PVP-NiB amorphous catalyst for selective hydrogenation of phenol and its derivatives

Article abstract of DOI:10.1016/S1872-2067(14)60203-5

PVP-NiB amorphous catalysts were prepared by the chemical reduction of nickel chloride with sodium borohydride, and characterized by infrared, X-ray diffraction, transmission election microscopy, and inductively coupled plasma. The relationship between the catalytic activity and nature of the active sites was discussed. PVP is a protective agent for preparing PVP-stabilized NiB catalysts, which improved the dispersion of the catalyst and stabilized its amorphous structure. The catalysis of phenol and its derivatives was evaluated in the aqueous phase. 99.9% conversion of phenol and 99.9% selectivity to cyclohexanol were obtained at 30 °C and 0.2 MPa H₂ after 18 h over PVP-NiB. The generality of the PVP-NiB catalyst for this reaction was demonstrated by the selective hydrogenation of other phenol derivatives, which showed that the PVP-NiB catalyst was selective for the formation of cyclohexanol.

Full text of DOI:10.1016/S1872-2067(14)60203-5

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Chinese Journal of Catalysis 35 (2014) 1793–1799
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Communication
PVP‐NiB amorphous catalyst for selective hydrogenation of phenol
and its derivatives
Qinsheng Zhanga, Haifeng Lia, Ping Gaob,#, Lailai Wanga,*
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000,
Gansu, China
b State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, Gansu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
PVP‐NiB amorphous catalysts were prepared by the chemical reduction of nickel chloride with
sodium borohydride, and characterized by infrared, X‐ray diffraction, transmission election mi‐
croscopy, and inductively coupled plasma. The relationship between the catalytic activity and na‐
ture of the active sites was discussed. PVP is a protective agent for preparing PVP‐stabilized NiB
catalysts, which improved the dispersion of the catalyst and stabilized its amorphous structure. The
catalysis of phenol and its derivatives was evaluated in the aqueous phase. 99.9% conversion of
phenol and 99.9% selectivity to cyclohexanol were obtained at 30 °C and 0.2 MPa H2 after 18 h over
PVP‐NiB. The generality of the PVP‐NiB catalyst for this reaction was demonstrated by the selective
hydrogenation of other phenol derivatives, which showed that the PVP‐NiB catalyst was selective
for the formation of cyclohexanol.
Received 25 June 2014
Accepted 24 July 2014
Published 20 November 2014
Keywords:
Nickel
Phenol
Catalytic hydrogenation
Amorphous catalyst
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Phenol is a byproduct of the petrochemical industry and can
cause much damage to the environment. The hydrogenation of
phenol is of commercial and environmental significance be‐
cause the cyclohexanone and cyclohexanol produced are the
intermediates for caprolactame and adipic acid used to manu‐
facture nylon 6 and nylon 66, respectively. Cyclohexanone and
cyclohexanol are also important intermediates for medicine,
dyes and other chemicals. Therefore, the hydrogenation of
phenol for the synthesis of cyclohexanone and cyclohexanol is
an important chemical process that has been extensively stud‐
ied [1–3].
coking during the reaction. The products from the hydrogena‐
tion of phenol are highly dependent on the properties of the
support [4]. Liquid phase hydrogenation of phenol saves cost
and energy because the reaction can be performed at relatively
low temperatures and pressure. Many researchers have con‐
tributed to this area, and a number of catalysts have been
screened. However, important drawbacks of liquid phase hy‐
drogenation are the use of more sophisticated conditions (su‐
percritical CO2 as solvent which requires high H2 and CO2
pressures > 7.0 MPa) and need of a cocatalyst [5–9]. Recently,
Wang and co‐workers achieved both excellent conversion and
selectivity in the hydrogenation of phenol in an aqueous media
by using a heterogeneous catalyst. A conversion and selectivity
higher than 96% was obtained. Nevertheless, the preparation
Traditionally, the hydrogenation of phenol has been carried
out in the gas phase at 120–300 °C over supported Pd catalysts.
However, high temperatures cause catalyst deactivation due to
* Corresponding author. Tel: +86‐931‐4968161; Fax: +86‐931‐4968129; E‐mail: wll@licp.cas.cn
# Corresponding author. Tel: +86‐931‐4968177; Fax: +86‐931‐4968163; E‐mail: gaoping@licp.cas.cn
This work was supported by the National Natural Science Foundation of China (21174115) and the Youth Foundation of Gansu Province
(1308RJYA036).
DOI: 10.1016/S1872‐2067(14)60203‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 11, November 2014

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of the mpg‐C3N4 support involved the use of aqueous ammo‐
nium bifluoride (NH4HF2) and/or hydrogen fluoride (HF)
which are hazardous and not environmentally friendly [10].
Rode et al. [11] used supercritical CO2 as a solvent, which re‐
quires high H2 and CO2 pressures > 7.0 MPa. Liu et al. [12]
achieved both excellent conversion and selectivity in the hy‐
drogenation of phenol using a dual‐supported Pd Lewis acid
catalyst. However, the catalyst contains Lewis acids such as
AlCl3, phosphotungstic acid, which imposes severe limitations
on their use in hydrogenation applications in general and adds
a chemical sensitivity that restricts substrates, purity, and reac‐
tion conditions. Therefore, the design and preparation of a
novel catalyst with high activity and selectivity is still a chal‐
lenge.
As is well known, nanoscale amorphous alloy catalysts with
long range disorder and short range order usually exhibit
higher activity and better selectivity in hydrogenation. Their
unique structure and high concentration of coordinatively un‐
saturated sites lead to catalytic activity and selectivity superior
to those of their crystalline counterparts [13,14]. For example,
Li et al. [15,16] synthesized a novel mesoporous Ce‐doped Pd
catalyst with a hollow chamber. This catalyst exhibited a higher
activity and selectivity to cyclohexanone in the liquid phase
hydrogenation of phenol. The hydrogenation of bio‐oil model
compounds was carried out using Ni‐B amorphous catalysts.
The results showed that the conversion of model compounds
(acetone, furfural and phenol) and the selectivity of saturated
alcohols reached 99.9% and 95% at 110 °C, 4 MPa H2 for 4 h
[17]. Poly(N‐vinyl‐2‐pyrrolidone) (PVP) is a water‐soluble
polymer, and is applied as a protective agent for preparing na‐
noscale catalysts [18]. In this paper, we present a new method
for the synthesis of cyclohexanol by the aqueous phase selec‐
tive hydrogenation of phenol using a PVP‐NiB amorphous cat‐
alyst for the first time.
and analyzed by a GC 112A equipped with a FID detector and
an SE‐54 column (30 m × 0.25 mm × 0.25 µm film thickness),
column temperature 140 °C, detector 230 °C, sample injector
220 °C.
The IR spectra of PVP and the PVP‐NiB amorphous catalyst
were recorded using a Nicolet iS10 FTIR spectrometer. The
results are shown in Fig. 1. It was found that the peak positions
from 3000 to 400 cm–1 and the intensity of the absorption peak
were changed. This may be due to the coordinative bond be‐
tween the oxygen atom and nitrogen atom of the PVP molecule
with the surficial Ni atom [19]. For example, there were ab‐
sorption intensity weakening and a blue‐shift of the C=O
stretch vibrational band (1662 cm–1) for PVP‐NiB compared
with pure PVP [20]. In addition, the peak was broadened and
there were blue shifts of the bending vibration at 1463 cm–1
(–CH2–) and stretch vibrational band at 1291 cm–1 (–C–C–).
These were due to the coordination of the lone pair electrons of
N and O with the empty orbitals of Ni [21]. The results showed
that PVP molecules existed on the surface of the catalyst, and
the N and O of PVP coordinated with the metal Ni atom.
Selected PVP‐NiB catalysts were synthesized with the molar
ratio of Ni to PVP monomer of 8:27. According to the ICP analy‐
sis, the compositions of the Ni and B were 47.9% and 11.4%
(weight percent), respectively and the ratio of Ni to B (mo‐
lar/molar) was 1:1.4. Figure 2 shows the XRD patterns of the
PVP‐NiB catalysts. As can be seen, catalysts with different pro‐
portions of n(Ni):n(PVP) have similar XRD patterns. Only one
broad diffraction peak was observed at around 45°, which is
indicative of a typical Ni‐B amorphous structure [22]. When
PVP‐NiB (n(Ni):n(PVP) = 8:27) was applied in the hydrogena‐
tion of phenol at 30 °C, 0.2 MPa H2, and 18 h, one broad diffrac‐
tion peak was observed at around 45° in the obtained sampe,
the same as the fresh one. The results showed the high stability
of the catalyst, which can be reused.
The PVP‐NiB amorphous catalyst was prepared by the re‐
duction of nickel chloride with NaBH4 [18]. The water‐soluble
polymer served as both a protective reagent and support. Be‐
fore the reduction, PVP (0.3 g, 0.027 mol) and nickel chloride
(2.0 g, 0.008 mol) were dissolved in methanol (20 mL) at 80 °C
for 3 h. NaBH4 (1.0 g) was slowly added to the solution. The
resulting black precipitate was separated with a high speed
centrifuge, and thoroughly washed three times with distilled
water. The fresh wet catalyst was dried at 45 °C overnight in a
vacuum oven. In a similar way, other catalysts of the different
molar ratios of Ni to PVP monomer were synthesized, respec‐
tively. The PVP‐NiB amorphous catalysts were characterized by
their infrared spectra (IR), X‐ray diffraction (XRD), transmis‐
sion electron microscopy (TEM), X‐ray photoelectron spectra
(XPS) and inductively coupled plasma analysis (ICP).
Figure 3 shows the TEM micrographs and corresponding
particle size distribution of the PVP‐NiB samples. The images
revealed well dispersed particles with a mean size of 3 nm, a
narrow size distribution, and no aggregation. The correspond‐
ing mean particle diameters were measured and calculated by
counting 190 particles from the enlarged photographs.
(5)
(4)
(3)
(2)
(1)
A typical procedure for the hydrogenation of phenol was as
follows. PVP‐NiB (0.5 g), phenol (0.1 g) and water (6 mL) were
placed in a 20 mL reactor. The reactor system was purged with
N2 three times followed by H2 three times. The reaction was
started under 0.2 MPa H2. The reaction mixture was stirred
vigorously at the reaction temperature. The products were
separated from the water. First, the catalyst was removed from
the liquid by filtration. Then the organic phase was extracted
C=O
CH
4000 3600 3200 2800 2400 2000 1600 1200 800 400
Wavenumber (cm1)
Fig. 1. IR spectra of PVP (1) and PVP‐NiB catalyst with different molar
ratios of Ni:PVP. (2) 2:27; (3) 4:27; (4) 8:27; (5) 16:27.

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Qinsheng Zhang et al. / Chinese Journal of Catalysis 35 (2014) 1793–1799
1795
Ni 2p3/2 PVP-NiB
(a)
(1)
(2)
(3)
70
890
880
870
860
850
840
Binding energy (eV)
20
30
40
50
60
80
B 1s PVP-NiB
2 /(o)
(b)
Fig. 2. XRD patterns of PVP‐NiB with different molar ratios of Ni:PVP.
(1) 8:27; (2) Used (1); (3) 16:27.
196 194 192 190 188 186 184 182 180
Binding energy (eV)
Fig. 4. XPS spectra of Ni 2p (a) and B ls (b) of PVP‐NiB sample.
boron on the catalytic surface can be oxidized, but it was not
confirmed. The BE of boron in the alloyed state (188.6 eV) dis‐
played a positive shift of 1.4 eV with respect to the BE of
amorphous boron (187.2 eV), and the BE of Ni decreased by 0.7
eV. This suggested that partial electron transfer occurred from
elemental B to Ni, making the metal Ni a rich electronic state,
and B a deficient electronic state [23].
(b)
0.20
3  0.4 nm
0.15
0.10
0.05
Table 1 presents the results of phenol hydrogenation under
different conditions over the PVP‐NiB catalysts. The activity
and selectivity of the reaction using four kinds of catalysts syn‐
thesized with the molar ratios of Ni to PVP monomer (molar
/molar) of 2:27, 4:27, 8:27, 16:27 were evaluated. The conver‐
sion of phenol was 43.2%, 66.1%, 86.2%, 83.1% at 30 °C, 0.2
MPa for 12 h with the cyclohexanol selectivity above 99.9%
(Table 1, entries 1–4), when the n(Ni): n(PVP) ratios increased.
The conversion of phenol was gradually increased when the
ratioes of Ni to PVP monomer (molar/molar) were from 2:27 to
8:27. But with more increase in the amount of Ni to PVP mon‐
omer, the conversion began to decline. We selected catalyst
PVP‐NiB synthesized with the ratio of Ni to PVP monomer
(molar/molar) of 8:27, and investigated the effect of reaction
time, dosage of catalyst, and temperature on the activity and
selectivity of the reaction. With increasing dosage of the cata‐
lyst, the conversion of phenol was obviously elevated (entries
5, 6, and 7). When the dosage of the catalyst was 0.25 g, the
conversion of phenol reached 99.9% at the elevated tempera‐
ture and 3 MPa H2 in 4 h (entry 8). On prolonging the reaction
time to 18, 22, and 60 h, the conversion of phenol and the se‐
lectivity of cyclohexanol still exceeded 99.9% (entries 9–11).
The reaction was accelerated at higher temperature. For exam‐
ple, a high conversion of 99.9% in 12 h was obtained at 60 °C
0.00
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2
Partical size (nm)
Fig. 3. TEM micrograph (a) and corresponding particle size distribution
(b) of PVP‐NiB with molar ratio of Ni:PVP = 8:27.
The PVP‐NiB amorphous catalysts were characterized by
XPS. The results are shown in Fig. 4. From the energy levels of
Ni 2p3/2 of the PVP‐NiB samples, there were Ni atoms in the
PVP‐NiB samples in the metallic Ni state with the binding en‐
ergy (BE) of 852.1 eV, and Ni atoms in the oxide state with the
BE of 855.3 eV. From the energy levels of B 1s, the boron al‐
loyed state (BE, 188.6 eV) and the boron oxide state (BE, 191.7
eV) were detected on the PVP‐NiB samples. One can conclude
that the presence of these species was not due to the surface
oxidation of the Ni‐B amorphous alloy. Perhaps they resulted
from the hydrolysis of NaBH4, since the reduction of nickel ions
by NaBH4 was performed in solution [22]. We think that the

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Qinsheng Zhang et al. / Chinese Journal of Catalysis 35 (2014) 1793–1799
Table 1
Hydrogenation of phenol using PVP‐NiB catalyst in water under various conditions.
Selectivity (%)
C–OH C=O
Entry
n(Ni):n(PVP)
PH2 (MPa)
T (°C)
t (h)
Conversion (%)
1
2
3
4
2:27
4:27
8:27
16:27
8:27
8:27
8:27
8:27
8:27
8:27
8:27
8:27
8:27
8:27
8:27
0.2
0.2
0.2
0.2
0.2
0.2
0.2
3
0.2
0.2
0.2
0.2
0.2
1.0
2.0
30
30
30
30
30
30
30
100
30
30
30
60
100
100
100
12
12
12
12
18
18
18
4
18
22
60
12
10
10
8
43.2
66.1
86.2
83.1
40.2
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5a
6b
7c
8d
9
10
11
12
13
14
15
60.1
76.5
99.9
99.9
99.9
99.9
99.9
99.9
99.9
99.9
Reaction conditions: phenol 0.1 g, PVP‐NiB 0.5 g, water 6 mL. a PVP‐NiB 0.1 g; b PVP‐NiB 0.25 g; c PVP‐NiB 0.4 g; d PVP‐NiB 0.25 g.
(entry 12), at 100 °C in 10 h, 99.9% conversion could be
reached (entry 13). The conversion and selectivity of up to
Table 2
Hydrogenation of phenol derivatives using PVP‐NiB catalyst in water
under the optimization conditions.
99.9% were achieved by increasing the hydrogen pressure to
1.0 and 2.0 MPa at 100 °C for 10 and 8 h (entries 14 and 15).
Therefore, the reaction temperature had a considerable effect
on the conversion of phenol and selectivity of the reaction. The
product of the hydrogenation of phenol was cyclohexanol over
the PVP‐NiB amorphous catalyst at a lower temperature and
pressure. It was found that the selectivity did not change on
extending the reaction time. We increased the reaction time to
60 h, and the selectivity to cyclohexanol did not decrease.
The PVP‐NiB amorphous catalyst exhibited high activity and
selectivity to cyclohexanol in the liquid phase phenol hydro‐
genation. These results are related to the morphology of the
catalyst. TEM image revealed well dispersed particles with a
mean size of 3 nm, a narrow size distribution, and no aggrega‐
tion. XPS analysis indicated that partial electron transfer oc‐
curred from elemental B to Ni metal, making the metal Ni a rich
electronic state, and B a deficient electronic state. The elec‐
tronic effect greatly promoted the hydrogenation activity of the
catalysts [23]. XRD results of samples indicated the catalyst had
an amorphous structure. The amorphous alloy catalysts with
long range disorder and short range order usually exhibit
higher activity and better selectivity during the hydrogenation.
A high concentration of coordinatively unsaturated sites led to
catalytic activity and selectivity superior to other catalysts in
the hydrogenation of phenol [24].
To illustrate the general applicability of PVP‐NiB, other
phenol derivatives were tested. Table 2 shows the results of the
hydrogenation. As can be seen, the conversions of the phenol
derivatives were lower than phenol. The selectivity to cyclo‐
hexanol was similar to the phenol. The conversion of p‐cresol
and o‐cresol were 88.3% and 90.1% at 120 °C, 1 MPa H2 and 16
h. However, the conversion of p‐tert‐butylphenol and guaiacol
were only 20.1% and 20.0% at 120 °C, 2 MPa H2 for 24 h. When
the substitution of the aromatic ring was varied, the conversion
and selectivity of the reaction were different. This may be due
to the lower aqueous solubility of the phenol derivatives com‐
PH2
(MPa)
Time Conversion
Selectivity
(%)
Substrate
Product
(h)
16
(%)
OH
OH
1
1
88.3
99.9
99.9
H3C
H3C
OH
OH
H3C
CH3
16
90.1
OH
OH
2
2
24
24
20.1
20.0
99.9
99.9
OH
OH
H3CO
H3CO
Reaction conditions: PVP (Ni‐B) 0.5 g, water 6 mL, 120 °C.
pared with phenol [7].
In conclusion, PVP‐NiB catalysts were prepared by the
chemical reduction method and successfully applied in the hy‐
drogenation of phenol and its derivatives. PVP‐NiB exhibited
high activity for the hydrogenation of phenol to the corre‐
sponding alcohols with water as solvent under mild conditions.
The reaction was accelerated at higher temperature. PVP‐NiB
showed low activity and high selectivity to alcohols for the hy‐
drogenation of p‐cresol and o‐cresol. The selectivity to the cor‐
responding alcohols was up to 99.9%. However, the conversion
was lower in the hydrogenation of p‐tert‐butylphenol and
guaiacol. How to improve the catalytic activity for the hydro‐
genation of phenol derivatives, and the reusability of the
PVP‐NiB catalysts will be the subject of future studies.
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