Catalytic hydrodeoxygenation of anisole over nickel supported on plasma treated alumina-silica mixed oxides

Article abstract of DOI:10.1039/c7ra02594g

Hydrodeoxygenation (HDO) of anisole, a representative of lignin-derived bio oil, was investigated on SiO₂-Al₂O₃ supported Ni nano-particles at low hydrogen pressure. Plasma was used for the surface modification of the support. The supports and catalysts were characterized by N₂ physisorption, FT-IR spectroscopy, Temperature Program Desorption of ammonia (NH₃-TPD), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results showed that the plasma treatment improved both the SiO₂-Al₂O₃ surface characteristics and pore structure. The catalyst with a plasma treated support had a higher dispersion and smaller NiO particle size, leading to an improved hydrodeoxygenation activity and product selectivity. Phenol and benzene were the major products of anisole HDO. Demethylation, hydrodeoxygenation and transalkylation reactions are the main chemical reactions for anisole upgrading using the Ni/Al₂O₃-SiO₂ catalyst. Compared to the untreated catalyst, the plasma treated Ni/Al₂O₃-SiO₂ catalyst gives higher anisole conversion at atmospheric pressure by which valuable products were obtained with higher selectivity.

Full text of DOI:10.1039/c7ra02594g

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Catalytic hydrodeoxygenation of anisole over
nickel supported on plasma treated alumina–silica
Cite this: RSC Adv., 2017, 7, 30990
mixed oxides
Hamed Taghvaei, Mohammad Reza Rahimpour *ab and Peter Bruggemanc
ac
Hydrodeoxygenation (HDO) of anisole, a representative of lignin-derived bio oil, was investigated on SiO
Al supported Ni nano-particles at low hydrogen pressure. Plasma was used for the surface modification
of the support. The supports and catalysts were characterized by N physisorption, FT-IR spectroscopy,
Temperature Program Desorption of ammonia (NH -TPD), X-ray diffraction (XRD), field emission
scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results showed
that the plasma treatment improved both the SiO –Al surface characteristics and pore structure. The
2
–
2 3
O
2
3
2
2 3
O
catalyst with a plasma treated support had a higher dispersion and smaller NiO particle size, leading to
an improved hydrodeoxygenation activity and product selectivity. Phenol and benzene were the major
products of anisole HDO. Demethylation, hydrodeoxygenation and transalkylation reactions are the main
Received 2nd March 2017
Accepted 6th June 2017
chemical reactions for anisole upgrading using the Ni/Al
catalyst, the plasma treated Ni/Al –SiO catalyst gives higher anisole conversion at atmospheric
pressure by which valuable products were obtained with higher selectivity.
2 3 2
O –SiO catalyst. Compared to the untreated
DOI: 10.1039/c7ra02594g
O
2 3
2
rsc.li/rsc-advances
To date, only few studies on bio-oil hydrodeoxygenation
HDO) at atmospheric pressure have been reported. A possible
1
. Introduction
(
Flash pyrolysis of lignin followed by upgrading of the produced solution that can enable a reduction of the hydrogen pressure is
1
bio-oil is a potential approach for CO
2
neutral fuel production.
the synthesis of effective bifunctional hydrodeoxygenation
13
The upgrading step is required since the produced bio-oil from catalysts which combines supports with acidic nature and
ash pyrolysis contains a high oxygen content (10–45 wt%) metal centers with hydrodeoxygenation (HDO) activity, such as
compared to crude oil. A high oxygen content hinders the Ni.

2–5
16,17
18
In 2015 Sankaranarayanan et al. reported that the
6–8
miscibility of bio-oil with petroleum derived fuels. Moreover, it combination of Ni with acidic support showed a high perfor-
9
–11
reduces the heating value and increases the viscosity of bio-oil.
mance for HDO of methoxyl-phenyl containing compounds.
Hydrogen plays a key role in the hydrodeoxygenation reac- The catalytic hydrodeoxygenation of lignin derived bio-oil has
tion for oxygen removal from lignin derived bio-oil. Hydro- recently been reviewed in ref. 9.
deoxygenation is the most common upgrading route but is
Various approaches have been proposed to improve catalyst
costly due to the large consumption of hydrogen and requires properties and characteristics as another solution for improving
1
2,13
high pressures.
saturated products are generated via unwanted hydrogenation
which leads to decrease in octane number and prevents the due to its low temperature operation, simplicity and short
At high hydrogen pressure, undesired ring HDO in term of hydrogen pressure. Among these approaches,
14
non-thermal plasma treatment has attracted a lot of attention
19–24
direct utilization of the upgraded bio-oil.
processing time.
The plasma treatment of catalysts has
25
Moreover, the use of hydrogen leads to other concerns recently been reviewed in our published article. However, the
including (1) hydrogen leakage and ignition at relatively low effect of this surface modication method in HDO reaction is
temperature (2) production of greenhouse gases in many not reported.
hydrogen production processes used and (3) hydrogen
production cost and economy.
Conventional hydrotreating catalysts are the most widely
investigated catalyst for HDO reactions. Among them, silica–
15
26
alumina supported Ni catalysts are commonly used for hydro-
desulfurization (HDS) and hydroprocessing of heavy oil.
However, only few works have been devoted to illustrate the
a
27
Department of Chemical Engineering, Shiraz University, Shiraz 71345, Iran. E-mail:
rahimpor@shirazu.ac.ir; mrahimpour@ucdavis.edu; Fax: +98-711-6287294; Tel:
activity of this catalyst in HDO reactions of lignin derived bio-
+
98-711-2303071
oil. Generally, the amorphous SiO –Al O support has been
b
2
2 3
Department of Chemical Engineering, University of California, Davis, CA 95616, USA
Department of Mechanical Engineering, College of Science and Engineering, University
c
used for hydroprocessing catalysts due to its favorable acidity
due to the presence of both Brønsted and Lewis acid sites.
of Minnesota, Minneapolis, MN 55455, USA
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Interestingly, the acidity obtained by a combination of silica
and alumina is higher than that of individual alumina or
28
silica.
In the present study, plasma modied SiO –Al O supported
2
2 3
Ni was used as catalyst for HDO reactions. The principal aim is
to decrease the hydrogen pressure of the HDO process. The
effect of the plasma treatment on the characteristics of the
catalyst and its performance as a HDO catalyst is investigated.
Anisole was used as model compound of lignin-derived bio-oil
since anisole, as one of the major component of bio-oil,
29–32
contains a methoxy-phenyl group.
2. Experimental methods
2
.1 Materials
Aluminum tri-sec-butylate (97%), tetraethyl orthosilicate (TEOS)
98%) and nickel nitrate hexahydrate (Ni(NO $6H O) were
used as the Al, Si and Ni precursors, respectively. Acetylacetone
H-acac) and n-butanol were used as the complexing agent and
(
3
)
2
2
(
solvent, respectively. All chemicals were purchased from Merck
and used without further purication. Hydrogen, nitrogen and
argon were used with purity of 99.999% as feed, carrier gas in
the catalytic reactor and carrier gas in the plasma system,
respectively. Anisole (99% purity) was used in this work as
a reactant.
Fig. 1 Schematic of glow discharge plasma reactor used for modifi-
2 3 2
cation of Al O –SiO .
2.2 Support preparation
In this study, silica–alumina mixed oxides (Si/Al ¼ 1) were used
plasma and the resulting powder is referred to as Al O –
SiO (P30) and Al O –SiO (P60) respectively.
2 2 3 2
2
3
33
as a support and prepared by a sol–gel method. A typical
synthesis procedure is as follows. Appropriate amounts of TEOS
and aluminum tri-sec-butylate were dissolved in n-butanol and
2.3 Catalyst preparation
ꢀ
the solution was heated to 60 C while stirring. When the
Ni/Al –SiO and Ni/Al O –SiO (P60) catalysts with 10 wt%
2
O
3
2
2 3 2
solution was well mixed and became clear, H-acac was added.
The solution was cooled down to ambient temperature and
subsequently hydrolyzed with deionized water. The nal solu-
tion was stirred until a transparent gel was formed. Aer drying
nickel loading were synthesized by incipient wetness impreg-
nation using an aqueous solution of nickel nitrate hexahydrate
(
Ni(NO ) $6H O). The aqueous mixture was stirred for 12 h at
3 2 2
ꢀ
ꢀ
ꢀ
room temperature. The solution was heated to 80 C to remove
water and subsequently placed in an oven at 110 C for 2 h. The
resulting samples were calcined at 550 C for 4 h to obtain nal
for 2 h at 110 C the sample was calcined at 500 C for 5 h. The
obtained product is named Al –SiO throughout the paper.
ꢀ
2
O
3
2
ꢀ
In the second step, a part of the synthesized support was
treated in a glow discharge plasma. A schematic diagram of the
plasma device is shown in Fig. 1. The plasma was generated in
a pyrex cylinder with a length of 30 cm and an inner diameter of
catalyst.
2.4 Characterization of the catalysts
7
cm. Two circular stainless still electrodes were placed in the The structural characteristics of the samples were analyzed by
chamber at a distance of 10 cm and connected to DC high X-ray diffraction (XRD) using a Bruker-AXS (Siemens) D5005
voltage power supply and ground, respectively. All impurities diffractometer with a Cu Ka (k ¼ 0.15406 nm) radiation source
were washed using deionized water and acetone. Al
2
O
3
–SiO
2
operated at 40 mA and 45 kV. XRD diffraction spectra were
ꢀ
ꢀ
powder was placed on a pyrex glass and positioned in the obtained between 10–70 with a step size of 0.04 and a count-
positive column of the plasma discharge. A 2-stage direct drive ing time of 1.5 s. Fourier Transform Infrared Spectroscopy
oil rotary vacuum pump (Uniweld HVP12) was used to evacuate (BRUKER EQUINOX 55) was carried out in the range of 400–
ꢁ
1
the chamber. Ar was used as a plasma forming gas. The ow 4000 cm wave number. Temperature-programmed desorption
rate was controlled by means of a mass ow controller and of ammonia (NH -TPD) was performed on a chemisorption
adjusted at 20 mL min . The inside pressure was measured by analyzer (Quantachrome ChemBet).
a vacuum gauge and kept constant at 100 Pa. The catalyst was N physisorption was performed by an automatic adsorption
treated by a plasma operating at voltage of 2 kV and a current of analyzer (ASAP 2020) to obtain the N
3
ꢁ
1
2
2
adsorption–desorption
50 mA. Samples were treated for 30 min and 60 min by the isotherms at 77 K and to measure textural properties (specic
1
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surface area, average pore diameter and pore volume) of was employed. 2 mL of each sample was injected into the GC.
samples. Before the measurement, the samples were degassed The major components were also detected by a GC-MS (Shi-
ꢀ
at 300 C for 6 h under vacuum to remove impurities. The madzu QP-5050, Kyoto, Japan).
Brunauer–Emmett–Teller (BET) method was used to evaluate
the specic surface area of samples, while the pore volume and (S
average pore diameter were calculated with the Barrett–Joyner–
Halenda (BJH) method.
The topography and particle size of the catalyst was charac-
terized by Field Emission Scanning Electron Microscopy
The anisole conversion percentage and product selectivity
) were dened as follows:
i
C
in ꢁ Cout
Anisole conversion ð%Þ ¼
ꢂ 100
(1)
(2)
C
in
produced moles of i component
consumed moles of anisole
Si ¼
(FESEM), which was equipped with a Mira3 microscope and an
energy-dispersive X-ray spectrometer (EDS).
with Cin and Cout the input and output concentrations of anisole
in the reactor, respectively.
The morphologies of the catalyst and Ni size were charac-
terized using transmission electron microscopy (TEM). A FEI
Tecnai T12 TEM operated at 200 kV was used. The sample was
prepared by depositing a drop of water suspension of ne
powder onto a copper grid coated with carbon.
The inuence of external mass transfer limitation was
negligible under the experimental conditions since variation of
catalyst mass and reactant ow at stable WHSV did not affect
the conversion. Moreover, no variation of anisole conversion
was observed by reducing the catalyst size which conrmed the
insignicancy of internal mass transfer limitation.
2.5 Experimental setup for catalytic activity measurements
The catalytic reaction experiments were conducted in the gas
phase using a xed bed tubular ow reactor (with an inside
ꢀ
diameter of 9 mm) at a temperature of 400 C and atmospheric
3
. Results and discussion
pressure. Liquid anisole at room temperature was fed by an
HPLC pump with 0.02 mL min ow rate into the preheating
zone to heat it to a temperature of 150 C. The vaporized anisole The textural properties of the untreated and plasma treated
ꢁ
1
2 3 2
3.1 Morphology of plasma-treated Al O –SiO
ꢀ
was mixed with the gas stream consisting of a mixture of N
and fed to the reactor. The ow rate of N and H
for each gas (room temperature and butions of the Al
2
and support are compared by nitrogen physisorption measurement.
was The N adsorption–desorption isotherms and pore size distri-
–SiO , Al –SiO (P30) and Al –SiO
2
H
2
2
2
2
ꢁ
1
adjusted at 10 L h
2
O
3
2
2
O
3
2
2
O
3
atmospheric pressure) using mass ow controllers to obtain (P60) supports are shown in Fig. 2. The BET surface area, pore
a H to anisole molar ratio of 40. Liquid products were collected volume and average pore diameter of the samples are listed in
2
from a condenser which was placed at the reactor outlet.
Table 1.
2
The N adsorption–desorption isotherm of the untreated and
Fresh catalyst, about 1 g with a particle diameter of 0.25–0.30
mm was used for each experiment. Before the reaction, the plasma treated supports are classied as type IV isotherms of
3
4
catalysts were reduced for 1 h in the reactor with pure hydrogen mesoporous materials according to the IUPAC classication.
ꢁ
1
ꢀ
at a ow rate of 6 L h at 500 C. The value of the weight hourly The mesoporous alumina–silica mixed oxides show high
space velocity (WHSV) was 1.2 (g of anisole)/(g of catalyst ꢂ h). specic surface area of 517 m g , with a small enhancement
All experiments typically lasted 3 h of continuous operation and aer plasma treatment which is in consistent with the results in
2
ꢁ1
25
liquid products were collected every 30 min.
other literature. As shown in Fig. 2 the hysteresis loops of the
In order to analyze the products, a gas chromatograph plasma treated supports are shied to lower P/P values. The
0
(GC112A) using a SGE-BPX5 capillary column and FID detector reason is ascribe to the fragmentation of support particles as
Fig. 2
2
N adsorption–desorption isotherms of untreated and plasma treated supports.
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Table 1 Textural properties of the supports and the catalysts
a
a
S
BET
Pore volume
Pore size
(nm)
2
ꢁ1
3
ꢁ1
Samples
(m g
)
(cm g
)
Al
Al
Al
2
2
2
O
O
O
3
3
3
–SiO
–SiO
–SiO
2
2
2
517.3
532
528.4
151.6
171.7
0.82
0.41
0.43
0.19
0.21
4.94
3.29
3.23
3.88
2.91
(P30)
(P60)
1
0%Ni/Al
0%Ni/Al
2
O
O
3
–SiO
–SiO
2
1
2
3
2
(P60)
a
Calculated by BJH desorption theory.
2 3 2 2 3 2
Fig. 4 FESEM images of (A) Al O –SiO (B) Al O –SiO (P60).
a consequence of support surface bombardment by energetic
ions and potentially other plasma species.
fragmentation of support particles. Moreover, when objects such
The obtained results are in accordance with the pore size as the support are inserted in the plasma they tend to be charged
distributions obtained by N physisorption is shown in Fig. 3. negatively by the energetic electrons in the plasma. This leads to
The pore size distribution of the plasma treated Al O –SiO has the formation of a sheath between the support and the bulk
2
2
3
2
its maximum between 2–4 nm, with a maximum pore diameter plasma with local high electric elds. This charge distribution on
of 3.3 nm. However, untreated samples show a broader pore size a rough surface can cause repulsive Coulomb force between
distribution in the range of 2–8 nm. Moreover, the maximum of support particles and is suggested to potentially enhance elon-
the pore size distribution decreases from 6.2 nm to 3.7 nm, aer gation, distortion or fragmentation by the plasma.36
plasma treatment.
A narrower mesoporous structure of the plasma treated
3.2 FTIR analysis
support has signicant inuence on impregnated metal particle
size and can prevent the agglomeration of the active phase
through a geometrical connement effect which restricts the
FTIR spectra of plasma treated and untreated Al O –SiO are
2
3
2
shown in Fig. 5. All samples have similar peak positions and
there is no signicant difference between the FTIR spectra of
treated and untreated support. All samples show absorption
35
growth of Ni crystallites during high temperature reaction.
Increasing the plasma treatment time from 30 min to 60 min
has no signicant effects on the nitrogen physisorption.
Fig. 4 displays the surface morphology of the untreated and
plasma-treated support. The FESEM graphs show that the
plasma treatment has considerable effects both on the
morphology and grain sizes of the support.
The spherical particles of plasma treated support has smaller
diameter with a uniform dispersion. In contrast, the untreated
support consists of large particles and shows a comparatively
rough surface. These results are consistent with the nitrogen
physisorption results.
ꢁ
1
peaks around 2900–3800 and 1050 cm which are related to OH
of (Si/Al)O units of the Al –SiO and physically adsorbed water
4
2
O
3
2
ꢁ
1
molecules. Moreover, the broad band at around 600–900 cm is
corresponding to stretching vibrations modes of X–O, O–X–O and
X–O–X bonds, where X represents Si and Al, and O is the atom of
ꢁ
1
oxygen. The observed bands at 2925–2940 and 2854–2877 cm
for all samples are attributed to the –CH stretching mode of
2
atmospheric hydrocarbons on the surface of the support.
3
.3 Temperature program desorption of ammonia (NH
3
-TPD)
As mentioned above, the bombardment of the catalytic The acidity of Al
2
O
3
–SiO aer plasma treatment is compared
2
3
surface by plasma species and in particularly ions can cause with the untreated sample. NH -TPD was performed to
Fig. 3 Pore size distribution of untreated and plasma treated supports.
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Fig. 7 XRD spectra of support and catalysts. The spectra of Al
2 3
O –
Fig. 5 FTIR spectra of plasma treated and untreated support. The
spectra of Al O –SiO P30 and P60 are shifted for clarity.
2 3 2
SiO P60 and 10%Ni/Al –SiO are shifted for clarity.
2
2
O
3
2
although the intensities are almost at the noise level. These
poor intensities suggesting that NiO crystal size exists either in
small size or they are well dispersed on a high surface area of
characterize the distribution of weak and strong acid. The low-
and high-temperature peaks represent the weak acid and strong
acid sites, respectively. As shown in Fig. 6, the weak acid sites
decrease aer plasma treatment while the strong acid sites
increase. This can be attributed to diffusion of Al from
aluminum oxides (Al–O–Al) or isolated aluminum graed to
silica into the silica network (Al–O–Si), which induces the
28
the mesostructure support. The small crystallite size of NiO
40
can be due to strong interaction between NiO and support.
Weaker NiO peaks are observed for Ni/Al –SiO (P60)
compared to Ni/Al –SiO , indicating slightly smaller crystal
size and higher dispersion for NiO.
2
O
3
2
2
O
3
2
37
Brønsted acidity. Indeed, larger number of aluminum atoms
37,38
have been tetrahedrally coordinated into the silica network.
Previous studies showed that supports with a strong acidity are 3.5 TEM studies on the catalyst
39
crucial for the catalytic hydrodeoxygenation reaction. There-
fore, besides improving textural properties, plasma treatment
can improve the HDO reaction through increasing strong acid
functionality.
Transmission electron microscopy (TEM) images of NiO sup-
ported nanocatalysts, shown in Fig. 8, revealing a smaller size of
nickel particles in the case of Ni/Al O –SiO (P60) compared to
2
3
2
the Ni/Al O –SiO nanocatalyst. This result is consistent with
2
3
2
the observed small NiO diffraction peaks with XRD.
3.4 X-ray diffraction (XRD) of the catalysts
Some nickel oxide agglomerates up to 17 nm in size can be
2 3 2
clearly observed for the Ni/Al O –SiO catalyst. In contrast, the
plasma treated catalysts contain Ni particles with smaller sizes
and more homogeneous distribution. Nanoparticles of around
Fig. 7 shows the XRD patterns of the Al –SiO , Ni/Al O –SiO
2
O
3
2 2 3 2
and Ni/Al
2
O
3
–SiO
2
(P60). The amorphous alumina–silica can be
ꢀ
observed by a broad peak in the 15–35 2q range. Diffraction
peaks at 37.2 , 43.3 , and 62.9 (2q) correspond to the (111),
200), and (220) planes of NiO phase and seem to be present
ꢀ
ꢀ
ꢀ
2 3 2
1–10 nm are observed for the Ni/Al O –SiO (P60) catalyst.
The interaction of ions with the support surface could
improve the kinetics of metal particle nucleation and crystal
growth by generation of defects which can enhance the forma-
tion of seed crystals and the rate of metal particle nucle-
(
19,41
ation.
In addition, the narrower mesoporous structure of
3
Fig. 6 NH -TPD profiles of plasma treated and untreated support.
2 3 2 2 3 2
Fig. 8 TEM images of (A) Ni/Al O –SiO (B) Ni/Al O –SiO (P60).
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plasma treated support can have a signicant inuence on
35
metal particle size due to geometrical connement and lead to
better impregnation of the nickel on the support. Indeed, the
narrower pore size of plasma treated support can prevent the
growth and aggregation of nickel particles. The conned nickel
particles in the plasma treated catalyst can be conned by
a smaller drop in pore volume of plasma treated catalyst aer
impregnation of nickel. N
that the pore volume of the plasma treated catalyst drops by
1% aer impregnation of nickel on the support, while this
2
physisorption results (Table 1) show
5
value is 76% in the case of untreated catalyst.
Therefore, less pore plugging occurs in the Ni/Al O –SiO
2
2
3
(
P60) sample due to the smaller NiO particles and leads to
a relatively higher surface area of Ni/Al –SiO (P60) sample in
comparison with Ni/Al –SiO (Table 1).
2
O
3
2
2
O
3
2
Fig. 10 Time-on-stream behavior of anisole conversion on Ni/Al
SiO and Ni/Al –SiO (P60) nanocatalysts.
2 3
O –
2
O
2 3
2
3.6 FESEM and EDS dot mapping analysis
The existance of different elements (Ni, Si and Al) and also, their
distribution in the structure of the nanocatalyst are conrmed
by EDX dot-mapping. Fig. 9 shows the elemental mapping of the
test time. Plasma treated Al O –SiO supported nickel catalyst
2
3
2
exhibits higher HDO activity of anisole compared to the Ni/
Al –SiO . The conversion of anisole increases from 61.1% to
5.5% when Ni/Al –SiO catalyst were replaced with Ni/
Al –SiO (P60) catalyst. The increased conversion can be
2
O
3
2
2 3 2
Ni/Al O –SiO (P60) nanocatalyst. All the elements used for the
7
O
2
3
2
catalyst preparation (Ni, Al and Si) can be seen in the EDS
analysis. The EDX data suggests that highly homogeneous and
well-dispersed nanocatalyst particles are obtained by using
plasma treated supports. No sintering or particle growth was
observed in the Ni particles. These ndings are consistent with
the TEM and XRD results.
2
O
3
2
attributed to smaller Ni particle size and a better dispersion of
nickel along with higher specic surface area of Ni/Al O –SiO
2
2
3
(
P60) compared to Ni/Al O –SiO nanocatalyst as shown in
2 3 2
previous sections. The enhancement in the conversion is also
believed to be the result of increasing the strong acid sites of
39,42
Moreover, an intertwined dispersion of Ni, Si and Al is
support aer plasma treatment.
The acid site on support
2 3 2
observed in the NiO supported plasma treated Al O –SiO . This
would further affect the interaction between reactant and
support material. Lin et al. employed the chemisorption of
guaiacol and proved that the higher acid strength had stronger
represents successful preparation of alumina and silica mixed
oxides. In addition, the synergism effect of active sites and acid
sites for HDO reaction can be improved.
43
bonding with the model compound supports.
Phenol, methylphenols and benzene are the major products
of anisole hydrodeoxygenation over both catalysts as shown in
Fig. 11. A reaction network to major and minor products is
shown in Fig. 12. The selectivity of phenol reaches almost 37.1%
3
.7 Catalytic activity
Fig. 10 shows the variation of conversion for the Ni/Al O –SiO
2
2
3
(P60) and Ni/Al O –SiO nanocatalysts over 300 min for time-on-
2 3 2
in the case of the Ni/Al
when Ni/Al –SiO is used. This monooxygenated product is
a result of breaking the C O–CH bond which is the weakest
2 3 2
O –SiO (P60) and it is close to 34.4%
stream experiments. In the blank test without catalyst, no ani-
sole conversion is observed under the reaction conditions. As
can be seen, conversion remains almost constant during the
2
O
3
2
6
H
5
3
2 3 2
Fig. 9 FESEM and EDX mapping of the Ni/Al O –SiO (P60) nanocatalyst.
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Fig. 11 Product selectivity of anisole conversion, TOS ¼ 30 min.
Fig. 12 Reaction network to major and minor products.
bond in the chemical structure of anisole. Therefore, the rate of
The high amount of strong acid sites in the plasma treated
anisole demethylation to phenol is higher than other reactions. catalyst could also accelerate the production of toluene and
The production of benzene is also signicant for both cata- xylens through alkylation of benzene ring.
lysts, especially for Ni/Al O –SiO (P60), which shows a selectivity
Actually, plasma treatment can have both negative and
of 21.2% toward this valuable deoxygenated product. Benzene positive inuence on alkylation reaction. On one side, it can
could be produce through hydrodeoxygenation of phenol. reduce the active metal particle size which can result in higher
2
3
2
44
In addition to benzene, a signicant amount of methyl oxygen removal reaction compared to alkylation. As a result of
substituted phenols are also produced since the Caromatic–H this effect, methyl substituted phenol products were generated
15
6 5
bond can break easier than the C H –OH bond. The produc- lower than benzene. On the other side, it can enhance the
tion of methyl substituted compounds like methylphenols and strong acid sites which results in higher alkylation reaction
dimethylphenols result from the transalkylation reaction. than other reactions. Due to this effect, the generated benzene
However, higher selectivity of benzene was achieved than can convert to toluene and xylens through alkylation of benzene
methyl substituted phenol products especially in the case of the ring.
plasma treated catalyst. This result can be related to the high
hydrodeoxygenation ability of the synthesized catalysts espe- is because the conversion took place at atmospheric pressure.
cially in the case of the Ni/Al –SiO (P60) catalyst which has In summary, the obtained results reveal that promoting the
smaller NiO particles. This result is consistent with previous characteristics of Al –SiO supported nickel catalyst through
results that showed that smaller nickel particles are more plasma modication of the support, not only elevated consid-
Interestingly, no ring saturated products are observed which
2
O
3
2
2
O
3
2
16
favorable for hydrodeoxygenation reactions. Moreover, the erably the catalytic activity for HDO, but also increased anisole
catalytic roles of metal nanoparticles on acidic supports were conversion to more valuable chemicals, such as phenol and
elucidated using the acid-site-measurement-dependent catal- benzene at atmospheric pressure. Moreover, considering the
ysis results in previous studies, which demonstrated that metal- formation of desirable products and high conversion at low
2 3 2
deposited acidic supports were indispensable to the deoxygen- hydrogen pressure, the Al O –SiO based catalyst was found to
44
ation of oxygenates.
be highly appropriate for upgrading of lignin-derived bio-oil.
30996 | RSC Adv., 2017, 7, 30990–30998
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Paper
RSC Advances
1
3 Y. Yang, C. Ochoa-Hern ´a ndez, V. A. de la Pe n˜ a O'Shea,
P. Pizarro, J. M. Coronado and D. P. Serrano, Appl. Catal.,
B, 2014, 145, 91–100.
4
. Conclusions
2 3 2
In this study, Ni supported on Al O –SiO were synthesized by
impregnation method have been evaluated for anisole hydro- 14 T. Prasomsri, M. Shetty, K. Murugappan and Y. Rom ´a n-
deoxygenation at atmospheric pressure. Glow discharge plasma
Leshkov, Energy Environ. Sci., 2014, 7, 2660.
treatment was used for modication of support. It is revealed by 15 H. Taghvaei and M. R. Rahimpour, RSC Adv., 2016, 6, 98369–
nitrogen physisorption and SEM that plasma treated support
98380.
has narrower pore size distribution (2–4 nm), smaller particles 16 P. M. Mortensen, J.-D. Grunwaldt, P. A. Jensen and
and more uniform surface compared to untreated support.
A. D. Jensen, Catal. Today, 2016, 259, 277–284.
These led to smaller NiO particle size, higher surface areas and 17 A. B. Dongil, I. T. Ghampson, R. Garc ´ı a, J. L. G. Fierro and
better distribution of NiO, as evidenced by XRD, nitrogen
N. Escalona, RSC Adv., 2016, 6, 2611–2623.
physisorption, SEM, elemental mapping and TEM measure- 18 T. M. Sankaranarayanan, A. Berenguer, C. Ochoa-
ments. Moreover, the plasma treated catalyst showed higher
strong acid sites as shown by NH -TPD. As a consequence,
the catalyst with plasma-treated support showed signicantly
Hern ´a ndez, I. Moreno, P. Jana, J. M. Coronado,
D. P. Serrano and P. Pizarro, Catal. Today, 2015, 243, 163–
172.
3
improved anisole conversion. Demethylation, hydro- 19 N. Wang, K. Shen, X. Yu, W. Qian and W. Chu, Catal. Sci.
deoxygenation and transalkylation reactions take place over the
Technol., 2013, 3, 2278.
Ni/Al O –SiO catalyst, suggesting it is a suitable catalyst for 20 Y. Zhao, Y.-x. Pan, Y. Xie and C.-j. Liu, Catal. Commun., 2008,
2
3
2
upgrading of bio oil in order to attain valuable products at
atmospheric pressure.
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22 X. Zhu, P. Huo, Y.-p. Zhang, D.-g. Cheng and C.-j. Liu, Appl.
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