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2. Experimental
2.1. Catalyst preparation
Pure siliceous SBA-15, MCM-41, and HMS mesoporous
molecular sieves were synthesized according to the well-
established procedures [17–19] and a commercial meso-
porous silica was obtained from Qingdao Haiyang Chemical
Corp. All silicas were crushed and sieved to a particle size
of 40–60 mesh.
The amorphous Ni–B particles were introduced to silicas
by a reductant-impregnation method described as follows.
The silica (1.0 g, 40–60 mesh) was first immersed into the
potassium borohydride solution (3.0 M, 13.74 mmol) for
15 min, then the excessive solution was removed. Reduction
commenced as soon as the nickel chloride solution (0.42 M,
3.41 mmol) was added to the borohydride-impregnated sup-
port. The mixture was placed undisturbedly until no bubbles
were generated. The resulting black catalyst was washed
with distilled water to neutrality, and then with ethanol three
times to replace water. The catalyst was finally kept in
ethanol for characterization and prior to activity test.
The Raney Ni catalyst (Degussa) was used for compar-
ison. Since all catalysts can be oxidized easily, great care
must be taken to avoid their exposure to air.
Scheme 1.
one can develop a catalyst exhibiting exclusive selectivity to
eAQH2 rather than to H4eAQH2; i.e., the catalyst is exclu-
sively selective in hydrogenating the carbonyl group rather
than the aromatic ring.
Recently, amorphous alloy catalysts with short-range or-
dering and long-range disordering structure have attracted
much attention owing to their special physical and chem-
ical properties such as unique isotropic structure and high
concentration of coordinatively unsaturated sites [7–9]. In-
dustrial application of those amorphous alloy catalysts is
limited, however, due to their low surface area and poor ther-
mal stability. One of the most promising ways to overcome
those drawbacks is to deposit them on a support with high
surface area. The supported amorphous alloy catalysts have
been shown to be of better thermal stability than the corre-
sponding unsupported amorphous ones, higher activity and
selectivity than the crystalline counterparts, and less pollu-
tion than the Raney metal catalysts [10–14].
Regular mesoporous molecular sieves have shown great
potential in catalysis, which is closely related to their spe-
cific features such as extremely high surface area and narrow
pore-size distribution [15]. Their large channels allow dif-
fusion of bulky compounds and present different types of
shape selectivity such as reactant, product, and transition
state. These unique features of mesoporous molecular sieves
offer new possibilities for obtaining highly dispersed metal
catalysts and motivate us to study nickel boride amorphous
alloy catalyst supported on mesoporous molecular sieves.
In a recent research note, we have briefly reported the
excellent selectivity of the SBA-15-supported amorphous
nickel boride alloy catalyst in eAQ hydrogenation to eAQH2
[16]. This paper addresses the effects of pore structure on
the composition, size, and distribution of the Ni–B parti-
cles and catalytic behavior in eAQ hydrogenation of amor-
phous Ni–B catalysts supported by mesoporous silicas.
Both regular and commercial mesoporous silicas were used
as catalyst supports. Inductively coupled plasma-atomic
emission spectroscopy (ICP-AES), nitrogen physisorption,
X-ray diffraction (XRD), transmission electron microscopy
(TEM), X-ray photoelectron spectroscopy (XPS), and H2
chemisorption were used to characterize the catalysts and
the different catalytic behaviors were correlated.
2.2. Characterization
The bulk compositions of the as-prepared catalysts were
determined by ICP-AES (Thermo Elemental IRIS Intrepid).
The Brunauer–Emmett–Teller surface areas (SBET) and
pore-size distribution (PSD) of mesoporous silicas were
measured using N2 physisorption at 77 K. Prior to mea-
surement, samples were transferred to the glass adsorption
tube and degassed at 383 K under ultrahigh pure nitrogen
flow for 2.0 h. The nitrogen adsorption–desorptionisotherms
were acquired on the Micromeritics TriStar 3000 appara-
tus. The pore volume was calculated from the amount of N2
adsorbed at a relative pressure of 0.995. The pore-size distri-
bution curves were calculated from the desorption branches
of the isotherms using Barrett–Joyner–Halenda (BJH) for-
mula [20].
The pore structure and the Ni–B particle size of the as-
prepared catalysts were observed by TEM (JEOL JEM2011)
fitted with an energy-dispersive X-ray emission analyzer
(EDX) with mapping facility. The amorphous character of
the catalysts was verified by selected-area electron diffrac-
tion (SAED).
The XRD patterns were collected on a Bruker AXS D8
Advance X-ray diffractometer using Cu-Kα radiation (λ =
0.15418 nm). The tube voltage and current was 40 kV and
40 mA, respectively. Catalyst with solvent was put on the
sample stage, with argon flow (99.9995%, deoxygenated by
an Alltech Oxy-trap filter) purging the sample during the de-
tection to avoid oxidation. Crystallization of the catalyst was