K.-i. Shimizu et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 50–54
Table 1
51
2
−1
Society of Japan. SiO2 (Q-10, 300 m g ) was supplied from Fuji
2
−1
Hydration of triethylsilane by supported metal (5 wt%) catalysts and reference
catalysts.
Silysia Chemical Ltd. ZrO2 (60 m g ) was prepared by hydrolysis
of zirconium oxynitrate 2-hydrate in distilled water by gradually
adding an aqueous NH OH solution (1.0 mol dm ), filtration of
a
−
3
Entry
Catalyst
Yield/%
4
b
precipitate, washing with distilled water three times, drying at
1
Raney Ni
Ni powder
NiO/C
Ni/C
Ni/C-air
Cu/C
Co/C
Fe/C
C
Ni/TiO2
Ni/SiO2
Ni/CeO2
Ni/ZrO2
Ni/SiO2–Al2O3
Ni/Al2O3
1
1
0
37
0
1
1
1
0
25
5
◦
◦
b
1
1
00 C, and calcining at 500 C. ␥-Al O (with surface area of
2
3
4
5
6
7
8
9
0
1
2
3
2
−1
24 m g ) was prepared by calcination of ␥-AlOOH (Catapal
◦
B Alumina purchased from Sasol) at 900 C for 3 h. NiO/C was
prepared by an impregnation method; a mixture of carbon (9.5 g)
c
3
and an aqueous solution of Ni(NO ) ·6H O (0.17 M, 50 cm ) were
3
2
2
◦
◦
evaporated at 50 C, followed by drying at 100 C for 12 h, calci-
d
◦
nation in air at 300 C for 1 h. Before each catalytic experiment,
1
1
Ni/C catalysts were prepared by in situ pre-reduction of NiO/C in
3
−1
a glass (pyrex or quartz) tube under a flow of H2 (20 cm min
)
12
13
14
5
4
1
1
◦
at 500–700 C for 0.5 h. Typically, the Ni/C catalyst pre-reduced
at 500 C with Ni loading of 5 wt% was used as a standard
◦
1
5
catalyst.
a
Conditions: catalyst (M: 0.3 mol%), Et3SiH (1 mmol), H2O (16 mmol) in acetone
◦
◦
(
1.6 g), 25 C, 0.5 h. The catalysts pre-reduced in H2 at 500 C were used without
exposure to air except for entries 3 and 5.
2
.3. Characterization of catalysts
b
Ni = 1 mol%.
c
Pre-reduced Ni/C was exposed to air at room temperature after H2-reduction at
◦
Ni K-edge X-ray absorption fine structure (XAFS) measure-
500 C.
d
Active carbon = 0.10 g.
ments were performed in transmission mode at the BL01B1 in
the SPring-8 (Proposal No. 2011B1137). The storage ring was
operated at 8 GeV. A Si(1 1 1) single crystal was used to obtain a
monochromatic X-ray beam. The catalyst pre-reduced in a flow
of 100% H2 (20 cm min ) for 30 min at 500 C was cooled to
room temperature in the flow of H2 and was sealed in cells
3. Results and discussion
3
−1
◦
First, various non-noble metal catalysts were tested for the
selective hydration of triethylsilane (Et SiH, 1a) to triethylsilanol
3
made of polyethylene under N , and then the XAFS spectrum
2
(
Et SiOH, 2a) as shown in Table 1. Conventional Ni catalysts (Raney
3
was taken at room temperature. The analyses of X-ray absorp-
tion near-edge structures (XANES) and extended X-ray absorption
fine structure (EXAFS) were performed using the REX version 2.5
program (RIGAKU). The Fourier transformation of the k -weighted
EXAFS oscillation from k space to r space was performed over the
Ni and Ni powder) and NiO/C were inactive for the formation of 2a.
The active carbon was inactive, which excluded a contribution of
the support itself as a catalyst. The Ni/C catalyst was prepared by
3
◦
the H -reduction of NiO/C at 500 C for 0.5 h, followed by cooling it
2
in H to room temperature. Then, the reaction mixture was injected
2
−1
range 30–140 nm
inversely Fourier filtered data were analyzed with a usual curve
to obtain a radial distribution function. The
to the pre-reduced catalyst inside the glass tube through a rubber,
and then the mixture was stirred under air at 25 C. Ni/C effectively
◦
−
1
fitting method in the k range of 30–140 nm . The parameters
for the Ni–O and Ni–Ni shells were provided by the FEFF6. The
number of free parameters for curve fitting can be estimated as
Pfree = 2ꢀk ꢀR/ ≈ 14, indicating that we can model the EXAFS data
with three shells.
X-ray diffraction (XRD) patterns of the powdered catalysts were
recorded with a Rigaku MiniFlex II/AP diffractometer with Cu K␣
radiation. Ni particle size distributions of Ni/C catalysts were deter-
mined by using a JEOL JEM-2100F TEM operated at 200 kV.
catalyzed the selective hydration of 1a to 2a. Ni/C showed higher
activity than Cu, Co, and Fe-loaded carbon (entries 6–8) and Ni-
loaded metal oxides (entries 10–15) under the same pre-reduction
and reaction conditions.
The precursor NiO/C and the catalyst Ni/C were characterized by
spectroscopic characterizations. The XRD pattern of NiO/C (Fig. 1)
showed a line due to NiO. The Ni K-edge XANES spectrum of
NiO/C was nearly identical to that of NiO (Fig. 2A). As shown in
Table 2, the curve-fitting analysis of EXAFS (Fig. 2B) confirmed the
2.4. Catalytic tests
Ni
NiO
Metal-loaded catalysts were prepared by the H -reduction of
the metal oxide-loaded precursors (such as NiO/C) at 500 C for
2
◦
0
.5 h, followed by cooling it in H2 to room temperature. Then, a
mixture of silane (1.0 or 5.0 mmol), water (16 mmol) and acetone
1.6 g) was injected to a pre-reduced Ni catalyst (typically 0.3 mol%
(
Ni with respect to silane) in the glass tube, and the mixture was
stirred. Then, an injection needle was inserted to the rubber. Thus,
the reaction vessel was open to air and H2 was released outside of
the reactor. For the kinetic experiments, initial rates of the silanol
formation were determined by changing the initial concentration
of Et SiH and H O in the reaction mixture. The products were con-
Ni/C-air
NiO/C
3
2
firmed by comparison of their GC retention times, GC–MS spectra,
1
and H NMR spectra with those of authentic data. Conversion of
silane and yields of products were determined by GC using n-octane
as an internal standard. GC analysis of the gas phase product was
carried out by Shimadzu GC-6A with TCD detector, molecular sieve
30
40
50
60
2
θ / deg.
5
A column and Ar carrier.
Fig. 1. XRD patterns.