Amorphous Co-Mo-B catalyst with high activity for the hydrodeoxygenation of bio-oil

Article abstract of DOI:10.1016/j.catcom.2010.11.001

Co-Mo-B amorphous catalysts with different Mo/Co molar ratios were prepared with chemical reduction method. Phenol, benzaldehyde and acetophenone were used as model compounds to test the catalyst hydrodeoxygenation activity. The catalyst surface composition had a great effect on catalyst activity. Both the conversion and the total deoxygenation rate could reach to 100%. The high catalytic activity of the Co-Mo-B amorphous catalyst depended on the sufficient supply of free hydrogen and the high content of Mo⁴⁺ Br?nsted acid on the catalyst surface.

Full text of DOI:10.1016/j.catcom.2010.11.001

Catalysis Communications 12 (2011) 436–440
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Amorphous Co–Mo–B catalyst with high activity for the hydrodeoxygenation
of bio-oil
⁎
Weiyan Wang, Yunquan Yang , Hean Luo, Tao Hu, Wenying Liu
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 6 August 2010
Received in revised form 28 October 2010
Accepted 3 November 2010
Available online 11 November 2010
Co–Mo–B amorphous catalysts with different Mo/Co molar ratios were prepared with chemical reduction
method. Phenol, benzaldehyde and acetophenone were used as model compounds to test the catalyst
hydrodeoxygenation activity. The catalyst surface composition had a great effect on catalyst activity. Both the
conversion and the total deoxygenation rate could reach to 100%. The high catalytic activity of the Co–Mo–B
amorphous catalyst depended on the sufficient supply of free hydrogen and the high content of Mo4+
Brønsted acid on the catalyst surface.
Keywords:
© 2010 Elsevier B.V. All rights reserved.
Co–Mo–B amorphous catalyst
Hydrodeoxygenation
Phenol
Benzaldehyde
Acetophenone
Bio-oil
1. Introduction
carried out at high temperature using H2S or CS2 as sulfiding agent,
which was inevitable to exhaust poisonous gas H2S. Moreover,
With the growing environmental concerns and the rapid
decrease of fossil fuel reserves, more and more attention has been
paid to the renewable, sustainable and environment friendly liquid
fuels [1,2]. Bio-oil, derived from biomass pyrolysis, has been
considered as the only practical source of renewable liquid fuel
[3] because of the renewability and huge amounts of biomass, a
negligible content of sulfur and nitrogen in bio-oil, and zero
emission of carbon dioxide to the atmosphere during bio-oil
combustion [2,4]. However, the oxygen content in bio-oil is high
up to 50%, leading to some deleterious properties such as low
heating value, thermal and chemical instabilities, immiscibility with
fossil fuels and tendency to polymerization [5], which hinder its
extensive application as liquid transportation fuel. Therefore, it is
necessary to remove the oxygen from bio-oil by hydrodeoxygena-
tion (HDO).
additional sulfiding agent was required to be added in the feed to
maintain the sulfidation level of metal sulfide catalyst because the
negative effect of oxygen would significantly decrease the catalytic
activity [7,8]. Hence, it is very important to develop a new kind of
non-sulfur-based, cheap and high active catalyst for the HDO of bio-
oil.
Amorphous catalyst has attracted much attention owing to its
unique isotropic and high concentration of coordinative unsaturated
sites. It exhibited excellent activity and good selectivity in the catalytic
reaction [17–23]. As far as we know, however, there are still few
reports of the HDO of bio-oil on amorphous catalysts except for our
studies [24,25]. In the previous study, the Ni–Mo–B amorphous
catalyst has been prepared and successfully applied in the HDO of bio-
oil [24]. Moreover, Co was added as a dopant in the Ni–Mo–B
amorphous catalyst. The results showed that Co–Ni–Mo–B exhibited
higher catalytic activity in the HDO of phenol than Ni–Mo–B
amorphous catalyst [25], but the thermal stability and the deoxygen-
ation activity of these amorphous catalysts were not improved
significantly. In this study, we tried to prepare Co–Mo–B amorphous
catalyst and determined whether Co–Mo–B amorphous catalyst could
overcome the disadvantages of the Ni–Mo–B amorphous catalyst
mentioned earlier and focused on the effects of Mo/Co molar ratio on
catalyst activity. Phenol, benzaldehyde and acetophenone were used
as model compounds to test the HDO activity of the Co–Mo–B
amorphous catalyst. Dodecane with high boiling point and good
Great efforts have been focused on the HDO of bio-oil on con-
ventional metal sulfide catalysts [6–10] and noble metal catalysts
[11–16]. In comparison with metal sulfide catalyst, high cost was
the primary disadvantage of noble catalyst. Metal sulfide catalysts
had good deoxygenation activity and thus were investigated
extensively, but the sulfidation process of these catalysts was
⁎
Corresponding author.
E-mail address: yangyunquan@xtu.edu.cn (Y. Yang).
1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.11.001

W. Wang et al. / Catalysis Communications 12 (2011) 436–440
437
chemical stability was selected as solvent because it can be recycled
3. Results and discussion
with a simple distillation.
3.1. Characterization of the amorphous catalysts
2. Experimental
The XRD patterns of fresh Co–Mo–B samples with different Mo/Co
ratios are illustrated in Fig. 1. There appeared a broad peak around
2θ=45° in each catalyst pattern, revealing that the fresh catalysts had
a typical amorphous structure [20–24]. However, the intensity of peak
at 2θ=45° was decreasing with the increase of Mo content, which
might have resulted from the following fact. Mo, a large radius atom
(r=2.01 Å), acted as dispersant in Co–Mo–B amorphous catalysts
[18]. It could decrease the diffusion rate of Co atom and thus inhibited
the agglomeration. The more serious the Co atom agglomeration, the
stronger the intensity of peak at 2θ=45° would be. Besides, another
broad peak appeared around 2θ=27° in the XRD patterns of fresh
Co–Mo–B samples, attributing to the boron oxide, which resulted
from the ineluctable oxidation of boron in the solution [24]. The fresh
Co–Mo–3 catalyst was heat-treated at 573 K for 10 h and then
donated as Co–Mo–3–C. As shown in Fig. 1, there was not any
diffraction peak in the XRD pattern of Co–Mo–3–C, but the intensity of
the peak at 2θ=45° was increased slightly, which suggested that the
Co–Mo–3 amorphous catalyst could keep its amorphous structure at
573 K and the thermal stability of the Co–Mo–3 amorphous catalyst
was much higher than that of Ni–Mo–B amorphous catalysts [25]. The
increase of peak intensity was attributed to the particle agglomeration
at high temperature.
As shown in Fig. 2, the XPS characterization results showed that
the binding energies of Co, B and Mo in Co–Mo–B amorphous catalysts
were much higher than the standard binding energies of elemental Co
(778 eV [20]), elemental B (187 eV [26]), and elemental Mo (228 eV
[27]), respectively. The binding energy in Fig. 2a around 780.7 eV was
attributed to CoO while the others were attributed to the electron
shakeup peak of Co(OH)2 and CoO multiple splitting peaks [28]. At the
level of B 1s, the only peak observed was located at around 192 eV,
which was assigned to B2O3. The peaks around 230.5 eV, 231.9 eV and
233.4 eV in Fig. 2c were ascribed to Mo4+ and the others to Mo6+ [27],
indicating that Mo6+ could be partially reduced by NaBH4.
2.1. Catalyst preparation
Co–Mo–B amorphous catalysts were prepared by chemical
reduction. A 100 mL aqueous solution containing ammonium hepta-
molybdate (1.764 g) and cobalt nitrate was placed in a 250 mL three-
necked flask. The composition of the samples was adjusted by
changing the initial Mo/Co ratio in the solution. An 80 mL sodium
borohydride aqueous solution (1 mol/L) was added dropwise to the
three-necked flask with vigorous agitation at 273 K. Then, the black
precipitate was produced and washed with ultrapure water several
times until the pH=7 to remove the soluble boron species and Na+
ions, followed by washing with absolute ethanol several times to
remove the residual water and water-soluble impurities. Finally, the
resulting product was dried under vacuum at 323 K for 8 h. The
resulting product was denoted as Co–Mo–X where X represented the
Mo/Co ratio in the initial solution. For comparison, Co–B amorphous
catalyst containing no Mo was also prepared.
2.2. Catalyst characterization
X-ray diffraction (XRD) test was carried on a D/max2550 18 kW
rotating anode X-Ray diffractometer with Cu Kα (λ=1.5418 Å) radia-
tion (40 kV, 300 mA). The 2θ was scanned over the range of 15–85° at a
rate of 10°/min to identify the amorphous structure. Specific surface
area was measured by a Quantachrome's NOVA-2100e Surface Area
instrument by physisorption of nitrogen at 77 K. Bulk compositions
were identified by Inductively Coupled Plasma analysts (ICP) on a
Varian VISTAMPX. The surface composition and surface electronic
state were analyzed by X-ray Photoelectron Spectroscopy (XPS) using
Kratos Axis Ultra DLD instrument at 160 eV pass energy. Al Kα
radiation was used to excited photoelectrons. The relative content of
each state on the catalyst surface was calculated according to the XPS
data and the corresponding peak area in the XPS spectra.
The bulk composition and surface composition are presented in
Table 1. The relative content of Co in the catalyst surface was increased
with the increase of Mo in the initial material. The Co/Mo atom ratio of
surface composition was much larger than that of the corresponding
bulk composition, indicating that many Mo atoms were covered by the
Co atom. These might have resulted from the reaction rate of MoO42−
with NaBH4 being quicker than that of Co2+ with NaBH4. The specific
surface area results were also consistent with the bulk composition
results. As shown in Table 1, the SBET of Co–Mo–1, Co–Mo–2 and
Co–Mo–3 was 22.3 m2/g, 21.5 m2/g and 18.4 m2/g, respectively, which
2.3. Catalyst activity measurement
The catalyst activity tests were carried out in a 300-mL sealed
autoclave. The 1000 ppmw catalyst, the model reactant (11.76 wt.%
phenol, 13.25 wt.% benzaldehyde, or 15.00 wt.% acetophenone) and
dodecane were placed into the autoclave and the air was evacuated by
pressurization–depressurization cycles with nitrogen and subse-
quently with hydrogen. The mixture was heated at 10 K/min to
desired temperature, then pressurized with hydrogen to 4.0 MPa, and
stabilized the stirring speed at 700 rpm. During the reaction, liquid
samples were withdrawn from the reactor and identified by Agilent
6890/5973N GC–MS. The quantities of compounds were analyzed
with Agilent 7890 gas chromatography using a flame ionization
detector (FID) fitted with a capillary column (AT-5, 30 m×0.32 mm×
0.25 μm). The conversion, selectivity and deoxygenation rate for each
experiment were calculated as follows:
Co-B
Co-Mo-1
ꢀ
ꢁ
Co-Mo-2
Co-Mo-3
moles of residual phenol
moles of initial phenol
Conversion ð%Þ = 1−
× 100%
Co-Mo-3-C
moles of product ðAÞ
Selectivity ðA;%Þ =
× 100%
moles of reacted phenol compound
10
20
30
40
50
60
70
80
90
2 Theta (degree)
Deoxygenation rate ðwt:%Þ
ꢀ
ꢁ
oxygen content in the final organic compounds
Fig. 1. XRD patterns of fresh Co–B, Co–Mo–1, Co–Mo–2, Co–Mo–3 and Co–Mo–3 heat-
=
1−
× 100%:
total oxygen content in the initial material
treated at 573 K.

438
W. Wang et al. / Catalysis Communications 12 (2011) 436–440
ratio of the initial solution, which suggested that some of Co2+ was not
(a)
reacted by NaBH4 to produce precipitate because MoO24− had an
inhibition effect for the reaction of Co2+ and NaBH4. For the Co–Mo–2
amorphous catalyst, the amount of Co2+ in the initial solution of
Co–Mo–2 was half the amount of Co2+ in the initial solution of
Co–Mo–1, the Co2+ might be almost reacted by NaBH4. Therefore, the
Co–Mo bulk composition of the Co–Mo–2 amorphous catalyst was
close to the Co–Mo composition of the initial solution. Maybe the
Co/Mo atomic ratio of the Co–Mo–1 bulk composition will be increased
to near 1:1 with the increase of preparation time. Table 1 showed that
the Mo4+ content of each sample was high up to 55%, suggesting that
Co–Mo–B amorphous catalysts would have excellent deoxygenation
activity because the high deoxygenation rate depended on the high
content of Mo4+ [24].
Co 2p
Co-Mo-1
Co-Mo-2
Co-Mo-3
792
776
780
784
788
3.2. HDO activity test
Electron Binding Energy (eV)
As shown in Table 2, the conversion of the HDO of phenol on Co–B
was high up to 100% with a selectivity of 91.4% cyclohexanol and a
selectivity of 11.2% deoxygenation at 523 K. When Mo was added in
the Co–B, both the cyclohexane selectivity and the deoxygenation rate
increased rapidly, indicating that the Mo site rather than the Co site
had the deoxygenation activity and the HDO reaction was the result of
the synergistic effect of Co and Mo. The HDO activity of the Co–Mo–B
amorphous catalyst increased with the increase of the Mo content in
the initial solution, which was in agreement with the Co content
changes of the catalyst surface composition. The conversion and the
deoxygenation rate in the HDO of phenol on Co–Mo–3 at 523 K
increased to 100% and 69.6%, respectively. The main products were
cyclohexane and cyclohexanol. When the temperature was increased
to 548 K, the main product was changed to cyclohexane and the
deoxygenation rate selectivity was increased to 100%. Hence, it could
be concluded that high temperature was beneficial to the HDO of
phenol on Co–Mo–B amorphous catalysts.
As shown in Fig. 3, the differences on catalyst activity were very clear
in the HDO of phenol. The catalyst activity for the HDO of phenol
decreased in the order of Co–Mo–3NCo–Mo–2NCo–Mo–1. According to
the changes of product distribution versus reaction time, it could
presume that the HDO of phenol on Co–Mo–B amorphous catalysts also
proceeded with the hydrogenation–dehydration route and the direct
deoxygenation route. Taking the HDO of phenol on the Co–Mo–3
catalyst as an example, the selectivity of benzene produced with the
direct deoxygenation route was increased very slowly and then kept
unchanged, which could be limited within 1.5% during the reaction. The
selectivity of cyclohexane which was produced via the hydrogenation–
dehydration route increased rapidly high up to 98.2%. Obviously, the
main HDO route of phenol on Co–Mo–B catalysts was hydrogenation–
dehydration, which was much different from that on sulfide and
phosphide catalysts [8,29].
(b)
B 1s
Co-Mo-1
Co-Mo-2
Co-Mo-3
184 186 188 190 192 194 196 198 200
Electron Binding Energy (eV)
(c)
Mo 3d
Co-Mo-1
Co-Mo-2
Co-Mo-3
It was well known that the difficulty degree of deoxygenation
mainly depended on the C–O bond energy. To determine whether
Co–Mo–B amorphous catalysts had high catalytic activity for the HDO
of other oxide-containing compounds or not, benzaldehyde and
acetophenone were also used as model compounds to study the
HDO properties of the Co–Mo–3 catalyst. The changes of the
conversion and the product selectivity versus reaction time are
showed in Fig. 3(d) and (e). Both the conversions of benzaldehyde
and acetophenone could reach to 100% with a selectivity of 100%
deoxygenation within 3 h. Therefore, it could be concluded that the
HDO of benzaldehyde or acetophenone was much easier than that of
phenol, which was consistent with previous investigation [5]. The
deoxygenation products toluene and ethylbenzene could be further
hydrogenated to alkane compounds, but the hydrogenation of toluene
was more difficult than that of ethylbenzene, which was due to the
high electron–donor ability of ethyl.
228
230
232
234
236
238
Electron Binding Energy (eV)
Fig. 2. XPS spectra of (a) Co 2p, (b) B 1s and (c) Mo 3d levels of Co–Mo–B amorphous
catalysts.
was caused by the small SBET of Mo oxides [24]. If ammonium
heptamolybdate and cobalt nitrate were reacted by NaBH4 completely
to produce precipitate, the Co–Mo composition of Co–Mo–1 and
Co–Mo–2 should be Co1.00Mo1.00 and Co1.00Mo2.00, respectively.
However, the Co/Mo atomic ratio of the bulk composition of the
Co–Mo–1 amorphous catalyst was much lower than the Co/Mo atomic

W. Wang et al. / Catalysis Communications 12 (2011) 436–440
439
Table 1
Structural properties of Co–Mo–1, Co–Mo–2 and Co–Mo–3 amorphous catalysts.
Catalyst
SBET (m2/g)
Bulk
composition
Surface
composition
Co (%)
Co0
Mo (%)
Mo4+
B (%)
B0
Co2+
Mo6+
B3+
Co–Mo–1
Co–Mo–2
Co–Mo–3
22.3
21.5
18.4
Co1.00Mo2.33B0.48
Co1.00Mo2.21B0.42
Co1.00Mo3.46B0.34
Co1.00Mo0.83B1.13
Co1.00Mo0.51B0.92
Co1.00Mo0.36B0.77
0
0
0
100
100
100
55.7
55.1
55.4
44.3
44.9
44.6
0
0
0
100
100
100
Table 2
The HDO of phenol on Co–B, Co–Mo–1, Co–Mo–2 and Co–Mo–3 amorphous catalystsa.
Among Mo oxides, only MoO2 was in the form of Mo–OH and acted
as the Brønsted acid site [30]. Our previous studies [24,25] had
confirmed that ① the HDO reaction required two types of active sites:
one for the activation of dihydrogen, while the other for the activation
of oxy-groups; ② only MoO2 acted as Brønsted acid site that could
activate the C–O bond and ③ the higher the content of MoO2 was, the
higher the deoxygenation activity the catalyst had, and the higher the
deoxygenation rate was. Therefore, it was easy to conclude that the
HDO activity depended on the supply of free hydrogen and Brønsted
acid sites on the catalyst surface and the HDO of phenol, benzaldehyde
and acetophenone on the Co–Mo–B amorphous catalyst was the
synergistic effect between the Co active site and the MoO2 active site.
The excellent HDO activity of Co–Mo–3 could be explained by the
following facts. XRD results showed that the Co–Mo–3 catalyst
displayed an amorphous structure, which had a high concentration
of coordinative unsaturated sites and could enhance the adsorption
capacity of hydrogen. XPS results showed that the Mo4+ content and
the Co/Mo atom ratio on the Co–Mo–3 catalyst surface were high up
to 55% and 2.78, respectively. The amorphous structure and the high
content of Co on the Co–Mo–3 catalyst surface were beneficial to
adsorb enough hydrogen and provide sufficient free hydrogen while
the high content of MoO2 was beneficial to supply enough Brønsted
acid sites to activate the oxy-groups, which guaranteed that the HDO
reaction went on smoothly.
Catalyst
Co–B
523
Co–Mo–1
523 548
96.0 97.9 100
Co–Mo–2
523 548
100
Co–Mo–3
523
548
Conversion (%)
Cyclohexanol
Cyclohexanone
Benzene
100
91.4 41.2
2.1
0
100
27.8
100
0
6.3
0.5
3.4
28.1
0.9
1.3
2.0
0
2.1
1.0
2.1
0.7
0.8
0
1.5
Cyclohexane
Cyclohexene
Deoxygenation rate (%)
6.5 50.8 80.1
4.8 9.5
11.2 53.8 90.3
66.5
2.3
69.1
91.3
4.4
97.7
68.3
2.2
69.6 100
98.2
0.3
0
a
Reaction conditions: 0.10 g catalyst, 11.76 g phenol, 88.24 g dodecane, P(H2)=
4.0 MPa, stirring speed=700 r/min, and reaction time 10 h.
Besides, the complicated mixture containing 3.92 g phenol, 4.42 g
benzaldehyde and 5.0 g acetophenone was used as simulative bio-oil
to further study the HDO properties of the Co–Mo–3 catalyst. As shown
in Fig. 4, the conversion of the mixture could reach to 100% within 3 h
and there was not any O-containing compound in the final products,
suggesting that the deoxygenation rate was high up to 100%. However,
the deoxygenation rate of cyclohexanol, the methylcyclohexane
selectivity and the ethylcyclohexane selectivity were decreased
compared with that in the HDO of the single compound, respectively.
The reasons of these changes were hard to understand, but one could
conclude that Co–Mo–3 had high activity for the HDO of this mixture.
Therefore, it could be believed reasonably that the direct HDO of crude
bio-oil mixture on Co–Mo–3 was feasible based on the high similarity
of the composition of crude bio-oil mixture to the product composition
during the HDO of this mixture.
4. Conclusions
Co–Mo–B amorphous catalysts were prepared and exhibited high
catalytic activity in the hydrodeoxygenation of phenol, benzaldehyde
100
(a)
(b)
(c)
90
80
70
60
50
40
30
20
10
0
Conversion
Cyclohexane
Cyclohexene
Cyclohexanol
Benzene
Cyclohexanone
0 1 2 3 4 5 6 7 8 9
Time (h)
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
Time (h)
Time (h)
100
90
80
70
60
50
40
30
20
10
0
(d)
(e)
Conversion
Methylcyclohexane
Toluene
Conversion
Ethylcyclohexane
Ethylbenzene
Benzylalcohol
0 1 2 3 4 5 6 7 8 9
Time (h)
0 1 2 3 4 5 6 7 8 9
Time (h)
Fig. 3. The HDO of phenol on (a) Co–Mo–1, (b) Co–Mo–2 and (c) Co–Mo–3 amorphous catalysts and the HDO of (d) benzaldehyde and (e) acetophenone on the Co–Mo–3 amorphous
catalyst at 548 K.

440
W. Wang et al. / Catalysis Communications 12 (2011) 436–440
and acetophenone. The catalyst activity was increased with the Co/Mo
100
90
80
70
60
50
40
30
20
10
0
ratio increase of surface composition. Both the conversion and the
total deoxygenation rate could be high to 100%. This new kind of
amorphous catalyst with low cost, simple preparation, high thermal
stability and high HDO activity will be a potential candidate for the
HDO process. But the Co on the catalyst surface was in the form of
oxides and the Mo6+ content was still very high, the catalyst activity
could be further improved.
(P)
Conversion
Cyclohexane
Cyclohexene
Cyclohexanol
Benzene
Cyclohexanone
Acknowledgements
This research was supported by the Scientific Research Fund of
Hunan Provincial Education Department (10K062), the Foundation of
Hunan Provincial Key Laboratory of Green Catalysis and Chemical
Reaction Engineering, and the Hunan Provincial Innovation Founda-
tion for Postgraduate (CX2009B135).
0
1
2
3
4
5
6
7
8
9
Time (h)
100
90
80
70
60
50
40
30
20
10
0
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(A)
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Fig. 4. The HDO of the mixture on the Co–Mo–3 amorphous catalyst versus reaction
time. Reaction conditions: 3.92 g phenol (P), 4.42 g benzaldehyde (B), 5.0 g acetophe-
none (A), 86.66 g dodecane, 0.10 g catalyst, P(H2)=4 MPa, stirring speed=700 r/min,
and temperature=548 K.
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