Supported Ru?Ni Catalysts for Biogas and Biohydrogen Conversion into Syngas

Article abstract of DOI:10.1134/S0023158418040080

Catalytic properties of monometallic Ni and bimetallic Ru–Ni supported on Al₂O₃, CaO–Al₂O₃, and MgO–Al₂O₃ have been studied in mixed reforming of methane. Physicochemical properties of the

Full text of DOI:10.1134/S0023158418040080

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 4, pp. 509–513. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © P. Mierczynski, R. Ciesielski, M. Zakrzewski, B. Dawid, M. Mosinska, A. Kedziora, W. Maniukiewicz, S. Dubkov, D. Gromov, M. Szynkowska, I. Witonska,
O. Shtyka, T. Maniecki, 2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 4, pp. 493–498.
3rd RUSSIAN CONGRESS ON CATALYSIS
(MAY 22–26, 2017, NIZHNY NOVGOROD)
Supported Ru−Ni Catalysts for Biogas and Biohydrogen
Conversion into Syngas
P. M i ercz yn s ki a, *, R. Ciesielskia, M. Zakrzewskia, B. Dawida, M. Mosinskaa,
A. Kedzioraa, W. Maniukiewicza, S. Dubkovb, D. Gromovb, M. Szynkowskaa, I. Witonskaa,
O. Shtykaa, and T. Manieckia
aInstitute of General and Ecological Chemistry, Lodz University of Technology, Lodz, 90-924 Poland
bNational Research University of Electronic Technology, Zelenograd, Moscow, 124498 Russia
*e-mail: pawel.mierczynski@p.lodz.pl
Received September 14, 2017
Abstract—Catalytic properties of monometallic Ni and bimetallic Ru–Ni supported on Al2O3, CaO–Al2O3,
and MgO–Al2O3 have been studied in mixed reforming of methane. Physicochemical properties of the cata-
lytic systems have been studied by X-ray diffraction, scanning electron microscopy with energy dispersive
spectroscope and temperature-programmed reduction by hydrogen. It has been shown that, of all the studied
samples, the highest conversion of methane and carbon dioxide is achieved in the presence of the
Ru−Ni/MgO–Al2O3 bimetallic catalyst. Temperature-programmed reduction has confirmed the effect of
hydrogen spillower from ruthenium to NiO. The formation of Ru–Ni alloy has also been found.
Keywords: ruthenium–nickel catalysts, biogas, methane reforming, hydrogen spillower
DOI: 10.1134/S0023158418040080
INTRODUCTION
Biogas can be used in syngas production with its
further conversion into fuel components using the
Fischer−Tropsch process. The conversion of methane
into syngas occurs via two reactions:
The final products of anaerobic fermentation of
molasses, which is very important for the cycling of
matter and energy in ecosystems, are methane and
carbon dioxide. The anaerobic fermentation of bio-
mass, which often takes place in waste treatment facil-
ities, is widely used in biogas synthesis [1, 2]. This
complex process carried out by microorganisms and
includes four main stages [3–6]:
Steam conversion of methane:
CH4 + H2O = CO + 3H2, ∆H = 206 kJ/mol
Carbon dioxide conversion of methane:
CH4 + CO2 = 2CO + 2H2, ∆H = 247 kJ/mol
These reactions are carried out on nickel catalysts
promoted by noble metals. Crisafulli et al. [11] studied
monometallic Ni/SiO2 and bimetallic Ru−Ni/SiO2
and Pd–Ni/SiO2 catalysts in reforming of methane
process. They found that promoting the catalyst by
ruthenium or palladium considerably affects the cata-
lytic activity of a nickel catalyst. The maximum activ-
ity was achieved in the case of a Ru−Ni/SiO2 catalyst.
This was explained by the high dispersion of nickel on
the catalyst surface due to the formation of Ru−Ni
clusters with a surface covered mostly by nickel. Lui-
setto et al. [12] also found positive effect of ruthenium
on the activity of a Ni/γ-Al2O3 catalyst in reforming of
methane with carbon dioxide process. Authors
reported, that the role of ruthenium is to facilitate the
reduction of NiO. Ruthenium did not improve the dis-
persion of nickel. Takehira et al. [13] came to similar
conclusion. They confirmed the alloy Ru–Ni forma-
(1) hydrolysis of organic compounds to monomers;
(2) acidogenesis, which results in the formation of
hydrogen and carbon dioxide;
(3) acetogenesis, which is related to the oxidation of
nongaseous products into hydrogen, carbon dioxide,
and acetate (syntrophic degradation); and
(4) methanogenesis.
The two last stages can produce hydrogen in sub-
stantial amounts if appropriate conditions of fermen-
tation are provided. Nevertheless, its commercial
implementation is prevented by the low efficiency of
the process and by detrimental compounds in the
products [7, 8]. However, recent studies of this process
confirm, that hydrogen production from biomass by
fermentation will soon become technologically effi-
cient [8–10].
Biochemical conversion of molasses makes it pos- tion and limitation of oxidizing process of Ni due to
sible to obtain a gaseous mixture with a CH4/CO2/H2 spillover effect. For these reasons, a bimetallic
ratio of 2/2/1 [10].
Ru−Ni0.5/Mg2.5(Al)O catalyst was much more stable
509

510
MIERCZYNSKI et al.
in steam conversion of methane than a monometallic about 10°C/min. The resulting catalytic systems were
Ni0.5/Mg2.5(Al)O catalyst.
reduced in a mixture of hydrogen and argon (5%
H2−95% Ar).
The phase composition of the catalytic systems was
studied using an X’Pert PRO MPD analyzer (PANa-
lytical, Netherlands) with CuKα radiation (λ= 154.05 μm)
in the 2θ range from 20° to 90°.
The morphology and composition of the catalyst
was studied using a scanning electron microscope
S-4700 (HITACHI, Japan), equipped by the energy-
dispersive spectrometer ThermoNoran (Thermo
Fisher Scientific, USA).
Methane conversion was carried out in a flow-type
quartz microreactorwith an inner diameter of 6 mm at
an atmospheric pressure and temperatures of 700 and
900°С. The volume composition of the reaction mix-
ture was CH4/CO2/H2/H2O/Ar = 2/2/1/0.9/1.25.
The catalytic activity was measured after preliminary sta-
bilization for 0.5 h. The catalyst sample weight in each
run was 0.1 g. The overall gas flow was 100 cm3/min. The
composition of gases before and after the reaction was
measured using gas chromatographs Varian 3300 (Agi-
lent Technologies, USA) and Chrom 4 (Laboratorní
přístroje, Czech Republic) equipped with thermal
conductivity detectors.
In the course of methane reforming process, unde-
sirable processes may also occur and they lead to the
formation of carbon deposits resulting in catalyst
deactivation. It is known that the carbon deposit for-
mation depends on the composition of the reaction
mixture used in reforming reaction. For instance, the
low concentration of CO2 or steam in the reaction
mixture favors carbon deposit formation. There are
several types of carbon deposits (carbon fibers, carbon
tubes, graphitic carbon) some of which are capable of
mechanically destructing a catalyst [14, 15]. This
undesirable phenomenon can be excluded by choos-
ing appropriate components of the catalytic system
[12–19].
In this work, we show how to use of biogas obtained
from biomass for syngas production. Mixed methane
reforming process was carried out over both mono-
and bimetallic supported catalysts at 700 and 900°С,
respectively. We studied physicochemical properties of
the catalytic systems by XRD, scanning electron
microscopy (SEM) and temperature-programmed
reduction by hydrogen (TPR-Н2) methods.
Methane and carbon dioxide conversions were cal-
EXPERIMENTAL
Preparation of Supports and Supported Catalysts
culated using the following formulas:
W (CH ) ⋅W (Ar)
⎛
⎜
⎝
⎞
⎟
⎠
i
4
0
Alumina was obtained by precipitation from an
aqueous solution of aluminum nitrate using ammonia
as a precipitation agent (up to pH 9−10). The mixture
thus prepared was left to stay for 24 h and then filtered
and washed by distilled water to pH 7. The resulting
Al(OH)3 gel was dried in air at 100°С for 12 h and cal-
cined in an atmosphere of air at 500°С for 4 h.
The modification of Al2O3 was carried out by the
method of wet impregnation of prepared support by
the corresponding amounts of the aqueous solutions
of magnesium or calcium nitrates. Impregnated sup-
port was left to stay for 24 h, and then the solvent was
evaporated. The resulting samples (5% CaO–Al2O3
and 5% MgO–Al2O3) were dried in air at 100°C for 12
h and calcined in air at 500°C for 4 h.
Monometallic nickel catalysts were obtained by wet
impregnation. The nickel phase was supported on the
support surface from an aqueous solution of nickel(II)
nitrate. Upon impregnation and evaporation of the sol-
vent, the samples were calcined in air at 500°С for 4 h.
Bimetallic (1% Ru−20% Ni) catalysts were
obtained by the subsequent wet impregnation of mono-
metallic nickel catalysts by an aqueous solution of ruthe-
nium(III) chloride according to the procedure described
above. Samples were calcined at 400°С for 4 h.
(1)
(2)
XCH = 1 −
× 100%,
×100%,
4
W (CH ) ⋅W (Ar)
0
4
i
W (CO ) ⋅W (Ar)
⎛
⎜
⎝
⎞
⎟
⎠
i
2
0
XCO = 1 −
2
W (CO ) ⋅W (Ar)
0
2
i
where W0 and Wi are the volume concentration of the
component in the reaction mixture before and after
reaction.
RESULTS AND DISCUSSION
Figure 1 shows the results of TPR-Н2 experiments
for monometallic nickel and bimetallic Ru–Ni cata-
lysts supported on nonpromoted and promoted CaO–
Al2O3 or MgO–Al2O3 supports. The curve recorded
for Ni/Al2O3 catalyst show three hydrogen consump-
tion peaks (Fig. 1a). The first two have maximums at
260 and 380°С related to the reduction of surface NiO
compounds that are bound and not bound to the sup-
port [21]. The third reduction peak located in the tem-
perature range 500–900°C is related with the Ni–O–
Al (like in spinel NiAl2O4) linkage reduction. On the
TPR-Н2 profile of the Ni/CaO–Al2O3 catalyst, one
can see the same reduction stages as in the above case
(Fig. 1a). However, the proportions between individ-
ual effects have changed. At ~450°C, there is an inten-
sity peak assigned to the reduction of NiO interacting
with the support. The lower intensity of the high tem-
Methods of Catalyst Study
TPR-Н2 was carried out using automated TPR sys- perature reduction peak can be explained by the fact
that calcium oxide covering the catalyst surface which
prevents the Ni-O-Al species formation. The TPR-Н2
tem AMI-1 (Altamira Instruments, USA) in a range of
temperatures of 25−900°C with a heating ramp of
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2018

SUPPORTED Ru−Ni CATALYSTS FOR BIOGAS
511
shows three stages analogous to other catalytic systems
which are described abov. It is also worth to note that all
observed reduction stages are shifted towards higher
temperature range compared to monometallic nickel
catalyst supported on Al2O3.
(а)
20%Ni/MgO–Al2O3
Figure 1b show the results of reduction studies for
bimetallic systems. The reduction of the 1%Ru-
20%Ni/Al2O3 shows similar reduction behavior
recorded for monometallic Ni catalyst. The only dif-
ference is the appearance of an additional effect
related to the reduction of RuO2 situated at tempera-
ture below 200°C. This has also been noted in our ear-
lier studies [21, 22]. It is well known that promotion of
nickel catalyst by ruthenium facilitates its reduction
what is confirmed by the shift of the reduction effect
towards lower temperature range. This is explained by
the spillover effect between ruthenium and nickel (II)
oxide.
20%Ni/CaO–Al2O3
20%Ni/Al2O3
200 300 400 500 600 700 800 900
100
0
Temperature, °С
(b)
1%Ru–20%Ni/MgO–Al2O3
XRD of reduced monometallic and bimetallic cat-
alysts are shown in Fig. 2. The diffraction pattern of
the Ni/Al2O3 sample has peaks at 2θ of 35°, 46°, and
67° related to the γ-Al2O3 phase. The same pattern has
additional reflexes related to NiO and Ni phases.
Results described in [22] for nickel catalysts were anal-
ogous. The presence of both Ni and NiO phases con-
firmed the partial reduction of the active phase of the
supported catalyst at 500°C. Taking into account ionic
of Al3+, Mg2+, and Сa2+, we suggest that spinel struc-
ture is formed only in the case of Mg2+ and Al3+ com-
pounds. On the diffraction patterns, there are reflexes
at 2θ = 35° and 67°, which can be due to the γ-Al2O3
phase or МgAl2O4 spinel structure. The formation of
the spinel phase can be indicated by a small shift and
broadening of the corresponding reflexes. There is
also a noticeable shift of the characteristic nickel reflex
(at 2θ = 45°) toward lower reflection angles, which
1%Ru–20%Ni/CaO–Al2O3
1%Ru–20%Ni/Al2O3
200 300 400 500 600 700 800 900
100
0
Temperature, °С
Fig. 1. TPR-H profiles for (a) the monometallic 20%
2
Ni/Al O catalyst after calcination in air for 4 h at 500°С
2
3
and (b) the bimetallic 1% Ru–20% Ni/Al O catalyst after
2
3
calcination in air for 4 h at 400°С.
recorded for 20% Ni/MgO–Al2O3 has a simial shape
for the profile of Ni/Al2O3 catalyst (Fig. 1a). The
TPR-H2 curve of 20% Ni/MgO–Al2O3 reduction
Al2O3
NiO
А
B
C
А
B
C
Ni
MgAl2O4
1
3
1
1
1
2
1%Ru–20%Ni/MgO–Al2O3
1%Ru–20%Ni/CaO–Al2O3
1%Ru–20%Ni/Al2O3
4
3
4
3
3
4
20%Ni/MgO–Al2O3
5
6
20%Ni/CaO–Al2O3
20%Ni/Al2O3
Δ2θ = 0.3
Δ2θ = 0.7
Δ2θ = 0.4
Δ2θ = 0.7
30
40
50
60
70
80
90
2θ, deg
20
41
47.0
63.5
70.0
34
41.3
Fig. 2. XRD patterns for mono and bimetallic catalysts reduced at 500°C for 2 h in the 5% H –95% Ar mixture.
2
KINETICS AND CATALYSIS Vol. 59 No. 4 2018

512
MIERCZYNSKI et al.
(b)
(а)
(c)
Intensity of radiation, pulse
1500
Intensity of radiation, pulse
Intensity of radiation, pulse
Al
Al
Al
1500
500
Ni
400
300
1000
1000
500
Ni
200
100
Mg
Ni
500
O
Ni
O
Cl
Ca
Ca
O
Ni
С
Ni
Ni
Cl
С
Cl
С
Ni
Ni
0
1 2 3 4 5 6 7 8 9 10 0
Energy, keV
1 2 3 4 5 6 7 8 9 10 0
Energy, keV
1 2 3 4 5 6 7 8 9 10
Energy, keV
(а)
(b)
(c)
NiK
0
14 NiK
0
10 NiK
0
10
5 μm
5 μm
5 μm
Fig. 3. SEM images and energy-dispersive spectra for the catalysts (a) 20%Ni–1%Ru/Al O , (b) 20%Ni–1%Ru/5%CaO–Al O , and
2
3
2 3
(c) 20%Ni–1%Ru/5%MgO–Al O calcined in air at 500°C for 4 h.
2
3
confirms the formation of the ruthenium–nickel alloy cium and magnesium on the surface of the modified
formation.
by MgO and CaO nickel catalysts. Based on the analy-
sis of energy-dispersive spectra, one may conclude that
the highest dispersion of nickel was observed in the case
of 20%Ni-1%Ru/5%MgO–Al2O3.
The surface morphology and elemental composi-
tion of bimetallic Ru-Ni supported catalysts were
determined by scanning electron microscope
equipped with energy dispersive spectrometer. The
It is also worth to notice, that the presence of chlo-
analysis of the surface composition of bimetallic cata- rine on the surface of the all bimetallic supported cat-
lysts (Fig. 3) showed the presence of nickel, alumi- alysts was also detected. The presence of chlorine on
num, chlorine, and oxygen. The results obtained for the catalyst surface is explained by its introduction
promoted catalysts confirmed also the presence of cal- during impregnation step of the catalyst. The lowest
Table 1. The effect of reaction temperature on the catalytic activity in methane conversion for mono- and bimetallic cata-
lysts supported on 5%Al2O3–95%MgO Al2O3 and 5%CaO–95%Al2O3
Conversion of СН4, % Conversion of СО2, % Conversion of СН4, % Conversion of СО2, %
Catalyst
700 °C
900 °C
20%Ni/Al2O3
57
52
54
48
54
66
62
60
58
56
60
69
100
98
99
98
98
99
93
91
93
92
91
93
20%Ni/Al2O3–CaO
20%Ni/Al2O3–MgO
1%Ru–20%Ni/Al2O3
1%Ru–20%Ni/Al2O3–CaO
1%Ru–20%Ni/Al2O3–MgO
KINETICS AND CATALYSIS
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2018

SUPPORTED Ru−Ni CATALYSTS FOR BIOGAS
513
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Table 1 shows the results of the catalytic activity
tests performed for the investigated catalysts in mixed
reforming of methane process expressed as methane
and carbon dioxide conversions. The catalytic activity
studies show that the higher temperature of reaction
leads to a higher conversion of methane and carbon
dioxide. Monometallic catalysts have a similar catalytic
activity at 700°C. The catalytic measurements showed
also that only bimetallic Ru-Ni/MgO–Al2O3 sup-
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carbon dioxide conversions.
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In this work we propose an efficient method for
biomethane and biohydrogen conversion to syngas.
The promotion effect of ruthenium on nickel catalyst
reduction was proven by TPR-H2 method. Catalytic
activity tests showed that the highest methane and car-
bon dioxide conversion were obtained for the Ru–
Ni/MgO–Al2O3 bimetallic catalysts. This is likely to
be due to the uniform distribution on nickel of the sup-
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ACKNOWLEDGMENTS
This work was supported under the project BIO-
STRATEG2/297310/13/NCBiR/2016.
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KINETICS AND CATALYSIS Vol. 59 No. 4 2018