Influences of Various Supports, γ-Al2O3, CeO2, and SBA-15 on HDO Performance of NiMo Catalyst

Article abstract of DOI:10.1007/s10562-014-1412-4

Hydrodeoxygenation (HDO) of guaiacol (GUA), has been carried out over γ-Al₂O₃, CeO₂, SBA-15 supported NiMo catalysts in an autoclave at 250°C and a hydrogen pressure of 5 MPa. In comparison with NiMo/γ-Al₂O₃, both NiMo/CeO₂ and NiMo/SBA-15 catalysts showed their higher activities. NiMo/SBA-15 has been found to be the most potential one for HDO of GUA with GUA conversion and HDO degree of 90 and 67.5 %, respectively. The main product was cyclohexane with its yield of 56 mol%. The outstanding activity of this catalyst results from a high dispersion of its active sites on SBA-15 as catalyst support. For CeO₂ supported catalyst, some interactions of Ce-Mo can be occurred, leading to an enhancement of its HDO performance. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1412-4

Catal Lett
DOI 10.1007/s10562-014-1412-4
Influences of Various Supports, c-Al O , CeO , and SBA-15
2
3
2
on HDO Performance of NiMo Catalyst
Binh M. Q. Phan
Phuong T. Ngo Thu H. Nguyen
Luong H. Nguyen Duc A. Nguyen
•
Quan L. M. Ha
Tung T. Dang
Loc C. Luu
•
Nguyen P. Le
•
•
•
•
•
•
Received: 31 July 2014 / Accepted: 27 October 2014
Ó Springer Science+Business Media New York 2014
Abstract Hydrodeoxygenation (HDO) of guaiacol
GUA), has been carried out over c-Al O , CeO , SBA-15
organic chemicals with high oxygen content and it is
necessary to remove oxygen from bio-oil to stabilize its
composition and improve its quality [2]. Recently, studies
of bio-oil upgrading were usually conducted with hydro-
deoxygenation (HDO) reaction, which can be applied to
fully remove oxygen from bio-oil [3]. Therefore, HDO can
be used at various levels to deeply upgrade bio-oil for
alternative fuel [4] or refinery feed blending purposes [5].
One of the typical supports for HDO catalyst is alumina.
However, in bio-oil HDO process, there are some main
drawbacks associated with boehmite formation due to the
presence of large amounts of water as well as the occur-
rence of potential carbon precursors during reaction [6–8].
The aim of this work is to determine the influences of
various supports, c-Al O , CeO , and SBA-15 on HDO
(
2
3
2
supported NiMo catalysts in an autoclave at 250 °C and a
hydrogen pressure of 5 MPa. In comparison with NiMo/c-
Al O , both NiMo/CeO and NiMo/SBA-15 catalysts
2
3
2
showed their higher activities. NiMo/SBA-15 has been
found to be the most potential one for HDO of GUA with
GUA conversion and HDO degree of 90 and 67.5 %,
respectively. The main product was cyclohexane with its
yield of 56 mol%. The outstanding activity of this catalyst
results from a high dispersion of its active sites on SBA-15
as catalyst support. For CeO supported catalyst, some
2
interactions of Ce–Mo can be occurred, leading to an
enhancement of its HDO performance.
2
3
2
Keywords Hydrodeoxygenation ꢀ Guaiacol ꢀ c-Al O ꢀ
performance of NiMo catalyst. SBA-15 is well known for
2
its high surface areas (up to 1000 m /g), which can
2
3
CeO ꢀ SBA-15 ꢀ NiMo-base catalyst
2
improve metal dispersion [9, 10]. Ceria is claimed to
improve the oxycompound activation, with the formation
of intermetallic M–Ce bonds [3, 11]. The catalytic per-
formance was determined on guaiacol (GUA), which is a
common model compound of bio-oil [12–14]. Up to now,
1
Introduction
Fast pyrolysis technology is commonly used for biomass
conversion into bio-oil, which is considered as a source of
alternative fuels [1]. Bio-oil is a complex mixture of
there have been studies of CeO and SBA-15 as catalyst
2
supports for HDO of similar model compounds but with
different catalyst formulations [3, 11, 15, 16].
B. M. Q. Phan ꢀ Q. L. M. Ha ꢀ N. P. Le (&) ꢀ
P. T. Ngo ꢀ T. H. Nguyen ꢀ T. T. Dang ꢀ
L. H. Nguyen ꢀ D. A. Nguyen
2
Experimental
Petrovietnam R&D Center for Petroleum Processing (PVPro),
Vietnam Petroleum Institute (VPI), 4 Nguyen Thong, District 3,
Ho Chi Minh City, Vietnam
2.1 Catalyst Preparation
e-mail: nguyenlp@pvpro.com.vn
Chemical compositions of supported Mo and NiMo cata-
lysts are listed in Table 1. All the catalysts used in this
L. C. Luu
Hochiminh City University of Technology, 268 Ly Thuong Kiet,
District 10, Ho Chi Minh City, Vietnam
work were prepared by impregnation method. The c-Al O
2 3
was obtained from Merck. CeO2 was produced by
123

B. M. Q. Phan et al.
Table 1 Chemical composition of studied catalysts
Table 2 BET surface area and pores volume (PV) of supports and
NiMo catalysts
Composition (wt%)
Catalyst
2
BET (m g
-1
)
3
PV (cm g
-1
)
NiO
MoO
3
c-Al
2
O
3
CeO
2
SBA-15
c-Al
2
O
3
132
83
0.25
0.24
0.88
0.17
0.11
0.52
6
6
6
–
30
30
30
30
64
–
–
–
2 3
NiMo/Al O
CeO
2
64
–
–
NiMo/CeO
2
SBA-15
853
86
–
64
70
NiMo/SBA-15
Mo/SBA-15
NiMo/c-Al
NiMo/CeO
2
O
3
–
–
2
27
NiMo/SBA-15
270
calcining Ce(NO ) ꢀ6H O (Sigma Aldrich) at 500 °C for
3
3
2
After 3-hour reaction, the reactor was cooled to room
temperature. The gas was analyzed by gas chromatography
3
h. The SBA-15 was prepared by following a defined
process [17]. The (NH ) Mo O ꢀ4H O (Sigma Aldrich)
4
6
7
24
2
(GC, HP 5890). The liquid products were analyzed by
and Ni(NO ) ꢀ6H O (Sigma Aldrich) chemicals, were used
3
2
2
GCMS (Agilent 7890A Gas Chromatography, 5975C Mass
Selective Detector).
as Mo, Ni precursors, respectively. Solutions of precursors
were prepared and then impregnated onto supports under
stirring at 60 °C until all water vaporized. Samples were
then dried at 110 °C and calcined in air at 500 °C for 3 h.
Prior to reaction tests, catalysts were pre-treated with
hydrogen in a batch reactor at 350 °C and 1 MPa for 1 h.
Catalyst activity was estimated according to GUA
conversion XGUA (%) and HDO degree (%), which were
calculated as follows [18]:
0
GUA
final
GUA
n
ꢁ n
GUA
XGUAð%Þ ¼
HDOð%Þ ¼
0
n
2
.2 Catalyst Characterizations
P
0
GUA
n
ꢂ X ꢂ 2 ꢁ
niai
i
ꢂ 100%
Surface areas (SA) and pore volumes (PV) of the supports
and catalysts were determined from nitrogen isotherms at
0
n
ꢂ X ꢂ 2
GUA P
0
@
1
A
n a
i
i
-
196 °C on a TRISTAR 3020 Micromeritics apparatus.
i
¼
1 ꢁ
ꢂ 100%
0
GUA
Prior to measurements, samples were degassed at 260 °C in
n
ꢂ X ꢂ 2
o
N flow for 4 h. XRD patterns were recorded in the 20
o
2
0
final
B 2h B 70 range on a Bruker D8 Advance diffractometer
using scintillation counter detector, equipped with a CuK
where, nGUA and nGUA are initial and final amount of GUA
(mol), respectively, n is amount of i-product (mol) in the
i
o
o
radiation source. Small-angle XRD (2h = 0.5 -10 ) was
performed on a Bruker D8 Advance diffractometer using
lynxeye detector. TPR experiments were carried out in an
AMI—902 (Altamira) automatic analyzer equipped with a
TCD detector. Prior to the TPR test, samples were pre-
treated in situ under Ar at 400 °C for 30 min and cooled to
room temperature. The reduction step was performed with
liquid phase (except for unreacted GUA), a
oxygen atoms in the molecule of i-product.
is number of
i
The product distribution was calculated as follows [18]:
ni
u ð%Þ ¼
ꢂ 100
i
k
P
ni
i¼j
where u (%) is molar fraction of i-product in the liquid
an mixture containing 10 % H in Ar, by a heating rate of
2
i
phase, taking into account unreacted GUA.
1
0 K/min, up to 1000 °C. TEM images were obtained on a
The coke deposition on the catalysts was also evaluated
with a Leco CS-600 analyzer after 3 h of reaction time.
JEM-1010 (JEOL) transmission electron microscope with a
magnification range of 950–x500 K and an accelerating
voltage range of 40–100 kV.
3
Results and Discussions
2
.3 HDO Measurements
3.1 Characterization of Catalysts
In a typical test, 40 g of 3 wt% GUA in n-hexadecane and
g catalyst were loaded into an autoclave reactor (Parr
2
The surface area and pore volume (V ) of the studied
p
Instruments). The reactor was flushed with nitrogen, pres-
samples are given in Table 2. The SBA-15 possess a very
large surface area therefore the active phase NiMo is
supposed to be better dispersed on SBA-15 than alumina or
ceria. Compared with supports, addition of NiMo (36 wt%)
surized with H (99.999 %) to 5 MPa at room temperature,
2
and then heated to 250 °C. The starting time (t = 0) was
recorded when the required reaction temperature was
reached (250 °C), while stirring speed was set at 1000 rpm.
1
23

HDO Performance of NiMo Catalyst
Fig. 1 X-ray diffraction
diffractograms of NiMo
catalysts (a) and low angle
X-ray diffraction diffractograms
of SBA-15 and NiMo/SBA-15
catalyst (b)
attributed to a lower crystallinity of MoO or a smaller
3
crystalline size of MoO . In NiMo/CeO , the most peaks
3
2
belong to CeO crystalline phase.
2
Low angle XRD diffractograms for SBA-15 and NiMo/
SBA-15 are shown in Fig. 1b. The peaks at 2h of 0.84°,
1.45° and 1.68° show that a two dimensional hexagonal
SBA-15 was prepared successfully and still remained in
NiMo/SBA-15 catalyst. It is worthy to note that in all of
these XRD diffractograms, there are no peaks associated
with oxide of Ni, suggesting the existence of very small Ni
grains [19, 20].
TPR profiles of Mo and NiMo based catalysts are shown
in Fig. 2. In order to have a better understanding of the Mo-
support interaction, a mechanical mixture of MoO and
3
c-Al O , which is supposed to have no Mo-support inter-
2
3
action, is also studied. TPR profile of this sample exhibits
two main peaks, one at 554 °C and the other at 910 °C, as
well as a shoulder around 670 °C. The low-temperature
(
LT) peak can be assigned to a partial reduction step of
6
?
4?
Molybdenum trioxide (Mo ?Mo ) of amorphous,
multilayered Mo oxides or octahedral Mo species [21]. The
high-temperature (HT) peak at 910 °C is ascribed to a deep
reduction of all Mo species including less reducible tetra-
hedral Mo species, bulk MoO or the reduction of isolated
3
6
tetrahedral Mo species in strong interaction with the
?
Fig. 2 TPR profiles of studied catalysts
support [22, 23]. The shoulder at 670 °C may be due to the
intermediate-reducible of orthorhombic MoO [24, 25].
3
leads to a significant decrease of BET surface area as well
TPR profile of Mo/Al O shows two more peaks at LT
2 3
as V . It can be attributed to the coverage of active phase as
p
region, one at 400 °C and the other at 500 °C. Those peaks
can be assigned to the reduction of polymeric octahedral
well as the blockage of support pores. NiMo/SBA-15
exhibits the higher BET surface area, with 270, versus
Mo species, which were more reducible than MoO
species [21, 22, 26, 27]. Comparing to TPR profile of
mechanical mixture of MoO and c-Al , the HT peak
bulk
3
2
2
8
6 m /g and 27 m /g for NiMo/Al O and NiMo/CeO ,
2 3 2
respectively.
3
O
2 3
Figure 1a presents XRD diffractograms of NiMo cata-
shifted to 900 °C. For Mo/SBA-15, this HT peak even
shifted to lower temperature (850 °C). On the contrary,
lysts. XRD peaks assignable to MoO were detected for all
3
the samples. However, the intensities of MoO diffraction
3
with Mo/CeO sample, the LT reduction peak moved to
2
peaks (2h = 23.4°; 25.7°; 27.4°; 33.6° and 39.1°) are quite
higher temperature at 620 °C and the HT one became a
very broad peak completed beyond 1000 °C. Thus, it can
lower in cases of NiMo/CeO and NiMo/SBA-15. It can be
2
123

B. M. Q. Phan et al.
Table 3 HDO performance and coke deposition of catalysts at
2
50 °C, 5 MPa and 3 h
NiMo/ NiMo/ NiMo/
CeO
2
Mo/
SBA-15 SBA-15
2
Al O
3
X
GUA (%)
15.0
18.5
2.3
23.0
20.0
0.7
90.0
67.5
2.6
7.0
HDO (%)
26.0
0.9
Coke deposition (wt%)
Product
Non-oxygen compounds
Methylcyclopentane
Cyclohexane
–
–
–
–
–
0.6
–
–
–
–
5.0
–
55.8
2.1
Methylcyclohexane
0
1
,1 -Bicyclohexyl
–
1.3
1
-Oxygen compounds
Cyclopentanemethanol
Cyclohexanol
–
1.3
27.1
–
4.1
6.3
4.7
–
–
–
–
Methoxycyclohexane
Cyclohexanone
Phenol
–
–
–
–
5.3
41.0
5.6
32.5
4.5
0.8
–
–
p-Cresol
–
2
-Oxygen compounds
1
2
,2-Cyclohexanediol
–
4.2
43.0
–
–
–
-Methoxycyclohexanol
–
6.7
12.6
5.8
–
–
1
,2-Dimethoxycyclohexane
–
–
1
3
,2-Dimethoxybenzene
-Methylmequinol
51.8
–
16.8
1.8
–
45.0
–
Methyl GUA
11.2
–
3.1
species in NiMo/SBA-15. It can be seen in its TPR profile
?
6
that Mo species were reduced at 450 °C for the first step
and 700 °C for the complete step, which were both simi-
larly reported in another study [28].
Regarding the HT peaks of all samples, the use of SBA-
1
5 as a support for NiMo catalyst can limit the formation of
6
MoO bulk species or isolated tetrahedral Mo species in
?
3
strong interaction with the support. Consequently, MoO3
can be well dispersed on the surface of SBA-15. The better
dispersion of MoO species on SBA-15 can also be seen on
3
Fig. 3 Transmission electron microscopy images of (a), b SBA-15
support and c NiMo/SBA-15 catalyst
TEM images (Fig. 3) and XRD patterns where intensities
of the characteristic XRD signals of MoO of NiMo/SBA-
3
15 were much lower than those of NiMo/Al O and NiMo/
2 3
be suggested that the interaction between Mo species and
CeO (Fig. 1a).
2
CeO support is stronger than that between Mo species and
2
Figure 3 shows TEM micrographs of SBA-15 support
and NiMo/SBA-15 catalyst. The TEM analysis of SBA-15
(Fig. 3a, b) indicates that a well-ordered hexagonal array of
mesopores can be observed when electron beam was par-
allel to the main axis of cylindrical pores. When electron
beam is perpendicular to the main axis, cylindrical pores
are viewed from the side as a striped image. Distance
between centers of two adjacent pores was about 10 nm,
and their pore diameters were about 6 nm. On NiMo/
alumina or SBA-15. Then, even if X-ray diffraction does
not evidence the presence of Mo–Ce mixed oxides species,
interactions between these two compounds can not be
excluded.
After the addition of Ni, the reduction of Mo species
generally occurred at lower temperatures, indicating the
promotional effect of Ni on Mo reduction [26, 28, 29].
Among NiMo catalysts, there are more easily reducible
1
23

HDO Performance of NiMo Catalyst
SBA-15 TEM image (Fig. 3c), it can be seen that active
phase is well dispersed on the support with the average
diameter of the mean particle size about 5 nm.
For the NiMo/SBA-15 catalyst, a high surface area of
SBA-15 leads to a better active phase dispersion, which can
be observed on TEM images and TPR profiles (Figs. 2, 3).
This result seems to indicate a higher GUA conversion
performance compared with NiMo/Al O and NiMo/CeO
2
2
3
3
.2 HDO Measurements
catalysts. Then, about 95 mol% of the products contained
no benzene ring, nearly 60 mol% of those contained no
oxygen and other 15 mol% of those contained only one
oxygen atom in their molecules. Moreover, well-dispersed
Ni can play a key role in GUA conversion and HDO per-
formance since the activity of Mo/SBA-15 catalyst is much
lower than NiMo/SBA-15 catalyst (Table 3). Only 7 % of
GUA is converted with Mo/SBA-15 and the main product
is phenol. As the result, Ni can take part in HDO activity as
proposed in other studies by increasing Mo dispersion [28,
32]. It can be further discussed about another possible
pathway that well-dispersed Ni, through its ring hydroge-
nation activity, create high yield of saturated oxygenate
compounds (Table 3) which were identified more reactive
for hydrogenolysis reaction [3]. This pathway can be found
in other study with the HDO reaction conducted with noble
metal type catalyst [30].
Table 3 shows catalytic activity tests of NiMo based cat-
alysts with GUA as feed at 250 °C, 5 MPa. In the blank
test without catalyst, no GUA conversion is observed under
the reaction conditions. The standard deviations of repeti-
tion are all below 10 %, indicating an acceptable repeat-
ability for HDO degree. The metal leaching was also
examined by ICP after 3 h of reaction time. Only trace
amounts of Mo and/or Ni (\100 ppm) are found in the
leaching solution. In all experiments, the gas obtained
contained mainly unreacted H , with minor amounts of
2
methane. Hence, comparison of the catalysts was based on
liquid products only. These products were homogeneous in
our experiments, and no phase separation was detected in
any sampling and analyzing processes.
Comparing to NiMo/Al O as reference catalyst, both
3
2
NiMo/CeO and NiMo/SBA-15 exhibit higher performances
2
As shown in Table 3, the ceria catalyst shows less coke
deposition in comparison with any other catalysts of this
in HDO reaction of GUA. Furthermore, NiMo/SBA-15 is
found as the most effective catalyst that gives more than 90 %
of GUA conversion and 67.5 % of HDO degree at 250 °C.
For the NiMo/Al O catalyst, liquid products contain
study. CeO -based materials have been widely used as an
2
oxygen storage material associated to the redox property of
Ce [33]. Therefore, the use of ceria as support can effec-
tively inhibit coke formation [34]. In addition, the con-
2
3
mainly 1,2-dimethoxybenzene (51.8 mol%) and main
deoxygenated product is phenol. Also, no saturated ring is
detected in the product. The high yield of phenol is
attributed to the reaction route proposed in literature with
NiMo and CoMo based catalysts [12, 30, 31], where the
GUA tranformation is found to initialize with the
demethylation (DME) and/or demethoxylation (DMO) step
to form catechol and/or phenol.
siderably lower acidity of Ni/CeO catalyst (results not
2
shown) may also suppress the coke deposition [35].
4 Conclusions
In this study, the influences of different supports, c-Al O ,
2
3
Compared to NiMo/Al O , the use of CeO as catalyst
2
CeO , and SBA-15, on NiMo based catalyst for bio-oil
2
3
2
support results in a slight increase in catalyst performance as
well as in products distribution despite its lower surface area
HDO reaction was investigated. It can be pointed out that
the beneficial effect of SBA-15 support for HDO perfor-
mance is associated with the high dispersion of NiMo.
NiMo/SBA-15 is a very promising catalyst for bio-oil HDO
reaction with its GUA conversion of 90 % and HDO
degree of 67.5 %. This catalyst also exhibits a significant
hydrogenation promotion effect that created a high yield of
cyclohexane and other saturated ring compounds. NiMo/
(
Table 2). 2-methoxycyclohexanol is detected with highest
yield (43.0 mol%) for NiMo/CeO2. Cyclohexanol
27.1 mol%) is observed as the highest deoxygenated product
(
aswell ascyclohexane isalsoobservedinthe product mixture.
Then,thehigheractivityofNiMo/CeO comparedwiththatof
2
NiMo/Al O can be attributed to the strong interaction
2
3
between Mo species and ceria even if this parameter should be
not the only one (Figs. 1, 2). Besides, the high yield of
CeO also shows benzene hydrogenation promotion effect
2
which enhanced formation of cyclohexane. As evidenced
from TPR studies, interaction of Mo and CeO2 which
creates a new active phase probably promoting its hydro-
genation acivity. The use of ceria as support also inhibits
the coke formation as compared with alumina or SBA-15
based catalysts.
2
-methoxycyclohexanol shows the benzene ring hydrogena-
tion promotion effect of the Ni supported on ceria catalyst.
This result is in accordance with the study of Barrault [29].
They have proposed the high hydrogenation activity of Ni–Ce
catalyst resulted from the synergy effect of Ni and Ce.
123

B. M. Q. Phan et al.
Acknowledgments This work was carried out at PVPro, VPI and
supported by Vietnam National Oil and Gas Group and the Ministry
of Industry and Trade of Vietnam.
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