Highly selective catalytic conversion of phenols to aromatic hydrocarbons on CoS2/MoS2 synthesized using a two step hydrothermal method

Article abstract of DOI:10.1039/c5ra27066a

CoS₂/MoS₂ catalysts were prepared using a two-step hydrothermal procedure for the first time, i.e., MoS₂ was synthesized and then CoS₂ was prepared and deposited on the surface of the MoS₂. The characterization results presented that CoS₂ and MoS₂ are separated in the resultant catalysts and the surface area of CoS₂/MoS₂ was much higher than that of Co-Mo-S prepared using a one step method. In the hydrodeoxygenation (HDO) of p-cresol, the presence of CoS₂ enhanced the conversion, but excessive CoS₂ on the surface of the MoS₂ reduced its activity. With an appropriate amount of CoS₂, the catalyst presented an unprecedented HDO activity and direct deoxygenation (DDO) selectivity: 98% deoxygenation degree with a selectivity of 99% toluene at 250 °C for 1 h. This CoS₂/MoS₂ catalyst also exhibited high DDO activity for other phenolic monomers, which minimized hydrogen consumption and improved the economic efficiency.

Full text of DOI:10.1039/c5ra27066a

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DOI: 10.1039/C5RA27066A
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Highly selective catalytic conversion of phenols to aromatic
hydrocarbons on CoS2/MoS2 synthesized by two steps
hydrothermal method
Received 00th January 20xx,
Accepted 00th January 20xx
Weiyan Wang,* a,b Lu Li,a Wu Kui,a Guohua Zhu,a Song Tan,a Yan Liu a and Yunquan Yang * a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
CoS2/MoS2 catalysts were prepared by two-step hydrothermal always chose to study the activity of the catalysts and the HDO
procedure for the first time, i.e., MoS2 was synthesized and then reaction mechanism.5-11 It had been inferred that oxygen in phenols
CoS2 was prepared and deposited on the surface of MoS2. The was removed via two parallel pathways: hydrogenation-dehydration
characterization results presented that CoS2 and MoS2 were (HYD) and direct deoxygenation (DDO).4, 5 The former involved the
separated in the resultant catalysts and the surface area of saturation of the aromatic ring of phenols, which resulted in a high
CoS2/MoS2 was much higher than that of Co-Mo-S prepared by one hydrogen consumption and a decrease on octane number after
step method. In the hydrodeoxygenation (HDO) of p-cresol, the HDO.12 Therefore, allowing C–O bond scission without substantial
presence of CoS2 enhanced the conversion, but excessive CoS2 on phenyl ring saturation was an economical and favorable process for
the surface of MoS2 reduced its activity. With an appreciate of CoS2, the HDO of phenols.13
the catalyst presented unprecedented HDO activity and direct
Based on that Fe-based catalysts were effective for the activation
deoxygenation (DDO) selectivity: 98% deoxygenation degree with a of aromatic carbon–oxygen bond of phenols, Sun et al.14 studied the
selectivity of 99% toluene at 250 °C for 1 h. This CoS2/MoS2 catalyst activity of Fe/C in the gas-phase HDO of guaiacol and confirmed its
also exhibited high DDO activity for other phenolic monomers, high DDO activity but a low HDO activity. After adding Pd to form Pd-
which minimized hydrogen consumption and improved the Fe/C, the HDO activity enhanced markedly: 83.2% yield to aromatics
economic efficiency.
at 450 °C. In addition, MoS2 was established to be a good HDO
catalyst and its DDO activity was further improved by adding Co.15
We had obtained a 100% p-cresol conversion with a selectivity of
92.2% toluene on Co-Mo sulfide catalyst at 275 °C for 4 h.16 These
demonstrated that Co-Mo sulfide was a potential catalyst for the
HDO of phenols, but its activity was structure-dependent, which
could be improved by optimizing the preparation methods.
The rapid growth in global energy demand, steadily decline in
fossil fuels reserves and worldwide serious environment problems
had motived us to look for other renewable sources.1 Bio-oil, derived
from the biomass by liquefaction or pyrolysis, was an interesting
alternative to supplement fuels.2 However, lignocellulosic-derived
bio-oil contained a relatively high amount of phenols, furans, esters
and ketones, which leaded to some detrimental properties such as
low heating value, high viscosity, chemical and thermal instability.3
This bio-oil required to be lowered its oxygen content if it was used
as a supplementary fuel. Hydrodeoxygenation (HDO) was one of the
most common and efficient technologies to selectively remove
oxygen in a form of water in the presence of hydrogen, and the
deoxygenation degree and product selectivity depended on the
selected catalysts.4
Until now, various technologies had been developed for the
preparation of Mo based sulfide catalysts.11,
15, 17, 18
Previous
literatures had almost adopted Co–Mo–S phase to elucidate the HDO
15
mechanism when added Co promoter into MoS2 catalysts.6,
However, this phase was unstable and would decompose during the
reactions, which was just regarded as the precursor of the real active
phase.19 Fortunately, Gil-Llambías et al.20 had evidenced the
synergism between the separated CoSx and MoS2. Recently, it had
been concluded that the catalytic activity of Co-Mo sulfide was
directly proportional to the increase of the contact surface area
between MoS2 and Co9S8 phases.21 For an uniformly simultaneous
precipitation procedure, Co sulfides inserted into MoS2 and were not
always accessible, leading that the prepared catalyst had low surface
area and much of promoter Co could not play its role,22 which in turn
reduced the overall activity. Hence, to emphasize the effect of Co and
enhance the HDO activity, CoS2/MoS2 catalysts were synthesized by
Phenols, as the important lignin based monomeric model
substrates and recalcitrant oxygenated species in bio-oil, were
a. School of Chemical Engineering, Xiangtan University, Xiangtan City, Hunan
411105, P R China
E-mail: wangweiyan@xtu.edu.cn, yangyunquan@xtu.edu.cn.
b. National & Local United Engineering Research Center for Chemical Process
Simulation and Intensification, Xiangtan University, Xiangtan 411105, P. R. China.
Electronic Supplementary Information (ESI) available. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 2015
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two-step hydrothermal method for the first time and applied into the eV and 232.5 eV presented in the Mo 3d level of each catalysts,
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2-
DOI: 10.1039/C5RA27066A
assigning to the S2p contribution for S , Mo 3d5/2 and Mo 3d3/2 of
HDO of phenols.
In a typical procedurefor the synthesis of CoS2/MoS2, ammonium MoS2,25, 26 respectively. Two peaks located at 162.2 eV and 163.6,
heptamolybdate (2.3 g) and thiourea (3.0 g) were dissolved in 150 mL matching well with the S 2p3/2 and S 2p1/2 in MoS2 and CoS2 phases,
ultra-pure water and its pH value was adjusted to 0.9 by hydrochloric 25, 26 respectively. Previous study had claimed that the binding energy
acid. This mixed solution was added into a reactor, and sealed and of Co 2p3/2 in Co9S8 was at ranging between 777.8 eV and 778.1 eV
heated to 200 °C for 12 h. Then the reactor was cooled to room while that for Co–Mo–S phase was 778.6 eV.27 However, there only
temperature and opened and added 30 mL solution contained cobalt displayed one main peak appeared at 779.0 eV in the Co 2p level
nitrate and thiourea, and sealed and heated to 200 °C for 12 h again. spectrums, corresponding to CoS2. In addition, another peak at
After reaction, the black precipitate was collected and washed with higher binding energy (782.1 eV) was assigned to Co oxides.21, 28
water and ethanol and dried under vacuum at 50 °C for 8 hours. The These demonstrated that Co did not decorate in MoS2 slab to form
resultant catalysts were denoted as Co-Mo-X, where X represented Co–Mo–S phase and it presented as a CoS2 phase rather than Co9S8
the initial molar ratio of Co/Mo. The HDO activity tests were carried pahse.
out in a 100-mL sealed autoclave. The prepared catalyst (0.03 g), p-
Generally, CoS2 was deposited on the surface of MoS2, resulting
cresol (4.8 g) and dodecane (28.3 g) were placed into the autoclave. in a enrichment of Co and high Co/Mo molar ratio on the catalyst
Air was evacuated by pressurization-depressurization cycles with surface. However, the XPS results showed that the Co/Mo molar
nitrogen and subsequently with hydrogen. The system was heated to ratio on the surface of Co-Mo-0.05, Co-Mo-0.1, Co-Mo-0.2, Co-Mo-
desired temperature, then pressurized with hydrogen and adjusted 0.3 and Co-Mo-0.4 was 0.03, 0.05, 0.09, 0.16 and 0.24, respectively,
the stirring speed to 900 rpm. During the reaction, liquid samples being much lower than the corresponding ratio in the raw solution.
were withdrawn from the reactor and analysed. Conversion = (the These suggested that much of CoS2 was not dispersed uniformly but
amount of aromatic-ring change during reaction/total amount of aggregated together on the catalyst surface. The SEM images
aromatic-ring) × 100 %; Selectivity = (C atom in each product/total C provided the direct evidence (Fig. S2, ESI†). Mo-S presented a loose
atom in the products) × 100 %; Deoxygenation degree (D.D., wt %) is flower-like structure composed of nanosheets in random orientation.
defined as [1-oxygen content in the final organic compounds / total Co-Mo-0.2 and Co-Mo-0.3 displayed some spinel-like paricles,
oxygen content in the initial material] × 100%.
coexisting with the flower-like morphology, which was attributed to
As shown in Fig. 1, the XRD pattern of Mo-S presented four CoS2. After adding excessive Co, e.g., Co-Mo-0.4, the flower-like
diffraction peaks at 2θ=14°, 33°, 39° and 59°, matching to (002), (100), MoS2 was not obvious and there appeared large spinel CoS2 particles,
(103) and (110) crystal plane of hexagonal MoS2 (JCPDS Card No. 37- suggesting more CoS2 and less MoS2 active sites on this catalyst
1492),23 respectively, suggesting that MoS2 structure had been surface. These also demonstrated that MoS2 and CoS2 phases were
completely formed after hydrothermal reaction for 12 h. With the separated and CoS2 only deposited on the surface of MoS2 and
increment of Co sulfide, there appreared some diffraction peaks at trended to aggregate together.
2θ= 28°, 32°, 36°, 39°, 46° and 55°, corresponding to crystalline CoS2
(JCPDS Card No. 41- 1471).24 These indicated that Co existed in the
form of CoS2 phase after the second hydrothermal synthesis.
Previous studies had claimed that the promoter Co incorporated into
the MoS2 structure to form Co–Mo–S active phase and the excessive
Co presented as Co9S8 phase,15, 21 but which were different from our
results that CoS2 and MoS2 were separated and no Co9S8 phase was
detected in the resultant catalysts.
▼
CoS2 # MoS2
▼
▼
▼
▼
▼
▼
Co-Mo-0.4
Co-Mo-0.3
Co-Mo-0.2
Co-Mo-0.1
Co-Mo-0.05
Mo-S
#
#
#
#
10
20
30
40
50
60
70
80
Fig. 2 HRTEM images of Mo-S and CoS2/MoS2 catalysts
2 Theta (degree)
HRTEM was taken to measure the microstructure of Mo-S and
CoS2/MoS2 catalysts, which could provide tracks from direct
observations to determine the interaction between CoS2 and MoS2
sulfide phases.21 Fig. 2 presents that Mo-S has a highly disordered
organization of stacked layers with a spacing of fringe of 0.63 nm,
Fig. 1 XRD patterns of Mo-S and CoS2/MoS2 catalysts
The separated CoS2 and MoS2 phases were further confirmed by
the XPS characterization on the electron bonding energy of each
element. As presented in Fig. S1 (ESI†), three peaks at 226.6 eV, 229.3
2 | RSC Adv., 2015, 00, 1-6
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typifying the d002 interplanar spacing of MoS2.23,
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After the Co/Mo mole ratio, the surface area gradually decreased to 78 m2/g
29
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deposition of Co sulfide on MoS2, such as for Co-Mo-0.3 and Co-Mo- and the small pores dramatically decreaseDdO(IF:i1g0..1S033,9/ECS5I†R)A.2T70h6e6sAe
0.4, another group of lattice fringes with a interplanar spacing of 0.25 were resulted from the deposition of CoS2 on the surface or in the
nm were observed, corresponding to (210) plane of cubic CoS2 pore channel of MoS2. For the one-step synthesis, Co and Mo
pyramids,30 and these fringes increased with the amount of Co dispersed uniformly in Co-Mo bimetallic sulfide and consequently
sulfide. From these HRTEM images, it clearly showed that CoS2 the obtained catalyst had a very small surface area (lower than 10
covered and spreaded on the MoS2 slabs substrate, resulting that m2/g). However, in this study, MoS2 produced in the first step had
some MoS2 slabs were invisible or some HRTEM zones presented large surface area, when CoS2 produced and deposited on the
both MoS2 and CoS2 phases.
surface of MoS2 in the second step, only a samll part of CoS2 particles
The surface area, pore volume, and pore size distribution of Mo- inserted into MoS2 pores, preventing the decrease of surface area
S and CoS2/MoS2 catalysts are listed in Table 1. Mo-S had a surface and exposing more active sites for the reaction, which was expected
area of 183 m2/g with a pore volume of 0.8 cm3/g and bi-modal pore to enhance its catalytic activity.
distribution centered at 2.3 nm and 10.7 nm. With the increment of
Table 1 The structure properties of Mo-S and CoS2/MoS2 catalysts and their activities in the HDO of p-cresol[a]
[b]
Catalyst
Mo-S
Co-Mo-0.05
Co-Mo-0.1
Co-Mo-0.2
Co-Mo-0.3
Co-Mo-0.4
CoS2+MoS2
Surface area (m2/g)
Pore volume (cm3/g)
Pore size (nm)
183
0.8
165
0.7
149
0.7
105
0.6
91
78
--
--
0.6
0.5
2.3, 10.7
18
2.2, 11.6
40
2.2, 12.8
53
2.4, 16.5
77
2.1, 16.0
98
19.2
93
--
19
Conversion (mol %)
Products selectivity (mol %)
Methylcyclohexane
3-Methylcyclohexene
Toluene
12
8
˂1
2
1
˂ 1
˂1
99
74
˂1
˂1
99
98
˂1
˂1
99
92
14
7
˂1
98
49
80
16
98
36
79
17
D. D. (wt %)
[a] Reaction conditions: 0.03 g catalyst, 4.8 g p-cresol, 28.5 g dodecane, 4.0 MPa hydrogen pressure, temperature 250 °C and time 1 h.
[b] The catalysts was composed by 0.01 g CoS2 and 0.03 g MoS2.
The comparison of Mo-S and CoS2/MoS2 catalysts on the activity
1.0
and product distribution in HDO of p-cresol is shown in Table 1. The
conversion over Mo-S was 18% with a selectivity of 80% toluene and
0.8
a deoxygenation degree of 16% at 250 °C for 1 h. In the presence of
CoS2, the products remained unchanged, but both the conversion
p-Cresol
0.6
0.4
0.2
0.0
and toluene selectivity were incresed greatly, suggesting that CoS2
was beneficial to significantly enhance the HDO activity and DDO
activity, which was in line with previous investigations.6, 15 With the
increment of CoS2, the conversion increased firstly and then
decreased but toluene selectivity increased continually. When the
Co/Mo mole ratio in the raw solution increased to 0.3, the catalyst
exhibited the highest HDO activity. The deoxygenation degree
reached to 98%, which was 6-fold higher than that on Mo-S. In
contrast, at high Co/Mo molar ratio, e.g., for Co-Mo-0.4, because of
the excessive coverage of MoS2 by CoS2, the conversion decreased to
93%. Consequently, an appropriate CoS2 on MoS2 surface maximized
the HDO activity. We also tested the HDO activity of physically mixed
CoS2 and MoS2 under the same reaction conditions. The conversion
was 19% with a selectivity of 79% toluene. This meant that large CoS2
particles had little promoting effect on the HDO activity of MoS2 and
only CoS2 disperse on MoS2 surface with small size could enhance the
HDO activity. Hence, the change of p-cresol conversion versus Co/Mo
molar ratio on the catalyst surface obtained from XPS data was
summerized (Fig. S4, ESI†). Under a low CoS2 content, the conversion
was linearly related to the Co/Mo molar ratio in the catalyst surface.
Therefore, CoS2 should be dispersed on MoS2 surface uniformly and
its monolayer dispersion would maximize the HDO activity.
Methylcyclohexane
3-Methylcyclohexene
Toluene
0.5
1
1.5
2
3
Time (h)
Fig. 3 The curves of concentration changes of p-cresol and product
versus reaction time on Co-Mo-0.3 at 225 °C
Fig.3 presents the curves of concentration changes of p-cresol
and product versus reaction time on Co-Mo-0.3 at 225 °C. With the
increase of time, p-cresol concentration decreased while toluene
concentration increased. During the whole reaction, both
methylcyclohexane and 3-methylcyclohexene concentrations were
very low. Obviously, the dominant reaction route for the HDO of p-
cresol on Co-Mo-0.3 was DDO. After reaction for 3 h, the conversion
was higher than 99% with a selectivity of 99% toluene. These
suggested that Co–Mo sulfide catalysts prepared by this new method
had very high HDO activity and direct deoxygenation activity. The
above characterization results demonstrated that CoS2 and MoS2
phases but no Co–Mo–S phase presented in CoS2/MoS2 catalysts.
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Consequently, Remote Control model was reasonable to explaine the reaction. Fig. 5 shows the HDO of p-cresol on on Co-Mo-0.3 under
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HDO reaction mechanism on these CoS2/MoS2 catalysts20, 31, 32, as different hydrogen pressures and reactioDnOIt:e1m0.p10e3r9a/tCu5reRsA.27A0f6t6eAr
presented in Fig. 4. CoS2 acted as a donor phase while MoS2 acted as reaction for 1 h, the conversion was 86% with a selectivity of 99%
acceptor phase. Hydrogen adsorbed on CoS2 active sites and toluene under 250 °C and 2 MPa hydrogen pressure. When the
converted into spillover hydrogen and migrated to MoS2 active site hydrogen pressure was raised to 5.0 MPa, the conversion increased
for the HDO reaction. It had been reported that p-cresol molecules to 100% and toluene selectivity was still higher than 99%. These
were adsorbed on catalyst surface via two modes: vertical adsorption suggested that high hydrogen pressure favored the p-cresol
and co-plane adsorption, which decided the DDO route and HYD conversion but had little effect on toluene selectivity. As presented
route.17 However, according to the reaction equation, it required 6 in Fig. 4, hydrogen was activated into spillover hydrogen on CoS2, but
mol spillover hydrogen for the hydrogenation of 1 mol p-cresol to 4- CoS2 had a very low activation ability. Even thought the hydrogen
methylcyclohexanol, which was 3-fold larger than that for the pressure was was very high, the spillover hydrogen created on Co-
deoxygenation of 1 mol p-cresol to toluene. Due to the low activity Mo-0.3 was still unsufficient to meet the required spillover hydroge
of CoS2 for the creation of spillover hydrogen, the hydrogen for for the santuration of phenyl ring. These suggested that it did not
santurating phenyl ring became hard with the increase of CoS2 on need to consider the increase of hydrogen consumption with the
MoS2 surface and then the HYD route was inhibited, resulting in a hydrogen pressure in the HDO of p-cresol on Co-Mo-0.3 at high
very high toluene selectivity.
hydrogen pressure, which was industrially desirable.
However, low temperature was beneficial to create spillover
hydrogen on the catalyst surface because of a high hydrogen
solubility in the solvent in this case,34 which supplied more hydrogen
for the HDO reaction and enhanced the HYD products selectivity. As
shown in Fig. 5(b), the conversion was droped from 98% to 56% when
the reaction temperature decreased from 250 °C to 225 °C, but
toluene selectivity changed very little, which was still higher than
99%. This was also attributed to the low hydrogen activation ability
of Co-Mo-0.3. Although the hydrogen concentrationt in the solvent
at low temperature was higher than that at high temperature, but
the created spillover hydroge was still unsufficient and presented a
very high toluene selectivity.
Fig. 4 The proposed reaction mechanism for p-cresol HDO on
CoS2/MoS2 catalysts
Conversion
3-Methylcyclohexene
Methylcyclohexane
Toluene
(a)
100
The high HDO activity of CoS2/MoS2 catalyst was attributed to the
following reasons. At first, CoS2/MoS2 catalyst had a large surface
area and supplied sufficient active sites for p-cresol absorption.
Compared with our previous study16 that p-cresol conversion was 94%
with a toluene selectivity of 90% on Co-Mo sulfide catalyst prepared
by one-step hydrothermal method at 250 °C for 6 h with a p-
cresol/catalyst weight ratio of 50, the surface area of Co-Mo-0.3
catalyst in this study was high to 91 m2/g, which exposed more active
sites for the reaction and exhibited higher HDO activity. Secondly, the
spillover hydrogen could promote the metal-sulfur bond scission,19
creating more coordinatively unsaturated sites for the adsorption of
p-cresol molecules. When the spillover hydrogen on CoS2 was
sufficient, the DDO reaction would proceed smoothly and enhance
the deoxygenation degree. Although more spillover hydrogen was
provided for the HDO reaction when CoS2 was excessive, but which
was still unsufficient for the HYD route and then presented an
increase on toluene selectivity. In this case, the serious coverage of
CoS2 on MoS2 active sites prevented the adsorption of p-cresol
molecules and resulted in a decrease on deoxygenation degree.
Compared with other catalysts (Table S1, ESI†), it obviously showed
that CoS2/MoS2 catalyst prepared by two-step hydrothermal method
presented unprecedented HDO activity and DDO selectivity: the
deoxygenation degree and toluene selectivity reached to 98% and 99%
in the HDO of p-cresol at 250 °C for 1 h, respectively.
80
60
40
20
0
2
3
4
5
Hydrogen pressure (MPa)
Conversion
3-Methylcyclohexene
Methylcyclohexane
Toluene
(b)
100
80
60
40
20
0
225
250
275
Reaction temperature (oC)
Fig. 5 The conversion and products distribution in the HDO of p-
cresol on Co-Mo-0.3 under different hydrogen pressure (a) and
reaction temperature (b) for 1 h
The reusability of Co-Mo-0.3 in the HDO of p-cresol is shown in
Fig. 6(a). Because the catalyst loss was inevitable during the reaction
and separation, more parallel reactions were carried and recovered
more catalyst to compensate the lost catalyst. It could observe that
both p-cresol conversion and toluene selectivity were still higher
The hydrogen pressure had a great effect on the conversion in
the HDO of phenols, especially for the product distribution.33
Generally, high hydrogen pressure enhances the hydrogenation
4 | RSC Adv., 2015, 00, 1-6
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energy. These CoS2/MoS2 catalysts also exhibited high activity in the
than 99% after cycle 3. These results suggested that Co-Mo-0.3
catalyst had a good stability, but which did not meant that there was
no deactivation for this catalyst during HDO reaction. Previous study
had reported that the sulfide catalyst underwent a continuous sulfur-
oxygen exchange at its edge sites.35 Hence, the recovered catalyst
after each cycle reaction was characterized by XRD, as presented in
Fig 6(b). We noticed that the peaks to MoS2 became sharper after
reaction and the intensity of (0 0 2) peak to MoS2 edge decreased but
others' intensity changed very little with the cycle number. These
indicated that the enlarged MoS2 crystallite size and the continuous
destruction of (0 0 2) plane might be the reason for the catalyst
deactivation during the HDO reaction, and it needed to be further
confirmed.
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hydrodesulfurization (HDS) of benzothiophene (seen in Table S2,
DOI: 10.1039/C5RA27066A
ESI†). In the presence of CoS2, e.g., on Co-Mo-0.2, the conversion and
ethylbenzene selectivity raised to 98% and 100% at 300 °C for 3 h,
respectivily.
Table 2. HDO of phenol derivatives on Co-Mo-0.3 [a]
Substrate
Weight (g) Conversion (%)
Selectivity (%)
C6 backbone
4.2
2.5
2.8
2.8
100
100
100
99
99
1
1
1
1
99
85
84
Conversion
Toluene
(a)100
C7 backbone
C8 backbone
98
96
94
92
90
4.8
4.8
100
100
99
99
1
1
5.4
100
99
1
[a] Reaction conditions: 0.1 g catalyst, the total weight 33.3 g, H2 pressure
4.0 MPa, temperature 300 °C and reaction time 1 h.
Run-1
Run-2
Reaction time
Run-3
(b)
(100)
(103)
Conclusions
(002)
(110)
A new method was developed for the synthesis of Co-Mo sulfide
catalysts with high activity. The characterization results showed that
the prepared catalysts were composed with separate CoS2 and MoS2
phases rather than Co–Mo–S phase. CoS2/MoS2 catalysts exhibited
unprecedented HDO activity and DDO selectivity: the deoxygenation
degree reached to 97.8% with a toluene selectivity of 99.2% at 250 °C
for 1 h, which was attributed to the synergistic effect between CoS2
and MoS2, uniform dispersion of CoS2 on MoS2 surface and large
surface area. The conversion of p-cresol increased with the reaction
temperature and hydrogen pressure, but which had little effect on
toluene selectivity. These catalysts also exhibited a high direct DDO
activity for other diverse substituted phenolic monomers and high
HDS activity for benzothiophene, which minimized the consumption
of precious hydrogen energy and exhibited a high potential
superiority.
Fresh catalyst
Run-1
Run-2
10 20 30 40 50 60 70 80 90
2 Theta (degree)
Fig. 6 (a) the reusability of Co-Mo-0.3 in the HDO of p-cresol and (b)
the XRD patterns of fresh Co-Mo-0.3 and spent Co-Mo-0.3 after
different cycles
To demonstrate the versatility of CoS2/MoS2 catalyst, several
monomeric phenol derivatives were investigated using Co-Mo-0.3 as
an optimized catalyst and the results are shown in Table 2. All the
selected substrates were efficiently converted into aromatics, with a
conversion of >99% and selectivity to aromatics of >98% under the
investigated conditions, except for 4-methoxyphenol and guaiacol.
These results indicated that CoS2/MoS2 had a high activity for the
direct scission of C-O bonds in phenolic hydroxyl group. Moreover,
previous literatures5, 36-38 had reported that the full conversions of
phenols with the high selectivities (>90%) toward alkanes were
obtained on the noble metal catalysts, where the HDO reaction
temperature was reduced, but it consumed numerous hydrogen and
the corresponding octane value of the products was decreased. In
this study, due to the special structure of CoS2/MoS2 catalyst, the
DDO was the predominant route in the HDO phenols on these
catalysts, which minimized the consumption of precious hydrogen
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (No. 21306159, 21376202) and Scientific
Research Fund of Hunan Provincial Education Department
(15B234).
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View Article Online
DOI: 10.1039/C5RA27066A
Highly selective catalytic conversion of phenols to aromatic hydrocarbons on
CoS2/MoS2 synthesized by two steps hydrothermal method
Weiyan Wang, Lu Li, Wu Kui, Guohua Zhu, Song Tan, Yan Liu and Yunquan Yang
School of Chemical Engineering, Xiangtan University, Xiangtan, Hunan, PR China
CoS2/MoS2 composite catalysts were synthesized by two-step hydrothermal method and
presented very high hydrodeoxygenation and direct deoxygenation activity in phenols
conversion, which minimized the hydrogen consumption and improved the economic
efficiency.