Deoxyalkylation of guaiacol using haggite structured V4O6(OH)4

Article abstract of DOI:10.1039/c9cy00024k

When V₂O₅ is used for the deoxygenation of guaiacol in methanol, it is reduced in situ to haggite structured V₄O₆(OH)₄. Guaiacol prevents further reduction of the haggite phase in methanol and haggite catalyzes the partial deoxygenation of guaiacol. Haggite is a metastable redox catalyst for the deoxygenation of guaiacol, which follows the reverse Mars-van Krevelen mechanism. In addition, haggite is also a Lewis acid catalyst and catalyzes the alkylation of guaiacol with methanol as the alkylation reagent. The main products of the guaiacol deoxyalkylation are 2,6-dimethylphenol, 2-methoxy-6-methylphenol, 2,4,6-trimethylphenol, 2,3,6-trimethylphenol, 2,3,5,6-tetramethylphenol and 6-methyl-2-tert-butylphenol. Oligomerization takes place during the reaction but it is reversible. When the reaction is performed at 300 °C for 6 h, the 83.5% total selectivity for alkylphenols is achieved with a 99.0% conversion.

Full text of DOI:10.1039/c9cy00024k

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: F. Yan, Z. Wen, K.
Wu, K. Cui, F. Mai, Z. Ma, Y. Sang, Y. Bai, H. Chen and Y. Li, Catal. Sci. Technol., 2019, DOI:
10.1039/C9CY00024K.
This is an Accepted Manuscript, which has been through the
Volume 6 Number 1 7 January 2016 Pages 1–308
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
Accepted Manuscripts are published online shortly after
www.rsc.org/catalysis
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
ISSN 2044-4753
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/catalysis

Page 1 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Deoxyalkylation of Guaiacol with Catalysis of Haggite Structured
V4O6(OH)4
Fei Yan,[b] Zhe Wen,[b] Kai Wu,[b] Kai Cui,[b] Fuhang Mai,[b] Zewei Ma,[b] Yushuai
Sang,[b] Yunfei Bai,[b] Hong Chen [a] and Yongdan Li *[b,c]
[a] School of Environmental Science and Engineering, Tianjin University, Tianjin
300072, China
[b] State Key Laboratory of Chemical Engineering (Tianjin University), Tianjin Key
Laboratory of Applied Catalysis Science and Technology, School of Chemical
Engineering, Tianjin University, Collaborative Innovation Center of Chemical Science
and Engineering (Tianjin), Tianjin, 300072, China
[c] Department of Chemical and Metallurgical Engineering, School of Chemical
Engineering, Aalto University, Kemistintie 1, Espoo, P.O. Box 16100, FI-00076 Aalto,
Finland
Abstract: When V2O5 is used for the deoxygentaion of guaiacol in methanol, it is reduced
in-situ to Haggite structured V4O6(OH)4. Guaiacol prevents the further reduction of
Haggite phase in methanol and Haggite also catalyzes the partial deoxygenation of
guaiacol. Haggite phase is a metastable redox catalyst for the deoxygenation of guaiacol.
The deoxygenation of guaiacol follows the reverse Mars-van Krevelen mechanism. In
addition, Haggite is also a Lewis acid catalyst and catalyzes the alkylation of guaiacol
with methanol as the alkylation reagent. The main products of guaiacol are 2,6-
 All correspondence should be addressed to Hong Chen. Email: chenhong_0405@tju.edu.cn; Tel: +86-22-27409405
1

Catalysis Science & Technology
Page 2 of 37
View Article Online
DOI: 10.1039/C9CY00024K
dimethylphenol, 2-methoxy-6-methylphenol, 2,4,6-trimethylphenol, 2,3,6-trimethylphenol,
2,3,5,6-tetramethylphenol and 2-methyl-6-tert-butylphenol. Oligomerization happens
during the reaction but is reversible. When the reaction is carried out at 300 oC for 6 h,
an 83.5% total selectivity to alkylphenols was achieved with a 99.0% conversion.
Keywords: Catalytic deoxygenation • Guaiacol • Haggite • Metastable catalyst •
Vanadium oxide
1. Introduction
Fast pyrolysis of lignocellulosic biomass produces bio-oil containing phenols substituted
with methoxyl, aldehyde and alkyl groups.1-3 Catalytic depolymerization of lignin in
organic solvents also generates substituted phenols.4, 5 For instance, catalytic
depolymerization of Kraft lignin with Mo-based catalysts in ethanol produces five sorts
of products including esters, alcohols, arenes, phenols and benzyl alcohols with high
yields.6-10 Guaiacol is an important product in the aforementioned lignin
depolymerization reactions and still needs further transformation before utilization.11
Conventional hydrotreating catalysts can convert guaiacol to products with lower oxygen
content in the presence of H2 but always causes undesirable saturation of benzene ring.12-
17 For example, Bui et al.12 carried out the hydrodeoxygenation (HDO) of guaiacol with
unsupported or γ-Al2O3 supported MoS2 and CoMoS at 300 oC under 4 MPa H2
pressure. When the HDO conversion is 13%, the total yields of cyclohexene and
cyclohexane are about 12%, 7%, 10% and 5% for MoS2, MoS2/γ-Al2O3, CoMoS, and
CoMoS/γ-Al2O3, respectively, and toxic H2S was continuously supplied to maintain the
2

Page 3 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
catalyst in the sulfided state during the experiments. Lee et al.14 used Rh/SiO2-Al2O3 and
Ru/SiO2-Al2O3 for the HDO of guaiacol at 250 oC for 1 h under 40 bar H2 pressure, and
the yields of cyclohexane are 57% and 60% for the two catalysts. Bykova et al.15 used a
series of Ni-based catalysts for guaiacol HDO at 320 oC under 17 MPa H2 and the main
products are cyclohexane, 1-methylcyclohexane-1,2-diol and cyclohexanone. Ishikawa et
al.17 reported that Ru–MnOx/C catalyzed the HDO of guaiacol at 160 oC under 1.5 MPa
H2 pressure and the yield of cyclohexanol was 81%. In comparison, a number of recently
reported catalysts catalyze the deoxygenation of guaiacol without benzene ring saturation.
For example, guaiacol was deoxygenated into phenol on a V2O5/Al2O3 catalyst with α-
terpinene as the hydrogen donor.18 Prasomsri et al.19 demonstrated that MoO3 catalyzed
the HDO of guaiacol in H2, and the major products are benzene and phenol. We reported
that MoC1-x/AC and MoO3 converted guaiacol to alkylphenols in alcohol solvents
without benzene ring saturation.20, 21 The major products of MoC1-x/AC catalyzed
guaiacol deoxygenation in ethanol are phenol and phenols substituted with ethyl and
isopropyl. The major products of MoO3 catalyzed guaiacol deoxygenation in ethanol are
mono- and di-ethylphenol, di- and tri-isopropylphenol, and di-butylphenols.
Haggite is a rare vanadium mineral found in the 1950s and its chemical formula has been
described as V2O2(OH)3 for about half a century since then.22 Due to the lack of a
synthetic method, its property information only came from its mineral sample until the
work of Wu et al.23 and Besnardiere et al.24 Wu et al. reported a multi-step method to
prepare Haggite and studied its electrical properties. They corrected its chemical formula
to V4O6(OH)4 in which all vanadium was V4+. Later on, Besnardiere et al. reported a 4.5-
day aqueous method to prepare Haggite and studied its electrical properties. Recently, we
3

Catalysis Science & Technology
Page 4 of 37
View Article Online
DOI: 10.1039/C9CY00024K
reported that Haggite was easily prepared by heating V2O5 in guaiacol-methanol
solution.25 In this reaction, methanol reduces V2O5 to Haggite while guaiacol protects
Haggite from being over-reduced to V2O3. Guaiacol is an oxidant for Haggite and is
deoxygenated by Haggite. However, the detailed information about the conversion of
guaiacol has not been reported.
Here, we report that Haggite catalyzes the deoxygenation of guaiacol via the reverse
Mars–van Krevelen mechanism without external H2. No benzene ring saturation is
observed in the reaction. The major products are 2,6-dimethylphenol, 2,3,6-
trimethylphenol, 2,3,5,6-tetramethylphenol and 6-methyl-2-tert-butylphenol. Among
them, 2,6-dimethylphenol is used to prepare insulating material.26 2,3,6-trimethylphenol
can be aerobically oxidized to trimethyl-1,4-benzoquinone, a key intermediate for
industrial production of vitamin E.27
2. Experimental
2.1. Materials
AR reagent grade chemicals and solvents including guaiacol, methanol, catechol, anisole,
phenol, and diphenyl ether were purchased from Guangfu Inc. Divanadium pentaoxide
were purchased from Fangzheng Inc. Divanadium trioxide were purchased from Strem
Chemicals, Inc.
2.2. Catalyst activity measurements
The reactions were carried out in an autoclave (Parr Instruments, 300 mL). In a typical
experiment, the reactor was loaded with catalyst (0.5 g), substrate (1 g), methanol (60
4

Page 5 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
mL), sealed and purged with N2 for five times. The reactor was heated to the reaction
temperature (240–300 °C) within 1.5 h and kept at this temperature for the prescribed
reaction time with stirring at 500 rpm. The reaction time was denoted as 0 h when the
prescribed reaction temperature was reached. After the reaction, the reactor was cooled
down by immersing it into cold-water.
The post-reaction liquid and the spent catalyst were separated by filtration. The liquid
mixture was analyzed on an Agilent Technologies 6890N GC equipped with a HP-5 MS
capillary column (Agilent, 30 m × 0.25 mm × 0.25 μm) and an FID detector. The organic
products are quantified with anisole as the GC internal standard and the correction factors
are calculated according to the efficient carbon number method. Note: when the substrate
was anisole, benzene was chosen as the internal standard. The GC parameters used for
analysis were as follows: inlet temperature 280 oC, detector temperature 300 oC, split
ratio 1:50. The oven temperature program was set from an initial temperature of 45 oC to
a final temperature of 250 oC at 10 oC·min−1, and then held at the final temperature for 2
min. Products were identified using a mass selective detector (MSD, Agilent
Technologies, model 5973). The fragmentation pattern acquired on the MS was
compared to those in the NIST Mass Spectral Library to identify the structure of each
product.
Substrate conversion, mass balance, product yield and overall yield of alkylphenols were
calculated according to Equations (1), (2), (3) and (4). The selectivities of products are
calculated according to Equation (5). Relative quantities of methyl, ethyl, propyl and tert-
butyl in the products of guaiacol are defined as Equations (6), (7), (8) and (9). In these
5

Catalysis Science & Technology
Page 6 of 37
View Article Online
DOI: 10.1039/C9CY00024K
equations, n represents the amount of the species in moles. These values were determined
by averaging the data measured in three times.
푖푛푖푡푖푎푙 푠푢푏푠푡푟푎푡푒 ― 푛푓푖푛푎푙 푠푢푏푠푡푟푎푡푒
Conversion = 푛
× 100%
(1)
푛푖푛푖푡푖푎푙 푠푢푏푠푡푟푎푡푒
∑
+
푛푝푟표푑푢푐푡 푖
푀푎푠푠 푏푎푙푎푛푐푒 = 푛
× 100%
푓푖푛푎푙 푠푢푏푠푡 푟푎푡푒
(2)
푛푖푛푖푡푖푎푙 푠푢푏푠푡푟푎푡푒
푛푝푟표푑푢푐푡 푖
(3)
푌푖푒푙푑푖 =
× 100%
푛푖푛푖푡푖푎푙 푠푢푏푠푡푟푎푡푒
∑
(4)
푂푣푒푟푎푙푙 푦푖푒푙푑 표푓 푎푙푘푦푙푝ℎ푒푛표푙푠 = 푖 = 푎푙푘푦푙푝ℎ푒푛표푙푌푖푒푙푑푖
푛푝푟표푑푢푐푡 푖
(5)
푆푒푙푒푐푡푖푣푖푡푦푝푟표푑푢푐푡 푖
=
× 100%
푛푖푛푖푡푖푎푙 푠푢푏푠푡푟푎푡푒 ― 푛푓푖푛푎푙 푠푢푏푠푡푟푎푡푒
푅푒푙푎푡푖푣푒 푞푢푎푛푡푖푡푦 표푓 푚푒푡ℎ푦푙 푖푛 푝푟표푑푢푐푡푠 =
푖 = 푝푟표푑푢푐푡푁푢푚푏푒푟 표푓 푚푒푡ℎ푦푙 푖푛 푖 ∗ 푌푖푒푙푑푖
∑
(6)
푅푒푙푎푡푖푣푒 푞푢푎푛푡푖푡푦 표푓 푒푡ℎ푦푙 푖푛 푝푟표푑푢푐푡푠 = 1 ∗ 푌푖푒푙푑4 ― 푒푡ℎ푦푙 ― 2 ― 푚푒푡ℎ표푥푦푝ℎ푒푛표푙 +1 ∗
(7)
푌푖푒푙푑2 ― 푒푡ℎ푦푙 ― 5 ― 푝푟표푝푦푙푝ℎ푒푛표푙
(8)
푅푒푙푎푡푖푣푒 푞푢푎푛푡푖푡푦 표푓 푝푟표푝푦푙 푖푛 푝푟표푑푢푐푡푠 = 1 ∗ 푌푖푒푙푑2 ― 푒푡ℎ푦푙 ― 5 ― 푝푟표푝푦푙푝ℎ푒푛표푙
푅푒푙푎푡푖푣푒 푞푢푎푛푡푖푡푦 표푓 푡푒푟푡 ‒ 푏푢푡푦푙 푖푛 푝푟표푑푢푐푡푠 = 1 ∗
(9)
푌푖푒푙푑6 ― 푚푒푡ℎ푦푙 ― 2 ― 푡푒푟푡 ― 푏푢푡푦푙푝ℎ푒푛표푙
2.3. Characterization
X-ray diffraction (XRD) patterns were obtained at room temperature using a Rigaku
D/max 2500 v/pc instrument (Rigaku Corp. Japan) with Cu Kα radiation, 40 kV and 200
mA, at a scanning rate of 6 o/ min. H2-TPR (temperature programmed reduction) was
carried out on an AutoChem II 2920 instrument (Micromeritics). About 0.1 g sample was
6

Page 7 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
preheated at 300 oC for 2 h in He flow (50 mL/min). After cooling to 50 oC, the sample
was exposed to 10% H2/Ar flow (50 mL/min) for 0.5 h. Then, the sample was heated to
680 oC at a heating rate of 8 oC/min in 10% H2/Ar flow (50 mL/min). The surface
morphology of materials was observed with a Hitachi S-4800 scanning electron
microscope (SEM) and a JEOL JSM-6301F SEM.To analyse the V-2p state of the spent
catalyst, X-ray photoelectron spectroscopy (XPS) was recorded using a PHI1600 XPS
system with Al-Kα radiation. An aliquot of liquid product was dried at 50 oC to remove
solvent and then some water was added to dissolve the residue with the assistance of
ultrasonic. Then the solution is analyzed with ICP-OES to determine the concentration of
leaching vanadium.
Pyridine adsorption infrared spectra (Py-IR) were recorded with a Nicolet 380 FT-IR
apparatus (Thermo Fisher Scientific). The sample was pressed into a self-supporting
wafer of 13 mg, and then was degassed in vacuum at 350 oC for 1 h. Then the sample was
cooled down to room temperature and the background spectrum was recorded. After that,
the sample was exposed to pyridine vapor at 150 oC for 30 min. The sample was then
treated in vacuum at 150 oC for 30 min, and the Py-IR spectrum of 150 oC was recorded
after the sample was cooled down to room temperature; the spectra of 200 oC and 350 oC
were recorded after vacuum treatment at 200 oC and 300 oC and cooling down to room
temperature. NH3-TPD (temperature programmed desorption) was carried out on an
AutoChem II 2920 instrument (Micromeritics). About 0.1 g sample was preheated at 300
oC for 2 h in He flow (50 mL/min). After cooling to 50 oC, the sample was exposed to 10%
NH3/He flow (50 mL/min) for 1 h. Then, the sample was left in He flow (50 mL/min) for
7

Catalysis Science & Technology
Page 8 of 37
View Article Online
DOI: 10.1039/C9CY00024K
1 h. Finally, the desorbed NH3 was monitored with a TCD when the sample was heated to
600 oC at a heating rate of 10 oC/min in He flow (50 mL/min).
3. Results
3.1. Reduction of V2O5 in methanol
We heated V2O5 in methanol to see whether they react with each other. The resultant
solid was analysed with X-ray diffraction (XRD) and the patterns are presented in Figure
1. When V2O5 is heated in methanol for 0 h, the resultant solid contains both Haggite
structured V4O6(OH)4 (PDF #29-1380), a vanadium (IV) species, and V2O3 (PDF #34-
0187). When V2O5 is heated in methanol for 1.5 h, it is completely reduced to V2O3.
Therefore, Haggite is the intermediate of the reduction from V2O5 to V2O3.
The H2-TPR pattern of V2O5 shows that the consumption of H2 starts around 400 oC and
has two peaks at 635 oC and 671 oC (Figure 2).
3.2. Guaiacol conversion catalyzed by V2O5 in methanol
3.2.1. Effect of temperature on guaiacol conversion
The effect of temperature on guaiacol conversion is illustrated in Figure 3. As
temperature increases, the conversion increases from 47.6% (at 240 oC) to 98.7% (at 280
oC) and then stays constant. Meanwhile, the mass balance increases from 55.4% to 97.4%.
The major products are 2,6-dimethylphenol (2), 2-methoxy-6-methylphenol (5), 2,4,6-
trimethylphenol (6), 2,3,6-trimethylphenol (8), 2,3,5,6-tetramethylphenol (11) and 6-
methyl-2-tert-butylphenol (13). The yields of 2, 6, 8 increase throughout 0-6 h and their
maxima are 20.2%, 5.7% and 19.0%, respectively. The yields of 11, 13 increase from 240
8

Page 9 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
oC to 280 oC and then decrease, with the maxima being 22.9% and 15.2%, respectively.
The yield of 5 fluctuates with time. At 300 oC, the selectivities of 2, 5, 6, 8, 11 and 13 are
20.4%, 10.9%, 5.7%, 19.2%, 22.0% and 11.7% (totally 89.9%), respectively. In addition,
the colour of the liquid product gets clearer as the temperature increases from 240 oC to
300 oC.
3.2.2. Composition changes of the post-reaction solution with time
The effect of reaction time is examined at 280 oC and illustrated in Figure 4. 13 products
are quantified by GC. 9 out of them are alkylphenols. With time increasing, the
conversion of guaiacol increases gradually from 31.1% to 98.6% and then keeps stable.
The mass balance decreases during 0 h-1 h and then increases from 1 h to 6 h. The major
products are 2, 5, 6, 8, 11 and 13. The yields of 5 and 1 increase during 0 h-1.5 h and then
decrease from 1.5 h to 6 h, with the maxima being 14.4% and 2.4%, respectively. The
yields of 2 and 8 increase during 0 h-3 h and then go down from 3 h to 6 h, with the
maxima being 22.6% and 13.9%, respectively. Hence, the four compounds are the
intermediates of guaiacol conversion. The yields of 11and 13 keep increasing throughout
0 h-6 h with the maxima being 22.9% and 15.2%, respectively. The two compounds are
the terminal products in guaiacol conversion. The overall yield of alkylphenols is only
1.9% at 0 h, increases to 79.9% from 0 to 3 h and then remains constant. In fact, the
deoxygenation of guaiacol happens from 0 to 3 h. After 3 h, the main reaction is
alkylation.
At 3 h, the selectivities of 2, 5, 6, 8, 11 and 13 are 22.9%, 6.9%, 6.5%, 14.1%, 19.6% and
10.8% (totally 80.8%), respectively.
9

Catalysis Science & Technology
Page 10 of 37
View Article Online
DOI: 10.1039/C9CY00024K
There are four kinds of alkyls in the products of guaiacol, including methyl, ethyl, propyl
and tert-butyl. Their relative quantities are calculated based on the amount of initial
guaiacol, and are presented in Figure 5. These quantities keep increasing throughout 0-6
h, and follows the order, methyl ≫ tert-butyl ≫ ethyl > propyl. At 6 h, their relative
quantities are 199.6%, 15.2%, 3.5% and 2.4%, respectively.
Propanol and isobutanol are detected in the post-reaction liquids by GC-MS so they are
produced from methanol in the reaction. Ethanol is not observed in the post-reaction
liquid probably because its GC-MS peak is covered by the big methanol peak. As shown
in Figure 6, the mass of propanol keeps increasing throughout 0 h-6 h, with the maximum
being 3.5×10-3 g. The mass of isobutanol also shows an increasing trend, with the
maximum being 3.0×10-3 g. The mass of isobutanol is always higher than that of
propanol from 0 h to 5 h.
3.3. Reactions with possible intermediates of guaiacol and V2O5
The results with catechol or phenol as substrates and V2O5 as catalyst are listed in Table 1.
The results with guaiacol as substrate and V2O5 as catalyst is also listed for comparison.
Since V2O3 appears in the reaction of methanol and V2O5, we also carried out an
experiment with V2O3 as the catalyst.
As shown in Table 1, both guaiacol and catechol is completely converted, and their
products are the same, which indicates guaiacol and catechol have similar reaction
pathways. In both reactions, the major products are 2, 5, 6, 8, 11, 13. However, the yields
of 2, 5, 6, 8 are much lower for the reaction of catechol, and the mass balance of this
10

Page 11 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
reaction is pretty poor (only 59.7%). The liquid product of this reaction is also pretty
turbid. The two phenomena imply that serious oligomerization happens in this reaction.
After 6-hour reaction, phenol is totally converted to 6 products among which 2 is the
major product with an 89.1% selectivity.We tried to convert anisole with V2O5 as the
catalyst in methanol at 300 oC for 6 h, as it’s a possible intermediate in the deoxygenation
of guaiacol. However, this reaction only produces trace amount of 2-methyl-1-
methoxybenzene (yield<0.1%) with the conversion and mass balance being 1.7% and
98.3%, respectively. Since the products of phenol and anisole are quite different from
those of guaiacol, the two compounds are not the intermediates of guaiacol.
We also carried out a reaction with guaiacol as the substrate and V2O3 as the catalyst at
280 oC for 3 h. The conversion and mass balance of this reaction (68.5% and 40.7%) are
much lower than those of the reaction with V2O5 as the catalyst under the same
conditions (98.6% and 85.1%). 7 products are produced with very low yields and the
overall yield of alkylphenols is only 6.8% (74.9% for V2O5), which demonstrates the low
activity of V2O3.
3.4. Characterization
The XRD patterns of the catalyst samples both fresh and used are shown in Figure 7.
Fresh V2O5 shows a well-defined diffraction pattern of V2O5 (PDF#65-0131). The
catalysts used at 280 oC for 0 to 3 h are determined to be Haggite. The sample used at 280
oC for 6 h generates both the peaks of Haggite and V2O3. Fresh V2O3 and used V2O3
generate the same XRD pattern, which means V2O3 cannot be further reduced by
methanol.
11

Catalysis Science & Technology
Page 12 of 37
View Article Online
DOI: 10.1039/C9CY00024K
The SEM images of V2O5 both fresh and used are presented in Figure 8. Fresh V2O5 are
many flat blocks composed of a lot of layers (Figure 8a). However, the sizes of these
blocks are not uniform. The V2O5 heated in methanol at 280 oC for 0 h seems amorphous
(Figure 8b). The amorphous structure is consistent with its weak XRD signal (Figure 1).
The V2O5 heated in methanol at 280 oC for 1.5 h, i.e. V2O3, are uniform round flakes
around 220 nm (Figure 8c). Its regular structure is consistent with its strong XRD signal
(Figure 1). Figure 8a-c clearly shows the morphology transformation of the solid , when
it’s reduced from V2O5 to V2O3. Haggite obtained in guaiacol conversion reaction are
some uniform flowers around 1.5 µm composed of numerous curved flakes (Figure 8d).
The XPS result indicates that both V4+ and V3+ exist on the surface of Haggite (Figure 9).
The post-reaction liquid obtained from guaiacol conversionwas analysed with ESI-MS
(Figure 10). The result clearly shows that oligomers with m/z as high as 415 appears.
Figure 11 presents the Py-IR spectra of Haggite. IR peaks at 1446 and 1535 cm-1 are
caused by the vibration absorption of Pyridine adsorbed on Lewis and Brönsted acid sites,
respectively.28 The intensity of 1535 cm-1 peak is pretty weak, which indicates the
amount of Brönsted acid sites on Haggite is small. The 1446 cm-1 peak shows up from
150 oC to 350 oC and its intensity decreases with temperature increasing, which indicates
Haggite has both strong and weak Lewis acid sites. In total, Lewis acid sites are the major
acidity of Haggite and their acid strengths are different. The NH3-TPD pattern of Haggite
has a big NH3 desorption peak at 302 oC and a small shoulder peak at 430 oC (Figure 12),
which also indicates Haggite has both strong and weak acid sites.
3.5. Catalyst recycling and leaching
12

Page 13 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
The catalyst used in the guaiacol deoxyalkylation experiment at 280 oC for 6 h was
calcined in air at 500 oC for 3 h and reused in the same reaction, and the results are shown
in Figure 13. The converision of guaiacol fluctuates with recycling and is always higher
than 97%. The mass balance has a decreasing trend in the first 4 runs, while, in the 5th run,
the mass balance is a little higher than the 4th run. In total, the mass balance is always
higher than 80.9%. The overall yield of alkylphenols decreases slowly from 74.4% to
71.2% in the first 4 runs and increases a little in the 5th run. In the recycling reactions, the
results didn’t change significantly, so the catalyst can be reused.
The post-reaction liquid obtained at 300 oC was analyzed with ICP-OES. The vanadium
concentration of this solution is 2.49 mg/L which is equivalent to 0.04% loss of initial
V2O5. Hence, the leaching of catalyst is negligible.
4. Discussion
4.1. Reaction pathways of guaiacol
As mentioned in Section 3.2.2, 1, 2, 5, 8 are the intermediates and 11, 13 are the terminal
products in guaiacol conversion. Based on this info and the structures of products, we
propose the reaction pathways in Scheme 1. At first, guaiacol is alkylated to 5 by
methanol (Scheme 1a). 5 is then deoxygenated into 1. 1 is subsequently alkylated into
2,5-dimethylphenol (4) and 2. 4 is alkylated into 2,3,5-trimethylphenol (9) and 8. 2 is
further alkylated into 8 and 6. 8 and 9 are further alkylated into 11.
2-Methyl-1-propanol was detected in the post-reaction liquid of guaiacol conversion, so
13 is directly formed by the alkylation of 1 with 2-methyl-1-propanol (Scheme 1b).As
mentioned in Section 3.3, guaiacol and catechol have similar reaction pathways. It is
13

Catalysis Science & Technology
Page 14 of 37
View Article Online
DOI: 10.1039/C9CY00024K
likely that 5 and catechol are converted into 2-methylcatechol (15) that is then
dehydroxylated into o-cresol (Scheme 1c). The dehydroxylation is so rapid that 15 is not
detected by GC-MS.
At 280 oC, the colour of the post-reaction liquid obtained in guaiacol conversion gets
darker during 0 h-1 h and then gets clearer from 1 h to 6 h. On the other hand, the mass
balance decreases during 0 h-1 h and then increases from 1 h to 6 h (Figure 4). That is, a
better mass balance gives a clearer colour. We speculate that the darkness of the liquid is
due to the oligomers formed in the reaction which also lead to a poor mass balance. At
280 oC, the mass balance is the lowest at 1 h and then recovers with time elapsing (Figure
4). It is evident that oligomers form in the beginning of the reaction and are converted
back into monomers later on.
4.2. The active catalyst for guaiacol deoxygenation
As mentioned in Section 3.2.2 & 3.4, the deoxygenation of guaiacol mainly happens from
0-3 h when the solid is Haggite. Hence, Haggite is the active catalyst for guaiacol
deoxygenation instead of V2O5, which is different from the mechanism proposed by
Filley et al. for the gas-phase reaction.18 In fact, V2O5 is reduced to Haggite in the
heating-up process and then Haggite catalyzes the deoxygenation and alkylation of
guaiacol from 0-3 h. After 3 h, Haggite is further reduced to V2O3.25 The heating-up
process is the period for catalyst formation so the total yield of alkylphenols is only 1.9%
at 0 h because of the lack of catalyst. From 0 to 3 h, Haggite catalyzes the deoxygenation
and alkylation of guaiacol. After 3 h, Haggite still exists so the further alkylation of
alkylphenols still happens.
14

Page 15 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
As mentioned in Section 3.1, Haggite is not stable in methanol at 280 oC because of the
strong reducibility of methanol. However, it stays stable during 0 to 3 h in guaiacol
conversion reaction. In this period, Haggite catalyzes the deoxygenation of guaiacol so it
accepts oxygen from guaiacol and is oxidized. At the same time, Haggite is reduced by
methanol. The oxidizing effect of guaiacol offsets the reducing effect of methanol so
Haggite stays stable in this period. Pure methanol is not a stable environment for Haggite.
When guaiacol is present together with methanol, they form a stable environment for
Haggite. In this sense, Haggite is a metastable catalyst for guaiacol deoxygenation. In fact,
Haggite relies on the deoxygenation of guaiacol to stay stable in methanol and guaiacol
also relies on Haggite to deoxygenate.
Hence, we propose the mechanism for the transformation from V2O5 to V2O3 (Scheme
2).25 V2O5 is reduced to Haggite by methanol without the influence of guaiacol. Then the
surface of Haggite is further reduced by methanol. Consequently, some superficial lattice
oxygen atoms of Haggite are removed to oxidize methanol, and meanwhile the adjacent
vanadium(IV) is reduced to vanadium(III). That’s why both vanadium(IV) and
vanadium(III) are detected by XPS. Afterwards, guaiacol is deoxygenated at the oxygen
vacancy on the surface of Haggite and refills the vacancy. The adjacent vanadium(III) is
oxidized back to vanadium(IV) at the same time. Hence, the removal of superficial
oxygen atom from Haggtie by methanol and the deoxygenation of guaiacol at the oxygen
vacancy froms a cycle. In fact, the deoxygenation of guaiacol happens via the reverse
Mars-van Krevelen mechanism.29 The deoxygenation of guaiacol protects Haggite from
being over-reduced to V2O3 and meanwhile Haggite catalyzes the deoxygenation of
15

Catalysis Science & Technology
Page 16 of 37
View Article Online
DOI: 10.1039/C9CY00024K
guaiacol. Later on, when guaiacol is depleted, Haggtie is further reduced to V2O3 by
methanol.
4.3. Alkylation of products
As depicted in Section 3.2.2, propanol and isobutanol are detected in the post-reaction
liquid of guaiacol conversion. Methanol is the solvent of the reaction and its amount is
still far more than other components after reaction. These alcohols are the alkylation
reagents for guaiacol. As discussed in Section 3.4 based on the Py-IR spectra in Figure 11,
Haggite is a Lewis acid. The acid catalyzed alkylation of benzene ring with alcohol
follows the Friedel-Crafts alkylation mechanism.30 As shown in Scheme 3, methanol,
ethanol, propanol and isobutanol can be converted to methyl, ethyl, propyl and isobutyl
carbocations on the Lewis acid sites of Haggite. Later, isobutyl carbocation will
isomerize into tert-butyl carbocation spontaneously because tert-butyl carbocation is
much more stable than isobutyl carbocation. These carbocations react with aromatic rings
to form alkylated products and proton. Finally, proton reacts with Haggite to restore the
Lewis acid sites. The equilibrium constants of the reactions in Scheme 3a follow the
order, K5≫K4≈K3≈K2≫K1, because the stability of carbocations follows the order, tert-
butyl carbocation≫isobutyl carbocation≈propyl carbocation≈ethyl carbocation≫methyl
carbocation. Methanol is the solvent in the reaction and its initial mass is 47.5 g. Its
concentration is higher than that of isobutanol by four orders of magnitude (Figure 6).
+
However, K4K5≫K1. Therefore, [CH3 ] is higher than [t-Bu+] to a less significant extent
(equations 1&4 in Scheme 3a), and consequently the relative quantity of methyl in
products is higher than that of tert-butyl by only one order of magnitude (Figure 5). The
concentration of isobutanol is higher than that of propanol during 0-5 h (Figure 6) and
16

Page 17 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
+
K4K5>K3, so [t-Bu+] is higher than [CH3CH2CH2 ]. As a result, the relative quantity of
tert-butyl in products is higher than that of propyl (Figure 5).
5. Conclusions
In summary, Haggite is a metastable redox catalyst and a Lewis acid catalyst, and
catalyzes the deoxyalkylation of guaiacol to alkylphenols via the reverse Mars-van
Krevelen mechanism and the Friedel-Crafts reaction. In the redox, Haggite relies on the
deoxygenation of guaiacol to stay stable in methanol and guaiacol also relies on Haggite
to deoxygenate. That is, Haggite has a symbiotic relationship with the deoxygenation of
guaiacol. The main products of guaiacol are 2,6-dimethylphenol, 2-methoxy-6-
methylphenol, 2,4,6-trimethylphenol, 2,3,6-trimethylphenol, 2,3,5,6-tetramethylphenol
and 2-methyl-6-tert-butylphenol. When the reaction was performed at 300 oC for 6 h, the
total selectivity to the six products was 89.9%. Guaiacol is firstly methylated and then
deoxygenated into o-cresol which is then alkylated to other alkylphenols. No benzene
ring saturation happens during the reaction. The leaching of catalyst is negligible, and the
catalyst can be reused after simple calcination. In addition, this catalyst is only active for
the deoxyalkylation of guaiacol and catechol among the 5 substrate molecules tested.
Acknowledgements
The financial support from the Natural Science Foundation of China under Contract No.
21336008, 21808163 and 21690083, the Ministry of Science and Technology of China
under Contract No. 2011DFA41000 are gratefully acknowledged. This research was also
supported in part by the Program of Introducing Talents to the University Disciplines
17

Catalysis Science & Technology
Page 18 of 37
View Article Online
DOI: 10.1039/C9CY00024K
under File No. B06006 and the Program for Changjiang Scholars and Innovative
Research Teams in Universities under File No. IRT 0641.
References
1.
2.
3.
G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106, 4044-4098.
H. Wang, J. Male and Y. Wang, Acs. Catal., 2013, 3, 1047-1070.
J. Zakzeski, P. C. A. Bruijnincx, A. L. Jongerius and B. M. Weckhuysen, Chem. Rev., 2010,
110, 3552-3599.
4.
5.
6.
7.
8.
P. Ferrini and R. Rinaldi, Angew. Chem. Int. Ed., 2014, 53, 8634-8639.
X. Ma, Y. Tian, W. Hao, R. Ma and Y. Li, Appl. Catal. A-Gen., 2014, 481, 64-70.
R. Ma, W. Hao, X. Ma, Y. Tian and Y. Li, Angew. Chem. Int. Ed., 2014, 53, 7310-7315.
X. Ma, K. Cui, W. Hao, R. Ma, Y. Tian and Y. Li, Bioresour. Technol., 2015, 192, 17-22.
X. Ma, R. Ma, W. Hao, M. Chen, F. Yan, K. Cui, Y. Tian and Y. Li, Acs. Catal., 2015, 5, 4803-
4813.
9.
M. Chen, X. Ma, R. Ma, Z. Wen, F. Yan, K. Cui, H. Chen and Y. Li, Ind. Eng. Chem. Res.,
2017, 56, 14025-14033.
10.
11.
12.
13.
14.
15.
16.
17.
M. Chen, W. Hao, R. Ma, X. Ma, L. Yang, F. Yan, K. Cui, H. Chen and Y. Li, Catal. Today,
2017, 298, 9-15.
M. Shetty, K. Murugappan, T. Prasomsri, W. H. Green and Y. Roman-Leshkov, J. Catal.,
2015, 331, 86-97.
V. N. Bui, D. Laurenti, P. Afanasiev and C. Geantet, Appl. Catal. B-Environ., 2011, 101,
239-245.
V. N. Bui, D. Laurenti, P. Delichère and C. Geantet, Appl. Catal. B-Environ., 2011, 101,
246-255.
C. R. Lee, J. S. Yoon, Y.-W. Suh, J.-W. Choi, J.-M. Ha, D. J. Suh and Y.-K. Park, Catal.
Commun., 2012, 17, 54-58.
M. V. Bykova, D. Y. Ermakov, V. V. Kaichev, O. A. Bulavchenko, A. A. Saraev, M. Y.
Lebedev and V. A. Yakovlev, Appl. Catal. B-Environ., 2012, 113, 296-307.
Y.-K. Hong, D.-W. Lee, H.-J. Eom and K.-Y. Lee, Appl. Catal. B-Environ., 2014, 150-151,
438-445.
M. Ishikawa, M. Tamura, Y. Nakagawa and K. Tomishige, Appl. Catal. B-Environ., 2016,
182, 193-203.
18.
19.
J. Filley and C. Roth, J. Mol. Catal. A: Chem., 1999, 139, 245-252.
T. Prasomsri, M. Shetty, K. Murugappan and Y. Roman-Leshkov, Energ. Environ. Sci.,
2014, 7, 2660-2669.
20.
21.
R. Ma, K. Cui, L. Yang, X. Ma and Y. Li, Chem. Commun., 2015, 51, 10299-10301.
K. Cui, L. Yang, Z. Ma, F. Yan, K. Wu, Y. Sang, H. Chen and Y. Li, Appl. Catal. B-Environ.,
2017, 219, 592-602.
22.
23.
24.
H. T. Evans and M. E. Mrose, Acta Crystallogr., 1958, 11, 56-58.
C. Wu, J. Dai, X. Zhang, J. Yang and Y. Xie, J. Am. Chem. Soc., 2009, 131, 7218-7219.
J. Besnardiere, X. Petrissans, F. Ribot, V. Briois, C. Surcin, M. Morcrette, V. Buissette, T.
Le Mercier, S. Cassaignon and D. Portehault, Inorg. Chem., 2016, 55, 11502-11512.
F. Yan, Y. Bai, Y. Sang, L. Yu, K. Wu, K. Cui, Z. Wen, F. Mai, Z. Ma, H. Chen and Y. Li, Inorg.
Chem., 2018, 57, 8705-8708.
25.
18

Page 19 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
26.
Y. M. Chi, H. Tomoya, S. H. Wen, U. Mitsuru and C. Wen‐Chang, J. Polym. Sci., Part A:
Polym. Chem., 2016, 54, 3218-3223.
27.
28.
29.
30.
H. Sun, K. Harms and J. Sundermeyer, J. Am. Chem. Soc., 2004, 126, 9550-9551.
R. Ueda, T. Kusakari, K. Tomishige and K. Fujimoto, J. Catal., 2000, 194, 14-22.
P. Mars and D. W. van Krevelen, Chem. Eng. Sci., 1954, 3, 41-59.
T. Odedairo and S. Al-Khattaf, Catal. Today, 2013, 204, 73-84.
19

Catalysis Science & Technology
Page 20 of 37
View Article Online
DOI: 10.1039/C9CY00024K
Figure 1. XRD patterns of V2O5 heated in methanol for different time. Reaction conditions: 0.625
g V2O5, 75 mL methanol, 280 oC, 0 MPa N2. Note: The two XRD patterns have been reported in
another paper.25

Page 21 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Figure 2. H2-TPR result of V2O5.

Catalysis Science & Technology
Page 22 of 37
View Article Online
DOI: 10.1039/C9CY00024K
Figure 3. Results of guaiacol conversion in methanol at different temperatures. Reaction
conditions: 0.5 g V2O5, 1.0 g guaiacol, 60 mL methanol, 6 h.

Page 23 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Figure 4. The results of guaiacol conversion in methanol at 280 oC for different time. Reaction
conditions: 0.5 g V2O5, 1.0 g guaiacol, 60 mL methanol.

Catalysis Science & Technology
Page 24 of 37
View Article Online
DOI: 10.1039/C9CY00024K
Figure 5. Relative quantity of methyl, ethyl, propyl and tert-butyl in the products of guaiacol
conversion at different time. Reaction conditions: 0.5 g V2O5, 1.0 g guaiacol, 60 mL methanol,
280 oC.

Page 25 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Figure 6. The amounts of propanol and isobutanol in the post-reaction solutions at different
time. Reaction conditions: 0.5 g V2O5, 1.0 g guaiacol, 60 mL (i.e. 47.5 g) methanol, 280 oC.

Catalysis Science & Technology
Page 26 of 37
View Article Online
DOI: 10.1039/C9CY00024K
Table 1. The results of lignin model compounds conversion in methanol. [a]
Substrate
Product & Yield (%)
OH
OH
OH
OH
OH
OH
OH
O
O
O
O
Conv. 99.0%
M.B. 97.4%
1.0
20.2
1.0
0.9
10.8
19.0
1.4
OH
OH
OH
OH
OH
O
O
OH
5.7
1.4
0.6
21.8
1.1
11.6
OH
OH
OH
OH
OH
OH
OH
OH
O
O
O
Conv. 100.0%
M.B. 59.7%
0.4
6.4
0.2
0.3
2.9
7.5
1.2
OH
OH
OH
OH
OH
O
O
OH
3.0
0.6
0.5
18.7
1.1
16.4
OH
OH
OH
OH
OH
OH
O
Conv. 100.0%
M.B. 97.2%
0.4
3.6
OH
89.1
OH
0.5
OH
5.6
OH
0.8
OH
OH
OH
O
O
O
O
O
Conv. 68.5%
M.B. 40.7%
1.4
0.7
1.3
1.4
1.6
0.3
2.5
[a] Reaction conditions: 0.5 g V2O5, 1.0 g substrate, 60 mL methanol, 300 oC, 6 h. Note: the reaction conditions for the last reaction are 0.5
g V2O3, 1.0 g guaiacol, 60 mL methanol, 280 oC, 3 h; Conv.: conversion; M.B.: mass balance.

Page 27 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Figure 7. XRD patterns of V2O5 both fresh and used at 280 oC for different time as well as XRD
patterns of V2O3 both fresh and used at 280 oC for 3 h. Reaction conditions: 0.5 g catalyst, 1.0 g
guaiacol, 60 mL methanol. Note: The first five XRD patterns from the top have been reported in
another paper.25

Catalysis Science & Technology
Page 28 of 37
View Article Online
DOI: 10.1039/C9CY00024K
Figure 8. SEM images of (a) fresh V2O5, (b) V2O5 heated in methanol at 280 oC for 0 h, (c) V2O5
heated in methanol at 280 oC for 1.5 h, (d) V2O5 used in guaiacol conversion reaction at 280 oC
for 0 h.

Page 29 of 37
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY00024K
Figure 9. XPS of the V (2p) energy region of the used V2O5 sample. Reaction conditions: 0.5 g
V2O5, 1.0 g guaiacol, 60 mL methanol, 280 oC, 1 h. Note: this XPS result has been reported in
other form in another paper.25