (XRD) data was recorded with a
Rigaku Multi Flex (Rigaku) using CuK␣ radiation. Field emis-
sion scanning electron microscopy (FE-SEM) images were taken
using a S4500 (Hitachi) operated at an accelerating voltage of
2.0 kV. To examine the particle size, dynamic light scattering (DLS)
measurement was performed using an LB-500 (Horiba). Before
measurement, particles were dispersed in water using sonication
for 30 min. Infra-red spectroscopic analysis of the catalysts was
using FT/IR-460 plus (JASCO). The samples were pressed into self-
supporting wafer, and then placed into the spectrometer.
Triethoxysilyl-terminated PDMS was synthesized by the
hydrosilylation of vinyl-terminated PDMS (molecular weight:
6000; Gelest) with triethoxysilane (Tokyo Chemical Industry Co.)
catalyzed by Pt/carbon. The mixture of 0.30 g of Pt/carbon (2%
(w/w) Pt), 3.2 g of vinyl-terminated PDMS, 40 mL of dry toluene
and 0.29 mL of triethoxysilane was refluxed for one night under
a nitrogen atmosphere. The Pt catalyst was removed by filtration,
and toluene and unreacted triethoxysilane were removed by vac-
uum. The ratio of unreacted vinyl groups in the obtained polymer
was 27% (determined by NMR analysis, see Supplementary Data,
Fig. S1). We obtained (3-methyldimethoxysilyl)propyl terminated
PPO (molecular weight: 600–800) from Gelest.
2.1.3. Linkage with the polymers
3.1. Polymer-linked zeolite
In a Schlenk flask, triethoxysilyl-terminated PDMS (3.2 g) or
(3-methyldimethoxysilyl)propyl terminated polypropylene oxide
(2.26 g) was mixed with nanoZSM-5 (2.0 g) dispersed in dry ethyl
acetate formed by sonication. After removal of ethyl acetate by
vacuum, the mixture was heated at 100 ◦C for 17 h. The resul-
tant catalyst was thoroughly washed with toluene and collected
by decantation. Finally remnants of toluene in the catalyst were
removed by vacuum. The catalysts linked with polydimethylsilox-
ane and polypropylene oxide are represented as PDMS-nanoZSM-5
and PPO-nanoZSM-5, respectively.
We prepared ZSM-5 nanoparticles (nanoZSM-5) via Grieken’s
S2). SEM observation (Fig. 1a) revealed that nanoparticles formed
as aggregates of small particles (ca. 30 nm). The aggregates, with
their size around 300 nm, were determined using analyses of the
morphology and DLS of the nanoparticles (Fig. 1). Thus, we linked
the small aggregates of the nanoparticles with polymers. BET and
external surface areas of nanoZSM-5 were 479 and 64 m2 g−1
,
respectively. The Si/Al ratios obtained from elemental analysis and
temperature programmed desorption of ammonia were the same,
58.
2.2. Reaction procedures
2.2.1. Esterification of acetic acid with 1-propanol or
cyclohexanol
To confirm the linkage of two aggregates of nanoparticle,
we used mono-triethoxysilylated polydimethylsiloxane instead
of the polysiloxane terminated by triethoxysilyl groups at
both the ends. The catalyst prepared from the mono-silylated
polymer (monoPDMS-nanoZSM-5) was powdery, whereas PDMS-
nanoZSM-5 was block (see Supplementary Data, Fig. S3). After
the catalysts (0.1 g) were dispersed in 50-mL toluene by stir-
ring for 1 h, the mixture settled for 1 min, and 40 mL of the
supernatant was removed. We dried and weighed the remains.
PDMS-nanoZSM-5 was almost recovered; however, recoveries
of monoPDMS-nanoZSM-5 and nanoZSM-5 were 34% and 40%,
respectively, indicating linkage between the particles with the
polymer. Recovery of monoPDMS-nanoZSM-5 was slightly lower
than that of nanoZSM-5, because hydrophobicity of PDMS proba-
bly makes monoPDMS-nanoZSM-5 dispersed in toluene more than
nanoZSM-5 with hydrophobic external surface due to hydroxyl
groups.
In a 50-mL flask, the polymer-linked zeolite (0.17 g excluding
the polymer weight), toluene (10 mL) as a solvent and acetic acid
(93 mmol) was mixed and heated at 100 ◦C. Alcohol (93 mmol) was
added to the mixture and the reaction started. Products are ana-
lyzed by gas chromatography. Dodecane was used as an internal
standard.
2.2.2. Hydrolysis of ethyl acetate
Hydrolysis of ethyl acetate was performed in a 50-mL autoclave.
The polymer-linked zeolite (0.13 g excluding the polymer weight),
ethyl acetate (1.0 g) and water (19 g) were put into the autoclave.
The hydrolysis was performed at 100 ◦C. After the reaction, the
autoclave was cooled, and cyclohexanone as an internal standard
was added to the reaction mixture.
2.2.3. Dehydration of 1-phenylethanol
Infra-red analysis of the polymer-linked zeolites revealed that
polymer structure remained after linkage between nanoZSM-5 and
the polymers (see Supplementary Data, Fig. S4). 29Si MAS NMR
spectra of the polymer-linked zeolites showed slight decrease of
the Q3(HOSi*(OSi)3)/Q4(Si*(OSi)4) ratio (see Supplementary Data,
Fig. S5), indicating that the polymers were linked with nano-ZSM-
5 by the reaction of silanol groups in nanoZSM-5 with alkoxysilyl
groups in the polymers. The amounts of nanoZSM-5 in the polymer-
linked zeolites were examined by elemental analysis. PDMS-
and PPO-nanoZSM-5 contained 35 and 53%(w/w) of nanoZSM-5,
respectively. The numbers of PDMS and PPO per the external sur-
face area of nanoZSM-5 were estimated to be 2.8 and 12 nm−2. The
PPO number was higher, possibly because part of PPO was immobi-
lized by one side of the polymer chain due to much shorter length
of PPO (3 nm) than the size of the aggregates.
In a 30-mL flask, the polymer-linked zeolite (0.10 g exclud-
ing the polymer weight), toluene (10 mL) as
a solvent and
1-phenylethanol (5 g) was mixed and heated at 110 ◦C. Products
are analyzed by gas chromatography. Dodecane was used as an
internal standard.
In all reactions, mass balances were almost 100%; errors were
less than 2.5%.
2.2.4. Recycling the catalyst
The used catalyst was recovered by decantation. The catalyst
with 5 mL of the solvent was decanted from the reaction mixture
after settling for 1 min, and 15 mL of the solvent was added to the
catalyst. After stirring for 3 min and settling for 1 min, we decanted
the mixture again. This entire process was carried out three times.