Ruthenium-containing SBA-12 catalysts for anisole hydrodeoxygenation

Article abstract of DOI:10.1016/j.cattod.2020.03.006

Hexagonally ordered mesoporous silica SBA-12 catalysts containing various amounts of Ru (1 or 3 wt.percent) were obtained by wet impregnation. These catalysts were thoroughly characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM)

Full text of DOI:10.1016/j.cattod.2020.03.006

Journal Pre-proof
Ruthenium-containing SBA-12 catalysts for anisole hydrodeoxygenation
Agnieszka Feliczak-Guzik, Paulina Szczyglewska, Mietek Jaroniec,
Izabela Nowak
PII:
S0920-5861(19)30113-0
DOI:
https://doi.org/10.1016/j.cattod.2020.03.006
CATTOD 12719
Reference:
To appear in:
Catalysis Today
Received Date:
Revised Date:
Accepted Date:
12 June 2019
3 February 2020
4 March 2020
Please cite this article as: Feliczak-Guzik A, Szczyglewska P, Jaroniec M, Nowak I,
Ruthenium-containing SBA-12 catalysts for anisole hydrodeoxygenation, Catalysis Today
(2020), doi: https://doi.org/10.1016/j.cattod.2020.03.006
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Ruthenium-containing SBA-12 catalysts for anisole hydrodeoxygenation
1
1
2
1
Agnieszka Feliczak-Guzik, Paulina Szczyglewska, Mietek Jaroniec, Izabela Nowak
Authors
1Adam Mickiewicz University in Poznań, Faculty of Chemistry, Uniwersytetu Poznanskiego 8,
6
1-614 Poznan, Poland
2Kent State University, Department of Chemistry and Biochemistry, Kent Ohio 44242, USA
Corresponding author
Izabela Nowak
Adam Mickiewicz University in Poznań, Faculty of Chemistry, Uniwersytetu Poznanskiego 8,
6
1-614 Poznan, Poland
Email: nowakiza@amu.edu.pl
Graphical abstract
Highlights:




Synthesis of stable Ru-containing mesoporous materials.
High conversions in the hydrodeoxygenation of anisole.
Upgrading anisole, a product of thermal conversion of lignin.
Study of mechanism of the HDO reactions over RuSBA-12.
1

Abstract
Hexagonally ordered mesoporous silica SBA-12 catalysts containing various amounts of Ru (1
or 3 wt.%) were obtained by wet impregnation. These catalysts were thoroughly characterized
by X-ray diffraction (XRD), transmission electron microscopy (TEM), and low-temperature
nitrogen adsorption/desorption (N ads/des). Anisole conversion was measured over catalysts
2
at different process conditions, where the process temperature was 90-130 °C and the hydrogen
pressure – 25-60 bar. Prior the experiments the process was optimized, i.e., the amount of
catalyst used in the reaction and the time of reaction were adjusted. This study shows a
significant effect of hydrogen pressure and process temperature on the hydrodeoxygenation of
anisole, the conversion of which increased (16-100%) with both increasing parameters. For all
the catalysts studied, the highest selectivity was obtained to two main reaction products,
methoxycyclohexane and 1-methoxycyclohexene. Along with increasing conversion of anisole,
the selectivity to the main reaction product - methoxycyclohexane generally increased (65-
9
6%) reducing the amount of 1-methoxycyclohexene (0-27%).
Keywords
ordered mesoporous silica, biomass upgrading, biooil processing
1
. Introduction
Depletion of natural energy resources (crude oil, natural gas, solid fuels) has prompted
a great interest in the use of renewable energy sources, mainly biomass [1]. Increased interest
in the biomass conversion is not only because of the energy related reasons but also ecological
reasons, mainly the need to restrict the emission of greenhouse gases [2, 3]. Biomass composed
of cellulose, hemicellulose and lignin units [4, 5], thanks to its chemical decomposition and
processing abilities is a valuable raw material that can be processed into a number of useful
products, e.g., substitutes of crude oil fuels [6, 7]. This aspect is very important because at
present transport uses up to 1/5 of energy on the global scale [8, 9].
One of the technologies used for transformation of biomass is fast pyrolysis, which is
thermal decomposition of high-molecular chemical compounds to simpler components under
anaerobic conditions [10, 11]. At these conditions, the building blocks of biomass undergo
degradation leading to the formation of a liquid fraction known as biooil or pyrolytic oil [12].
2

It is a mixture of over 300 different chemical compounds containing a significant number of
oxygen atoms [13], mainly in the form of oxygen lignin derivatives, aldehydes (including
heterocyclic furfurals), alcohols, phenols, ketones, carboxylic acids or carbohydrates [6, 14].
Biooil has a high energy potential as it maintains up to 70% of the initial biomass energy [5].
However, it cannot be applied directly as a fuel because of a too high content of water (up to
2
5 wt.%) and oxygen (up to 40 wt.%), which finally results in a low calorific value [5, 9]. In
order to make its properties more resembling those of crude oil, biooil must be subjected to
physicochemical processing [15].
A promising pathway to get high quality hydrocarbon fuel from biooil is the catalytic
hydrodeoxygenation (HDO) [16-18]. This process is based on the reaction of chemical
compounds contained in biooil with gaseous hydrogen, under elevated pressure, elevated
temperature and in the presence of a catalyst. Under these conditions the reagents are
transformed to simpler compounds, mainly hydrocarbons [18, 19]. This process permits a
removal of oxygen atoms from chemical compounds of biooil but also leads to the saturation
of multiple bonds of the reagents, which improves the system stability. Finally, the process
brings a decrease in the O/C ratio at the simultaneous increase in the H/C ratio, which means
that the improved biooil, called a biofuel, can be used as a motor vehicle fuel [9]. The HDO
process is usually carried out at a temperature between 200 and 500 °C under hydrogen at a
pressure reaching 200 bar [20]. Under such conditions, the majority of chemical compounds
are able to convert into their deoxygenated analogues [6]. In the laboratory scale the mechanism
of HDO is studied using the so-called model chemical compounds that are identical to those
contained in biooil [21]. Very often anisole is selected for investigation because it contains an
isolated methoxyl group (-OCH
22-24].
High yield of HDO process depends on the catalyst which should by characterized by
3
) which is the most often met in the chemical structure of biooil
[
high activity even at lower pressure and temperature [21, 25]. The most effective catalysts for
this process are those with transition metal ions (Pt, Pd, Ru, Rh, Ir, Co, Ni) as the active
components because they show high activity in the processes involving hydrogen [26, 27].
Because of their high cost [28], they are usually deposited on supports in order to enlarge the
surface area of the active phase and improve the mechanical strength and thermal stability of
the system [29]. A particularly interesting group of supports are ordered mesoporous silicas
[
30-32], characterized by well-developed system of pores with diameters between 2 and 50 nm,
3
2
high pore volume (~0.7 cm /g) and large surface area reaching even 1000 m /g [29, 33]. Very
attractive silicas are those of SBA (Santa Barbara Amorphous) type materials because they are
3

non-toxic, possess ordered mesoporous structure with interconnected micropores in the
mesopore walls and can be easily synthesized by block copolymer soft templating [30, 34].
The best-known representative of the SBA class of materials is SBA-15 silica with two-
dimensionally ordered mesopores. Below are some examples from the literature where this
material was used as catalyst in the HDO reaction.
A very interesting silica from the SBA group is SBA-12, which has a hexagonal
distribution of channels with the p6 /mmc space group. The specific surface area of this silica
3
2
often exceeds 1000 m /g [35]. The pores of the SBA-12 material have a three-dimensional
architecture that essentially facilitates the transport of larger reagent molecules, which in turn
provides easier access to active sites. The material in question has not yet attracted much
attention , although there is a good chance that it will because, like the SBA-15 silica, it has
thick pore walls, thanks to which it is thermally and hydrothermally stable.
Catalytic systems based on mesoporous silicas have been explored by many authors in
hydrodeoxygenation of anisole. Yang et al. [36] have studied the mechanism of HDO of anisole
catalyzed by a catalyst having nickel atoms on SBA-15 type mesoporous silica. The process
was performed at 310 °C under hydrogen pressure of 30 bar for 6 h. The products formed in
large amounts at 100% anisole conversion were hexane (selectivity 26%), cyclohexane (30%)
and benzene (26%). Results of this experiment proved high activity of the catalyst used because
it was possible to obtain a high degree of deoxygenation and anisole hydrogenation.
Similar studies have been carried out by Sankaranarayanan et al. [5] who investigated
the catalytic activity of ordered mesoporous silica, specifically SBA-15 with deposited cobalt
atoms as the active phase. The process was performed at 220 °C under hydrogen pressure of 50
bar for 2 h. These authors achieved 99% anisole conversion to the following products:
methoxycyclohexane (selectivity 72%), cyclohexane (12%), cyclohexanone (1%) and
cyclohexene (0.5%). The catalytic system was also very active, although the highest selectivity
was achieved to methoxycyclohexane, to the compound with single bonds between carbon
atoms but still having oxygen in the structure. Although the results of hydrodeoxygenation of
chemical compounds of biooil are good, the search for catalytic systems capable of providing
high yields but at possibly lower temperatures and pressures is continued [26]. According to
literature, the HDO process is the most effective at elevated temperatures and pressures, but at
these conditions it is an energy consuming process, uneconomical from industrial viewpoint
[
37].
Previously only SBA-15 among the SBA-family materials was used as a support of the
HDO catalyst. Here we report data for hydrodeoxygenation of anisole over the ruthenium
4

catalyst deposited on SBA-12 silica at relatively low temperature (90-130 °C) and under low
pressure of gas hydrogen (25-60 bar). We studied the effect of the reaction time, the amount of
catalyst and the active phase loading on the conversion process. The impact of these parameters
on the degree of anisole conversion, types and amounts of the reaction products is discussed. It
is the first attempt of using SBA-12 silica with transition metal catalysts in the HDO conversion.
Such ordered mesoporous silica with symmetry group p6 /mmc can be of consideration when
3
outstanding stability and three-dimensional mesopore structure is desired for the proper
adsorption/diffusion necessary in heterogeneous catalysis. A comparison with other catalysts is
assessed.
2
2
. Experimental
.1. Synthesis of SBA-12 silica with deposited ruthenium
SBA-12 silica was synthesized by adding structure-directing agent BRIJ 76 surfactant
(Sigma Aldrich; 8 g) to a mixture of water (40 g) and 0.1M chloric acid (160 g) and stirring for
2
h. Then, 17.6 g of tetraethyl orthosilicate (TEOS, Fluka, 99% purity) was added and the
mixture was stirred for 20 h. After this time, the mixture was poured to PP bottles and placed
in a drying apparatus at 80 ºC for 24 h. The solid product was filtered, dried and calcined in
order to remove the template at 550 ºC for 6 h. The resulting silica was subjected to wet
impregnation in order to introduce different amounts of ruthenium to obtain catalysts with
different amount (wt.%) of Ru with respect to the mass of the support (the incremental dosage
was 0.5 wt.% up to maximum 3 wt.%, i.e., catalysts with 0.5; 1; 1.5; 2; 2.5 and 3 wt.% were
prepared). Ethanol solution of ruthenium(III) chloride was introduced dropwise to the dry SBA-
1
2 support in the amount sufficient to fill the pores and wet the external surface of particles.
The content of the beaker was stirred. The beaker was tightly closed with a polyolefin-paraffin
foil Parafilm® and left to rest for 24 h to allow penetration of the solution into the pores of
SBA-12. Afterwards, the foil was removed and the beaker was placed under fume hood at room
temperature until the entire solvent was evaporated under stirring the content from time to time.
Next, the catalysts were dried for 1 h at 30 ºC, 1 h at 40 ºC, and 18 h at 60 ºC, followed by
reduction in a tube furnace in hydrogen atmosphere. To remove air from the system argon of
3
N5.0 purity (Linde Gas Poland) (50 cm /min) was blown to the furnace, then hydrogen (50
3
cm /min) was introduced and after 0.5 h the furnace was switched into the heating mode. The
catalysts were reduced at 250 ºC for 3 h (the temperature was established based on the TPR
5

results). The catalysts studied were labelled as y RuSBA-12, where y is the wt.% content of
ruthenium in relation to the support.
2
.2. Hydrodeoxygenation of anisole
The process of anisole hydrodeoxygenation was carried out in a high-pressure reactor
(CAT 24 HEL) placed on a magnetic stirrer and equipped with a thermocouple and manometer
to measure the initial pressure in the reactor. The catalysts dispersed on SBA-12 silica support
and containing 1 or 3 wt.% ruthenium (labelled as 1% RuSBA-12, 3% RuSBA-12) with respect
to the support, were placed in a furnace at 250 °C for 3.5 h under dry argon flow prior to the
hydrodeoxygenation in order to remove traces of water. An appropriate amount of the catalyst
(0.025, 0.05 or 0.1 g) together with anisole (1 g) was placed in a glass vessel equipped with a
magnetic stirrer. No solvent was added as anisole was in the liquid state. The glass vessel with
the reaction mixture was placed in a high-pressure reactor, which was tightly closed and flushed
with argon of N5.0 purity in order to remove air from the reactor. Then hydrogen of N5.0 purity
was introduced to the reactor and then the reactor was filled with hydrogen up to the pressure
of 25, 40 or 60 bar. The reaction was conducted at three temperatures 90, 110 or 130 °C, for the
time of 1, 2.5 or 4 h. The reaction mixture was stirred at 700 rotations per minute. After the
reaction time, the reactor was cooled to room temperature. The reaction mixture was
centrifuged (VWR) in order to separate the liquid reaction products from the solid catalyst.
The reaction substrates and products were analyzed using a gas chromatograph made by
VARIAN 3900 GC equipped with a capillary column CPWAX57CB (length 25 m, diameter
0
.32 mm, film thickness 1.2 µm) and a flame-ionization detector. The products were identified
on the basis of comparison of retention times of the compounds obtained with those of the
standards. The results were confirmed by the results of gas chromatography analysis using a
chromatograph coupled with a mass detector made by VARIAN 4000 GC and a capillary
column VF-5MS (length 30 m, diameter 0.25 mm, film thickness 0.25 µm).
3
. Characterization of catalysts
The Ru content in all synthesized catalysts was evaluated by inductively coupled plasma
(
ICP) analysis. In addition, these catalysts were characterized by X-ray diffraction (XRD),
transmission electron microscopy (TEM), low-temperature nitrogen adsorption/desorption (N
2
ads/des). The XRD diffractograms were recorded on a diffractometer Bruker AXS D8 Advance,
using CuKα (0.154 nm) radiation, in the range 2Ɵ=0.6-10° with 0.02° step (small-angle range)
6

and 2Ɵ=4-60° with 0.05° step (wide-angle range). TEM images were recorded on a JEOL-2000
TEM microscope at 80 kV.
Low-temperature nitrogen adsorption/desorption isotherms were recorded on Nova
Quantachrome instrument at 176 °C, after prior degassing of the sample in vacuum at 350 °C
for 24 h. The surface area of the catalysts was determined by the BET (Brunauer – Emmet –
Teller) method. The pore volume was determined using the KJS-BJH method based on the BJH
(Barret – Joyner – Halenda) algorithm [38, 39].
4
4
. Results and discussion
.1. Characterization of SBA-12 type materials containing ruthenium
All the materials studied were characterized by using some of the techniques described
in chapter 3. This allowed selection two for detailed characterization. Additionally, due to the
lack of space, only data for 1 and 3 wt.% are discussed here. Fig. 1 presents the diffractograms
recorded for pristine SBA-12 and SBA-12 support with deposited ruthenium, in the small-angle
range (Fig. 1a) and wide-range range (Fig. 1b). The small-angle diffractograms show one main
reflection at 2Ɵ=1.8° corresponding to the plane [002] and a lower-intensity reflection at
2
Ɵ=1.27°, corresponding to the plane [100]. The material of SBA-12 type structure belongs to
the space group (p6 /mmc) and has hexagonal symmetry [40, 41] so the elementary cell
3
parameters were calculated for hexagonal symmetry.
7

1
3
% RuSBA-12
% RuSBA-12
d002
d100
SBA-12
a)
0
1
2
3
4
5
6
7
8
9
2
theta (degree)
1
3
% RuSBA-12
% RuSBA-12
SBA-12
b)
0
10
20
30
40
50
60
2
theta (degree)
Figure 1. XRD profiles: a) 1% RuSBA-12, 3% RuSBA-12 and SBA-12 (small angle); b) 1% RuSBA-12,
% RuSBA-12 and SBA-12 (wide angle).
3
The a and c lengths of the elementary cell for hexagonal RuSBA-12 sample vary in the
range 8.0 to 9.6 nm, as shown in Table 1. The unit cell parameters of the SBA-12 (a = 8.0-8.4
nm, c = 8.9-9.1 nm, c/a = 1.63) are in good agreement with previously reported results [42, 43].
After introduction of ruthenium in the amounts smaller than 1 wt.% the values of a and c lengths
decrease and then increase when the content of ruthenium increases from 1 to 3 wt.%.
Table 1. Structure and textural properties of SBA-12 and RuSBA-12.
Catalyst
XRD
N2-physisorption
8

Unit cell parameters
(nm)
d
100
d
002
Surface area
Pore width
(nm)
Structure
2
(
nm)
(nm)
(m /g)
a
c
Hexagonal/
SBA-12
7.2
6.9
7.2
4.8
4.4
4.5
8.4
9.6
1002
956
5.02
4.96
4.83
3
p6 /mmc
1
3
% RuSBA-12
% RuSBA-12
8.0
8.4
8.9
9.1
967
*Unit cell parameter for SBA-12 containing ruthenium: a = 2d100/√3 and c = 2d002 [39, 41].
The nitrogen adsorption/desorption isotherms recorded for samples 1% RuSBA-12 and
% RuSBA-12 (Fig. 2) are of type IVa, characteristic of mesoporous materials. Also, the type
3
of hysteresis loop is typical for mesoporous materials [40, 44, 45]. As was mentioned above,
the isotherms obtained for the SBA-12 samples studied match the patterns reported for other
mesoporous materials with p6 /mmc symmetry [40]. The additional hysteresis loop recorded
3
for samples with 1 wt.% of Ru can be interpreted as a result of the presence of voids between
2
particles [42, 46]. Surface area of the samples is close to 1000 m /g, while the average pore size
is 5 nm, as shown in Table 1.
7
6
5
4
3
2
00
00
00
00
00
00
1
3
% RuSBA-12
% RuSBA-12
0
.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Figure 2. N
2
– adsorption/desorption isotherms of 1% RuSBA-12 and 3% RuSBA-12. The isotherm
3
measured for 3% RuSBA-12 is shifted by 200 cm /g STP.
The TEM images presented in Fig. 3, confirm the ordered mesoporous structure of the materials
studied. They have hexagonal 3D structure with densely packed mesopores (hcp) [47]. No
9

crystalline ruthenium oxide species were observed (wide-angle XRD, TEM), which can suggest
that agglomerates at the outer surface were not formed. Thus, Ru probably exists in the catalyst
in the form of isolated Ru atoms The results of SEM/EDX analysis (not shown here) confirm
homogeneous distribution of ruthenium species.
Figure 3. TEM images of 1% RuSBA-12 and 3% RuSBA-12.
4
.2. Catalytic activity
Hydrodeoxygenation of organic compounds is the process of obtaining hydrocarbons in
the presence of gaseous hydrogen supplied under elevated pressure that takes place at elevated
temperature and in the presence of a catalyst, as shown in Fig. 4.
Organic
compound
containing
Catalyst
p, T
Hydrogen
Hydrocarbon
H O
2
oxygen species
Figure 4. The idea of the hydrodeoxygenation process.
In this study a series of hydrodeoxygenation reactions of anisole were performed using
SBA type silica loaded with different amounts of ruthenium catalyst. The reaction does not
proceed without a catalyst and proceeds with low conversion with unmodified SBA-12 catalyst
(Table 2, entry 19). The effects of the reaction time, the amount of catalyst, hydrogen pressure
and temperature were evaluated. According to literature data, the sequence of transformations
of anisole molecules under elevated pressure and temperature includes a few reactions such as
hydrogenation, dehydration, demethoxylation and demethylation [12, 48]. The type and
1
0

amounts of products of HDO of anisole depend on many parameters, including the type of
catalyst and conditions of the process.
Figure 5. Scheme of the possible routes for anisole hydrodeoxygenation.
The main products of HDO of anisole identified by GC or GC-MS, irrespective of the
conditions, are methoxycyclohexane and 1-methoxycyclohexene, as shown in Fig. 6-9. Besides
the above main products, the formation of cyclohexane, cyclohexene, benzene,
1
,1’-dimethoxycyclohexane, cyclohexanone, cyclohexanol, was confirmed. The selectivities to
these products are listed in Table 2. However, these products are not presented on the plots as
their total content did not exceed 20%. Based on the identified products of the reaction, three
pathways of HDO of anisole to a fully hydrodeoxygenated compound - cyclohexane - are
proposed (Fig. 5). The first pathway involves hydrogenation of the aromatic ring, leading to 1-
methoxycyclohexene and subsequently to methoxycyclohexane, then the C-O bond between
the carbon from the aromatic ring and the oxygen from methoxyl group is broken, which leads
to cyclohexane formation. The formation of undesirable product of 1,1’-dimethoxycyclohexane
(that contains more oxygen atoms than the initial compound) as a result of methanol attachment
to 1-methoxycyclohexene is also possible.
1
1

In the second pathway, cyclohexane is obtained via an intermediate product benzene.
This pathway starts with direct demethoxylation of anisole to the aromatic structure and then
the aromatic ring is hydrogenated.
In the third pathway, the first reaction is demethylation of the substrate, leading to the
formation of phenol, which is converted to cyclohexanol via total hydrogenation of the aromatic
ring. Cyclohexanol can undergo isomerization to cyclohexanone, dehydration of which gives
cyclohexene. Cyclohexene having a double bond in its structure can easily undergo
hydrogenation to cyclohexane. Because of possible cyclohexanol dehydration, the reaction can
also give dicyclohexyl ether.
Analysis of Fig. 6-9 and Table 2 data suggests that in this study the main pathway seems
to be the first one, involving direct hydrogenation of aromatic ring: anisole 
1
-methoxycyclohexene  methoxycyclohexane  cyclohexane. The domination of this
pathway may be related to the character of transition metal used as a catalyst that prefers
hydrogenation of aromatic ring [37] and to the fact that the reactions were run at low
temperatures and low pressure, at which the energy needed for hydrogenation of aromatic ring
is lower than that needed to break the bond between the carbon atom from the aromatic ring
and the methoxyl group or the oxygen atom and carbon from the methyl group [5]. A general
conclusion is that in the HDO reaction of anisole catalyzed by SBA-12 silica with deposited
ruthenium atoms the hydrogenation of aromatic ring is preferred over demethylation and
demethoxylation. The product forming in the largest amount is methoxycyclohexane with
higher H/C ratio to be achieved in the process. The teams of Shi [49], Khromov [50] and
Sankaranarayanan [5] studied also HDO of anisole and reported the highest selectivity to
methoxycyclohexane.
1
2

Table 2. By-product distribution for anisole HDO over 1% RuSBA-12 and 3% RuSBA-12 under different
conditions.
Selectivity (%)
Reaction conditions/
No.
Catalyst
1
h, 110 °C, 60 bar, 0.05 g of catalyst
1
2
1% RuSBA-12
3% RuSBA-12
1.0
1.3
-
-
0.1
-
1.6
3.3
0.6
0.1
1.1
0.5
0.6
2.3
2
.5 h, 110 °C, 60 bar, 0.05 g of catalyst
3
4
1% RuSBA-12
3% RuSBA-12
2.7
3.2
0.1
0.2
-
-
3.1
2.9
-
-
1.4
1.3
0.5
0.5
4
h, 110 °C, 60 bar, 0.05 g of catalyst
5
6
1% RuSBA-12
3% RuSBA-12
2.1
1.7
0.1
0.4
-
-
1.8
-
-
-
1.2
1.1
0.8
1.1
4
h, 110 °C, 60 bar, 0.025 g of catalyst
7
8
1% RuSBA-12
3% RuSBA-12
0.9
1.3
-
0.1
-
0.5
1.0
0.4
-
0.6
0.7
0.3
0.7
0.2
4
h, 110 °C, 60 bar, 0.1 g of catalyst
9
1% RuSBA-12
3% RuSBA-12
2.4
3.5
0.1
0.6
-
-
3.5
-
0.1
-
1.6
1.5
3.8
2.8
1
0
1
2
3
4
5
6
7
4
h, 90 °C, 25 bar, 0.05 g of catalyst
1
1
1
1
1
1
1
3% RuSBA-12
1.6
0.2
0.2
0.1
-
0.9
-
0.6
-
1.3
0.9
0.7
1.6
1.6
2.3
2.1
0.4
0.5
0.5
0.8
1.2
5.0
2.5
4
h, 90 °C, 40 bar, 0.05 g of catalyst
3% RuSBA-12
1.0
0.1
-
4
h, 90 °C, 60 bar, 0.05 g of catalyst
3% RuSBA-12
0.8
2.5
-
-
4
h, 110 °C, 25 bar, 0.05 g of catalyst
3% RuSBA-12
0.2
0.3
0.1
0.5
-
-
-
4
h, 110 °C, 40 bar, 0.05 g of catalyst
3% RuSBA-12
3.2
0.1
0.2
4.6
5.5
3.9
0.1
1.2
-
4
h, 130 °C, 25 bar, 0.05 g of catalyst
3% RuSBA-12
4.4
4.6
4
h, 130 °C, 40 bar, 0.05 g of catalyst
3% RuSBA-12
0.3
4
h, 130 °C, 60 bar, 0.05 g of catalyst
1
1
8
9
3% RuSBA-12
SBA-12
3.8
4.5
0.3
0.1
-
-
-
-
-
-
1.9
1.3
2.3
1.5
The reactions without catalyst do not occur (conversion ~ 0%), whereas with pristine SBA-12 (without
ruthenium species) occurs with a small (~1.5%) conversion of anisole.. Others: i.e.: 1,1’-
dimethoxycyclohexane, dicyclohexyl ether.
1
3

The plots illustrating the influence of the reaction time, the amount of catalyst, catalyst
loading, pressure and temperature of the reaction are shown below.
4
.2.1. Influence of reaction time
a)
b)
1
00
100
80
60
40
20
0
80
60
40
20
0
1
2.5
4
1
2.5
4
Reaction time (h)
Reaction time (h)
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
Figure 6. Effect of reaction time on the conversion and product selectivity for anisole HDO over a) 1%
RuSBA-12 b) 3% RuSBA-12 catalysts. Conditions: reaction temperature 110 °C, hydrogen pressure 60
bar, amount of catalyst 0.05 g.
Preliminary studies of hydrodeoxygenation of anisole were carried out to establish the
optimum time of the process. The reaction was carried out for 1, 2.5 or 4 h at 110 °C, under
hydrogen pressure of 60 bar and in the presence of 0.05 g SBA-12 containing 1 or 3 wt.% of
ruthenium. Decomposition of the main products of the reaction and the degree of anisole
conversion as a function of time are presented in Fig. 6, while the selectivities to the side
products are given in Table 2 (entries no. 1, 3, 5 for the catalyst 1 wt.% RuSBA-12, and 2, 4, 6
for the catalyst 3 wt.% RuSBA-12). The results unambiguously show that the quantitative
composition of the products and anisole conversion depend significantly on the time of the
HDO process. In the experiment with 1% RuSBA-12 catalyst the time of reaction had a great
effect on the anisole conversion, which increased from 24% after 1 h to 93% after 2.5 h, to
1
00% after 4 h (Fig. 6a). Moreover, the catalyst became increasingly selective towards
methoxycyclohexane with time of the reaction because the amount of this compound increased.
A similar correlation was observed for the process with 3% RuSBA-12, for which after 4 h of
the process the selectivity towards methoxycyclohexane increased to 96% (Fig. 6b). Using the
3
1
% RuSBA-12 catalyst, the degree of anisole conversion was smaller than in the presence of
% RuSBA-12. The conversion of anisole was already high - 93% after 1 h of the process, then
1
4

after 2.5 h it increased to 95% and after 4 h it was 100%. Greater activity of 3% RuSBA-15
catalyst after 1 h of the process was a direct consequence of a greater content of metal with
respect to the substrate. Based on the results of these experiments, we decided to carry out
further experiments for 4 h.
4
.2.2. Influence of the amount of the catalyst
a)
b)
1
00
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
0
.025
0.05
0.1
0.025
0.05
0.1
Amount of catalyst (g)
Amount of catalyst (g)
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
methoxycyclohexane
conversion of anisole
Figure 7. Effect of amount of catalyst on the conversion and product selectivity for anisole HDO over a)
% RuSBA-12 b) 3% RuSBA-12 catalysts. Conditions: reaction temperature 110 °C, hydrogen pressure
0 bar, reaction time 4 h.
1
6
At the next stage, our aim was to establish the optimum amount of the catalyst used in
the process. The HDO of anisole was performed at 110 °C under a hydrogen pressure of 60 bar
for 4 h, in the presence of 0.025, 0.05 or 0.1 g of samples 1% RuSBA-12 or
3
% RuSBA-12. Analysis of HDO of anisole in the presence of sample 1% RuSBA-12 (Fig. 7a)
(Tab. 2, items 5, 7, 9) reveals that the greatest catalytic activity was obtained for the catalyst
amount of 0.05 g. The use of catalyst in this amount gave the maximum conversion of anisole
to 94% of methoxycyclohexane. The reaction in the presence of 0.025 or 0.1 g of the catalyst
led to the formation of noticeable amounts of 1-methoxycyclohexene - a compound of a lower
content of hydrogen than methoxycyclohexane - and the degree of anisole conversion was lower
than when an intermediate amount of catalyst was used, i.e., 0.05g. When 0.1 g catalyst was
used in the reaction, a decrease in the anisole conversion and a decrease in the selectivity to
methoxycyclohexane were observed compared to the reaction catalyzed by 0.05 g of silica. A
decrease in the catalyst activity can be attributed to the physico-chemical properties of the
catalyst, and of course the reaction conditions according the Sabatier principle stating that the
1
5

bond strength between reactants and catalyst should be intermediate (i.e., not too weak, so that
the reactants adsorb on the catalyst surface but not too strong to avoid, its poisoning).
For the processes in the presence of 3% RuSBA-12 (Fig. 7b) (Table 2, entries no. 6, 8,
1
0) no significant effect of the amount of the catalyst was observed as in all reactions the
selectivity to methoxycyclohexane was greater than 90% and the anisole conversion was
maximum. Based on these results, we decided to use in the further study the catalyst in the
amount of 0.05 g.
4
.2.3. Influence of catalyst loading
The studies aimed at establishment of the optimum reaction time and optimum amount
of the catalyst also provided information on the activity of the catalysts used, 1% RuSBA-12 or
% RuSBA-12, differing in ruthenium loading. The more selective catalyst with higher anisole
3
conversion was 3% RuSBA-12. Its higher activity can be directly related to the greater content
of metal on the support surface. Therefore, further studies on the effect of pressure and
temperature on HDO of anisole were performed with the catalyst 3% RuSBA-12.
4
.2.4. Influence of hydrogen pressure
The influence of hydrogen pressure on the distribution of the reaction products and the
degree of anisole conversion was studied for three pressure values, 25, 40 or 60 bar at three
temperatures 90 °C (Fig. 8a), 110 °C (Fig. 8b) or 130 °C (Fig. 8c). Table 2 gives the amounts
of products of HDO of anisole besides the main ones (entries no. 6, 11-18). The reaction was
performed for 4 h using 0.05 g of 3% RuSBA-12 catalyst. The results imply a significant effect
of hydrogen pressure on the character of HDO of anisole. For each temperature, the conversion
of anisole increased with increasing hydrogen pressure. Under the hydrogen pressure of 60 bar
the aromatic ring hydration occurred in the highest degree. It resulted in the formation of a large
amount of methoxycyclohexane and small amount of 1-methoxycyclohexene, which is
particularly evident for the processes carried out at 110 and 130 °C. For the reactions performed
at 90 °C, the change in hydrogen pressure had practically no effect on the distribution of the
main reaction products.
1
6

a)
b)
1
00
1
00
8
6
4
2
0
0
0
0
0
80
60
40
20
0
2
5
40
60
2
5
40
60
Pressure (bar)
Pressure (bar)
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
c)
1
00
8
0
0
0
0
0
6
4
2
Figure 8. Effect of hydrogen pressure on the
conversion and product selectivity for anisole HDO
over 3% RuSBA-12 catalyst. Conditions: reaction
time 4 h, reaction temperature a) 90 °C, b) 110 °C,
2
5
40
Pressure (bar)
60
c) 130 °C.
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
4
.2.5. Influence of reaction temperature
The influence of temperature on HDO of anisole on its conversion and selectivity of the
reaction towards individual reaction products is illustrated in Fig. 9a-c. The experiments were
performed at 90, 110 or 130 °C under hydrogen pressures of 25 bar (Fig. 9a), 40 bar (Fig. 9b)
or 60 bar (Fig. 9c). Table 2 presents the amounts of the reaction products other than the main
ones (entries no. 6, 11-18). These data show that the reaction temperature, similarly as pressure,
has a significant influence on the character of the process. At each pressure an increase in
temperature caused greater conversion of anisole. However, temperature changes had no effect
on the amounts of the particular reaction products. The catalyst became more selective with
increasing temperature, which is well visible for the processes at 130 °C.
As can be seen from Fig. 9a-c, anisole conversion at 90 °C is very low and the main
products are 1-methoxycyclohexene and methoxycyclohexane. At higher temperature, 110-130
1
7

°
C, the amount of generated cyclohexane increases (Tab. 2), while the amount of 1-
methoxycyclohexene decreases (Fig. 9a-c). In other words, the Caryl-O bonds cleave and anisole
is converted preferentially to cyclohexane at higher temperature, which indicates the occurrence
of the reaction according to the pathways I and II in Fig. 5.
a)
b)
1
00
80
60
40
1
00
8
6
4
2
0
0
0
0
0
2
0
0
9
0
110
130
9
0
110
130
Temperature (°C)
Temperature (°C)
methoxycyclohexane
1-methoxycyclohexene
methoxycyclohexane
conversion of anisole
1-methoxycyclohexene
conversion of anisole
c)
1
00
8
0
0
0
0
0
6
4
2
Figure 9. Effect of temperature on the conversion
and product selectivity for anisole HDO over 3%
RuSBA-12 catalyst. Conditions: reaction time 4 h,
hydrogen pressure a) 25 bar, b) 40 bar, c) 60 bar.
9
0
110
Temperature (°C)
1-methoxycyclohexene
130
methoxycyclohexane
conversion of anisole
4
.2.6. Comparison of current experimental results with literature data
The main reaction product in our experiment was methoxycyclohexane - chemical
compound with a higher H/C atom ratio than the starting substrate. According to the literature,
methoxycyclohexane is very often obtained in this reaction regardless of the type of catalyst
used. In accordance with the data collected in the Table 3 (examples 2 and 6), scientists also
reported methoxycyclohexane as the main product, however the reaction temperature used was
much higher. Moreover, in our experiments, methoxycyclohexane was obtained with higher
selectivity and higher conversion of anisole. Some research groups have reported deoxygenated
1
8

chemicals (Tab. 3, examples 1, 3, 4 ,7, 8), however, several factors contributed to this, such as
harsher process conditions and the presence of acid centers. The table below collects more
examples from the literature, where anisole was subjected to the hydrodeoxygenation reaction.
Tab. 3. Comparison of the results of anisole hydrodeoxygenation reactions obtained by
various research groups
Reaction
conditions
Conversion Main reaction product and
Catalyst
Ref.
[
%]
its selectivity [%]
T [°C] p [bar]
1
2
3
4
5
6
7
8
Ni/SBA-15
Co/SBA-15
310
220
300
400
300
200
250
300
30
50
60
1
100
99
68
46
72
3
cyclohexane, 30
methoxycyclohexane, 72
benzene, 28
[36]
[5]
x
Re-MoO /TiO
2
[51]
[52]
RuO /NiO/Al-SBA-15
2
benzene, 45
NiMo/SBA-15
Ni/HZSM-5
1
1-methoxycyclohexane, 57 [53]
68
methoxycyclohexane, 87
cyclohexane, 64
[54]
22
97
Ni
2
P/SiO
2
15
[55]
cyclohexane, 93
5
. Conclusions
The reaction of hydrodeoxygenation of chemical compounds obtained from biomass
degradation is generally considered as a new and attractive method for production of biofuels.
Further research needs to be conducted to optimize the process and make it energetically
efficient. Studies of hydrodeoxygenation of anisole, chosen as a representative of organic
compounds present in biooil, catalyzed by RuSBA-12 at varying pressures (25-60 bar) and
temperatures (90-130 °C), permitted the following conclusions: (I) ordered mesoporous silica
such as SBA-12 with ruthenium deposited on their surface are highly active in HDO of anisole,
(
II) larger content of ruthenium on the support surface is directly related to a higher conversion
of anisole, (III) the product obtained in the highest amount, irrespectively of the reaction
conditions, was methoxycyclohexane, (IV) the pressure and temperature of the process have
significant effect on the degree of anisole conversion and the selectivities to the reaction
products. The yield of the process increased with increasing pressure and temperature.
1
9

Briefly, Ru catalyst catalyzed aromatic C-O bonds to produce aromatic hydrocarbons
due to its oxophilicity. The strong metal oxophilicity of Ru favors the direct Caryl-O bond
cleavage to benzene, while the weak oxophilic catalyst (e.g. Pt/SiO ) favors the aliphatic Calkyl-
2
O bond breaking to phenol. Both demethylation and demethoxylation occur over the moderately
oxophilic Ru catalysts.
6
. Acknowledgements
To Maria, a very outstanding scientist, sincere thanks for all she has done and will
continue to do in the future in the field of heterogeneous catalysis. Thank you, for being always
ready to share your knowledge.
The authors wish to thank the National Centre for Science for financial support of the
studies reported within the research project HARMONIA-5 (no. DEC-2013/10/M/ST5/00652).
7
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