Preparation of Ni-W-P-B amorphous catalyst for the hydrodeoxygenation of p-cresol

Article abstract of DOI:10.1016/j.catcom.2014.11.023

Ni-W-P-B amorphous catalysts were prepared by a modified chemical reduction method. The formation of a complex between Ni^{2 +} and NH₃·H₂O inhibited the reaction rate of Ni^{2 +} with BH₄^-, leading to a high Ni⁰ content on the catalyst surface. The effects of Ni/W molar ratio on the catalytic activity in the hydrodeoxygenation (HDO) of p-cresol were studied. The deoxygenation degree reached to 100% with a toluene selectivity of 5.1% at 498 K. The HDO reaction temperature and aromatic yield decreased obviously. Some of toluene was produced from the dehydrogenation of 3-methylcyclohexene. Ni-W-P-B exhibited high HDO activity and dehydrogenation activity.

Full text of DOI:10.1016/j.catcom.2014.11.023

Catalysis Communications 60 (2015) 50–54
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Preparation of Ni–W–P–B amorphous catalyst for the
hydrodeoxygenation of p-cresol
Weiyan Wang, Sijun Yang, Zhiqiang Qiao, Pengli Liu, Kui Wu, Yunquan Yang ⁎
School of Chemical Engineering, Xiangtan University, Xiangtan City, Hunan 411105, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 August 2014
Received in revised form 18 November 2014
Accepted 20 November 2014
Available online 22 November 2014
Ni–W–P–B amorphous catalysts were prepared by a modified chemical reduction method. The formation of a
complex between Ni and NH ·H O inhibited the reaction rate of Ni with BH , leading to a high Ni content
3 2 4
on the catalyst surface. The effects of Ni/W molar ratio on the catalytic activity in the hydrodeoxygenation (HDO)
of p-cresol were studied. The deoxygenation degree reached to 100% with a toluene selectivity of 5.1% at 498 K.
The HDO reaction temperature and aromatic yield decreased obviously. Some of toluene was produced from the
dehydrogenation of 3-methylcyclohexene. Ni–W–P–B exhibited high HDO activity and dehydrogenation activity.
2+
2+
−
0
Keywords:
Hydrodeoxygenation
Ni–W–P–B
©
2014 Elsevier B.V. All rights reserved.
Catalyst preparation
p-Cresol
Bio-oil
1
. Introduction
2
conversion of 97.8% after 5 h reaction at 573 K and 3.0 MPa of H .
Yang et al. [16] had reported that the conversion of phenol on CoMoP/
MgO was 89.8% with a benzene selectivity of 64% at 723 K and 5 MPa
The increase of energy consumption and emissions of greenhouse
gases in the utilization of fossil fuels have aroused a wide research in
the exploration of a sustainable and renewable replacement for petro-
leum based fuel [1–3]. Bio-oil, a liquid fraction derived from the pyrolysis
of lignocellulosic materials, is considered as a significant candidate for fuel
of H
Ni–P catalyst was only 85.0% after 10 h reaction at 623 K and 4.0 MPa
of H
2
. Our previous study [17] had found that p-cresol conversion on
2
.
The HDO of phenols usually proceeds with two parallel routes:
direct hydrogenolysis (DDO) yielding aromatics and hydrogena-
tion–dehydration producing cycloalkanes (HYD). According to the
quality standards for clean fuel and World Fuel Oil Regulation IV,
benzene and aromatic contents in gasoline were strictly limited be-
cause of their harmfulness for human health. The latter one avoids
the direct scission of C–O σ-bond in phenolic hydroxyl, which can
decrease the HDO reaction temperature but require a high hydroge-
nation activity for the catalyst. We had reported that Ni–W–B amor-
phous catalyst exhibited high HDO activity and the activity
2 X
due to its CO -neutral and SO -free emission upon combustion [4]. How-
ever, this bio-oil contains high oxygen content, leading to some disadvan-
tages such as low heating value, chemical instability and immiscibility
with fossil fuels, which prevents its direct utilization as a transportation
fuel. The main challenge for upgrading bio-oil to liquid hydrocarbons is
to remove the oxygenated functionalities effectively. One of the most ef-
ficient technologies is catalytic hydrodeoxygenation (HDO).
Until now, many studies regarding HDO have been carried out by
using model compounds [5–13]. Among these oxygenated functionali-
ties in the bio-oil, phenolic hydroxyl oxygen is considered as the most
difficult one to remove because the direct scission of this C–O bond re-
quires the highest activation energy [4], leading to a high reaction tem-
perature for achieving the high deoxygenation degree. For example, K. J.
0
depended on the numbers of metal Ni sites and Brönsted acid
0
sites [18]. However, Ni /Ni on the surface of Ni–W–B catalyst was
only 0.27 [18], suggesting that its HDO activity, especially for hydro-
genation, could be further improved. Li et al. [19] had reported that
adding P into Ni–B catalyst enhanced its hydrogenation activity. In
Smith et al. [14] had studied the HDO of phenols on MoS
morphologies and found that the highest conversion of p-cresol was
5% after 7 h reaction at 623 K and 2.8 MPa of H . Adopting the synergis-
2
with different
fact, Ni2 can react with NH
+
+
4
to produce a complex, which might
2
+
−
7
2
decrease the reaction rate of Ni with BH
4
after forming the complex
and then promote the reduction of Ni2 to Ni . Therefore, aiming to pre-
pare a HDO catalyst with high activity, we used Ni(NO , Na WO
NH ·H O, NaH PO and NaBH as raw materials to synthesize Ni–W–P–
+
0
tic effect between W and Mo and the promoter effect, Wang et al. [15]
had studied the HDO of p-cresol on Ni–Mo–W–S and obtained a
)
3 2
2
4
,
3
2
2
2
4
B amorphous catalysts and studied their activity by taking the HDO of
⁎
Corresponding author.
E-mail address: yangyunquan@xtu.edu.cn (Y. Yang).
p-cresol as a probe.
http://dx.doi.org/10.1016/j.catcom.2014.11.023
566-7367/© 2014 Elsevier B.V. All rights reserved.
1

W. Wang et al. / Catalysis Communications 60 (2015) 50–54
51
2
. Experimental
spectrums displayed two peaks at 187.8 and 192.1 eV. The former one
was attributed to elemental B, while the latter one was attributed to
3
+
2
.1. Catalyst preparation
B
[20,21]. In the Fig. 1c, the peaks around 129.5 and 133.4 eV were
assigned to elemental phosphorus with metal nickel and oxidized phos-
phorus, respectively. In comparison with the standard binding energies
of pure Ni, B and P, a positive shift of the elemental B and a negative shift
of the elemental Ni and P were observed in all the as-prepared samples.
These observations implied that the elemental B donated partial elec-
trons to the metal Ni and the phosphorus accepted electrons from the
nickel metal, which was in good accordance with previous investiga-
tions [22,23]. The peaks around 31.4 eV and 33.4 eV in Fig. 1d were at-
Ni–W–P–B amorphous catalysts were prepared by the following
steps. NiSO
5 mL H O solution, and then NH
Na WO ·2H
a 250 mL three-necked flask. A 20 mL NaBH
4
·6H
2
O (1.57 g) and NaH
2
PO
2
(1.0 g) were dissolved in
O (25 wt.%, 1.6 g) and
2
2
3
·H
2
2
4
2
O were added into the above solution following placed in
(1.0 g) aqueous solution
4
was added dropwise to the three-necked flask with vigorous agitation
at 273 K. The resulting black precipitate was washed with water and
ethanol. Finally, the sample was dried under vacuum at 323 K for 4 h
and was donated as Ni–W-X, where X represented the Ni/W molar
ratio in the initial solution.
0
tributed to W , while the peaks around 35.6 eV and 37.7 eV were
attributed to WO
3
[20]. The appearance of W0 suggested that some
6
+
W
was reduced to metal W.
The surface compositions of Ni–W-2, Ni–W-1, Ni–W-0.5 and Ni–W-
2
.2. Catalyst characterization
0.33 samples are summarized and listed in Table 1. With the decrease of
Ni/W mole ratio in the raw material, Ni/W mole ratio on the catalyst
surface was decreased from 1:0.22 for Ni–W-2 to 1:4.36 for Ni–W-
Specific surface area was measured by a Quantachrome's NOVA-
100e Surface Area instrument by physisorption of nitrogen at 77 K.
2
+
−
2
0.33. This resulted from the reaction of Ni with NH
Ni in the reaction system decreased gradually, but the total of NH
4
. The amount of
2
+
−
The prepared samples were dehydrated at 460 K using vacuum
degassing for 12 h before analysis. X-ray diffraction (XRD) test was car-
ried on a D/max 2550 18 kW Rotating anode X-ray Diffractometer with
Cu Kα (λ = 1.5418 Å) radiation (40 kV, 300 mA). The surface composi-
tion and surface electronic state were analyzed by X-ray Photoelectron
Spectroscopy (XPS) using Kratos Axis Ultra DLD instrument.
4
−
kept constant. After forming the complex, the remained NH
4
was in-
creased with the decrease of Ni2 , leading to the rise on pH value for
+
the reaction solution. As a result, the reaction of Ni2 with BH
+
−
4
was
inhibited and then decreased Ni/W mole ratio on the catalyst surface.
On the other hand, the formation of complex hindered the precipitation
2
+
−
reaction between Ni and OH to produce Ni(OH)
2
, causing the in-
0
2
.3. Catalyst activity measurement
creasing Ni content and decreasing Ni(OH) on the catalyst surface.
Table 1 showed that Ni content on the catalyst surface in this study
2
0
The catalyst activity tests were carried out in a 300-mL sealed auto-
was much higher than that in the previous study [18]. This suggested
0
clave. The fresh catalyst (0.2 g, particle size ≤75 μm), p-cresol (13.51 g)
and dodecane (86.49 g) were placed into the autoclave. Air in the auto-
clave was evacuated by pressurization–depressurization cycles with ni-
trogen and subsequently with hydrogen. The mixture was heated at 10
K/min to 298 K, then pressurized with hydrogen to 4.0 MPa, and stabilized
the stirring speed at 900 rpm. During the reaction, the pressure, stirrer
speed, and temperature were kept constant. Liquid samples were with-
drawn from the reactor and analyzed by Agilent 6890/5973N GC–MS.
To separate the reaction products, the temperature in the GC oven was
heated from 313 K to 358 K with the ramp of 20 K/min, held at 358 K
for 4.0 min, then heated to 473 K at a rate of 20 K/min and kept at 473
K for 5.0 min. The carbon balance in the sample for each of experiment
was better than 95 ± 3%. External and internal mass transfer limitations
could be neglected because of the small catalyst particle size and high stir-
ring speed. The amounts of p-cresol and products were analyzed by
Agilent 7890 gas chromatography using a flame ionization detector
3 2
that adding NH ·H O was beneficial to improve the Ni content on the
catalyst surface, but adding exceeding NH
Ni content.
3 2
·H O lowered the total of
As shown in Fig. 2, all the samples displayed only one broad peak
centered at 2θ = 45°, presenting a typical amorphous structure [19–21].
The intensity of this peak (2θ = 45°) corresponded to amorphous de-
gree [22]. Ni–W-2 exhibited a weaker peak than Ni–W-1, indicating
the higher amorphous degree of Ni–W-2 and the lower amorphous de-
gree of Ni–W-1. It had reported that tungsten oxides and phosphorus
oxide could act as dispersant agents [20,24]. Hence, W6 and P spe-
cies could prevent the particle agglomeration efficiently, resulting in
the high amorphous degree. On the contrary, there existed a strong
+
n+
0
0
0
0
interaction between Ni and B and Ni and P in the prepared catalysts,
0
leading to the promoted agglomeration of particles. The more the B
and P contents on the catalyst surface are, the lower the amorphous
0
degree. The surface area results also supported this inference. As
(
FID) with a 30 m AT-5 capillary column. The deoxygenation degree
shown in Table 1, the surface area decreased in the order of Ni–W-
2
2
2
(DD) for each experiment was calculated as follows:
0.5 (28.0 m /g) N Ni–W-2 (24.5 m /g) N Ni–W-0.33 (22.4 m /g) N
2
Ni–W-1 (17.2 m /g). In addition, the XPS results demonstrated that the
0
6+
n+
Deoxygenationdegree ðDD; wt:%Þ
prepared catalysts contained W , W , P and P , but these species
were not observed in Fig. 2, indicating that these species were in amor-
phous state and dispersed evenly in the catalyst.
ꢀ
ꢁ
oxygencontentinthefinalorganiccompounds
total oxygencontentintheinitialmaterial
¼
1−
ꢀ 100%:
3.2. Hydrodeoxygenation of p-cresol on Ni–W–P–B catalysts
3
. Results and discussion
The conversion and product selectivity versus reaction time in
3
.1. Characterization of Ni–W–P–B catalysts
the HDO of p-cresol on Ni–W-1 at 498 K are shown in Fig. 3a.
Methylcyclohexane, 3-methylcyclohexene, toluene, 4-methylcyclo-
hexanol and 4-methylcyclohexanone were produced during
p-cresol HDO reaction. After 1 h, the conversion reached to 99.6% with a
selectivity of 51.1% 4-methylcyclohexanol. Then, the HDO reaction in
this system was changed to the HDO of 4-methylcyclohexanol. The
selectivity of methylcyclohexane increased to 92.6% while the selec-
tivity of toluene increased to 5.1% for 5 h. Hence, it was concluded that
the main reaction route was HYD, where 4-methylcyclohexanone and
4-methylcyclohexanol acted as intermediates. The toluene selectivity in-
creased from 2.1% to 5.1% in the following 4 h. However, according to
Fig. 1 shows the XP spectra of Ni 2p, B 1s, P 2p and W 4f levels of Ni–
W–P–B, samples. Each of the spectra was deconvoluted, and the relative
content of each state was calculated based on the corresponding peak
area. It had reported that the standard binding energy of elemental Ni,
B, P and W was 853.0, 187.0, 130.4 and 31.0 eV [19,20], respectively, re-
vealing that all species in the prepared catalysts were present in both
oxidized state and elemental state. Two strong peaks at 852.4 and
8
55.8 eV and one weak peak at 860.4 eV appeared in Fig. 1a, corre-
sponding to metal Ni, NiO and Ni(OH) [20,21], respectively. All B 1s
2

52
W. Wang et al. / Catalysis Communications 60 (2015) 50–54
Ni-W-0.33
Ni-W-0.33
Ni-W-0.5
Ni-W-1
(
a) Ni 2p
(b) B 1s
Ni-W-0.5
Ni-W-1
Ni-W-2
Ni-W-2
865
860
855
850
845
196
194
192
190
188
186
184
Electron Binding Energy (eV)
Electron Binding Energy (eV)
(c) P 2p
Ni-W-0.33 (d) W 4f
Ni-W-0.33
Ni-W-0.5
Ni-W-0.5
Ni-W-1
Ni-W-2
Ni-W-1
Ni-W-2
138
136
134
132
130
128
126
44
42
40
38
36
34
32
30
28
Electron Binding Energy (eV)
Electron Binding Energy (eV)
Fig. 1. XP spectra of (a) Ni 2p, (b) B 1s, (c) P 2p and (d) W 4f of Ni–W–P–B samples.
DDO route, this increase of toluene via the direct C–O bond scission was
impossible because there remained only 0.4% p-cresol in the reactor,
which might be derived from 4-methylcyclohexanol. To verify this
hypothesis, we studied the HDO of 4-methylcyclohexanol on Ni–W-1
amorphous catalyst under the same conditions. The results were showed
in Fig. 3b. At the end, the selectivity of 4-methylcyclohexanone and
toluene was 3.8% and 11.6%, respectively. This suggested that there exists
a dehydrogenation reaction. 4-Methylcyclohexanone was yielded by the
dehydrogenation of 4-methylcyclohexanol while toluene was generated
from the dehydrogenation of 3-methylcyclohexene, as shown in
Scheme 1. According to the HDO of 4-methylcyclohexanol, the DDO
route in the HDO of p-cresol might not occur at 498 K because the direct
scission of C–O bond in phenols needs a high activation energy. Moreover,
our previous study [18] had also found that Ni–W–B amorphous catalyst
had no DDO activity at 498 K. Therefore, it can be concluded that Ni–W–
P–B amorphous catalyst possesses HDO activity and dehydrogenation
activity simultaneously.
The conversion and product distribution in the HDO of p-cresol on
Ni–W-2, Ni–W-1, Ni–W-0.5 and Ni–W-0.33 at 498 K for 5 h are showed
in Table 2. p-Cresol conversion increased firstly and then decreased,
while toluene selectivity increased with Ni/W mole ratio. Ni–W-1 ex-
hibited the highest HDO activity: conversion was up to 100% with a de-
oxygenation degree of 100% and a selectivity of 5.1% toluene. This
indicated that the catalyst with an appropriate Ni/W mole ratio en-
hanced the HDO activity and increasing W content promoted dehydro-
genation activity. This was mainly attributed to the composition on the
catalyst surface. For the conversion, Ni–W–P–B amorphous catalyst had
0
0
0
high Ni , B and P contents and electron transfer, leading to its high
hydrogenation activity, which made the HDO of p-cresol proceeded
0
with HYD route [25]. Low total content of Ni contributed to the low
Table 1
Surface area and surface composition of Ni–-W–-P–-B catalysts.
2
Catalysts
S
BET (m /g)
Surface composition
Ni (%)
B (%)
B0
P (%)
P0
W (%)
W0
Ni0
Ni2+
B3+
Pn+
W6+
Ni–W-2
Ni–W-1
Ni–W-0.5
Ni–W-0.33
24.5
17.2
28.0
22.4
Ni1.00
Ni1.00
Ni1.00
Ni1.00
W
0.22
W
0.82
W
1.22
W
4.36
B
3.55
B
2.02
B
3.87
B
8.01
P
0.35
P
0.45
P
0.64
P
1.18
33.1
52.2
55.4
60.2
66.9
47.8
44.6
39.8
22.5
26.4
48.0
47.4
77.5
73.6
52.0
52.6
20.4
60.1
36.6
68.1
79.6
39.9
63.4
31.9
16.6
10.9
26.6
29.2
83.4
89.1
73.4
70.8

W. Wang et al. / Catalysis Communications 60 (2015) 50–54
53
Ni-W-0.33
Ni-W-0.5
Ni-W-1
Ni-W-2
10
20 30 40 50 60 70 80 90
2
Theta (degree)
Scheme 1. Proposed reaction routes for the HDO of p-cresol on Ni–W–P–B amorphous
catalyst.
Fig. 2. XRD patterns of Ni–W-2, Ni–W-1, Ni–W-0.5 and Ni–W-0.33.
conversion. For example, the conversion on Ni–W-1 with a surface com-
sites on the catalyst surface [24]. Although the Brönsted acid sites
increased, the total metal sites on catalyst surface reduced with
W content, leading to the high toluene selectivity and low 4-
methylcyclohexanol selectivity. Scheme 1 indicated that toluene
was generated from the dehydrogenation of 3-methylcyclohexene. The
relation between the characterization and HDO activity results seems to
mean that the toluene selectivity depends on the W content on the cata-
lyst surface, but which needs to be further studied.
0.82 2.02
position of Ni1.00W B P0.45 was 100%, but it decreased to 93.2% on
Ni–W-0.33 with a surface composition of Ni1.00
W
4.36 8.01
B P
1.18, as
shown in Tables 1 and 2. This HYD route avoided the direct deoxygen-
ation, which could reduce the HDO reaction temperature and aromatic
content in the product. Deoxygenation reaction required two kinds of
active sites: metal site and Brönsted acid site [26]. The product distribu-
tion was closely related to the balance between these two sites [27]. The
characterization results had displayed that W in Ni–W–P–B catalysts
existed in the form of WO
Moreover, unreduced phosphorus also increased the Brönsted acid
3
. This W oxide had Brönsted acidity [28].
4. Conclusion
3 2
When adding NH ·H O during the preparation of Ni–W–P–B
2
+
amorphous catalyst, the alone Ni concentration decreased and the re-
action rate of Ni2 with BH
+
−
4
was inhibited because of a formation of
2
+
2+
complex between Ni and NH
to Ni , which yielded a high Ni content on the catalyst surface. P in the
3
·H
2
O, promoting the reduction of Ni
(a)
0
0
100
0
n+
90
80
70
60
50
40
30
20
10
0
catalyst existed in the form of P and P , the former state could enhance
the hydrogenation while the latter state acted as Brönsted acid sites.
Ni–W–P–B amorphous catalyst exhibited high activity in the HDO of
p-cresol. The deoxygenation degree was high to 100% with a toluene
selectivity of 5.1% at 498 K. Both the HDO reaction temperature and
aromatic yield decreased obviously. Ni–W–P–B also possessed a dehydro-
genation activity.
Conversion
-Methylcyclohexanol
4-Methylcyclohexanone
Methylcyclohexane
4
4
-Methylcyclohexene
Toluene
Acknowledgments
This work was supported by Natural Science Foundation of Hunan
Province (13JJ4048), National Natural Science Foundation of China
0
1
2
3
4
5
Time (h)
(
no. 21306159, 21376202) and Specialized Research Fund for the
(b) 1
Doctoral Program of Higher Education (20124301120009).
00
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Table 2
Conversion
-Methylcyclohexanone
Methylcyclohexane
4-Methylcyclohexene
Toluene
Comparison of the HDO of p-cresol on Ni–W-2, Ni–W-1, Ni–W-0.5 and Ni–W-0.33 at
498 K for 5 h.
4
Catalysts
Ni–W-2
Ni–W-1
Ni–W-0.5
Ni–W-0.33
Conversion, mol%
98.1
100
99.7
93.2
Product distribution, mol%
4-Methylcyclohexanol
4-Methylcyclohexanone
3-Methylcyclohexene
28.8
2.3
4.2
59.8
4.9
67.5
0
0
9.3
2.9
12.2
62.6
13
18
7.6
0.6
56.5
17.3
72.6
0
1
2
3
4
5
2.4
92.5
5.1
100
Time (h)
Methylcyclohexane
Toluene
DD, wt.%
89.2
Fig. 3. HDO of (a) p-cresol and (b) 4-methylcyclohexanol on Ni–W-1 at 498 K.

54
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