Ni-La-B amorphous alloys supported on SiO2 and γ-Al 2O3 for selective hydrogenation of benzophenone

Article abstract of DOI:10.1016/j.molcata.2012.07.018

The liquid phase selective hydrogenation of benzophenone was studied over Ni-La-B amorphous alloys supported on SiO₂ and γ-Al ₂O₃, respectively, and the effect of the carriers was subject to detailed examination. Based on characterization data, SiO₂ was suggested to have a planar structure and γ-Al₂O ₃ a porous structure, which markedly influenced the activity and stability of the supported catalysts. Use of ultrasound during catalyst preparation was found to make the particle sizes of the samples smaller, leading to the active particles being more dispersed on the carrier and leading to an increase in the conversion of benzophenone. Using ultrasound protocols, a Ni-La-B amorphous alloy supported on SiO₂ (Ni-La-B/SiO₂-u) initially showed better activity and selectivity than a Ni-La-B amorphous alloy supported on γ-Al₂O₃ (Ni-La-B/γ-Al ₂O₃-u); whereas Ni-La-B/SiO₂-u showed poor stability compared to Ni-La-B/γ-Al₂O₃-u. The main reason for the deactivation of Ni-La-B/SiO₂-u was ascribed to the adsorption of reactants and products onto the catalyst surface and their coverage of the active Ni sites.

Full text of DOI:10.1016/j.molcata.2012.07.018

Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Ni–La–B amorphous alloys supported on SiO2 and ␥-Al2O3 for selective
hydrogenation of benzophenone
Guoyi Baia,∗, Libo Niua,b, Zhen Zhaoa, Na Lia, Fei Lia, Mande Qiua, Fei Heb, Guofeng Chena, Zheng Maa
a Key Laboratory of Medicinal Chemistry and Molecular Diagnosis of Ministry of Education, College of Chemistry and Environmental Science, Hebei University, Baoding, Hebei 071002,
PR China
b School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The liquid phase selective hydrogenation of benzophenone was studied over Ni–La–B amorphous alloys
supported on SiO2 and ␥-Al2O3, respectively, and the effect of the carriers was subject to detailed exami-
nation. Based on characterization data, SiO2 was suggested to have a planar structure and ␥-Al2O3 a porous
structure, which markedly influenced the activity and stability of the supported catalysts. Use of ultra-
sound during catalyst preparation was found to make the particle sizes of the samples smaller, leading to
the active particles being more dispersed on the carrier and leading to an increase in the conversion of ben-
zophenone. Using ultrasound protocols, a Ni–La–B amorphous alloy supported on SiO2 (Ni–La–B/SiO2-u)
initially showed better activity and selectivity than a Ni–La–B amorphous alloy supported on ␥-Al2O3
(Ni–La–B/␥-Al2O3-u); whereas Ni–La–B/SiO2-u showed poor stability compared to Ni–La–B/␥-Al2O3-u.
The main reason for the deactivation of Ni–La–B/SiO2-u was ascribed to the adsorption of reactants and
products onto the catalyst surface and their coverage of the active Ni sites.
Received 11 April 2012
Received in revised form 2 July 2012
Accepted 16 July 2012
Available online 22 July 2012
Keywords:
Benzophenone
Selective hydrogenation
Ni–La–B amorphous alloy
Carrier
Ultrasound
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Ru on a Ni–B amorphous alloy catalyst for p-chloronitrobenzene
hydrogenation, and these doped catalysts exhibited higher activ-
Benzhydrol is an important industrial precursor for many bioac-
tive products, such as treatments for hives, pollenosis, serum
disease, allergic conjunctivitis, and acute circumscribed edema
[1]. Considering that traditional chemical reduction methods are
not usually environmentally friendly [2], selective hydrogena-
tion of benzophenone to benzhydrol over metal catalysts is the
preferred protocol. Noble metals including palladium, platinum,
and rhodium have been studied extensively for this reaction,
but their application is limited due to high catalyst cost or low
selectivity to benzhydrol [3–5]. Raney Ni has been commonly
used in this conversion, but its pyrophoric nature and the conse-
quent serious safety hazards have limited its further application
[6].
ities than the undoped one and Raney Ni [15]. Whereas, poor
stability has limited further application of these unsupported amor-
phous alloy catalysts in industry, such supported Ni–B amorphous
alloy catalysts have attracted increasing attention in hydrogena-
tion reactions due to their better stability [16–19]. For example, Xie
et al. have reported that a Ni–Co–B amorphous alloy supported on
carbon nanofibers exhibited similar activity to Raney Ni and good
stability over five consecutive runs [19].
Recently, we have developed an ultrasound-assisted chemical
reduction method to synthesize a Ni–La–B amorphous alloy cata-
lyst for selective hydrogenation of benzophenone to benzhydrol.
The Ni–La–B nanoparticles thus obtained showed high activity and
selectivity owing to the synergistic effect between La addition and
ultrasound [11], but also exhibited poor stability for recycling.
Consequently, to achieve an active and stable Ni–B amorphous
alloy catalyst for the selective hydrogenation of benzophenone,
a series of carriers were examined to obtain supported Ni–La–B
amorphous alloy catalysts. SiO2 and ␥-Al2O3 were selected for
detailed investigation because they had different and typical struc-
tures and both showed good performances. Thus, special attention
has been concentrated on Ni–La–B amorphous alloys supported
on SiO2 and ␥-Al2O3 in an attempt to correlate their catalytic
performances with their structures based on a range of character-
izations.
On the other hand, Ni–B amorphous alloys have attracted much
attention due to their interesting intrinsic properties such as short-
range order, long-range disorder, and high dispersion, as well as
their potential applications, especially for catalytic hydrogenation
[7–15]. For instance, Chen et al. have studied the effects of W, Mo,
∗
Corresponding author at: No. 180 Wusi East Road, Baoding City, Hebei 071002,
PR China. Tel.: +86 312 5079359; fax: +86 312 5937102.
E-mail address: baiguoyi@hotmail.com (G. Bai).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.07.018

412
G. Bai et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
2. Experimental
2.1. Catalyst preparation
l
Unless otherwise stated, all chemicals were purchased from
Baoding Huaxin Reagent and Apparatus Co., Ltd. and were used
as received without further purification. The supported Ni–La–B
amorphous alloy catalysts were prepared by a reductive impreg-
nation method. The carrier M (M: SiO2 or ␥-Al2O3, 5.0 g) was first
calcined at 673 K for 4 h, and impregnated with an aqueous solu-
tion of 2.98 g NiCl2·6H2O and 0.14 g La(NO)3·6H2O (molar ratio
La:Ni = 1:40). It was then dried at 393 K for 2 h to exclude resid-
ual water. The precursor was reduced by adding 1.0 M aqueous
KBH4 aqueous dropwise with gentle stirring in an ice-water bath.
The molar ratio of B/Ni was adjusted to 4:1 to ensure that all the
nickel cations on the carrier were reduced. After the reduction was
complete, the black precipitate was first washed with oxygen-free
deionized water several times until neutral, followed by washing
with absolute ethanol three times to remove the residual water
and water-soluble impurities. Finally, the obtained catalyst was
denoted as Ni–La–B/M and the final material was kept under abso-
lute ethanol for future use. When ultrasound was applied during
the preparation process, the catalyst so obtained was denoted as
Ni–La–B/M-u.
0
10
20
30
40
50
60
70
80
90
2 Theta / deg.
Fig. 1. XRD patterns of the supported amorphous alloy catalysts. (a) Ni–La–B/SiO2;
(b) Ni–La–B/SiO2-u; (c) Ni–La–B/␥-Al2O3; (d) Ni–La–B/␥-Al2O3-u.
typical amorphous structure of the Ni–B amorphous alloy, indicat-
ing that the use of carriers and ultrasound had not changed the
amorphous structure of the Ni–La–B catalysts [17,20].
3.2. Structure properties
2.2. Catalyst characterization
The results of composition, Ni loading, BET surface area, pore
size, pore volume and Ni dispersion of the catalysts, together
with the structural properties of the carriers, are summarized in
Table 1. As can be seen, the catalysts have similar Ni loadings and
all lower than that of the pure Ni–La–B catalyst in our previous
study [11]. Particularly, SiO2 and the catalysts supported on SiO2
showed very small surface area and pore volume, indicating that
SiO2, Ni–La–B/SiO2 and Ni–La–B/SiO2-u may have planar struc-
tures, with almost no pores in them. Table 1 also shows that the
surface area and pore volume of the catalysts supported on ␥-Al2O3
decreased slightly compared with ␥-Al2O3 itself, which can be due
to the occupation of some pores of this carrier by small amorphous
alloy particles. Furthermore, the surface area and pore volume
of Ni–La–B/␥-Al2O3-u increased by 6.8% and 3.6%, respectively,
compared with Ni–La–B/␥-Al2O3. Noticeably, all the ultrasound-
assisted Ni–La–B samples showed lower pore size but higher Ni
dispersion than the conventionally prepared ones. Thus, the uses
of ultrasound are proved to inhibit the agglomeration of Ni–La–B
particles supported on both carriers, making the active Ni species
more dispersed on them.
X-ray diffraction (XRD) patterns were recorded on a Bruker
D8-ADVANCE X-ray diffractometer with Cu K␣ radiation. Bulk com-
positions were identified by inductively coupled plasma analysis
(ICP) on a Varian 710-ES spectrometer. BET surface area, pore
size and pore volume were measured using a Micromeritics Tris-
tar II 3020 surface area and pore analyzer. Scanning electron
microscopy (SEM) was performed on a JEOL JSM-7500 electron
microscope. X-ray photoelectron spectroscopy (XPS) measure-
ments were recorded with a PHI 1600 spectroscope using Mg K␣
X-ray source for excitation. H2-chemisorption, temperature pro-
grammed desorption of H2 (H2-TPD) and temperature programmed
desorption of NH3 (NH3-TPD) were carried out on a TP-5000 instru-
ment from Xianquan Ltd.
2.3. Catalytic tests
Liquid phase benzophenone hydrogenation was conducted as
follows: methanol (200 mL), benzophenone (6.0 g), and catalyst
(2.0 g) were mixed in a 500 mL stainless steel autoclave equipped
with a mechanical stirrer and electrical heating system. The reactor
was filled with H2 three times and evacuated to exclude air. It was
then filled with hydrogen to a pressure of 2.5 MPa, followed by slow
heating (4 K/min) to the reaction temperature. On reaching 403 K,
hydrogenation was started by stirring the reaction mixture vigor-
ously. The stirring rate was kept at 400 r/min and reaction allowed
to proceed for 60 min. Reaction mixtures were analyzed by gas
chromatography using a 30 m SE-54 capillary column. The used cat-
alysts were separated by leaching or centrifugation, washed with
absolute ethanol, and then kept in absolute ethanol for recycling.
3.3. Scanning electron micrography
Fig. 2 shows SEM images of the supported amorphous alloy cat-
alysts. Each sample displayed cotton-like morphology, consistent
with other reported Ni-based amorphous alloy catalysts [21]. It was
also observed that the particle sizes of the samples became smaller
when ultrasound was used, indicating that the Ni–La–B amor-
phous alloy particles in Ni–La–B/SiO2-u and Ni–La–B/␥-Al2O3-u
were homogeneously dispersed on the surface.
3. Results and discussion
3.4. X-ray photoelectron spectroscopy
3.1. X-ray diffraction
Chemical composition of the catalyst surface was determined by
XPS. These results, together with the corresponding characteristics
of binding energy values of Ni 2p3/2, B 1s and La 3d5/2, are listed in
Table 2.
Fig. 1 shows the XRD patterns of the four supported Ni–La–B
amorphous alloy samples. After subtracting the background spec-
trum of SiO2 and ␥-Al2O3, the patterns were almost the same. A
broad peak at 2ꢀ = 45◦ was observed, which was attributed to the
As can be seen, both Ni0 and Ni2+ were detected at about
852 and 856 eV, respectively, by applying the curve fitting

G. Bai et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
413
Table 1
Structural properties of the carriers and supported amorphous alloy catalysts.
Sample
Composition (atomic ratio)
Ni loading (wt %)
Surface area (m2/g)
Pore size (nm)
Pore volume (cm3/g)
Ni dispersiona (%)
SiO2
–
–
4
6
8
201
161
172
9.9
28.8
12.4
8.3
6.9
6.7
0.01
0.04
0.03
0.42
0.28
0.29
–
Ni–La–B/SiO2
Ni–La–B/SiO2-u
␥-Al2O3
Ni–La–B/␥-Al2O3
Ni–La–B/␥-Al2O3-u
Ni1La0.028B0.992/SiO2
Ni1La0.028B0.869/SiO2
–
Ni1La0.027B1.107/␥-Al2O3
Ni1La0.028B1.162/␥-Al2O3
7.5
8.1
–
7.2
6.8
7.3
8.4
–
7.5
8.8
a
Calculated from the H2-chemisorption [24].
Fig. 2. SEM images of the supported amorphous alloy catalysts. (a) Ni–La–B/SiO2; (b) Ni–La–B/SiO2-u; (c) Ni–La–B/␥-Al2O3; (d) Ni–La–B/␥-Al2O3-u.
procedure [22]. It is known that hydrogen molecules are adsorbed
and activated on the Ni0 sites before the hydrogenation process.
Therefore, the amount of Ni0 on the surface of the nickel-based
catalyst is crucial for its activity in catalytic hydrogenation. Fur-
thermore, Ni–La–B/SiO2-u had a higher surface Ni0 content than
Ni–La–B/SiO2, indicating that more active centers were distributed
on the surface of this ultrasound-produced catalyst. On the other
hand, for the Ni–La–B/␥-Al2O3-u sample, both Ni0 and Ni2+ content
were lower than those of Ni–La–B/␥-Al2O3, probably due to the
porous structure of ␥-Al2O3 and the use of ultrasound. Ultrasound
should make the active component more dispersed and cause some
small Ni particles to migrate into the pores of ␥-Al2O3, although
not detectable by XPS. Considering that boron oxide formation
is believed to be inevitable in Ni–B amorphous alloy catalysts
produced by aqueous KBH4 reduction [23], there were also two
characteristic peaks in B 1s spectra. The peaks of B 1s centered at
around 187 and 191 eV can be assigned to pure B and oxidized B,
respectively [22]. The La 3d peaks of the samples were found to be at
about 835 eV, indicating that lanthanum existed as La2O3 [12,13]
in the catalysts and was not reduced by KBH4 [11]. Furthermore,
Table 2
XPS results on the surface characters of the supported amorphous alloy catalysts.
Catalyst
Binding energy (eV)
Ni 2p3/2
Surface atomic ratio (%)a
B 1s
B0
La 3d5/2
La3+
Ni
B
La
Ni0
Ni2+
B3+
Ni0
Ni2+
B0
B3+
La3+
Ni–La–B/SiO2
852.6
852.6
852.5
852.4
855.7
855.7
856.0
856.0
187.7
187.1
187.9
187.7
191.7
191.7
191.8
191.6
835.5
835.5
835.5
835.5
19.6
24.9
15.9
13.9
30.4
22.8
28.0
24.7
7.3
30.9
23.6
42.4
51.2
11.8
11.4
1.2
Ni–La–B/SiO2-u
Ni–La–B/␥-Al2O3
Ni–La–B/␥-Al2O3-u
17.3
12.5
8.4
1.8
a
Relative amount.

414
G. Bai et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
only a little La could be detectable on the surface of Ni–La–B/␥-
Al2O3 and Ni–La–B/␥-Al2O3-u, probably due to the porous structure
of ␥-Al2O3. Most of basic La2O3 are believed to migrate into the
pores of acidic ␥-Al2O3, thus not detectable by XPS. The nearly same
amounts of La in the body of the catalysts based on the ICP results
(Table 1) proved this assumption.
A
a
b
3.5. Temperature programmed desorption
NH3-TPD profiles of ultrasound-assisted Ni–La–B catalysts are
presented in Fig. 3A. For Ni–La–B/␥-Al2O3-u, the peaks centered at
430–620 K are assigned to the weakly acidic sites and the peak cen-
tered approximately at 700 K is assigned to the moderately-strong
acidic sites; whereas, Ni–La–B/SiO2-u only showed one weak NH3
desorption peak at around 670 K. It is apparent that Ni–La–B/SiO2-
u showed smaller acidic amounts than Ni–La–B/␥-Al2O3-u, which
can be due to the stronger acidity of ␥-Al2O3 compared with
SiO2. It has been reported that acidic sites can accelerate the for-
mation of dehydration by-products [3]. Thus, Ni–La–B/␥-Al2O3-u
should result in lower selectivity resulting from its stronger and
larger amounts of acidic sites. Fig. 3B shows the H2-TPD profiles of
ultrasound-assisted Ni–La–B catalysts. It is obvious that the extents
of hydrogen desorption of Ni–La–B/␥-Al2O3-u are much larger than
those of Ni–La–B/SiO2-u, indicating that the porous structure of ␥-
Al2O3 might favor the dispersion of Ni–La–B particles in its pores,
resulting in the formation of more active Ni centers in it [14].
400
500
600
700
800
900
Temperature / K
B
a
b
3.6. Reaction results
A series of Ni–La–B amorphous alloy catalysts supported on
SiO2 or ␥-Al2O3 was prepared and tested in the hydrogenation of
benzophenone under the optimized reaction conditions, and the
results are listed in Table 3.
As can be seen, Ni–La–B/SiO2-u showed a good conversion
(91.5%) and selectivity (92.5%) to benzhydrol, only a little lower
than those of the unsupported one [11] and obviously higher
than those of Ni–La–B/␥-Al2O3-u. Considering the different struc-
ture of Ni–La–B/SiO2-u and Ni–La–B/␥-Al2O3-u, the hydrogenation
of benzophenone is suggested to occur on the outer surface of
the catalysts. The active Ni centers in Ni–La–B/SiO2-u are pro-
posed to be dispersed on the surface due to the planar structure
of SiO2; whereas the active Ni centers in Ni–La–B/␥-Al2O3-u
are mostly dispersed in the internal channels originally due to
300
400
500
600
700
800
900
Temperature / K
Fig. 3. TPD profiles of the supported amorphous alloy catalysts. (A) NH3-TPD and
(B) H2-TPD; (a) Ni–La–B/SiO2-u and (b) Ni–La–B/␥-Al2O3-u.
Table 3
Catalytic performance of the supported Ni–La–B catalysts.
Catalyst
Ni–La–B/SiO2
Ni–La–B/␥-Al2O3
Ni–La–B/SiO2-u
Conversion of benzophenone (%)
Selectivity to benzhydrol (%)
Selectivity to diphenylmathane (%)
Selectivity to others (%)
75.6
69.1
91.5
83.4
92.1
91.9
92.5
85.3
4.5
5.7
3.7
9.6
3.4
2.4
3.8
5.1
Ni–La–B/␥-Al2O3-u
Reaction conditions: 2.0 g catalyst, 6.0 g benzophenone, 200 mL methanol, temperature 403 K, initial hydrogen pressure 2.5 MPa, and reaction time 60 min.
Others: dicyclohexylmethanol, dicyclohexylketone, cyclohexylphenylmethanol, and cyclohexylmethylbenzene.
Table 4
XPS results on the surface compositions of the fresh and used catalysts.
Catalyst
BindingenergyofNi2p3/2 (eV)
Surface atomic ratio (%)
Ni0
Ni2+
C
O
Ni
B
La
0.5
0.3
0.1
Si
Al
Ni–La–B/SiO2-ua
852.6
852.6
852.4
852.5
855.7
855.7
856.0
855.8
47.6
61.5
35.1
47.1
31.7
25.4
41.8
36.0
2.1
1.5
2.2
2.3
1.8
<0.1
3.4
16.3
11.2
–
–
–
17.4
14.7
Ni–La–B/SiO2-ub
Ni–La–B/␥-Al2O3-ua
Ni–La–B/␥-Al2O3-ub
<0.1
<0.1
–
a
Signifies fresh catalyst.
Signifies used catalyst.
b

G. Bai et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
415
Scheme 1. Major processes of benzophenone hydrogenation.
the porous structure of ␥-Al2O3. This is believed to be the main
a
reason that the fresh Ni–La–B/SiO2-u showed higher activity than
the fresh Ni–La–B/␥-Al2O3-u, although the former had obviously
lower total hydrogen adsorption sites. Furthermore, GC–MS analy-
sis showed that the main by-product was diphenylmethane, which
is the product of dehydration of benzhydrol or direct hydrogenol-
ysis of benzophenone [3,4] (Scheme 1). The stronger and larger
amounts of acidic sites in Ni–La–B/␥-Al2O3-u, based on the NH3-
TPD results, which will accelerate dehydration of benzhydrol, are
believed to be the main reason for the lower selectivity of this cat-
alyst. On the other hand, the conversions of benzophenone were
found to increase about 15% after the use of ultrasound to prepare
the catalysts. Thus, the effect of ultrasound is proposed to favor
the dispersion of Ni–La–B alloy particles on the catalysts surface
and pores due to its acoustic cavitations, making them smaller and
more active.
100
75
50
25
0
Conversion%
Selectivity%
-25
-50
1
2
3
4
5
6
Cycle times
3.7. Stability test
b
Stability tests of Ni–La–B/SiO2-u and Ni–La–B/␥-Al2O3-u were
carried out and the results are shown in Fig. 4. As can be seen,
Ni–La–B/SiO2-u showed poor stability (Fig. 4a). A marked deacti-
vation occurred with the conversion of benzophenone dropping
from 91.5% to 44.2% in only the second run using the recycled
Ni–La–B/SiO2-u, implying that the catalyst deactivated quickly.
However, the selectivity to benzhydrol remained above 92.0%
during the whole test. On the other hand, Ni–La–B/␥-Al2O3-u
showed different performances in the stability test, as shown
in Fig. 4b. The conversion of benzophenone remained at a high
level and even exhibited a little increase after each cycle, and the
selectivity to benzhydrol first stabilized at about 80.0% and then
decreased to 68.8% after four cycles and finally reached 62.5% for
the sixth cycle. Therefore, Ni–La–B/␥-Al2O3-u was proved to have
better stability in comparison with Ni–La–B/SiO2-u in this reac-
tion.
100
75
50
25
0
Conversion%
Selectivity%
1
2
3
4
5
6
Cycle times
Fig. 4. Stability of Ni–La–B/SiO2-u (a) and Ni–La–B/␥-Al2O3-u (b). (Reaction con-
ditions: 2.0 g catalyst, 6.0 g benzophenone, 200 mL methanol, temperature 403 K,
initial hydrogen pressure 2.5 MPa, and reaction time 60 min.)
In order to find the reason for the above results, the used Ni–La–B
samples were characterized by XPS and compared with the fresh
ones. As can be seen from Table 4, the chemical states of Ni 2p3/2

416
G. Bai et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 411–416
Fig. 5. Proposed deactivation mechanism of Ni–La–B/SiO2-u (a) and Ni–La–B/␥-Al2O3-u (b).
kept stable after the usage, whereas the carbon content increased
for both the used samples. Thus, the adsorption of reactants and
products on the catalysts surfaces and their coverage on the active
Ni sites, as also proven by SEM images, TG and Ni dispersion results
of the used catalysts, are believed to be main reasons for the deac-
tivation of the catalysts.
Furthermore, the loss of active Ni species may be another pos-
sible reason, especially for Ni–La–B/SiO2-u (Fig. 5a). In particular,
the amount of Ni on the surface of the used Ni–La–B/␥-Al2O3-u
increased slightly even if the amount of C had increased. This can
be attributed to the structural properties and recycle process of
Ni–La–B/␥-Al2O3-u. The long time infusion and stirring at a high
speed should partly destroy the porous structure of Ni–La–B/␥-
Al2O3-u, breaking up the larger particles and causing the active
Ni species dispersed in the channel to migrate onto the surface of
the catalyst (Fig. 5b).
An interesting observation during the recycling of Ni–La–B/␥-
Al2O3-u supports this assumption. Simple filtration could not
separate the used Ni–La–B/␥-Al2O3-u from reaction mixtures
entirely even after two cycles, with many tiny particles suspended
in the solution, although centrifugation worked effectively. More-
over, the damage to the structure of Ni–La–B/␥-Al2O3-u should also
result in exposure of more acidic Al2O3 species on the catalyst sur-
face, resulting in the increase of the dehydrated by-products and
the decrease of the selectivity to benzhydrol. The NH3-TPD results
of the fresh and used Ni–La–B/␥-Al2O3-u samples also supported
this conclusion.
Acknowledgments
The authors thank Professor L.M. Harwood for his assistance.
Financial support by the National Natural Science Foundation
of China (20806018), the Natural Science Foundation of Hebei
Province (B2011201017) and the Science Project of the Hebei Edu-
cation Department (ZD200910) are gratefully acknowledged.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
molcata.2012.07.018.
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In conclusion, Ni–La–B amorphous alloy supported on SiO2 and
␥-Al2O3 showed relatively good activity for benzophenone hydro-
genation. It was found that ultrasound could make the particles
more dispersed on the carriers, providing more active centers and
enhancing the activity of both supported catalysts. Ni–La–B/SiO2-u
was proved to have the best initial activity due to its planar struc-
ture and more dispersed active Ni species on its surface, but showed
poor stability in this sequence. The main reason for the deactiva-
tion of Ni–La–B/SiO2-u was ascribed to the adsorption of reactants
and products onto the catalyst surface, covering the active Ni sites.
On the contrary, Ni–La–B/␥-Al2O3-u exhibited lower original activ-
ity, but stable activity with slightly decreasing selectivity, due to its
porous structure and exposure of more acidic Al2O3 species during
the recycle process.
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