A Nanospherical Mesoporous Ruthenium-Containing Polymer as a Guaiacol Hydrogenation Catalyst

Article abstract of DOI:10.1134/S096554411912003X

Abstract: A hybrid catalyst is synthesized using ruthenium nanoparticles deposited on a nanospherical mesoporous polymer. Catalytic properties are studied in guaiacol hydrogenation at a temperature of 200–250°С and a hydrogen pressure of 5.0 MPa. Effect of solvent and catalytic additives on the reaction is investigated. It is shown that the synthesized catalyst exhibits the highest activity in guaiacol hydrodeoxygenation in the two-phase system water/n-dodecane and when the reaction is carried out in the presence of scandium triflate.

Full text of DOI:10.1134/S096554411912003X

ISSN 0965-5441, Petroleum Chemistry, 2019, Vol. 59, No. 12, pp. 1300–1306. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Nanogeterogennyi Kataliz, 2019, Vol. 4, No. 2, pp. 111–117.
A Nanospherical Mesoporous Ruthenium-Containing Polymer
as a Guaiacol Hydrogenation Catalyst
M. P. Boronoeva, *, I. I. Shakirova, V. I. Ignat’evaa, A. L. Maximova, b, and E. A. Karakhanova
aFaculty of Chemistry, Moscow State University, Moscow, 119991 Russia
bTopchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: maxbv04@gmail.com
Received August 1, 2019; revised August 6, 2019; accepted August 9, 2019
Abstract—A hybrid catalyst is synthesized using ruthenium nanoparticles deposited on a nanospherical mes-
oporous polymer. Catalytic properties are studied in guaiacol hydrogenation at a temperature of 200–250°С
and a hydrogen pressure of 5.0 MPa. Effect of solvent and catalytic additives on the reaction is investigated.
It is shown that the synthesized catalyst exhibits the highest activity in guaiacol hydrodeoxygenation in the
two-phase system water/n-dodecane and when the reaction is carried out in the presence of scandium tri-
flate.
Keywords: mesoporous polymer, nanospheres, nanoparticles, ruthenium, guaiacol, hybrid catalyst, hydroge-
nation
DOI: 10.1134/S096554411912003X
Selection of a support for an active component is of
prime importance for the design of efficient heteroge-
neous catalysts [1–3]. The activity of the catalytic sys-
tem is affected by the distribution of nanoparticles on
EXPERIMENTAL
Initial Compounds
The reagents were phenol (Reakhim, high-purity
the support surface, their size, and the accessibility of grade), formaldehyde (37% aqueous solution, Sigma-
active sites. Catalysts based on metal nanoparticles Aldrich), triblock copolymer Pluronic F127 (Mn =
immobilized in the pores of ordered porous organic or
organometallic structures can potentially exhibit high
activity and selectivity owing to the possibility to con-
trol the support nature and structure [4–6].
12600, EO106–PO70–EO106, Aldrich), sodium hydrox-
ide (IREA 2000, reagent grade), sodium borohydride
(Acros Organics, 98%), ruthenium(III) chloride
(OAO Aurat, 47.8%), guaiacol C7H8O8 (Sigma-
Aldrich, Kosher, 98%), orthophosphoric acid
(85 wt %), sulfuric acid (IREA 2000, reagent grade),
magnesium oxide (Sigma-Aldrich, 97%), and scan-
dium(III) triflate (Sigma-Aldrich, 99%). Ethanol
(IREA 2000, analytical grade) and n-dodecane
(Sigma-Aldrich, 99%) were used as solvents.
Systems based on metal nanoparticles immobilized
within phenol-formaldehyde polymers manifest high
activity in the hydrogenation of acetylenes, dienes,
and phenolic and polyaromatic compounds [7–10].
However, these materials are characterized by the
presence of large particles (up to 2 μm) and a wide par-
ticle size distribution. Compared with these materials
mesoporous nanospherical materials prepared by
hydrothermal synthesis at low concentrations of initial
reagents are characterized by the presence of short
mesochannels and a smaller size of particles (100–
200 nm). Catalytic sites immobilized in them are more
accessible to reactants, which increases the mass
transfer rate and the catalyst activity [11–13].
Instruments and Analytical Procedures
Nitrogen adsorption/desorption isotherms were
measured at a temperature of 77 К on a Gemini VII
2390 surface area analyzer. Before measurements the
samples were outgassed at a temperature of 110°С for
5 h. The specific surface area (SBET) was calculated by
the Brunauer–Emmett–Teller (BET) method using
the adsorption data obtained in the relative pressure
(Р/Р0) range of 0.04–0.2. The pour volume and pore
size distribution were assessed from the adsorption
branches of the isotherms in terms of the Barrett–
Joyner–Halenda (BJH) model. Transmission electron
microscopy (TEM) studies were carried out on a
Thus, the goals of this study were the synthesis of
Ru-containing hydrogenation catalyst NSMP-Ru
immobilized in pores of the ordered mesoporous phe-
nol-formaldehyde polymer and the investigation of its
catalytic properties in the hydrogenation of guaiacol—
bio-oil model compound.
1300

A NANOSPHERICAL MESOPOROUS RUTHENIUM-CONTAINING POLYMER
1301
130
LEO912 AB OMEGA microscope. TEM images were
processed and the average particle size was determined
using the program ImageJ. X-ray photoelectron
microscopy (XPS) measurements were conducted on
a PHI5500VersaProbeII X-ray photoelectron spec-
trometer. Photoelectrons were excited using the AlKα
X-ray emission of the aluminum anode (1486.6 eV).
The binding energy scale was calibrated against the
C1s line of aromatic carbon (Еb = 284.7 eV). The sur-
vey spectra were measured in the range of 0–1100 eV at
an analyzer pass energy (Epass) of 117.4 eV with a step of
13C CPMAS
32.6
152.4
160 140 120 100 80 60 40 20
0
–20
180
25
1H MAS
1 eV. High-resolution spectra were taken at Epass
=
20 15 10
5
0
–5 –10 –15
23.5 eV with a step of 0.2 eV. Solid-state CP/MAS 13С
1
and H NMR studies were carried out on a Varian
13
1
Fig. 1. CP/MAS С and Н NMR spectra of the NSMP
NMR Systems instrument operating at a frequency of
125 MHz in the pulsed mode at a MAS frequency of
10 kHz. The quantitative determination of ruthenium
in the catalyst samples was conducted by inductively
coupled plasma atomic emission spectroscopy (ICP-
AES) on an IRIS Interpid II XPL instrument
(Thermo Electron Corp., United States) in radial and
axial viewing configurations at a wavelength of
245.5 nm. Substrates and reaction products were ana-
lyzed on a Kristallyuks 4000 M chromatograph
equipped with a flame ionization detector and a Pet-
rocol® DH 50.2 capillary column coated with the
polydimethylsiloxane stationary liquid phase (dimen-
sions, 50 m × 0.25 mm; carrier gas, helium; split ratio,
1 : 90). Analysis conditions: column temperature,
235°С; detector temperature, 300°С; and injector
temperature, 300°С. Chromatograms were recorded
and analyzed on a computer using the program
NetChrom. Conversion was calculated as a change
in the relative surface areas of the substrate and prod-
ucts (%).
sample.
Catalytic Testing Procedure
A steel thermostated autoclave equipped with an
insertable glass tube and a magnetic stirrer was loaded
with the calculated amounts of the catalyst, substrate,
and solvent. The autoclave was pressurized, filled with
hydrogen to a pressure of 5.0 MPa, and held at a tem-
perature of 200–250°С for 2 h under vigorous stirring.
When the reaction was completed, the autoclave was
cooled below room temperature and depressurized.
The reaction mixture was analyzed by gas-liquid chro-
matography. Catalytic activity (TOF) for each reac-
tion was calculated as the amount of the reacted sub-
strate per mol of metal on the surface of particles per
time unit.
RESULTS AND DISCUSSION
Catalyst Synthesis
Mesoporous phenol-formaldehyde nanospheres
NSMP were prepared under hydrothermal conditions
using low-concentrated reactant solutions. The result-
Catalyst Synthesis
The nanospherical mesoporous phenol-formalde-
hyde polymer NSMP was synthesized as described in
[14]. For the synthesis of catalyst NSMP-Ru
support NSMP (1.0 g) was suspended in water
(90 mL) in a 25-mL round-bottom flask equipped
with a magnetic stirrer and a reflux condenser, ruthe-
nium(III) chloride (85 mg) was added, and the result-
ing mixture was stirred for 24 h. The solvent was
removed on a rotor evaporator at 50°С. The residue
13
ing polymer was characterized by CP/MAS С and
1H NMR spectroscopy, low-temperature nitrogen
adsorption, and TEM (Figs. 1, 2).
The NMR spectra of NSMP samples show signals
typical of mesoporous phenol-formaldehyde poly-
mers; this confirms that the polymer structure of the
material is retained and the template is completely
removed [7]. In the NMR spectrum the signals are
was transferred into a 100-mL round-bottom flask considerably broadened because of a small relaxation
time in solids. In the 1H NMR spectrum of the sam-
ples there are signals at 7.5 and 1.65 ppm. The first sig-
equipped with a magnetic stirrer and a reflux con-
denser and suspended in a solution of ethyl alcohol
(50 mL) and water (10 mL). NaBH4 (0.15 g) was added nal corresponds to aromatic protons, and the second
signal is due to aliphatic protons of the CH2 group. In
in portions to the reaction mixture, and the mixture
was stirred for 12 h at room temperature. The obtained
suspension was centrifuged, and the catalyst was
washed several times with water and ethyl alcohol and
dried in air.
13
the C NMR spectrum there are three signals at 27,
128.5, and 154.5 ppm: the first signal is due to the car-
bon of the bridging CH2 group, the signal at 128.5 ppm
corresponds to the carbon of the aromatic ring, and
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BORONOEV et al.
(b)
(a)
(c)
35
30
25
20
15
10
5
0
100 140 180 220 260 300
Nanosphere diameter, nm
60
100 nm
200 nm
Fig. 2. (a, b) TEM images of the NSMP sample and (c) size distribution of nanospheres.
the signal at 154.5 ppm corresponds to the carbon of This indicates that the initial RuCl3 is reduced com-
the aromatic moiety linked to the OH group.
pletely. The presence of RuO2 may be explained by a
high affinity of ruthenium for oxygen [18] and the sub-
sequent oxidation of its surface during storage and
analysis. The oxidized form RuOх can result from
interaction between Ru atoms with phenolic and car-
boxyl groups present on the polymer surface.
The TEM images of the sample (Fig. 2) clearly
show mesoporous channels typical of such materials.
The statistical estimation of sizes for more than 500
nanospherical particles revealed that the size of nano-
spheres is within 60–320 nm and their average size is
151 39 nm.
In accordance with low-temperature nitrogen
adsorption, the characteristics of the synthesized poly-
mer are as follows: specific surface area, 309 m2/g;
pore size, 3.9 nm; and pore volume, 0.16 cm3/g.
According to the adsorption isotherm (Fig. 3), it can
be assumed that the material contains small pores with
sizes at the microporosity/mesoporosity boundary.
This implies that a rise of the adsorption curve is
observed in the range of low P/P0 values (0.05–0.1),
which is inherent of microporous materials, whereas
the hysteresis loop appearing owing to capillary con-
densation in material pores acquires the H-4-type
mode, as is characteristic of micro-mesoporous car-
bons and mesoporous zeolites [15]. It should be
emphasized that the desorption branch cannot form
the closed curve at low relative pressures, which is typ-
ical of isotherms of porous polymers [16].
Catalytic Experiments
In guaiacol hydrogenation the dependence of
NSMP-Ru catalyst activity on solvent nature
was studied. Systems water, n-dodecane, and water:
n-dodecane were used as solvents (Table 2). As
expected, the efficiency of the hydrogenation reaction
in n-dodecane was lower, because, as is known, when
phenol hydrogenation is carried out in aqueous
medium water can in situ generate H+ for further
deoxygenation of oxygen-containing groups [19]; this
contributes to the reaction acceleration. However, the
guaiacol hydrodeoxygenation was the most effective in
180
160
140
120
100
80
The catalyst was synthesized by impregnating the
mesoporous polymer NSMP with the calculated
amount of a RuCl3 aqueous solution followed by
reduction with NaBH4. The synthesized catalyst
NSMP-Ru with a nominal ruthenium content of 4%
was investigated by ICP-AES, TEM, and XPS.
As is clear from the microimages of the catalyst, Ru
nanoparticles are situated predominantly in support
pores (Fig. 4). It is found that the average size of Ru
60
40
20
nanoparticles is 1.4
0.5 nm, which conforms to
the characteristics of support pores. According to
ICP-AES, the content of ruthenium is 3.6 wt %.
0
0.2
0.4
0.6
0.8
1.0
Р/Р0
As evidenced by XPS studies (Table 1, Fig. 5),
ruthenium in the synthesized catalysts occurs both in
the zero-valence state (Ru0) and in the oxidized states
(RuO2, RuOх) [17], whereas no RuCl3 is detected.
Fig. 3. Nitrogen adsorption−desorption isotherm of the
NSMP sample.
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A NANOSPHERICAL MESOPOROUS RUTHENIUM-CONTAINING POLYMER
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(a)
(b)
25
20
15
10
5
100 nm
0
1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6
Size of Ru nanoparticles, nm
0.6 0.9
Fig. 4. (a) Micrograph and (b) size distribution of nanoparticles of the catalyst NSMP-Ru.
the two-phase system water–n-dodecane. An increase
The reaction of guaiacol hydrogenation was stud-
in efficiency in the case of the two-phase system is ied in the presence of the NSMP-Ru catalyst and
probably related to a rapid transition of the formed acidic or basic additives (Table 3).
products to the organic phase, whereas the substrate
Addition of a small amount of orthophosphoric
transformation proceeds in the aqueous phase.
acid (1 wt %) had no effect on the reaction, and
A high degree of phenol hydrodeoxygenation is
methoxycyclohexanol was the key product. As the
attained using mixed catalysts composed of a transi-
concentration of orthophosphoric acid was increased
tion-metal-based catalyst and an acidic catalyst [20–
to 19.2 wt %, methoxycyclohexanol predominated in
22] or bifunctional catalysts [23, 24]. It is also known
reaction products; however, they also contained
that the selective guaiacol conversion to cyclohexanol
cyclohexanediol, cyclopentanone, and С6-com-
can be reached with the use of basic compounds, for
pounds: cyclohexane, benzene, and cyclohexene. This
example, sodium hydroxide or magnesium oxide [25].
is evidence for the occurrence of hydrodeoxygenation
processes. When sulfuric acid was added to the cata-
lytic system, the degree of guaiacol hydrodeoxygen-
Table 1. Approximation parameters of C1s + Ru3d spectra and the proportion of C1s
Ru3d5/2
C1s
Proportion of C1s
in the C1s + Ru3d
spectrum
Parameters
4
5
6
7
1
2
3
s
Binding energy, Еb, eV
284.7 286.4 288.3 291.2 280.0 280.8 281.8 282.7
71%
Full width at half maxi-
mum, FWHM, eV
1.6
52
1.6
25
2.1
16
3.6
7
1.0
27
1.4
37
1.3
18
2.0
18
%
PETROLEUM CHEMISTRY Vol. 59 No. 12 2019

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BORONOEV et al.
с/s
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
4
5
6
3'
7
2'
s'
2
1'
1
s
3
0
290
285
280
275
295
Binding energy, eV
Fig. 5. Deconvolution of the C1s + Ru3d XPS spectrum of the catalyst NSMP-Ru. (1-1') Doublet of metallic ruthenium, (2-2')
doublet of RuO , (ss') satellites of doublet 2-2', (3-3') doublet of RuO , (4) aromatic carbon, (5) С–ОН group, (6) С=О group,
2
x
and (7) shake-up satellite of the aromatic carbon.
ation increased and cyclohexanol, cyclohexanediol, perature was increased to 250°С; this corresponded to
and cyclopentanone became the key products; selec-
tivity for С6 products was 4%. When the reaction was
conducted in the presence of sodium hydroxide, the
guaiacol conversion decreased to 87% and the selec-
tivity for compounds containing one oxygen atom was
13% higher than that without additives, whereas the
addition of magnesium oxide did not cause consider-
able changes. Hence, basic compounds insignificantly
influenced the guaiacol hydrogenation-hydrodeoxy-
the occurrence of guaiacol С–О bond hydrogenolysis
in water at this temperature in the presence of the
Lewis acid [26]. For example, selectivity for products
containing one oxygen-containing group was 86% and
selectivity for С6 products increased to 12%.
Thus, we examined the effect of solvent and cata-
lytic additives on the guaiacol hydrogenation in the
presence of the catalyst based on ruthenium nanopar-
genation reaction under the given conditions. If ticles immobilized in nanospherical mesoporous phe-
Sc(OTf)3 was added to the system the degree of hydro-
deoxygenation markedly increased only when tem- hydrodeoxygenation of guaiacol is the most effective
nol-formaldehyde polymer pores. It is shown that the
Table 2. Results of catalytic experiments on guaiacol hydrogenation over the NSMP-Ru catalyst in various solvents. Reac-
tion conditions: ν(guaiacol)/ν(Ru) = 221 mol/mol, 0.4 mmol of guaiacol, 5.0 MPa of Н2, 200°С, 2 h, and 1 mL of solvent
TOF, min–1
Solvent
Conversion, %
>99
Selectivity, %
H2O
116
Methoxycyclohexanol, 86
Cyclohexanol, 13
Methylcyclohexanol, <1
n-Dodecane
77
90
Methoxycyclohexanol, 78
Cyclohexanone, 2
Cyclohexanol, 17
С6-products, 3
H2O/n-dodecane
100
117
Methoxycyclohexanol, 67
Methoxycyclohexane, 1
Cyclohexanol, 21
Cyclohexane, 5
Cyclohexanediol, 6
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A NANOSPHERICAL MESOPOROUS RUTHENIUM-CONTAINING POLYMER
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Table 3. Guaiacol hydrogenation over the catalyst NSMР-Ru in the presence of various additives. Reaction conditions:
ν(subs)/ν(Ru) = 221 mol/mol, 0.4 mmol of guaiacol, 50 atm of Н2, 200°С (*250°С), 2 h, and 1 mL of H2O
TOF, min–1
Additive
–
Conversion, %
>99
Selectivity, %
116
Methoxycyclohexanol, 86
Cyclohexanol, 13
Methylcyclohexanol, <1
2.6 μL of H3PO4 (1 wt %)
50 μL of H3PO4 (ac)
>99
98
116
114
Methoxycyclohexanol, 85
Cyclohexanol, 14
Cyclohexanone, <1
Methoxycyclohexanol, 82
Cyclohexanol, 5
Cyclohexanediol, 4
Cyclopentanone, 6
С6 products, 2
50 μL of H2SO4 (ac)
90
105
Methoxycyclohexanol, 21
Methoxycyclohexanone, 7
Cyclohexanol, 37
Cyclopentanone, 12
Cyclohexanediol, 19
С6-products, 4
4 mg of NaOH (0.1 mmol)
50 mg of MgO
87
102
73
Methoxycyclohexanol, 73
Cyclohexanol, 27
Methoxycyclohexanol, 89
Methoxycyclohexanone, <1
Cyclohexanone, <1
100
Cyclohexanol, 10
10 mg of Sc(OTf)3
10 mg of Sc(OTf)*3
100
70
58
20
Methoxycyclohexanol, 90
Cyclohexanol, 7
Cyclopentanol, 2
С6-products, <1
Methoxycyclohexanol, 2
Cyclohexanone, 63
Cyclohexanol, 6
Cyclopentanol, 13
Anisol, 4
Cyclohexane, 9
Benzene, 2
Cyclohexene, <1
ADDITIONAL INFORMATION
when scandium(III) triflate is added to the system and
the reaction is carried out at 250°С.
M.P. Boronoev, ORCID https://orcid.org/0000-0001-
6129-598X
FUNDING
I.I. Shakirov, ORCID: https://orcid.org/0000-0003-
2029-693X
This work was supported by the Russian Science Foun-
dation (project no. 15-19-00099).
V.I. Ignat’eva, ORCID: https://orcid.org/0000-0003-
1319-1638
CONFLICT OF INTEREST
A.L. Maximov, ORCID: https://orcid.org/0000-0001-
9297-4950
A.L. Maximov is the editor-in-chief of the journal
Petroleum Chemistry. E. A. Karakhanov is a member of the
editorial board of this journal. Other authors declare that
there is no conflict of interest.
E. A. Karakhanov, ORCID: https://orcid.org/0000-
0003-4727-954X
PETROLEUM CHEMISTRY Vol. 59 No. 12 2019

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BORONOEV et al.
14. F. Zhang, C. Liang, X. Wu, and H. Li, Angew. Chem.
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Translated by T. Soboleva
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