Effect of support and solvent on the activity and stability of NiCoB amorphous alloy in cinnamic acid hydrogenation

Article abstract of DOI:10.1039/c4ra01837k

Selective hydrogenation of cinnamic acid was studied over different supported NiCoB amorphous alloys; a γ-Al₂O₃ supported NiCoB catalyst showed particularly good activity. The application of ultrasound during catalyst preparation was found to make the Ni active sites more dispersed, thus enhancing the catalyst activity. The NiCoB/γ-Al ₂O₃-u catalyst so obtained could be recycled effectively for nine runs in tert-butanol, in contrast it deactivated after only three runs in water. XPS, SEM and XRD characterizations indicated that loss of Ni and hydration of the γ-Al₂O₃ support were the main reasons for catalyst deactivation in water. Thus, an efficient and stable catalytic system involving NiCoB/γ-Al₂O₃-u and tert-butanol was established for cinnamic acid hydrogenation in this study.

Full text of DOI:10.1039/c4ra01837k

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PAPER
Effect of support and solvent on the activity and
stability of NiCoB amorphous alloy in cinnamic acid
hydrogenation
Cite this: RSC Adv., 2014, 4, 19800
Guoyi Bai,* Huixian Dong, Zhen Zhao, Hailong Chu, Xin Wen, Chen Liu and Fei Li
Selective hydrogenation of cinnamic acid was studied over different supported NiCoB amorphous alloys; a
g-Al
catalyst preparation was found to make the Ni active sites more dispersed, thus enhancing the catalyst
activity. The NiCoB/g-Al -u catalyst so obtained could be recycled effectively for nine runs in tert-
butanol, in contrast it deactivated after only three runs in water. XPS, SEM and XRD characterizations
indicated that loss of Ni and hydration of the g-Al support were the main reasons for catalyst
2 3
O supported NiCoB catalyst showed particularly good activity. The application of ultrasound during
2 3
O
Received 3rd March 2014
Accepted 15th April 2014
2
O
3
DOI: 10.1039/c4ra01837k
2 3
deactivation in water. Thus, an efficient and stable catalytic system involving NiCoB/g-Al O -u and tert-
www.rsc.org/advances
butanol was established for cinnamic acid hydrogenation in this study.
1
5,16
based noble metal catalysts,
but it also exhibited poor
1
. Introduction
stability during recycling. Consequently, in an effort to nd a
NiB amorphous alloys have attracted much interest due to their suitably active and stable catalyst for this transformation,
special properties such as short-range order and long-range various solid supports were examined in combination with
1
disorder and have been widely employed in catalytic hydroge- this type of NiCoB amorphous alloy catalyst. The effects of
2–5
nation. For instance, Fang et al. have studied the effect of Cr solvent on the stability of such supported NiCoB catalysts
doping on a NiB amorphous alloy catalyst for 2-ethyl- were also examined to search for optimal reaction conditions
anthraquinone hydrogenation and found that the doped cata- for this hydrogenation. This has resulted in the identication
lyst exhibited higher selectivity for 2-ethylanthrahydroquinone of a NiCoB/g-Al
2
O
3
-u catalyst, which shows both suitable
3
reduction than the undoped one. Unfortunately, most of these activity and stability, when used in tert-butanol, for the
pure NiB amorphous alloys deactivated quickly and usually selective hydrogenation of cinnamic acid.
could not be recycled in a second run.
As is well known, stability is an important character for a
good industrial catalyst and much effort has been devoted to
2
. Experimental
6
–9
achieve this.
loading the active species on a support is regarded as an
Specic to NiB amorphous alloy catalysts,
2.1. Catalyst preparation
1
0,11
effective method to improve their stability.
For instance, The supported NiCoB amorphous alloys were prepared by an
Liu et al. have reported that a NiB amorphous alloy impregnation-reduction method. The support S (S: TiO , acti-
2
supported on boehmite exhibited superior activity and rela- vated carbon (AC), ZSM-5, Hb, g-Al O , 2.0 g) was rst calcined
2
3
tively good stability over four runs in the selective hydroge- at 773 K for 4 h and then impregnated with an aqueous solution
1
1
nation of p-nitrophenol and p-chloronitrobenzene.
2 2 2 2
of 0.415 g (0.9 M) NiCl $6H O and 0.042 g (0.09 M) CoCl $6H O
However, there is still a lack of NiB amorphous alloys with (molar ratio Ni : Co ¼ 10 : 1). The resulting paste was then dried
sufficient stability, which of course limits their applications at 393 K for 2 h. The resulting precursor was reduced by adding
in industry.
4
7 mL of 1.0 M aqueous KBH containing 0.2 M NaOH dropwise
Very recently, we have prepared a Co-modied NiB amor- with vigorous stirring while cooling in an ice bath to furnish a
phous alloy catalyst for the selective hydrogenation of cin- black precipitate. This was ltered off and washed with deion-
1
2
namic acid to hydrocinnamic acid, which is an important ized water several times, followed by absolute ethanol three
1
3,14
chemical intermediate.
This catalyst showed excellent times. The catalyst so obtained (denoted as NiCoB/S) was kept
catalytic performance in this reaction, similar to that of Pd- under absolute ethanol for future use. When ultrasound was
applied during the preparation process, the catalyst thus
obtained was denoted as NiCoB/S-u. NiCoB catalyst was
Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry and
prepared by a chemical reduction method as described
previously.
Environmental Science, Hebei University, Baoding 071002, PR China. E-mail:
baiguoyi@hotmail.com; Fax: +86-312-5937102; Tel: +86-312-5079359
12
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.2. Catalyst characterization
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Table 1 Hydrogenation of cinnamic acid over NiCoB amorphous
2
a
alloys
Bulk compositions of the supported amorphous alloy catalysts
were identied by inductively coupled plasma analysis (ICP)
using a VISTA-MPX spectrometer. Brunauer–Emmett–Teller
Conversion of
cinnamic acid (%)
Selectivity for
hydrocinnamic acid (%)
Catalyst
(
BET) surface areas of the catalysts were measured by nitrogen
NiCoB/TiO
NiCoB/AC
NiCoB/ZSM-5
2
58.5
31.7
51.6
52.4
71.3
83.5
57.8
100.0
100.0
100.0
100.0
100.0
100.0
100.0
physisorption at 77 K on a Micromeritics Tristar II 3020 surface
area and pore analyzer. Powder X-ray diffraction (XRD) patterns
were accumulated with a Bruker D 8 diffractometer using a Cu NiCoB/Hb
Ka radiation source at 40 kV and 40 mA with a step size of 0.01
ꢀ
NiCoB/g-Al O3
2
ꢀ
NiCoB/g-Al
2
O
3
-u
2
q over the range 10 to 80 . Scanning electron microscopy (SEM)
b
NiCoB
was performed on a JEOL JSM-7500 electron microscope.
Transmission electron microscope (TEM) images and selected
area electron diffraction (SAED) were measured on a JEOL JEM-
a
Reaction conditions: 3.0 g cinnamic acid, 0.2 g catalyst (10 wt%
NiCoB), 60 mL water, temperature at 393 K, initial P(H
and reaction time 30 min. 0.02 g NiCoB.
2
) ¼ 2.0 MPa,
b
2
100F microscope. H
2
-chemisorption and temperature-pro-
-TPD) were
grammed desorption measurements of hydrogen (H
2
tested using a TP-5000 instrument equipped with a thermal
conductivity detector supplied by Xianquan Co. Ltd. X-ray
photoelectron spectroscopy (XPS) analysis was carried out on a
PHI 1600 spectrometer using monochromatic Mg Ka as the
excitation source.
3
.2. Catalyst characterization
Fig. 1 shows the XRD patterns of NiCoB, g-Al
Al , and NiCoB/g-Al
supported catalysts are similar, exhibiting the characteristic
peaks of g-Al . Aer subtracting the background spectrum of
2
O
3
, NiCoB/g-
and its
2
O
3
2
O
3
-u. The patterns of g-Al
2
O
3
2 3
O
g-Al
2
O
3
, the patterns of the two supported catalysts showed the
ꢀ
typical amorphous structure at about 2q ¼ 45 , indicating that
2.3. Catalyst activity test
the use of support and ultrasound had not changed the amor-
Cinnamic acid hydrogenation was carried out as follows: cin-
namic acid (3.0 g), catalyst (0.3 g) and solvent (60 mL) were
mixed in a 100 mL stainless steel autoclave equipped with a
mechanical stirrer and electric heating system. The reactor was
18,19
phous structure of the NiCoB amorphous alloy.
The results of composition, Ni loading, BET surface area,
pore volume and H
catalysts, together with the structural properties of g-Al
are summarized in Table 2. From the ICP analysis, it was
found that the Co and B ratio of the g-Al supported cata-
2
-chemisorption of the amorphous alloy
2
3
O ,

lled with H
2
three times followed by evacuation to exclude
to 3.0
residual air. The autoclave was then pressurized with H
2
2
O
3
MPa, and heated to 393 K. On reaching this temperature,
hydrogenation was started by stirring the reaction mixture
vigorously and allowed to proceed for 60 min. Reaction
mixtures were analyzed by gas chromatography using a 30 m SE-
lysts markedly increased when compared to the unsupported
NiCoB. The increase of the B content could increase the
amorphous degree and the thermal stability of the as-
prepared amorphous alloy catalysts, thereby enhancing
30 capillary column and the product structures were conrmed
20
their hydrogenation activity. The surface area and pore
using gas chromatography-mass spectrometry (GC-MS) on an
Agilent 5975C spectrometer. The used catalysts were separated
by leaching, washed with reaction solvent, and then kept in the
reaction solvent for recycling.
volume of the g-Al
compared with g-Al
of some pores of g-Al
Noticeably, the surface area of NiCoB/g-Al
slightly when compared with NiCoB/g-Al O . Furthermore,
2
O
3
supported catalysts decreased
itself, probably due to the occupation
by small amorphous alloy particles.
-u increased
2
O
3
2
O
3
2 3
O
2
3
the ultrasound-assisted NiCoB/g-Al O -u sample showed
2
3
3. Results and discussion
3.1. Catalyst selection
A series of supported NiCoB amorphous alloy catalysts was rst
prepared and tested in the hydrogenation of cinnamic acid; the
results are listed in Table 1. As can be seen, all supported NiCoB
amorphous alloy catalysts showed 100.0% selectivity for
hydrocinnamic acid formation;
a
NiCoB/g-Al
2
O
3
catalyst
exhibited the highest conversion (71.3%), which was also higher
than that obtained using the unsupported NiCoB (57.8%) under
the same reaction conditions. Considering the benet of
17
ultrasound, NiCoB/g-Al O -u was prepared and tested. As
2
3
anticipated, it showed higher conversion (83.5%) than NiCoB/g-
Al O , proving the positive effect of ultrasound in catalyst
2
3
2 3
preparation. Thus, NiCoB/Al O -u was chosen as the catalyst for
further study in cinnamic acid hydrogenation.
Fig. 1 XRD patterns of g-Al
2
O
3
and amorphous alloy catalysts. (a)
, (d) NiCoB/g-Al -u.
NiCoB, (b) g-Al , (c) NiCoB/g-Al
2
O
3
O
2 3
2 3
O
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Table 2 Structural properties of g-Al
2
O
3
and NiCoB amorphous alloys
a
Composition
(atomic ratio)
Ni loading
(wt%)
Surface area
Pore volume
2
H -chemisorption
(cm g )
2
ꢁ1
3
ꢁ1
3
ꢁ1
Sample
(m g
)
(cm g
)
g-Al
NiCoB
NiCoB/g-Al
NiCoB/g-Al
2
O
3
—
—
—
6.8
7.1
200.2
28.3
164.6
172.5
0.339
0.062
0.220
0.222
—
b
Ni1.00Co0.080
Ni1.00Co0.118
Ni1.00Co0.117
B
0.52
B
1.48
B
1.49
0.22
0.26
0.30
2
2
O
O
3
3
-u
a
b
Based on ICP results. Data from ref. 12.
higher H -chemisorption and Ni loading than the conven-
Fig. 3 shows the H -TPD proles of NiCoB/g-Al O and
2 2 3
2
2 3
tionally prepared material. Thus, the use of ultrasound NiCoB/g-Al O -u. There is only one strong peak at about 628 K
appears to inhibit the agglomeration of NiCoB particles on for these two supported catalysts, indicating the presence of one
g-Al , making the active Ni species more dispersed, hence kind of adsorption site for each sample. Furthermore, it is
accounting for the higher activity of NiCoB/g-Al -u. apparent that the hydrogen desorption peak of NiCoB/g-Al -u
The morphologies of the supported NiCoB amorphous is much larger than that of NiCoB/g-Al , in agreement with
catalysts were recorded by both SEM and TEM (Fig. 2). As can be the H -chemisorption results. This indicates that ultrasonic
seen, the two fresh samples displayed cotton-like morphology treatment favors the dispersion of NiCoB particles on g-Al O ,
2
O
3
2
O
3
2 3
O
2 3
O
2
2
3
(
Fig. 2a and b), similar to other supported amorphous alloy resulting in the formation of more active Ni centers and
21
2 3 2 3
catalysts. It was observed that the particles of NiCoB/g-Al O -u accounting for the higher activity of NiCoB/g-Al O -u.
became smaller and well dispersed when ultrasound was used,
a nding also supported by TEM (Fig. 2c and d). The SAED
patterns (Fig. 2 insets) of the samples showed successive
diffraction halos rather than distinct dots, conrming the
amorphous structure of the active component NiCoB, in good
agreement with the XRD results.
3
.3. Stability test
The reaction parameters such as reaction time, hydrogen
pressure and catalyst dosage were rst optimized before the
stability test (Fig. 4). The conversion of cinnamic acid and the
selectivity for hydrocinnamic acid can both reach 100.0%, when
2 3
using 0.3 g NiCoB/g-Al O -u catalyst under 3.0 MPa hydrogen
pressure for 60 min. Thus, the stability test was carried out
under these conditions in water. Unexpectedly, the conversion
of cinnamic acid decreased to 72.2% aer only two runs. To try
and improve the stability of this catalytic system, replacement
of water by a series of organic solvents were then investigated
2 3
(Table 3). As expected, NiCoB/g-Al O -u showed better stability
in most organic solvents but especially in alcohols. The best
result was obtained in tert-butanol with both 100.0% conversion
and selectivity in two runs; whereas, in ethanol or iso-propanol,
the selectivity for hydrocinnamic acid decreased below 90%,
mainly due to the formation of the esteried by-products. The
excellent selectivity in tert-butanol was ascribed to its large
22
steric effect, which suppresses esterication. Thus, the solvent
Fig.
NiCoB/g-Al
water (f); and TEM morphologies of NiCoB/g-Al
Al -u (d), and the insets are the SAED images.
2
SEM images of NiCoB/g-Al
2
O
3
(a), NiCoB/g-Al
2
O
3
-u (b),
-u used in
3
O (c), NiCoB/g-
2
O
3
-u used in tert-butanol (e), NiCoB/g-Al O
2 3
2
2
O
3
2 2 3 2 3
Fig. 3 H -TPD spectra of NiCoB/g-Al O (a) and NiCoB/g-Al O -u (b).
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carried out and the results are shown in Fig. 5. As can be seen,
NiCoB/g-Al O -u showed excellent stability with 100.0% selec-
2
3
tivity and over 99.5% conversion during nine runs in tert-
butanol. In contrast, a marked deactivation occurred with the
conversion of cinnamic acid dropping from 100.0% to only
38.0% aer three runs in water, implying that the catalyst
deactivated quickly in this solvent.
In order to nd the reason for the above results, the used
2 3
NiCoB/g-Al O -u samples were characterized by XPS and
compared with the fresh sample (Fig. 6). As can be seen, the
surface Ni atomic concentration decreased from 1.7% to 0.9%
aer three runs in water; whereas it remained in a high level
(
1.6%) even aer being used nine times in tert-butanol. We can
thus deduce that loss of active Ni is the main reason for
catalyst deactivation in water. On the other hand, some bar-
like material was observed on the NiCoB/g-Al O -u catalyst
2 3
surface that had been used in three runs in water (Fig. 2f),
which was suspected to be the hydrated phase of the g-Al O
2
3
2
3
support. Thus, the used NiCoB/g-Al O -u catalysts were
2
3
characterized by XRD and the results are shown in Fig. 7A. As
anticipated, the X-ray diffraction pattern of the catalyst used
three runs in water has markedly changed, with the appear-
ꢀ
ꢀ
ance of new strong diffraction peaks at around 2q ¼ 15 , 17.5 ,
ꢀ ꢀ ꢀ
2
4 , 31 and 38 , which can be assigned to g-AlO(OH).
Furthermore, the high-resolution XPS spectra of Al 2p (Fig. 6
insets) also shows that the binding energy of Al 2p has slightly
decreased from 74.3 to 74.1 eV aer the catalyst was used in
water, suggesting the transformation from g-Al O to g-
2
3
2
4
AlO(OH), and in agreement with the above XRD results.
Small peaks related to Al(OH) were also detected in this used
catalyst. Thus, much of the g-Al is transformed into
hydrated phases during reactions in water, similar to what
3
2 3
O
Fig. 4 Effect of reaction time (a), hydrogen pressure (b), and catalyst
dosage (c) on cinnamic acid hydrogenation.
Table 3 Hydrogenation of cinnamic acid in different solvents over
a
NiCoB/g-Al
2
O
3
-u
Run 1
Run 2
Conversion
(%)
Selectivity
(%)
Conversion
(%)
Selectivity
(%)
Solvents
Water
100.0
100.0
98.3
100.0
100.0
87.3
72.2
43.3
98.1
100.0
100.0
85.4
Dioxane
Ethanol
iso-
100.0
88.7
100.0
83.9
propanol
tert-Butanol
Ethyl
100.0
98.5
100.0
100.0
100.0
96.1
100.0
100.0
acetate
a
Reaction conditions: 3.0 g cinnamic acid, 0.3 g catalyst, 60 mL solvent,
) ¼ 3.0 MPa, and reaction time 60 min.
temperature at 393 K, initial P(H
2
is believed to play an important role on the stability of NiCoB/g-
Al -u and tert-butanol was chosen as the optimum solvent for
2 3
O
2 3
cinnamic acid hydrogenation. Further stability tests were then Fig. 5 Stability of NiCoB/g-Al O -u in tert-butanol (a) and in water (b).
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Fig. 6 XPS spectra of NiCoB/g-Al
2
O
3
-u (a), NiCoB/g-Al
O
2 3
-u used in tert-butanol (b) and in water (c), the insets are the high resolution spectra
of Al 2p.
2
5–28
occurs in hydrothermal synthesis, as previously reported.
In contrast, the X-ray diffraction pattern of the catalyst used
4. Conclusions
nine runs in tert-butanol is similar to that of the fresh mate- In conclusion, a NiCoB amorphous alloy supported on g-Al O3
2
rial, except for the weakness of the peak intensity, proving that showed good activity in cinnamic acid hydrogenation. Further
the original g-Al O structure is maintained during the reac- application of ultrasound was found to make the active Ni
2
3
tion in tert-butanol. Moreover, the surface area of the NiCoB/g- species more dispersed, enhancing the activity of the NiCoB/g-
Al -u catalyst used three runs in water markedly decreased Al O -u catalyst so obtained. This catalyst becomes deactivated
from 172.5 to 32.9 m g , which represents a loss of greater aer only three runs in water; whereas it can be recycled
2 3
O
2
3
2
ꢁ1
2
than 80% of its original surface area; while it was still 103.1 m
g
effectively for nine times in tert-butanol. The loss of Ni species
ꢁ
1
aer nine runs in tert-butanol. The different tendencies in and the hydration of the g-Al O support have been shown to
2
3
the N
2
adsorption–desorption isotherms of the NiCoB/g-Al
2
O
3
-
be the main reasons for catalyst deactivation in water. Thus,
u catalyst used in water and tert-butanol (Fig. 7B) also supports due to its good activity and stability, this catalytic system
this type of structural transformation of g-Al O3 during involving NiCoB/g-Al O -u and tert-butanol was not only
2
2 3
hydrogenation in water. Thus, the hydration of the g-Al O
economically viable but also potentially applicable to large-
2
3
support, which accounting for the decrease of its surface area, scale production of hydrocinnamic acid via cinnamic acid
is believed to be another reason for the deactivation of NiCoB/ hydrogenation.
g-Al O -u when used in water.
2 3
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