Effect of additive (Co, La) for Ni-Mo-B amorphous catalyst and its hydrodeoxygenation properties

Article abstract of DOI:10.1016/j.catcom.2010.02.019

Ni-Mo-B amorphous catalysts promoted by Co and La were prepared by chemical reduction of the corresponding metal salts with sodium borohydride. The effects of additives for the catalytic activity were studied using the hydrodeoxygenation of phenol as model reaction. Co- and La-promoted Ni-Mo-B amorphous catalysts exhibited higher catalytic activity. The total selectivity of oxygen-free products was increased to 93.1% with a selectivity of 3.2% aromatics on Co-Ni-Mo-B and the total H/C atomic ratio in the products was improved to 1.99 on La-Ni-Mo-B. Crown Copyright

Full text of DOI:10.1016/j.catcom.2010.02.019

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Catalysis Communications 11 (2010) 803–807
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Effect of additive (Co, La) for Ni–Mo–B amorphous catalyst and its
hydrodeoxygenation properties
⁎
Wei-yan Wang, Yun-quan Yang , He-an Luo, Wen-ying 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 January 2010
Received in revised form 8 February 2010
Accepted 16 February 2010
Available online 19 March 2010
Ni–Mo–B amorphous catalysts promoted by Co and La were prepared by chemical reduction of the
corresponding metal salts with sodium borohydride. The effects of additives for the catalytic activity were
studied using the hydrodeoxygenation of phenol as model reaction. Co- and La-promoted Ni–Mo–B
amorphous catalysts exhibited higher catalytic activity. The total selectivity of oxygen-free products was
increased to 93.1% with a selectivity of 3.2% aromatics on Co–Ni–Mo–B and the total H/C atomic ratio in the
products was improved to 1.99 on La–Ni–Mo–B.
Keywords:
Amorphous catalyst
Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
Ni–Mo–B
La
Co
Hydrodeoxygenation
Bio-oil
1. Introduction
minimize the aromatic hydrocarbons formation. The key point of this
problem is to prepare a novel catalyst.
With the decline of crude oil resources, developing renewable bio-
oils becomes very important and the European Union aims to
introduce 5.75% of bio-fuels into conventional fuels by December
2010 [1]. But these bio-oils derived from the pyrolysis of bio-mass
contain considerable quantity of oxygen, leading to poor heating
value, corrosiveness, thermal instability and immiscibility with
hydrocarbon fuels [2]. Consequently, the hydrodeoxygenating
(HDO) of bio-oils is necessary if these bio-oils are to be used as liquid
transportation fuel.
Some reports had indicated that the main HDO catalysts were
MoS2 [3], Ni–Mo–S [4,5], Co–Mo–S [6–8], Ni–W–S [9,10], Co–Mo–P
[11] and some noble metal catalysts [12,13]. Of these catalysts,
sulfiding agent was required to add into the feed to maintain the
sulfidation level of the sulphided catalysts because of the negative
effect of oxygen for the sulphided structure [4,7,8] and the demand of
evading the use of expensive noble metal as HDO catalysts. Moreover,
it had verified that the primary route of the HDO of phenol on
sulphide catalyst was direct hydrogenolysis and the main HDO
product was benzene [7]. However, the total content of aromatic
hydrocarbons in bio-oil will be limited to 14% by 2010 according to
the European regulations [10]. Therefore, for bio-oils refining, it is not
only very important to obtain high conversion, but also crucial to
Amorphous catalysts had showed excellent activity and high
selectivity in hydrogenation reactions [15–20] owing to their unique
isotropic and high concentration of coordinative unsaturated sites
[14]. However, to our knowledge, there were still very few reports of
the application of amorphous catalysts in the HDO except for our
study [21]. Aimed at improving the HDO activity of the amorphous
catalysts and decreasing the total content of aromatic hydrocarbons,
Co or La was added in Ni–Mo–B amorphous catalyst in this paper. The
effects of additives for the HDO properties and the products
distribution were also studied by using phenol as model compound.
2. Experimental
2.1. Catalyst preparation
Additive-containing Ni–Mo–B amorphous catalysts were prepared
by the following steps. 100 mL aqueous solution containing ammo-
nium heptamolybdate (1.764 g), a certain amount of nickel nitrate
and the third metal salt such as cobalt chloride or lanthanum nitrate
as additive was placed in a three-necked flask. The additive/Ni/Mo
molar ratio was 0.15:1:3 in each case. 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. The black precipitate was collected and washed with ultra-
pure water and anhydrous ethanol subsequently, and finally dried
under vacuum at 313 K for 8 h. The as-prepared sample was denoted
⁎
Corresponding author.
E-mail address: yangyunquan@xtu.edu.cn (Y. Yang).
1566-7367/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.02.019

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W. Wang et al. / Catalysis Communications 11 (2010) 803–807
as Co–Ni–Mo–B or La–Ni–Mo–B. For comparison, Ni–Mo–B catalyst
containing no additive was also prepared as described above.
2.2. Catalyst characterization
Specific surface area was measured by a Quantachrome's NOVA-
2100e Surface Area instrument by physisorption of nitrogen at 77 K.
The morphology was obtained by scanning electron microscopy
(SEM) on a JEOL JSM-6360 electron microscopy. X-ray diffraction
(XRD) test was carried on a D/max2550 18KW Rotating anode X-Ray
Diffractometer with Cu Kα (λ 1.5418 Å) radiation (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. 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.
2.3. Catalyst activity measurement
The catalyst activity tests were carried out in a 300-mL sealed
autoclave. The as-prepared catalyst (0.05 g), phenol (11.76 g) and
dodecane (88.24 g) were placed into the autoclave. Air in the
autoclave was evacuated by pressurization–depressurization cycles
with nitrogen and subsequently with hydrogen. The mixture was
heated at 10 K/min to desired temperature, then pressurized with
hydrogen to 4.0 MPa, stabilized the stirring speed at 700 rpm. During
the reaction, liquid samples were withdrawn from the reactor and
identified by Agilent 6890/5973 N GC–MS. The amounts of phenol and
products were analyzed by Agilent 7890 gas chromatography using a
flame ionization detector (FID) with a 30 m AT-5 capillary column.
3. Results and discussion
3.1. Characterization of the amorphous catalysts
Fig. 1 shows the morphologies of Ni–Mo–B, Co–Ni–Mo–B and La–
Ni–Mo–B samples. Ni–Mo–B showed eggshell morphology with
inhomogeneous particle size accompanied with agglomeration
phenomenon. The range of Ni–Mo–B particle size was 100 nm to
400 nm. The average particle diameters of Co–Ni–Mo–B and La–Ni–
Mo–B catalysts were both around 100 nm. But the agglomeration
phenomenon of Co–Ni–Mo–B was more obvious than that of La–Ni–
Mo–B. The corresponding surface areas of Ni–Mo–B, Co–Ni–Mo–B and
La–Ni–Mo–B, as shown in Table 1, were 38.42 m2/g, 52.67 m2/g and
116.64 m2/g, respectively, indicating that the additive Co or La could
decrease the particle size and increase the surface area of catalyst.
However, the addition of La increased two times the surface area
value in comparison with the addition of Co, which was related to the
agglomeration phenomenon of particles. La (r=2.74 Å), much larger
than Co (r=1.67 Å), was distributed in Ni–Mo–B amorphous catalysts
as dispersant agent and prevented agglomeration efficiently [22].
The XRD patterns of the fresh samples are shown in Fig. 2(a). A
broad diffraction peak was appeared around 2θ=45°, attributing to a
typical amorphous structure [19,20,23]. Another diffraction peak at
2θ=27° was mainly ascribed to boron oxides [15,24]. Compared with
Ni–Mo–B, the peaks of Co–Ni–Mo–B and La–Ni–Mo–B at 2θ=27°
were weaker, indicating that the additives Co or La could inhibit the
formation of boron oxide. As shown in Fig. 2(b), Co–Ni–Mo–B, heat-
treated at 548 K, showed three diffraction peaks at 2θ=38°, 44°, 52°,
corresponding to NiO, Ni (111) and Ni (200) [25], respectively, which
indicated that the amorphous state of Co–Ni–Mo–B catalyst began to
transform to crystalline state. However, La–Ni–Mo–B sample, heat-
treated at 548 K, showed only two small diffraction peaks at 2θ=44°
and 52° and the diffraction peak intensities of these two peaks were
Fig. 1. SEM images of (a) Ni–Mo–B, (b) Co–Ni–Mo–B and (c) La–Ni–Mo–B.
much weaker than that of Co–Ni–Mo–B(C) (heat-treated at 548 K),
suggesting that La–Ni–Mo–B also began to transform to crystalline
state. But the thermal stability of La–Ni–Mo–B was better than that of
Co–Ni–Mo–B.
The binding energies of metallic Ni combined with B in Ni–Mo–B,
Co–Ni–Mo–B and La–Ni–Mo–B, as shown in Fig. 3a, were 853.0 eV,
852.1 eV and 852.0 eV, respectively. The other peaks of each sample
were assigned to Ni2+ [16–19]. In Fig. 3b, all of the samples exhibited
two peaks. The low-binding energy (around 189.0 eV) was attributed
to B0 while the high-binding energy (around 193.0 eV) was attributed
to oxidized boron [16,26]. Notably, the binding energy of Ni0 in Ni–
Mo–B (853.0 eV) was higher than that of Co–Ni–Mo–B (852.1 eV) and
La–Ni–Mo–B (852.0 eV). Compared with the standard binding
energies of elemental nickel and boron, the binding energies of Ni0
shifted negatively while the binding energies of B0 shifted positively

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W. Wang et al. / Catalysis Communications 11 (2010) 803–807
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Table 1
Relative peak areas in the XPS analysis.
Catalysts
SBET
Bulk composition
Surface composition
Ni (%)
Ni0
Mo (%)
Mo4+
B (%)
B0
(m2/g)
Ni2+
Mo6+
B3+
Ni–Mo–B
Co–Ni–Mo–B
La–Ni–Mo–B
38.4
52.7
116.6
Ni1.00Mo3.02B1.31
Co0.14Ni1.00Mo2.99B0.32
La0.15 Ni1.00Mo2.91B0.37
Ni1.00Mo2.89B2.58
Co0.15Ni1.00Mo3.15B0.35
La0.13 Ni1.00Mo2.07B0.41
5.5
6.0
11.7
94.5
94.0
88.3
33.3
52.1
49.9
66.7
47.9
50.1
6.2
13.4
31.7
93.8
86.6
68.3
in Co–Ni–Mo–B and La–Ni–Mo–B. Therefore, it could be concluded
that Co or La promoted the electron transfer between B0 and Ni0,
making Ni to be more unsaturated [20] and resulting in a synergy
effect between B and Ni. At the energy level of Mo 3d, as shown in
Fig. 3c, the peaks of each sample at the binding energies lower than
232.4 eV were ascribed to Mo4+ in MoO2 while the high-binding
energy (around 235.2 eV) was ascribed to Mo6+ in MoO3 [26,27]. All
of the binding energies of Mo species in Fig. 3c were higher than the
standard Mo0 binding energy (227.3–228.1 eV [26]), suggesting that
Mo6+ was only partially reduced by NaBH4 and existed in the form of
oxides, which was consistent with the results reported by Parks et al.
[26].
correspondingly. The Ni0 content order of the catalysts was La–Ni–
Mo–B (11.7%)NCo–Ni–Mo–B (6.0%)NNi–Mo–B (5.5%). The molar
ratio of Mo4+/Mo6+ in Co–Ni–Mo–B and La–Ni–Mo–B was increased
to 1.1:1 and 1:1, respectively. These suggested that the additive Co or
La could improve the composition of active site and promote the
reduction of Mo6+
.
3.2. Hydrodeoxygenation of phenol
The time–conversion curves of the HDO of phenol on Ni–Mo–B,
Co–Ni–Mo–B and La–Ni–Mo–B amorphous catalysts are shown in
Fig. 4. The conversion of phenol on each catalyst could reach to 98%
and the active order per unit weight of catalyst was La–Ni–Mo–BNCo–
Ni–Mo–BNNi–Mo–B, indicating that the additives enhanced the
catalytic activity in the HDO of phenol. The conversion of phenol on
La–Ni–Mo–B reached to 98% within 1h and 100% within 1.5 h. The
higher catalytic activity of La–Ni–Mo–B could be accounted for the
higher surface area and the higher contents of Ni0 and Mo4+. It had
demonstrated that only MoO2 existed in form of Mo–OH and acted as
Brönsted acid adsorption site [21,27,28]. The oxy-organics molecules
were absorbed on the Brönsted acid sites and then the C–O bond was
polarized. Ni active sites, because of the amorphous structure and the
synergy effect between B and Ni, exhibited a high hydrogenation
activity [17–20]. As a result, the higher the content of Ni0 was, the
higher the catalytic activity would have, and the greater the reaction
rate would be.
The surface compositions of different amorphous catalysts are
shown in Table 1. By adding additive, the content of B on the surface of
the catalyst was decreased while Ni and Mo contents were increased
The HDO products of phenol on different catalysts were cyclohexanol,
cyclohexanone, benzene, cyclohexene and cyclohexane, as shown in
Table 2. Benzene was formed via the direct hydrogenolysis route while
cyclohexene and cyclohexane were produced by the combined
hydrogenation–dehydration route [2]. Cyclohexanol and cyclohexanone
were the intermediate products [2]. The total selectivity of oxygen-free
products on Co–Ni–Mo–B and La–Ni–Mo–B increased to 93.1% and 69.3%
at 523 K, respectively, being much higher than that on Ni–Mo–B (26.7%),
which was mainly attributed to the content of MoO2. Among these
catalysts, the relative contents of Mo and MoO2 on the surface of Co–Ni–
Mo–B were the highest. These could be explained by that the higher the
content of MoO2 was, the more the C–O bonds would be adsorbed on
catalyst, and then the higher was the total selectivity of the oxygen-free
products. The aromatic hydrocarbons content in the products decreased
to 3.2% and 0.1% on Co–Ni–Mo–B and La–Ni–Mo–B, respectively, being
much lower than the European regulations (aromatic hydrocarbons
content b14%, [10]). However, it reported that the conversion of phenol
was about 90% with a selectivity of 54% aromatics on CoMoS/γ-Al2O3
under the conditions (523 K, 7.5 MPa H2, 2 h) [8] and 51% with a
selectivity of 79% aromatics on MoS2 under the conditions (623 K,
2.8 MPa H2, 7 h) [3]. The results indicated that Co–Ni–Mo–B and La–Ni–
Mo–B had high activity and promoted the HDO of phenol to proceed
with hydrogenation–dehydration route, which could decrease the
aromatics content and increase the total H/C atomic ratio in the products
obviously.
As shown in Table 2, the total H/C atomic ratio decreased in the
order of La–Ni–Mo–B (1.99)NCo–Ni–Mo–B (1.97)NNi–Mo–B (1.95)
at 523 K, which was in line with the order of Ni0 content because the
hydrogenation activity mainly related to Ni0 active site. However, the
HDO conversion on each sample was decreased obviously while the
Fig. 2. (a) XRD spectra of the fresh Ni–Mo–B, Co–Ni–Mo–B, La–Ni–Mo–B catalysts;
(b) Co–Ni–Mo–B and La–Ni–Mo–B heat-treated at 548 K.

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W. Wang et al. / Catalysis Communications 11 (2010) 803–807
Fig. 4. Reaction activities of the HDO of phenol on Ni–Mo–B, Co–Ni–Mo–B and La–Ni–
Mo–B amorphous catalysts at 523 K.
direct hydrogenolysis and deoxygenation to improve the total
selectivity of oxygen-free products but harmful to the amorphous
structure of the catalyst and the decrease of aromatic content [21].
According to the products distribution, the reaction scheme for the
HDO of phenol on these amorphous catalysts might include direct
hydrogenolysis route and hydrogenation–dehydration route, which
was in agreement with the result reported by Furimsky [2] and Şenol
et al. [8]. But the hydrogenation–dehydration was the primary route
on Ni–Mo–B amorphous catalyst because of its high hydrogenation,
leading to the decrease of the aromatic content and the improvement
of the total H/C ratio. The additives (Co or La) improved the
hydrogenation activity of Ni–Mo–B amorphous catalysts, promoting
the HDO reaction of phenol to proceed with hydrogenation–
dehydration route and then limited the generation of aromatic.
4. Conclusion
The additives (Co, La) could enlarge the catalyst surface area and
promote the reduction of Mo6+ to Mo4+ and the synergy effect
between B and Ni. The total selectivities of oxygen-free products on
Co–Ni–Mo–B and La–Ni–Mo–B were 93.1% and 67.6% at 523 K,
respectively. The main HDO product was cyclohexane. The aromatic
hydrocarbons content in the products was limited in 5% and could
meet the European regulations. The total H/C atomic ratio was
increased from 1.00 as in model reactant of phenol to 1.99 as in the
products and the heating value was improved.
Table 2
Hydrodeoxygenation of phenol over different catalystsa.
Temperature (K)
Ni–Mo–B
523
Co–Ni–Mo–B
La–Ni–Mo–B
548
523
548
523
548
Conversion of phenol, %
Selectivity of HDO, %
Cyclohexanol
Cyclohexanone
Benzene
Cyclohexane
Cyclohexene
The total H/C atomic ratio
98.5
62.1
98.0
74.9
100.0
58.5
Fig. 3. XPS spectra of (a) Ni 2p, (b) B 1s and (c) Mo 3d levels of Ni–Mo–B, Co–Ni–Mo–B
and La–Ni–Mo–B amorphous catalysts.
72.5
0.7
5.0
21.3
0.4
1.95
45.5
7.3
7.4
26.8
13.0
1.88
6.5
0.3
3.2
89.8
0.1
1.97
1.3
0
13.2
57.9
27.5
31.8
0.5
0.1
67.3
0.2
1.99
1.3
0.6
1.6
75.4
20.9
1.91
total selectivity of oxygen-free products and unsaturated hydrocarbon
such as benzene or cyclohexene were increased when the reaction
temperature increased to 548 K, which was resulted from the
crystallization of Ni0 amorphous structure. This crystallization was
also verified by XRD. Therefore, high temperature was beneficial to
1.77
a
Reaction conditions: 0.05 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.