Different crystal form titania supported ruthenium nanoparticles for liquid phase hydrodeoxygenation of guaiacol

Article abstract of DOI:10.1166/jnn.2018.16392

Titania supported Ruthenium-based catalysts were prepared for liquid phase hydrodeoxygenation of guaiacol to cyclohexanol. The catalytic performance is affected by the different crystal forms of titania supports. Anatase and rutile titania supported catalyst 5%Ru/a-r-TiO₂ presents higher BET surface area, better dispersion of Ru particles with smaller particle size of 3-4 nm, more acidic centers, and more Ru^δ+ located at the boundary between anatase titania and rutile titania. Hence, 5%Ru/a-r-TiO₂ gives the best catalytic performance of 95.33% conversion of guaiacol and 79.23% selectivity to cyclohexanol, other products mainly include cyclohexane, benzene, cyclohexanone and 1,2-cyclohexanediol. Based on the results of this work, the possible reaction path for guaiacol hydrodeoxygenation was proposed.

Full text of DOI:10.1166/jnn.2018.16392

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 8426–8436, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
www.aspbs.com/jnn
Printed in the United States of America
Different Crystal Form Titania Supported
Ruthenium Nanoparticles for Liquid Phase
Hydrodeoxygenation of Guaiacol
Wei Long, Yang Lv, Pingle Liu∗, Fang Hao, Wei Xiong, Xie Li, Haishuai Cui, and He’an Luo
College of Chemical Engineering, Xiangtan University, Xiangtan 411105, People’s Republic of China
Titania supported Ruthenium-based catalysts were prepared for liquid phase hydrodeoxygenation
of guaiacol to cyclohexanol. The catalytic performance is affected by the different crystal forms of
titania supports. Anatase and rutile titania supported catalyst 5%Ru/a-r-TiO2 presents higher BET
surface area, better dispersion of Ru particles with smaller particle size of 3–4 nm, more acidic
centers, and more Ruꢀ+ located at the boundary between anatase titania and rutile titania. Hence,
5%Ru/a-r-TiO2 gives the best catalytic performance of 95.33% conversion of guaiacol and 79.23%
selectivity to cyclohexanol, other products mainly include cyclohexane, benzene, cyclohexanone
and 1,2-cyclohexanediol. Based on the results of this work, the possible reaction path for guaiacol
hydrodeoxygenation was proposed.
Keywords: Guaiacol, Interface, Hydrodeoxygenation, TiO2, Ruthenium Nanoparticles.
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
Copyright: American Scientific Publishers
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1. INTRODUCTION
Guaiacol hydrodeoxygenation can be carried out in gas
phase or liquid phase. The results of guaiacol hydrodeoxy-
genation in fixed bed tubular reactor are shown in Table I.
Phenol and catechol were the major products when the
sulfide was used as the catalyst or the catalyst was treated
in H2S. Benzene, toluene and xylene were the major prod-
ucts over Fe or Ni based catalysts. Also, the support had
obviously influence on product distribution and catalytic
activity.
Listed in Table II are the catalytic performances of liq-
uid phase hydrodeoxygenation of guaiacol. Phenol and cat-
echol were the major products over Mo based catalysts,
and cyclohexane was the major product over Ni, Cu, Pd
or Pt based catalysts.
Whether in liquid phase or gas phase hydrodeoxy-
genation of guaiacol, the reaction temperature was rel-
atively higher. Some researchers tried to study guaiacol
hydrodeoxygenation under mild conditions. Kim et al. has
found that guaiacol hydrogenation over bimetallic RuRe/C
catalyst can be carried out under 473 K and 2 MPa,
the selectivity to cyclohexane was 57.0%.38 He et al.
proposed that Pt/TiO2 catalyst can be used for highly
effective hydrodeoxygenation of guaiacol in a fixed-bed
reactor at 558 K and 4 MPa, the conversion of gua-
iacol was 70% and the selectivity to cyclohexane was
Clean and pollution-free energy is one hotspot of mod-
ern scientific research.1 Biomass derived liquid fuels
have the potential to provide a renewable, carbon-neutral
energy source so as to offset the shortage of fossil
energy.2 Some interesting specific feedstocks have been
investigated such as carbohydrate, triglycerides, glyc-
erol, 5-hydroxymethylfurfural, cellulose, hemicellulose
and pentose, lignin, and ligncellulose.3–11 The catalytic
conversion of biomass and derivatives over diverse cata-
lysts can obtain different chemicals,12–14 and the research
is interesting and valuable to the industrial promotion.
Compared with some typical biomass energy such as
glucose or pentose, lignin can not be obtained by hydrol-
ysis or fermentation.15 Pyrolysis is the traditional technol-
ogy to produce lignin, but the purity of lignin is not ideal.
Since lignin contains low concentration of sulfur, nitro-
gen and high concentration of oxygen (30–40 wt%), the
hydrodeoxygenation appears as a potential route for fur-
ther use of lignin.16 Guaiacol is a typical representative of
lignin which has two O-containing functional groups of
phenolic and methoxy, and hydrodeoxygenation studies
of guaiacol cause a wide range of concern.17
∗Author to whom correspondence should be addressed.
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1533-4880/2018/18/8426/011
doi:10.1166/jnn.2018.16392

Long et al.
Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Table I. The gas-phase hydrodeoxygenation of guaiacol.
Catalysts
Reaction conditions
Conv/%
Major product
Yield/%
Ref.
25.8 wt% CoMo/Al2O3
8.6 wt % Ni2P/SiO2
5 wt% Pd/ Al2O3
22 wt% Fe/SiO2
10 wt% Fe/AC
10 wt% NiCo/Al-MCM-41
15 wt% FeNi/HBeta
5 wt% NiPd/ꢀ-Al2O3
7 wt% NiFe/CNTs
573 K, 4 MPa, 100 ppm of H2S, LHSV = 1 h−1, 12 h
573 K, 0.1 MPa, LHSV = 59 h−1, 20.2 min
573 K, 0.1 MPa, LHSV = 59 h−1, 0.339 min
673 K, 0.1 MPa, LHSV = 1.5 h−1, 150 min
673 K, 0.1 MPa, LHSV = 0.6 h−1, 150 min
673 K, 0.1 MPa, LHSV = 1.67 h−1, 150 min
693 K, 0.1 MPa, LHSV = 1 h−1, 180 min
723 K, 0.1 MPa, LHSV = 0.6 h−1, 180 min
573 K, 3.0 MPa, WLHSV = 6.0 h−1, 120 min
85
59
70
74
82
100
100
29
Phenol
Methoxybenzene
Catechol
BTXa
Phenol
Phenol
BTXa
Phenol
Cyclohexane
25.5
22.4
70.0
38.3
71.2
40.0
56.8
18.4
82.6
[18, 19]
[20]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
99
Note: aBTX is the mixture of benzene, toluene and xylene.
Table II. The liquid-phase hydrodeoxygenation of guaiacol.
Catalysts
Reaction conditions
Conv/%
Major product
Yield/%
Ref.
10 wt% MoN/GCA
10 wt % MoCoN/SBA-15
55.4 wt% Ni/SiO2
10 wt% NiCu/ZrO2–SiO2
10 wt% ReS2/C
10 wt% NiCu/ZrO2–SiO2
3.7 wt% CoMo/ꢀ-Al2 O3
5 wt% MoS2/C
573 K, 3 MPa, 2∼8 h
573 K, 5 MPa, 3 h
593 K, 17 MPa, 1 h
573 K, 5 MPa, 8 h
72
79
phenol and catechol
phenol and catechol
cyclohexane
33
42
44ꢁ8
96
80
96ꢁ8
32ꢁ2
21ꢁ3
88
65
43ꢁ2
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
77ꢁ5
100
100
100
90
cyclohexane
phenol
cyclohexane
573 K, 5 MPa, 3∼4 h
573 K, 3 MPa, 8 h
523 K, 5.5 MPa, sulfided by H2S
573 K, 5 MPa, 4 h
phenol and catechol
catechol
30
2 wt% Pd/32 wt% WOx/ꢀ-Al2O3
15 wt% Ni/CNTm
0.5 wt% Pt/HBeta
573 K, 7 MPa, 2.5 h
573 K, 5 MPa, 2 h
523 K, 0.4 MPa, 2 h
100
100
95
cyclohexane
cyclohexane
cyclohexane
75%.39–40 Among Rh, Ru, Pd and Pt noble metal catalysts,
Ltd. Ethanol, Ammonia (30%), Nitric acid, Urea, Ammo-
Copyright: American Scientific Publishers
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
Ru based catalyst showed better catalytic performance in
nium bicarbonate, ethylbenzene, acetone and Sodium chlo-
guaiacol hydrodeoxygenation.41 Also, the reaction mecha-
nism of guaiacol hydrodeoxygenation over noble catalysts
were investigated by Ab initio studies and density function
theory.42–44
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ride with analytical grade were purchased from Sinopharm
Chemical Reagent Corporation Limited. H2 (99.99%) was
provided by Zhuzhou Diamond Gas Company.
As a magical material, titania has already performed
great success in the fields of photocatalysis, adsorption,
dye degradation, antibacteria, electrochemisy and medical
treatment. Its optical or catalytic properties can be changed
distinctly as the inner structure of titania is adjusted.
Therefore, different crystal forms of titania may effect the
catalytic activity,45 and this strange phenomenon is very
interesting, which can be investigated by catalytic reaction.
In this work, titania supported Ruthenium nanoparti-
cles catalysts were studied in guaiacol hydrodeoxygenation
under mild conditions, it exhibited high conversion of gua-
iacol and high selectivity to cyclohexanol, and the influ-
ence of the crystal form of titania support was focused on.
2.2. Catalyst Preparation
Anatase TiO2 supported Ru catalyst: Firstly, 5 mL butyl
titanate, 5 mL diethylene glycol and 20 mL tetrabutylam-
monium chloride were putted together in a flask and stirred
for 30 minutes. Then, the mixture was putted into the crys-
tallization kettle and placed in a muffle stove at 473 K for
24 h. After being cooled to room temperature, the grey
solid was washed for several times with distilled water in
order to remove the ammonium ion and chloride ion. After
washing with absolute ethanol for three times, the solid
was dried in air overnight at 393 K, crushed and calcined
at 573 K for 2 h in a muffle stove. The light grey powder
of anatase TiO2 was obtained.
Anatase TiO2 supported Ru catalyst was prepared by
the equal volume impregnation method. A certain amount
of RuCl3 · 3H2O was dissolved in distilled water. Then,
anatase TiO2 powder was added into the mixture and
stirred for 10 h. And the mixture was aged for 2 h
in a microwave washer and dried in air overnight at
393 K for 4 h and crushed. Then it was reduced under
a stream of pure H2 (100 mL/min) at 673 K for 2 h.
The prepared catalyst was labeled as x%Ru/a-TiO2, and
2. EXPERIMENTAL DETAILS
2.1. Materials
Titania P25 was purchased from Germany Degussa Co.,
Ltd. Ruthenium trichloride hydrate (RuCl3 · 3H2O) was
purchased from Sinopharm Chemical Reagent Corpora-
tion Limited. Butyl titanate, diethylene glycol, tetrabuty-
lammonium chloride, decahydronaphthalene and guaiacol
were purchased from Shanghai Macklin biochemical Co.,
J. Nanosci. Nanotechnol. 18, 8426–8436, 2018
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Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Long et al.
x% was the mass percentage of Ruthenium metal in the
catalyst.
above method for Ru/a-TiO2, the catalyst was labeled
as x%Ru/a-r-TiO2, and x% was the mass percentage of
Ruthenium metal in the catalyst.
Brookite TiO2 supported Ru catalyst: Firstly, 7.8 mL
butyl titanate was added into the ammonia with 1.1 g
sodium chloride and stirred for 5 h. Then, the mixture was
putted into a crystallization kettle and placed in a muffle
stove at 453 K for 6 h. After being cooled to room tem-
perature, the white solid was washed several times with
distilled water in order to remove the sodium ion and chlo-
ride ion. Then, after washing with absolute ethanol for
three times, the solid was dried in air overnight at 383 K,
crushed and calcined at 623 K for 2 h in a muffle stove.
The white powder of brookite TiO2 was obtained.
Brookite TiO2 supported Ru catalyst was prepared
according to the above method for Ru/a-TiO2, and the cat-
alyst was named as x%Ru/b-TiO2, and x% was the mass
percentage of Ruthenium metal in the catalyst.
Rutile TiO2 supported Ru catalyst: Actually, anatase
TiO2 can be converted into rutile TiO2 through roasting
under high temperature. Anatase TiO2 powder was putted
into a tube furnace for heat treatment at 1073 K under a
stream of pure N2 (100 mL/min). After being cooled to
room temperature, the white powder was washed several
times with distilled water and absolute ethanol, dried in
air overnight at 393 K. The white powder of rutile TiO2
was obtained.
Anatase TiO2 and brookite TiO2 (mass ratio of 1:1)
supported Ru catalyst: 9.0 mL of butyl titanate was dis-
solved in 15 mL of ethanol in flask A and stirred for
1 h. 4 mL of ethanol, 1.8 mL of distilled water, 0.6 mL
of nitric acid and 2 g of ammonium bicarbonate were
mixed together in flask B and stirred for 1 h (the molar
ratio of ammonium bicarbonate and butyl titanate was 2:1).
The mixture in flask B was dripped into flask A at the
speed of 1.0 mL/min. Then, the mixture was stirred for
4 h and aged overnight to yield a yellow homogeneous
gel, and the as-prepared gel was dried in air overnight at
383 K, the obtained sample was crushed and calcined at
573 K for 2 h in a muffle stove. The obtained powder con-
tained anatase TiO2 and brookite TiO2, and the mass ratio
was 1:1.
Anatase TiO2 and brookite TiO2 (mass ratio of 1:1) sup-
ported Ru catalyst was prepared according to the above
method for Ru/a-TiO2, the catalyst was labeled as x%Ru/
a-b-TiO2 where x% was the mass percentage of Ruthe-
nium metal in the catalyst.
2.3. Catalyst Characterization
The specific surface area, pore volume and pore size dis-
tribution of the samples were obtained by the nitrogen
adsorption–desorption on a Quantachrome NOVA-2200e
automated gas sorption system. Specific surface areas
and pore size distributions were calculated by Brunauer-
Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH)
methods.
Rutile TiO2 supported Ru catalyst was prepared accord-
ing to the above method for Ru/a-TiO , and the catalyst
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
C2opyright: American Scientific Publishers
was named as x%Ru/r-TiO2 where x% was the mass per-
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centage of Ruthenium metal in the catalyst.
Titania P25 supported Ru catalyst: Titania P25 white
powder contains anatase TiO2 and rutile TiO2, and the
mass ratio is approximately 4:1. So the titania P25 powder
was washed several times with distilled water, dried in air
overnight at 383 K. The as-prepared sample was crushed
after being cooled to room temperature.
Fourier transform infrared (FT-IR) spectra of the sam-
ples were recorded on a Nicolet 380 spectrometer. The
spectra of the samples were acquired in the wave number
range of 400–4000 cm−1
.
Titania P25 supported Ru catalyst was prepared accord-
ing to the above method for Ru/a-TiO2, and the catalyst
was labeled as x%Ru/p-TiO2 where x% was the mass per-
centage of Ruthenium metal in the catalyst.
Ammonia gas chemisorption was measured with Quan-
tachrome ChemBET 3000. The samples were previously
reduced in hydrogen stream and cooled to ambient tem-
perature under a nitrogen stream. The ammonia gas
chemisorption was performed at 333 K, and the ammonia
gas pulses (0.02 mL) were injected until the eluted areas
of consecutive pulses became constant.
Anatase TiO2 and rutile TiO2 (mass ratio of 1:1) sup-
ported Ru catalyst: 4.14 g of Urea was dissolved in 80 mL
of distilled water in flask A, Then, nitric acid was added
into the mixture and stirred for 1 h. 8 mL of butyl titanate
was dissolved in 10 mL ethanol in flask B and stirred
for 1 h. The molar ratio of urea and butyl titanate is 3:1.
The mixture in flask B was dripped into flask A at the
speed of 1.0 mL/min. Then, the mixture was stirred for
4 h and aged overnight to obtain the yellow homogeneous
hydrosol. The mixture was evaporated at 373 K to obtain
the yellow powder, and the powder was crushed, calcined
at 573 K for 2 h in a muffle stove. This yellow powder
contained anatase TiO2 and rutile TiO2, and the mass ratio
was 1:1.
Powder X-ray diffraction (XRD) patterns were deter-
mined on a D/max 2500 TC diffractometer using Cu Kꢂ
radiation (ꢃ = 1.542 Å). The tube voltage was 40 kV, the
current was 30 mA, and the scan range was 5–90ꢀ with
the scanning rate of 1ꢀ ·min−1
.
The pyridine adsorbed FT-IR spectra of the samples
were recorded on a Nicolet iSTM 10 spectrometer. The
samples were dried in a hot air oven for 1 h at 373 K prior
to pyridine treatment for IR measurements. The samples
(∼50 mg each) were poured loosely into a sample cup. The
loosely filled sample contacted with pyridine (∼0.1 cm3ꢄ
directly. Then the sample cup was kept in a hot air oven
at 393 K for 1 h to remove physisorbed pyridine. After
Anatase TiO2 and rutile TiO2 (mass ratio of 1:1)
supported Ru catalyst was prepared according to the
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Long et al.
Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
cooling, the IR spectrum was recorded in the spectral range
between 1700 and 1300 cm−1 with 256 scans and at a
resolution of 4 cm−1 using KBr background.
Carbon-based guaiacol conversion (wGuaꢄ, product selec-
tivity (Siꢄ was calculated according to the following
equations.46ꢆ47 In this work, we can ignore the carbon pro-
portion between the reactant and products because all the
concerned products contain hexatomic ring, and i means
the product i.
The morphologies of the samples were observed with
scanning electron microscope (SEM) on a JEOL JSM-
6610 LV scanning microscope operated at an acceler-
ating voltage of 5 kV. The surface morphologies and
particle sizes were observed with transmission electron
microscopy (TEM), and the microstructures of the sam-
ples were observed with high-resolution TEM (HRTEM)
on a TecnaiG220 ST electron microscope. The instrumen-
tal magnification ranged from 2 × 104 to 10 × 106. The
samples were deposited on a copper grid and coated with
a holey carbon film.
Molꢇguaꢄin −Molꢇguaꢄout
wGua ꢇ%ꢄ =
×100
Molꢇguaꢄin
Moli
Si ꢇ%ꢄ =
×100
Molreacted·Gua
3. RESULTS AND DISCUSSION
3.1. Characterization of Catalysts
The X-ray photoelectron spectroscopic (XPS) spectrum
was collected on a Perkin Elmer PHI5000C spectrometer
with Mg Kꢂ radiation (hv = 1253.6 eV) as the exicitation
source.
Shown in Figure 1 are three kinds of unit cell of TiO2
based on the inorganic crystal database (ISCD, http://
www.icsd.fiz-karlsruhe.de). Although the bond length
between Ti atom and O atom is 0.195∼0.198 nm in TiO2
with different crystal forms, the atomic arrangement of
anatase TiO2 is regular. The unit cell of brookite TiO2
shows obviously oblique cubic feature, and the unit cell of
rutile TiO2 presents apparently octahedron feature.
Table III demonstrates textural properties of different
catalysts with the same loading amount of Ru metal. It
can be seen from Table III that the textural properties vary
with the different crystal forms of titania. Anatase TiO2
2.4. Procedure for Catalytic Test
Catalytic test was carried out in a 15 mL Teflon-lined
stainless steel autoclave with a magnetic stirrer at 400 rpm.
Typically, 4.8 g of decahydronaphthalene, 1.2 g of guaiacol
and 0.2 g of catalyst powder (200–400 ꢅm) were added
into the autoclave. The reactor was sealed and purged with
H2 to exclude air for five times, and then it was pressur-
ized to 2.0 MPa with H2 under vigorous stirring after the
required temperature reached. After the reaction, the cat-
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
and rutile TiO with mass ratio of 1:1 supported Ru cat-
Copyright: American Scientific Publi2shers
alyst 5%Ru/a-r-TiO2 has the largest surface area and the
alysts were separated by filtration from the liquid phase
products. The contents of the reactants and the liquid phase
products were determined with gas chromatography (Agi-
lent Technologies, 7890 A) equipped with a DB-7501 cap-
illary column (0.50 mm in diameter and 30 m in length)
and a flame ionization detector (FID) using ethylbenzene
as the internal standard. The liquid phase products include
cyclohexane, benzene, cyclohexanol, cyclohexanone and
phenol.
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smallest particle size. The average pore size is 7.5 nm and
the pore volume is 0.23 cm3 ·g−1, which is at the interme-
diate level.
N2 adsorption–desorption isotherms and pore size distri-
butions of the samples are shown in Figures 2(a) and (b).
According to the IUPAC classification, it can be seen that
the hysteresis loop of 5%Ru/a-TiO2 is of type H1, the pore
diameter distribution is centered at 4.5 nm. The hystersis
Figure 1. The unit cell structures of TiO2.
J. Nanosci. Nanotechnol. 18, 8426–8436, 2018
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Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Long et al.
Table III. Textural properties of catalysts.
(f)
Surface
area
Average
pore
size (nm)
Pore
volume
(cm3 ·g−1
Particle
sizea
(nm)
(e)
Catalysts
(m2 ·g−1
ꢄ
ꢄ
5%Ru/a-TiO2
5%Ru/b-TiO2
5%Ru/r-TiO2
5%Ru/p-TiO2
5%Ru/a-r-TiO2
5%Ru/a-b-TiO2
58.3
63.4
14.5
50.8
93.7
88.2
4ꢁ3
29ꢁ6
11ꢁ7
32ꢁ8
7ꢁ5
0.09
0.44
0.04
0.42
0.23
0.17
82ꢁ9
94ꢁ7
414ꢁ6
118ꢁ2
64ꢁ0
(d)
(c)
7ꢁ3
68ꢁ0
(b)
(a)
Note: aAverage diameter of particle size determined by the nitrogen adsorption–
desorption.
1640
1500
3400
3500
1000
2000
2500
3000
4000
Wavenumbers (cm–1
)
loops of 5%Ru/b-TiO2 and 5%Ru/r-TiO2 are of type H4,
which is associated with narrow slit-shaped pores. As
shown in Figure 2(b), the hysteresis loops of 5%Ru/a-
r-TiO2 and 5%Ru/a-b-TiO2 are of type H4 with highly
ordered pores, and the pore diameter distribution are cen-
tered at 9.5 nm and 13.5 nm. It is shown that the mix-
ture of different crystal form titania can form mesoporous
materials.
Figure 3. FT-IR spectra. (a) 5%Ru/a-TiO2, (b) 5%Ru/b-TiO2 ,
(c) 5%Ru/r-TiO2, (d) 5%Ru/p-TiO2, (e) 5%Ru/a-r-TiO2 and (f) 5%Ru/a-
b-TiO2.
The XRD spectra of the samples are shown in Figure 5,
exhibiting the characteristic diffraction peaks of the tita-
nia with different crystal forms. The diffraction peaks of
5%Ru/a-TiO2, 5%Ru/b-TiO2 and 5%Ru/r-TiO2 are accord
with the diffractograms of anatase TiO2 (JCPDS 21-1272),
Brookite TiO2 (JCPDS 29-1360) and rutile TiO2 (JCPDS
21-1276).48 As to the titania support with mixed crystal
forms, the simple formula of AR/(AA +ARꢄ is used to judge
The FT-IR spectra of the samples are shown in Figure 3.
The bands around 1640 cm−1 in all the samples are
attributed to the bending and stretching vibration peak of
Ti–O. The band around of 3400 cm−1 in all the samples
are attributed to the bending peak of active hydroxy on the
surfaces of the catalysts. The broader the area of the band
the crystal form proportion, where AA and AR represent the
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
is, the more amount of the active hydroxy.
integrated intensities of the (101) peak of anatase and the
strongest (110) peak of rutile respectively.
Copyright: American Scientific Publishers
49ꢆ50
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The TPR profiles of the samples are given in Figure 4.
The TPR curves show that the initial reduction tempera-
ture of 5%Ru/r-TiO2 is 537 K, which is higher than other
samples. When the mixed crystal form of titania was used
as the support, the initial reduction temperature is about
427 K or 455 K, it indicate that the mixed crystal form
titania supported Ruthenium catalyst is more easier to be
reduced.
Hence,
the mass proportion of the different crystal form titania in
5%Ru/p-TiO2, 5%Ru/a-r-TiO2 and 5%Ru%/a-b-TiO2 can
be estimated. Obviously, the characteristic diffraction peak
at 2ꢈ = 44ꢀ is ascribed to the (101) crystalline plane of
Ru (JCPDS 88-1734). The diffraction peak of Ru(101) in
mixed crystal form titania supported catalyst is weaker
than that of single crystal form titania supported catalyst of
(a)
(b)
Figure 2. N2 adsorption–desorption isotherms and pore size distributions. (a) 5%Ru/a-TiO2 , 5%Ru/b-TiO2 and 5%Ru/r-TiO2; (b) 5%Ru/p-TiO2 ,
5%Ru/a-r-TiO2 and 5%Ru/a-b-TiO2 .
8430
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Long et al.
Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
B
L
455
(f)
(f)
427
(e)
(d)
(e)
(d)
427
(c)
(b)
537
(c)
(b)
473
(a)
436
(a)
400
500
600
700
800
1400
1450
1500
1550
1600
Temperature(K)
Wavenumber (cm–1
)
Figure 4. H2-TPR profiles of some catalysts. (a) 5%Ru/a-TiO2 ,
(b) 5%Ru/b-TiO2 , (c) 5%Ru/r-TiO2, (d) 5%Ru/p-TiO2, (e) 5%Ru/a-r-
TiO2 and (f) 5%Ru/a-b-TiO2 .
Figure 6. Pyridine adsorbed FT-IR spectra of some catalysts.
(a) 5%Ru/a-TiO2 , (b) 5%Ru/b-TiO2, (c) 5%Ru/r-TiO2, (d) 5%Ru/p-TiO2 ,
(e) 5%Ru/a-r-TiO2 and (f) 5%Ru/a-b-TiO2 .
5%Ru/a-TiO2, 5%Ru/b-TiO2 and 5%Ru/r-TiO2. The mixed
crystal form titania is in favour of Ru dispersion, and Ru
particles in 5%Ru/a-r-TiO2 show better dispersion.
The pyridine adsorbed FT-IR spectra of the samples are
shown in Figure 6. The IR band at 1450 cm−1 is the
adsorption peak of pyridine on Lewis acidic centers, the
band at 1490 cm−1 corresponds to the interaction of pyri-
acid sites exist in the mixed crystal form titania supported
catalysts of 5%Ru/p-TiO2, 5%Ru/a-r-TiO2 and 5%Ru/a-b-
TiO2, the different acidic center may have influence on the
catalytic performance.
The NH3-TPD results of the samples are given in
Figure 7. Compared with the mixed crystal form titania
supported catalysts, the single crystal form titania sup-
dine with Lewis and Brønsted acid sites, and the band at
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
ported catalysts presents cuspidal NH3 desorption peak and
possesses relatively less acidic centers.
1540 cm−1 is perceived as the adsorption peak of pyridine
Copyright: American Scientific Publishers
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on Brønsted acid centers. The results of the pyridine FT-IR
spectra indicate that the Brønsted acid centers predominate
in the anatase titania support while brookite titania support
possesses more Lewis acidic centers, and the acidic center
decreases when 5%Ru/r-TiO2 was calcined at higher tem-
perature. Both the Lewis acidic centers and the Brønsted
The scanning electron microscope (SEM) images of
the samples are shown in Figure 8. 5%Ru/a-TiO2 and
5%Ru/b-TiO2 show obvious lump and flake structure,
and 5%Ru/r-TiO2 calcined at higher temperature presents
coral structure. It can be seen form Figures 8(d)–(f)
that 5%Ru/p-TiO2 particles conglomerate, but there
are no obvious conglomeration in 5%Ru/a-r-TiO2 and
Ru(101)
brookite TiO2
anatase TiO2 rutile TiO2
661
(f)
(f)
(e)
(d)
647
(e)
621
(d)
(c)
(b)
(a)
638
(c)
568
573
(b)
(a)
500
600
700
800
20
40
60
80
2θ(°)
Temperature(K)
Figure 5. X-ray diffraction (XRD) patterns of some catalysts.
(a) 5%Ru/a-TiO2 , (b) 5%Ru/b-TiO2, (c) 5%Ru/r-TiO2, (d) 5%Ru/p-TiO2 ,
(e) 5%Ru/a-r-TiO2 and (f) 5%Ru/a-b-TiO2 .
Figure 7. NH3-TPD of some catalysts. (a) 5%Ru/a-TiO2 , (b) 5%Ru/b-
TiO2, (c) 5%Ru/r-TiO2 , (d) 5%Ru/p-TiO2 , (e) 5%Ru/a-r-TiO2 and
(f) 5%Ru/a-b-TiO2 .
J. Nanosci. Nanotechnol. 18, 8426–8436, 2018
8431

Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Long et al.
(a)
(b)
(c)
1 µm
1 µm
1 µm
(e)
(d)
(f)
1 µm
1 µm
1 µm
Figure 8. The SEM images. (a) 5%Ru/a-TiO2 , (b) 5%Ru/b-TiO2 , (c) 5%Ru/r-TiO2, (d) 5%Ru/p-TiO2, (e) 5%Ru/a-r-TiO2 and (f) 5%Ru/a-b-TiO2 .
5%Ru/a-b-TiO2. The proportion of different crystal form
of titania support has influence on its morphological
structure.
properties.49ꢆ50 The particle size distribution of 5%Ru/a-
r-TiO2 is shown in Figure 10, and the Ru particle sizes
centered at 3–4 nm.
The TEM images of 5%Ru/a-r-TiO2 are shown in
Figure 9. It can be seen from Figure 9 that Ru particles
are shown better dispersion and are centered at 3–4 nm.
The X-ray photoelectron spectroscopic (XPS) spectra
are shown in Figure 11. The spectra are deconvolved to
resolve the respective contributions because the peaks of
Ti2p partly overlap with the peaks of Ru3p3/2. A compar-
ison of the XPS spectra of Figures 11(a) and (b) reveals
that there is not any peak of Ruꢉ+ in 5%Ru/a-b-TiO2
(Fig. 11(b)) while the peaks around 485.5 and 463.7 eV
in 5%Ru/a-r-TiO2 (Fig. 11(a)) are attributed to Ruꢉ+3p1/2
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
The crystal lattices of anatase titania and rutile titania are
Copyright: American Scientific Publishers
shown in Figure 9, and there exists clear intersectant lat-
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tice. It is worth mentioned that some Ru particles are
located at the boundary between anatase titania and rutile
titania, which are defined as Ruꢉ+ and may show different
Figure 9. TEM images of 5%Ru/a-r-TiO2 catalyst.
8432
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Long et al.
Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Table IV. The deconvolution results of the Ru3p spectra.
50
Peak
position
(eV)
Integral
percentage
(%)b
FWHM
(eV)a
40
30
20
10
Catalyst
Peak
5%Ru/a-r-TiO2
Ru0 3p1/2
Ru0 3p3/2
Ruꢉ+ 3p1/2
Ruꢉ+ 3p3/2
Ru0 3p1/2
Ru0 3p3/2
483.3
461.1
485.5
463.7
483.3
461.1
2.83
2.87
2.94
2.96
3.12
3.11
30ꢁ7
56ꢁ3
6ꢁ1
6ꢁ9
34ꢁ6
65ꢁ4
5%Ru/a-b-TiO2
Notes: aThe full width at half maximum of the peak. bThe percentage of the integral
of each peak to the sum of the integrals of all the fitted Ru peaks.
0
1
2
3
4
5
6
crystal form titania and the guaiacol conversion increases
with the increment of the loading amount of Ru. When
the loading amount of Ru metal is greater than 5 wt.%,
the selectivity to cyclohexanol shows a decreasing trend
because more cyclohexanol can be transformed to cyclo-
hexane under such condition. Hence, the suitable loading
amount of Ru metal is 5 wt.%.
Particle Size(nm)
Figure 10. Particle size distribution of 5%Ru/a-r-TiO2 catalyst.
and Ruꢉ+3p3/2. Moreover, the titania satellite peak exists
both in 5%/a-b-TiO2 and 5%Ru/a-r-TiO2.51ꢆ52
The fitting results with regard to Ru are displayed in
Table IV. The peak around 483.3 eV is attributed to the
Ru03p1/2 spectral peak and the peak around 461.1 eV is
ascribed to the Ru03p3/2 spectral peak. There are only
Ru03p1/2 and Ru03p3/2 peaks in 5%Ru/a-b-TiO2. However,
besides Ru03p1/2 and Ru03p3/2 peaks, there are Ruꢉ+3p1/2
and Ruꢉ+3p3/2 peaks around 485.5 and 463.7 eV in
5%Ru/a-r-TiO2, and the integral percentages are 6.1% and
6.9%, respectively.
In general, mixed crystal form titania supported cata-
lysts show better catalytic performance than that of sin-
gle crystalline titania supported catalysts, moreover, it can
be seen from Table V that 5%Ru/a-r-TiO2 gives the best
catalytic performance of 95.33% conversion of guaiacol
and 79.23% selectivity to cyclohexanol. Compared with
other catalysts, 5%Ru/a-r-TiO2 presents higher BET sur-
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
face area, better dispersion of Ru particles with smaller
Copyright: American Scientific Publishers
particle size of 3–4 nm, more acidic centers, and more
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Ruꢉ+ located at the boundary between anatase titania and
rutile titania.
3.2. Catalytic Performance
Figure 12 shows the guaiacol conversion and product
selectivity over Ru supported on different crystal form
titania, the effects of the loading amount of Ru between
3 wt.% to 6 wt.% are tested. By comparing the catalytic
performance over Ru supported catalysts, one can find
that the catalytic performance is affected by the different
Besides cyclohexanol, the products of guaiacol
hydrodeoxygenation include cyclohexane, benzene, cyclo-
hexanone, phenol and 1,2-cyclohexanediol. Curve (h) in
Figure 12 refers to the selectivity to the products of others,
including anisole, catechol, toluene, xylene, dimethoxy-
benzene, methlguaiacol and methoxy cyclohexanol.
Effect of the reaction time on the hydrodeoxygenation
of guaiacol is shown in Figure 13. It can be seen that the
conversion of guaiacol gradually increases with the pro-
longed reaction time, while the selectivity to cyclohexanol
increases when the reaction time is less than 3 hours and
decrease apparently after 3 h. Hence, the suitable reaction
time for guaiacol hydrodeoxygenation over 5%Ru/a-r-TiO2
catalyst under 473 K and 2.0 MPa is 3 h.
Ti2p
3/2
Ru3p3/2
Ti2p1/2
Ru3p1/2
Ti satellite
(b)
(a)
Ti2p3/2
Ru3p3/2
3.3. The Possible Reaction Path
Ruδ+3p3/2
Ti 2p1/2
On the basis of the results in this work and some
literatures,48ꢆ49 the possible reaction path for guaia-
col hydrodeoxygenation over 5%Ru/TiO2 was shown in
Scheme 1. Guaiacol hydrodeoxygenation is a complex pro-
cess, cyclohexanol and cyclohexane can be obtained in
this reaction. There exist some routes to the product of
cyclohexanol, and cyclohexane is the product of the excess
hydrogenolysis process.
Ruδ+3p1/2
Ru3p1/2
Ti satellite
490
480
470
460
Binding Energy (eV)
Figure 11. The Ru3p and Ti2p spectra of (a) 5%Ru/a-r-TiO2 and
(b) 5%Ru/a-b-TiO2 .
J. Nanosci. Nanotechnol. 18, 8426–8436, 2018
8433

Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Long et al.
(A)
(B) 100
100
80
60
40
20
0
x%Ru/a-TiO2
x%Ru/b-TiO2
(a)
(b)
(a)
80
60
40
20
0
(b)
(h)
(h)
(c)
(f)
(d)
(c)
(e)
(g)
(d)
(f)
(e)
(g)
3
4
5
6
3
4
5
6
Loading of Ru metal (wt%)
Loading of Ru metal (wt%)
(C)
(D)
100
80
100
80
60
40
20
0
x%Ru/p-TiO2
x%Ru/r-TiO2
(a)
(a)
(b)
60
(b)
40
20
(h)
(h)
(e)
(c)
(c)
(f)
(d)
(d)
(f)
(e)
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
(g)
0
(g)
Copyright: American Scientific Publishers
Delive6red by Ingenta3
3
4
5
4
5
6
Loading of Ru metal (wt%)
Loading of Ru metal (wt%)
(E)
(F)
100
80
60
40
20
0
100
80
60
40
20
0
x%Ru/a-b-TiO2
x%Ru/a-r-TiO2
(a)
(b)
(a)
(b)
(h)
(h)
(c)
(g)
(c)
(f)
(g)
(e)
(d)
(e)
(d)
3
(f)
3
4
5
6
4
5
6
Loading of Ru metal (wt%)
Loading of Ru metal (wt%)
Figure 12. The catalytic performance under the loading amount of Ru metal. (A) x%Ru/a-TiO2, (B) x%Ru/b-TiO2 , (C) x%Ru/r-TiO2, (D) x%Ru/p-
TiO2, (E) x%Ru/a-r-TiO2 , and (F) x%Ru/a-b-TiO2 . (a) conversion, (b) cyclohexanol, (c) 1,2-cyclohexanediol, (d) cyclohexanone, (e) benzene, (f) cyclo-
hexane, (g) phenol, (h) others. Reaction conditions: 0.2 g of catalyst, temperature 473 K, H2 pressure 2.0 MPa, stirring rate 400 rpm and time 3 h.
In this work, we have found that benzene hydro-
genation in guaiacol hydrodeoxygenation prefers to
take place and demethylation process inevitably occurs
in this reaction, this is also in accordance with
the literatures.46ꢆ53ꢆ54 It can be seen from Scheme 1
that guaiacol can be hydrogenated to phenol, cate-
chol, 2-methoxy cyclohexanol and 2-methoxyclohexanone
which have been testified by GC-MS, and these inter-
mediates can be further transformed to cyclohexanol and
cyclohexane.
8434
J. Nanosci. Nanotechnol. 18, 8426–8436, 2018

Long et al.
Different Crystal Form Titania Supported Ruthenium Nanoparticles for Liquid Phase Hydrodeoxygenation of Guaiacol
Table V. Results of guaiacol hydrodeoxygenation.
Si(%)
Catalyst
wGua (%)
Cyclohexane
Benzene
Cyclohexanol
Cyclohexanone
Phenol
1,2-cyclohexanediol
Othersa
5%Ru/a-TiO2
5%Ru/b-TiO2
5%Ru/r-TiO2
5%Ru/p-TiO2
5%Ru/a-r-TiO2
5%Ru/a-b-TiO2
91.89
87.13
55.33
94.78
95.33
87.32
3.52
2.76
3.43
5.82
3.10
5.87
1.32
1.87
2.70
1.04
3.12
3.04
61.09
56.73
70.05
68.66
79.23
68.97
8.23
1.44
2.83
3.17
2.31
3.24
1.08
0.82
3.62
0.37
0.41
0.92
16ꢁ54
21ꢁ33
8ꢁ32
14ꢁ33
7ꢁ10
8.22
15.05
9.05
6.61
4.73
9.26
8ꢁ70
Notes: aThe others contain: anisole, catechol, toluene, xylene, dimethoxybenzene, methlguaiacol and methoxy cyclohexanol. Reaction conditions: 0.2 g of catalyst, temperature
473 K, H2 pressure 2.0 MPa, stirring rate 400 rpm and time 3 h.
100
SEM, HRTEM and XPS. The results showed that the cat-
alytic performance was affected by the different crystal
(a)
form titania support, and 5%-Ru/a-r-TiO2 presented higher
80
BET surface area, better dispersion of Ru particles with
smaller particle size of 3–4 nm, more acidic centers, and
(b)
60
more Ruꢉ+ located at the boundary between anatase titania
and rutile titania. Hence, it was found that 5%Ru/a-r-TiO2
gave the best catalytic performance of 95.33% conversion
40
of guaiacol and 79.23% selectivity to cyclohexanol, other
products mainly included cyclohexane, benzene, cyclohex-
anone and 1,2-cyclohexanediol. Finally, a possible reaction
20
(h)
(c)
(d)
(f)
(g)
path for guaiacol hydrodeoxygenation was proposed based
on this work and some literatures.
0
(e)
0
1
2
3
4
Acknowledgment: This work was supported by NSFC
Time (h)
IP: 185.250.42.110 On: Mon, 17 Sep 2018 13:59:01
(U1662127), Project of Hunan province Science and
Copyright: American Scientific Publishers
Figure 13. Effects of the reaction time over 5%Ru/a-r-TiO2 catalyst. (a)
Technology Department (2015GK1060) and Project of
Education Department of Hunan Province (17A209),
and Collaborative Innovation Center of New Chemical
Technologies for Environmental Benignity and Efficient
Resource Utilization.
Delivered by Ingenta
conversion, (b) cyclohexanol, (c) 1,2-cyclohexanediol, (d) cyclohexanone,
(e) benzene, (f) cyclohexane, (g) phenol, (h) others. Reaction conditions:
0.2 g of catalyst, temperature 473 K, H2 pressure 2.0 MPa, stirring rate
400 rpm.
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J. Nanosci. Nanotechnol. 18, 8426–8436, 2018
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