Synthesis Gas Production by Partial Oxidation of Methane and Dry Reforming of Methane in the Presence of Novel Ni–Co/MFI Catalysts

Article abstract of DOI:10.1134/S0965544118030052

Catalysts based on Ni, Co, and NiCo supported on MFI zeolites for the partial oxidation of methane and dry reforming of methane to synthesis gas have been synthesized and studied. The total metal content in the catalysts is 2 wt %. A commercial zeolite with a binder (alumina) and a binder-free zeolite synthesized by an accelerated microwave-assisted hydrothermal method are used as supports. The synthesis gas yield is 97% in the presence of Ni and NiCo catalysts supported on the MFI zeolite synthesized by the microwaveassisted hydrothermal method. The simultaneous presence of Ni and Co in the catalyst makes the sample resistant to coking during dry reforming of methane, whereas the Ni catalyst is characterized by the formation of a significant amount of carbon fibers.

Full text of DOI:10.1134/S0965544118030052

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 3, pp. 203–213. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © A.G. Dedov, A.S. Loktev, I.E. Mukhin, A.A. Karavaev, S.I. Tyumenova, A.E. Baranchikov, V.K. Ivanov, K.I. Maslakov, M.A. Bykov, I.I. Moiseev, 2018,
published in Neftekhimiya, 2018, Vol. 58, No. 2, pp. 154–164.
Synthesis Gas Production by Partial Oxidation of Methane
and Dry Reforming of Methane in the Presence
of Novel Ni–Co/MFI Catalysts
A. G. Dedova, A. S. Lokteva, *, I. E. Mukhina, A. A. Karavaeva, S. I. Tyumenovaa,
A. E. Baranchikovb, V. K. Ivanovb, K. I. Maslakovc, M. A. Bykovc, and I. I. Moiseeva
aGubkin Russian State University of Oil and Gas (National Research University), Moscow, Russia
bKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
cMoscow State University, Moscow, Russia
*e-mail: al57@rambler.ru, genchem@gubkin.ru
Received September 11, 2017
Abstract—Catalysts based on Ni, Co, and NiCo supported on MFI zeolites for the partial oxidation of meth-
ane and dry reforming of methane to synthesis gas have been synthesized and studied. The total metal content
in the catalysts is 2 wt %. A commercial zeolite with a binder (alumina) and a binder-free zeolite synthesized
by an accelerated microwave-assisted hydrothermal method are used as supports. The synthesis gas yield is
97% in the presence of Ni and NiCo catalysts supported on the MFI zeolite synthesized by the microwave-
assisted hydrothermal method. The simultaneous presence of Ni and Co in the catalyst makes the sample
resistant to coking during dry reforming of methane, whereas the Ni catalyst is characterized by the formation
of a significant amount of carbon fibers.
Keywords: synthesis gas, partial oxidation of methane, dry reforming of methane, cobalt, nickel, MFI zeolite,
microwave-assisted hydrothermal synthesis
DOI: 10.1134/S0965544118030052
Synthesis gas (CO–H2 mixture) is a key intermedi- oxidizer. The two reaction products (CO and H2)
ate in the production of petrochemicals and hydro- undergo oxidation more readily than the feed methane
gen—a promising environmentally friendly fuel—from does. A rapid removal of these products from the reac-
methane-containing feedstocks [1–8]. Partial oxida- tion zone makes it possible to eliminate the wastage of
tion of methane (POM) and dry reforming of methane carbon [6]. The activity of nickel-based catalysts is not
(DRM) have a number of advantages over the cur- inferior to that of platinum metals and is significantly
rently available synthesis gas production processes superior to the activity of cobalt catalysts at relatively
based on steam reforming of methane. Advantages of lower temperatures; however, nickel catalysts are
POM are the process exothermicity and the composi- prone to forming carbon deposits on their surface,
tion of the resulting synthesis gas (H2/CO = 2) that is particularly in DRM; these deposits not only block the
active sites of the catalyst, but also lead to the clogging
favorable for the Fischer–Tropsch synthesis of hydro-
carbons and methanol synthesis. The DRM process
(H2/CO = 1) is important from an environmental
point of view because it contributes to the utilization of
carbon dioxide, which is the main greenhouse gas. In
addition, the DRM process can be based on the con-
version of biogas, which is a renewable raw material.
Well-known POM and DRM catalysts are plati-
num group metals, nickel, and cobalt on oxide sup-
ports of various chemical origins [1–8]. In the pres-
ence of these catalysts, at about 1000°C, methane
molecules begin to lose hydrogen atoms to generate
intermediates, which form CO in the presence of an
oxidizer (CO2 and O2 in the case of DRM and POM,
of the reactor.
An approach to solving these problems is the use of
catalysts with a small size of active metal particles and
a high specific surface area of the support [7]. Among
the supports used for this purpose, an emphasis should
be put on zeolites of various structures and zeolite-like
mesoporous materials, which have a positive effect on
the properties of nickel catalysts. In addition, the
degree of coking of nickel catalysts can be decreased by
admixing nickel with another component that will
contribute to the oxidation of the surface carbon. One
of these components is cobalt [9].
The deposition of 5–10 wt % Ni on the BEA zeolite
respectively) and carbon deposits in the absence of an leads to the formation of a POM catalyst which pro-
203

204
DEDOV et al.
vides a quantitative yield of CO at 700–900°С [7]. The talline silica gel [14]. At 800°C, the best results
zeolite dealumination improves the catalyst stability; a were obtained in the presence of a catalyst containing
decrease in the nickel content to 1 wt % leads to a sig- 5 wt % Ni with Si/Al = 30; in this case, the conversion
nificant decrease in the catalyst activity.
of CO2 and CH4 was 98 and 95%, respectively, at
H2/CO = 0.91.
The 10%Ni/25%CeO2–ZrO2/ZSM-5 catalyst is
active in POM even at 400°C; it provides a methane
conversion of 50%. At 700°C, the methane conversion
achieves 90% [10].
The catalytic activity of nickel (1 wt %), platinum
(0.5 wt %), and mixed nickel–platinum catalysts sup-
ported on the dealuminated FAU, Y, and BEA zeolites
in DRM at 600–640°C was determined as the number
of moles of methane converted per gram of metal per
hour [15]. The mixed nickel–platinum catalysts were
less active than the platinum samples, whereas the
nickel catalysts were inactive and underwent severe
coking. The best support was the dealuminated BEA
zeolite; the activity of NiPtBEA and PtBEA was 1.9
and 3.2 mol/(g h), respectively.
Various zeolite supports and a number of cocata-
lysts that contribute to a decrease in the degree of cok-
ing were tested in DRM. POM catalysts synthesized
by calcination of a mixture of nickel nitrate or nickel,
potassium, and calcium nitrates with the ZSM-5 zeo-
lite (Si/Al > 200) containing 20% of alumina used as a
binder were studied [11]. A nitrogen-diluted mixture
of methane and CO2 was fed into the reactor. In the
presence of a 5.3 wt % Ni/ZSM-5 catalyst, the CO
yield was 77% at 700°C; in this case, significant coking
was observed. The addition of K and Ca led to a slight
increase in the CO yield; however, coking was elimi-
nated. A decrease in the Ni content in Ni/ZSM-5 to
2.4 wt % led to a decrease in the CO yield to 70% and
elimination of coking. With an increase in the Ni con-
tent to 9.7 wt %, the CO yield increased to 83%, while
coking became more significant. At 900°C, the
KNiCa/ZSM-5 catalyst provided a quantitative yield
of synthesis gas.
At 700°C, a bimetallic Ni(2.5%)Rh(2.5%)/BEA
catalyst [16] provided a methane and CO2 conversion
of 73 and 78%, respectively; the results were similar to
those obtained in the presence of 5% Rh/BEA. How-
ever, the rhodium catalyst was not prone to coking,
while the bimetallic sample contained 3% of coke after
2 h on-stream. The 5% Ni/BEA catalyst showed close
initial conversion values for the reactants; however, it
underwent rapid deactivation because of severe coking
(7% coke after 2 h).
The addition of 0.1 wt % Rh to a 7.5% Ni/NaY
DRM catalyst provided a 100% conversion of CO2 and
methane at 560–585°C [17].
Nickel, cobalt, and mixed NiCo catalysts deposited
on the ZSM-5 zeolite (Si/Al = 11.5) by impregnation
were tested in DRM [12]. The metal content in the
catalysts was 7 wt %. In a range of 600–800°С, close
hydrogen yields (58–65%) were observed in the pres-
ence of these catalysts, except for the cobalt sample. In
the presence of the cobalt catalyst, this hydrogen yield
was achieved only above 700°C. However, this catalyst
exhibited the highest CO selectivity at 600°C (68%).
At 800°C, the CO selectivity of all the catalysts was
approximately the same—at a level of 60–62%. It was
found that the nickel catalyst was prone to coking;
with respect to the methane and CO2 conversion, it
was inferior to the mixed nickel–cobalt catalysts. In
general, the catalyst with Ni/Co = 0.5 was the most
active and stable. At 800°C, the conversion of CO2 and
methane was 85 and 75%, respectively; the synthesis
gas selectivity was 63%. The degree of coking was less
than 1%.
The catalysts containing 5–7 wt % Ni supported on
the Y zeolite exhibited higher activity in DRM than
the activity of samples synthesized by the deposition of
Ni on A, X, and ZSM-5 zeolites [13]. At 800°C, the
methane and CO2 conversion remained at a stable
level of 92% for 5 h, while the hydrogen selectivity was
65%. The catalyst containing 3% Ni showed similar
results at the beginning of the test; however, over time,
the parameters decreased. It should be noted that less
active catalysts were less prone to coking.
Ultrasound irradiation of a catalyst containing
cobalt supported on the H–Y zeolite made it possible
to synthesize more active catalysts owing to an
increase in the degree of dispersion of the cobalt par-
ticles [18]. A catalyst containing 10 wt % of cobalt pro-
vided a hydrogen and CO yield of 61 and 80%, respec-
tively, at 850°C and 55 and 77%, respectively, at
750°C. However, the methane and CO2 conversion
values significantly decreased after 10 h on-stream.
Nickel–platinum catalysts supported on a silicalite
of the MFI structure (also known as ZSM-5) and
encapsulated in a silicate shell were tested in DRM
[19]. A catalyst containing 1.5 wt % Ni with the addi-
tion of 0.5 wt % Pt showed a methane and CO2 con-
version of about 80% at 800°C; however, after 20 h on-
stream, the conversion decreased to 60%. The plati-
num-free catalyst underwent deactivation much more
rapidly. The catalysts that were not encapsulated in
SiO2 completely lost their activity after 1–6 h.
The authors of [20] synthesized Ni DRM catalysts
using a silicate with the ferrierite (FER) zeolite struc-
ture, an MFI silicalite, and a silicate with an ordered
mesoporous MCM-41 structure. The Ni content was
5 wt %. At 700°C, the catalysts showed comparable
conversions of methane (63–77%) and CO2 (83–
DRM results depend on the Si/Al ratio in Ni cata- 90%); however, the best results were obtained in the
lysts containing the NaZSM-5 zeolite and semicrys- presence of Ni/FER, which was stable for 30 h.
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SYNTHESIS GAS PRODUCTION BY PARTIAL OXIDATION OF METHANE
205
The use of a mesoporous SBA-16 silicate for the thermal method, was used for comparison. The spe-
cific surface area was 325 m2/g. Hereinafter, it is
referred to as MFIht.
deposition of nickel led to the formation of an unstable
DRM catalyst [21]. At the same time, at 700°C, the
SBA-16-based catalyst containing 5 wt % Ni and
14.7 wt % Ce exhibited a stable methane conversion of
68–72%, a CO2 conversion of 74–77%, and an H2
selectivity of 85% for 100 h.
The authors of [22] synthesized DRM catalysts on
the basis of mesoporous alumina; nickel and cerium
were introduced at the hydrothermal synthesis stage.
The nickel content was 7 wt %, while the cerium con-
tent in the cerium–alumina matrix was varied in a
range of 1–4 mol %. It was found that the catalyst con-
taining 1 mol % cerium was the most effective. At
800°C, the methane and CO2 conversion achieved
85%, while the CO and H2 selectivity was 95%.
The zeolite fraction (0.5–1 mm) was dried at
300°C, weighed, and immersed in an aqueous solution
containing calculated amounts of cobalt nitrate hexa-
hydrate, nickel nitrate hexahydrate, or a mixture
thereof providing 2 wt % of the metal in the catalyst
subjected to drying and calcination at 500°C. The
mixed nickel–cobalt catalysts contained 1 wt % of
each of the metals; in the case of nickel and cobalt, this
concentration approximately corresponds to equimo-
lar amounts of the metals. Six catalyst samples
were prepared; hereinafter, they are referred to as
NiMFImw, CoMFImw, NiCoMFImw, NiMFIht,
CoMFIht, and NiCoMFIht.
The phase composition of the catalysts was deter-
mined on a Rigaku MiniFlex 600 diffractometer
(Japan) equipped with a detector with a graphite
monochromator and a copper anticathode using Cu
Kα radiation at λ = 1.54187 Å. The phase composition
was determined using the International Center for
Diffraction Data (ICDD) database.
The catalyst morphology before and after testing in
POM and DRM was studied using a Carl Zeiss NVi-
sion 40 scanning electron microscope (SEM)
equipped with secondary electron (SE or InLens) and
backscattered electron detectors (ESB) at an acceler-
ating voltage of 7 and 1 kV, respectively, and a magni-
fication of up to 200000× and a JEOL JSM-6390LA
SEM instrument (Japan) equipped a with secondary
electron detector at an accelerating voltage of 5–25 kV.
The described literature data are not exhaustive;
references in the cited papers contain data on a num-
ber of other studies of POM and DRM catalyzed by
nickel-containing zeolite systems. However, the cited
data elucidate the appropriateness of using these cata-
lysts. In particular, effective supports are MFI materi-
als exhibiting high thermal stability; in the literature,
they are commonly referred to as ZSM-5 [10–14]. All
the studied catalysts based on MFI zeolites, except for
samples comprising platinum group metals, contained
a significant amount of nickel (5 wt % and more); the
zeolites were synthesized by the conventional hydro-
thermal method. The use of microwave treatment
during the hydrothermal synthesis of MFI zeolites
provides a significant acceleration of the crystalliza-
tion process and the formation of materials with
improved morphological characteristics [23, 24].
The texture characteristics of the catalysts were
determined by low-temperature nitrogen sorption on a
Quantachrome AUTOSORB-1C/MS/TPR instru-
ment. The results were processed using the Quanta-
chrome AS1Win software package using the
Brunauer–Emmett–Teller (BET), t-plot, Barrett–
Joyner–Halenda (BJH), and nonlocal density func-
tional theory (NLDFT) methods.
The catalytic properties of the samples in the POM
and DRM reactions were studied in a heated flow-
type quartz reactor with a thermocouple pocket. The
end of the thermocouple was located in the middle of
the catalyst bed. For the POM reaction, the free vol-
ume of the reactor was filled with quartz chips. The
weight of the catalyst loaded into the reactor was 0.2 g;
the pellet size was 0.5–1 mm. The reactor was fed with
CH4–O2 or CH4–CO2 mixtures undiluted with an
inert gas (manufactured at Moscow Gas Refining
Plant; purity of 99.9%). The CH4/O2 ratio was 2;
CH4/CO2 = 1; the flow rate of the gas mixtures was
11–12 and 15–16 L/(g cat h), respectively. The cata-
lyst was heated to a predetermined temperature in a
stream of a CH4–O2 or CH4–CO2 mixture for 1 h;
The aim of this study is to synthesize and test POM
and DRM catalysts containing 2 wt % of nickel,
cobalt, or a mixture thereof supported on an MFI zeo-
lite synthesized by the microwave-assisted hydrother-
mal method. For comparison, similar catalysts sup-
ported on a commercial hydrothermally produced
MFI zeolite containing alumina as a binder were stud-
ied. The use of POM and DRM catalysts based on an
MFI zeolite containing less than 5 wt % of nickel and
no platinum metal additives and catalysts based on an
MFI zeolite synthesized by the microwave-assisted
hydrothermal method has not been described in the
literature.
EXPERIMENTAL
An MFI zeolite with a Si/Al molar ratio of 20 was
synthesized by the microwave-assisted hydrothermal
method [23] and transferred to the H form by ion
exchange with ammonium nitrate and calcination of
the ammonium form (hereinafter referred to
as MFImw). An MFI zeolite in the H form with
Si/Al = 38 containing 20 wt % of alumina as a binder,
which was manufactured at OAO Novosibirsk Chem- after analysis, the temperature was increased or
ical Concentrates Plant by the conventional hydro- decreased to specified values. The product composi-
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206
DEDOV et al.
Table 1. Texture characteristics of the catalysts according to low-temperature nitrogen sorption data
c, cm3/g
Vpore dif.diam
*, cm3/g
Vpore, total
a, m2/g
371
353
323
b, m2/g
Smicropore
Catalyst
Ssp
<1 nm
1–5 nm
5–50 nm
NiMFImw
0.195
Original
POM
DRM
367
346
309
0.131
0.128
0.118
0.027
0.017
0.010
0.014
0.020
0.055
0.190
0.295
CoMFImw
0.196
Original
POM
DRM
376
255
329
375
254
324
0.134
0.119
0.110
0.025
0.009
0.034
0.012
0.055
0.016
0.145
0.192
NiCoMFImw
0.194
Original
POM
DRM
380
329
361
379
323
355
0.135
0.115
0.137
0.025
0.023
0.015
0.012
0.017
0.017
0.180
0.188
NiMFIht
0.326
Original
POM
DRM
345
314
308
269
246
242
0.106
0.090
0.093
0.032
0.035
0.027
0.130
0.142
0.146
0.323
0.351
CoMFIht
0.322
Original
POM
DRM
347
308
277
274
227
226
0.106
0.077
0.090
0.033
0.044
0.027
0.130
0.137
0.062
0.319
0.218
NiCoMFIht
0.326
Original
POM
DRM
339
340
295
274
264
235
0.102
0.098
0.089
0.034
0.041
0.028
0.124
0.127
0.118
0.328
0.289
a
Calculated by BET.
Calculated by t-plot.
Calculated by NLDFT.
b
c
* Determined at P/P = 0.99.
0
tion was analyzed by chromatography as described adsorption–desorption isotherms suggests that the
in [9].
MFImw samples contain pores with a size of 2–5 nm.
The volumes of micro- and mesopores of different
sizes were determined by the NLDFT method. The
shape of the adsorption–desorption isotherms sug-
gests that the MFImw samples contain a negligible
amount of mesopores.
RESULTS AND DISCUSSION
All the samples based on the MFImw zeolite exhib-
ited nitrogen adsorption–desorption isotherms char-
acteristic of microporous MFI materials. It is evident
The hysteresis observed for some samples is appar-
that most of the pore volume and an even larger por- ently attributed to the presence of poorly accessible
tion of the surface area are attributed to the presence of micropores. This assumption is based on the increase
ultramicropores with a size of less than 1 nm (Table 1). in nitrogen absorption with decreasing pressure,
In the adsorption isotherm, the presence of these which is observed in desorption isotherms for some
micropores is evidenced by an abrupt absorption of MFImw samples. In fact, in this case, an equilibrium
nitrogen even at extremely low pressure. Owing to this adsorption isotherm cannot be obtained; therefore, an
feature, data on the pore sizes and surface cannot be additional “absorption” of nitrogen is recorded during
obtained using nitrogen as an adsorbate. The only desorption. In accordance with the recommendations
parameter that can be determined reliably is the vol- of IUPAC and the established practice for micropo-
ume of these pores. In addition, the shape of the rous materials, calculations in the region of low rela-
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SYNTHESIS GAS PRODUCTION BY PARTIAL OXIDATION OF METHANE
207
tive pressures (<0.02 P/P0) were conducted by the led to an improvement of the POM results, rather than
to worsening.
BET method.1 In general, it should be noted that, for
all the samples based on the MFImw zeolite, the total
specific surface area, the specific surface area of
micropores, and the volume of ultramicropores
decreased after POM and DRM catalysis. However,
the ultramicroporous structure remained dominant in
the composition of the used samples; in general,
this finding suggests that the texture of the catalysts is
stable.
The catalysts based on the MFIht zeolite also have
a significant specific surface area of micropores; how-
ever, the total pore volume in them is higher; this fact
is apparently associated with the presence of a
binder—alumina—in their composition. The determi-
nation of the volumes of micro- and mesopores by the
NLDFT method suggests that the volume of pores
with a size of more than 2 nm significantly increased.
At the same time, it was found that the total volume of
micro- and mesopores was two orders of magnitude
lower than the total pore volume; this finding indi-
cates the presence of a large volume of macropores
and a developed outer surface. This assumption is sup-
ported by a significant difference between the total
specific surface area and the specific surface area of
micropores. The involvement in the POM and DRM
catalysis led to a decrease in the total specific surface
area and the specific surface area of micropores; how-
ever, it had a slight effect on the total pore volume and
the volumes of micro- and mesopores.
The nature of the support and the supported metals
significantly affected the results of the conversion of a
methane–oxygen mixture by the POM process. In the
presence of the NiMFImw and NiCoMFImw cata-
lysts, the methane conversion and the synthesis gas
yield achieved high values even at 800°C; in addition,
the results did not change substantially with increasing
temperature (Table 2). The obtained results are almost
the same as those described in the literature [7, 10];
however, they were observed for catalysts containing a
significantly lower amount of nickel. With a decrease
in the nickel content from 5 to 1 wt %, the parameters
of the NiBEA POM catalyst considerably decreased
[7], whereas the NiCoMFImw catalyst containing
1 wt % nickel showed high values of methane conver-
sion and synthesis gas yield in POM; this finding
shows that the use of the MFImv zeolite as a support is
advantageous.
It was found that the nickel-free CoMFImw sam-
ple was nonselective in POM. The methane conver-
sion did not reach 40%; the hydrogen yield was negli-
gible; the formation of large amounts of deep oxida-
tion products (CO2 and water), methane condensation
products, coke, and resins was observed. However, it
should be noted that the addition of cobalt to nickel
The replacement of MFImw by MFIht led to a sig-
nificant worsening of the POM results in the presence
of the NiMFIht nickel catalyst, which exhibited a
behavior similar to that of CoMFImw. It was expected
that the CoMFIht catalyst will show poor results in the
tests; therefore, the catalyst was immediately heated to
950°C. This heating did not lead to a high synthesis gas
yield. After subsequent cooling to 920 and 900°C, the
hydrogen yield remained low; however, the methane
conversion and the CO yield unexpectedly increased.
In the set of catalysts based on the MFIht zeolite,
the mixed NiCoMFIht sample was the most selective.
Heating to 900–950°C provided a synthesis gas yield
of 60–65%. However, the catalyst was unstable; after
the subsequent decrease in the POM temperature to
920 and 900°C, the results became worse than those
observed at the same temperature during heating.
Thus, the MFI zeolite synthesized by the micro-
wave-assisted hydrothermal method is more advanta-
geous as a support for nickel and nickel–cobalt POM
catalysts. The difference of the catalysts supported on
this zeolite from the counterparts based on the com-
mercial sample consists in the dominance of the
microporous structure (Table 1); in addition, accord-
ing to SEM, the catalysts have different morphologies
(Fig. 1).
It is evident that the MFImw-based catalysts con-
tain larger well-crystallized zeolite particles. Their sur-
face contains nanoparticles comprising nickel and
cobalt (light areas detected by backscattered electron
imaging) and no significant carbon deposits. The
MFIht-based catalysts contain smaller arbitrarily
shaped zeolite particles.
Analysis of the diffraction patterns of the catalysts
before and after POM (Fig. 2) showed that all of them
exhibit intense reflections at 2θ = 7°–10° and 22°–25°
characteristic of MFI zeolites. Reliable identification
of phases corresponding to nickel, cobalt, and their
oxides is hindered because, at respective 2θ values,
broad low-intensity reflections attributed to a small
particle size are observed. However, it can be stated
that the diffraction patterns of the original monome-
tallic catalysts do not exhibit characteristic reflections
of cobalt and nickel oxides; this finding can be associ-
ated with both a low metal content and a small oxide
particle size.
The latter assumption is more reasonable because,
after POM, reflections attributed to divalent nickel
and cobalt oxides can be observed. The original bime-
tallic NiCoMFIht catalyst can contain the NiCo2O4
phase (possibly NiO). After POM, metal particles
were not recorded in the diffraction patterns of the
catalysts; this fact can be apparently attributed to small
particle sizes or to cooling of the catalysts in a meth-
ane–oxygen mixture, which contributes to their oxi-
1
In the case of microporous samples, the calculation of specific
surface area by the BET method is always not entirely correct in
terms of the BET theory.
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208
DEDOV et al.
Table 2. Results of methane partial oxidation
Yield, wt %
Conversion CH4, %
T, °C
H2
CO2
C2+
CO
NiMFImw
800
850
900
920
950
95
97
97
97
97
92
92
95
97
95
95
2
1
0
0
0
0
0
95
97
Traces
95
Traces
Traces
95
CoMFImw
800
850
900
920
950
28
36
37
33
35
8
4
3
2
2
3
18
18
14
7
Traces
10
1
4
7
6
10
9
11
11
NiCoMFImw
800
850
900
920
93
97
98
98
89
86
91
97
97
4
2
1
1
0
0
0
0
93
97
97
NiMFIht
800
850
900
920
950
25
29
31
33
33
6
3
2
2
3
4
18
15
12
12
9
0
1
1
2
3
9
12
13
17
CoMFIht
950
920
900
34
80
80
16
4
4
4
10
1
5
0
2
67
66
3
NiCoMFIht
800
850
900
920
950
920
900
20
22
43
70
70
35
28
7
12
35
65
64
26
19
3
4
11
63
7
1
3
29
60
58
14
6
1
Traces
Traces
2
5
4
7
6
3
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SYNTHESIS GAS PRODUCTION BY PARTIAL OXIDATION OF METHANE
209
NiMFImw
NiMFIht
1 μm
1 μm
×25.000
NiCoMFIht
NiСoMFImw
1 μm
1 μm
×25.000
Fig. 1. SEM micrographs after POM catalysis.
dation. The spent catalysts did not exhibit ferromag-
netic properties.
The replacement of MFImw by MFIht, which sig-
nificantly worsened the results of POM in the pres-
ence of the NiMFIht nickel catalyst, conversely led to
an improvement of the results in the case of DRM. In
the presence of NiMFIht, the reactant conversion and
the synthesis gas yield increased to values exceeding
90% with an increase in temperature from 800 to
950°C and decreased with subsequent cooling to
600°C. However, even at 700°C, the synthesis gas
yield was close to 60%. It should be noted that, in the
tests, an increase in temperature led to the suppression
of CO2 hydrogenation to CO, which is an undesired
reaction; with the subsequent decrease in tempera-
ture, the vigorous occurrence of the reaction was
observed.
It was found that nickel-free CoMFImw was inac-
tive and nonselective either in DRM (Table 3) so as in
a series of POM tests. The conversion of methane and
CO2 did not exceed 40 and 60%, respectively; the
hydrogen yield was significantly lower than the CO
yield. The fact that the conversion of CO2 is higher
than that of methane and the yield of CO is higher
than that of hydrogen can be attributed to the occur-
rence of the side reaction of CO2 hydrogenation
(reverse water gas shift reaction) [12]: CO2 + H2 =
CO + H2O. At the same time, in the presence of the
NiMFImw and NiCoMFImw catalysts, high reactant
conversion and synthesis gas yield values were
achieved even at 800°C; in this case, the mixed
NiCoMFImw catalyst showed the best results despite
the fact that the nickel content in it was lower because
of partial replacement of nickel by less effective cobalt.
According to expectations, the CoMFIht catalyst
showed poor results in DRM tests; however, unlike the
POM process, heating to 950°C provided a jump-like
increase in the synthesis gas yield. After subsequent
cooling to 800°C, the reactant conversion and the syn-
thesis gas yield abruptly decreased.
An increase in temperature provided a nearly quan-
titative yield of synthesis gas. The observed synthesis
gas yield values were almost the same as the literature
The mixed NiCoMFIht catalyst is not inferior to
data on the yields obtained in the presence of nickel the nickel counterpart in the DRM reaction; however,
catalysts supported on various zeolites with a signifi- the contribution of the undesired CO hydrogenation
cantly larger nickel content [11–22].
reaction is more significant.
PETROLEUM CHEMISTRY Vol. 58 No. 3 2018

210
DEDOV et al.
Before POM
∗
∗
Zeolite MFI (ZSM-5)
NiCo2O4
∗
∗
Zeolite MFI (ZSM-5)
∗
#
∗
∗
∗
∗
#
∗
NiMFIht
NiMFImw
NiCoFIht
NiCoFImw
CoMFImw
CoMFIht
8
13 18 23 28 33 38 43 48
7
12 17 22 27 32 37 42 47
3
2
2θ, deg
2θ, deg
After POM
Zeolite MFI (ZSM-5)
∗
∗
∗
Zeolite MFI (ZSM-5)
∗
∗
NiO(CoO)
#
∗
NiO(CoO)
∗
#
∗
#
#
NiMFIht
#
NiMFImw
#
NiCoFIht
NiCoFImw
CoMFImw
CoMFIht
8
13 18 23 28 33 38 43 48
20
30
2θ, deg
40
50
3
10
2θ, deg
Fig. 2. Diffraction patterns of powders of the catalyst samples before and after POM.
SEM studies of the catalysts after DRM showed DRM, as in the case of POM, exhibits reflections
that the cobalt-free NiMFImw and NiMFIht samples
underwent severe coking (Fig. 3).
attributed to NiO. Their absence in the diffraction pat-
tern of NiMFIht after DRM can be associated with
the small sizes of these particles. The diffraction pat-
tern of the bimetallic NiCoMFImw catalyst after
The micrographs show carbon fibers or nanotubes
with a thickness of 30–50 nm. The cobalt catalysts,
which were ineffective in POM, did not undergo cok- DRM exhibits reflections that can be attributed to the
ing. The simultaneous presence of nickel and cobalt
provided a significant decrease in the degree of coking
of NiCoMFIht and completely eliminated coking in
the case of NiCoMFImw.
formation of a Ni(II)–Co(III) mixed oxide phase; in
the case of NiCoMFIht—the NiCoMFImw counter-
part—the low-intensity reflection that apparently cor-
responds to the same phase present in the original
sample is preserved (see Fig. 2).
The results show that the nickel-containing DRM
catalysts based on the commercial MFIht zeolite are
highly efficient in DRM; however, the use of nickel–
cobalt catalysts supported on the MFImw zeolite syn-
thesized by the microwave-assisted hydrothermal
method makes it possible to eliminate catalyst coking,
which is the main disadvantage of the DRM process.
The diffraction patterns of the catalysts after DRM
(Fig. 4) preserved the reflections characteristic of MFI
zeolites. It was impossible to reliably record reflections
of metallic particles, apparently because the particles
were small. Their presence in the nickel-containing
catalysts after DRM is indirectly confirmed by the fer-
romagnetic properties of these samples (catalysts were
well attracted to a magnet).
Thus, on the basis of Ni, Co, and NiCo supported
on the MFI zeolite synthesized by the microwave-
assisted hydrothermal method and the commercial
MFI zeolite, catalysts for synthesis gas production by
POM and DRM have been synthesized and studied.
The total metal content in the catalysts (2 wt %) is sig-
nificantly lower than that described in the literature
for analogous POM and DRM catalysts containing no
platinum group metals. It has been shown that Ni and
NiCo catalysts supported on the MFI zeolite synthe-
sized by the microwave-assisted hydrothermal method
provide a nearly quantitative yield of synthesis gas in
the POM process; the same metals supported on each
of the zeolites used are effective in DRM. The simul-
taneous presence of nickel and cobalt in a catalyst sup-
The diffraction pattern of CoMFImw, which is an
inefficient DRM catalyst, exhibits reflections
attributed to the formation of the Co3O4 phase. In the ported on the zeolite synthesized by the microwave-
assisted hydrothermal method makes the catalyst
diffraction pattern of the NiMFImw catalyst after resistant to coking during DRM, whereas the nickel
case of CoMFIht, this phase was not recorded. The
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SYNTHESIS GAS PRODUCTION BY PARTIAL OXIDATION OF METHANE
Table 3. Results of dry methane reforming
211
Conversion, %
Yield, wt %
T, °C
CH4
CO2
H2
CO
NiMFImw
800
850
900
920
950
73
81
89
91
93
80
84
91
93
76
80
90
92
94
58
70
83
87
86
95
CoMFImw
800
850
900
920
950
3
6
17
28
40
15
23
40
50
0
3
28
37
49
2
4
8
10
13
59
NiCoMFImw
800
850
900
920
950
88
92
95
97
97
90
94
97
98
88
92
96
97
98
72
80
91
97
94
99
NiMFIht
800
850
900
920
950
800
750
700
650
600
81
89
92
93
94
77
79
61
44
24
81
89
92
93
94
87
85
72
80
85
91
92
92
87
75
63
44
25
81
86
92
93
94
88
78
57
38
19
56
37
CoMFIht
800
850
900
920
950
800
3
7
7
10
84
3
12
15
8
12
83
12
1
2
2
2
81
1
1
3
6
6
84
3
NiCoMFIht
800
850
900
920
950
90
96
98
98
99
92
96
98
98
99
89
95
97
97
98
76
80
91
87
88
PETROLEUM CHEMISTRY Vol. 58 No. 3 2018

212
DEDOV et al.
NiMFImw
NiMFIht
32.00 nm
50.00 nm
48.00 nm
33.94 nm
40.00 nm
1 μm
1 μm
×25.000
СoMFImw
CoMFIht
1 μm
1 μm
×25.000
NiCoMFIht
NiСoMFImw
40.00 nm
32.00 nm
40.00 nm
35.78 nm
1 μm
1 μm
×25.000
Fig. 3. SEM micrographs of the catalysts after DRM.
Zeolite MFI (ZSM-5)
∗
∗
∗
∗
∗
∗
∗
∗
Zeolite MFI (ZSM-5)
NiCo2O4
Co3O4
NiO
NiCo2O4
∗
#
s
@
∗
#
s
NiMFImw
#
@
#
NiMFIht
#
NiCoFIht
NiCoMFImw
CoMFImw
CoMFIht
8
13 18 23 28 33 38 43 48
7
12 17 22 27 32 37 42 47
3
2
2θ, deg
2θ, deg
Fig. 4. Diffraction patterns of the catalyst powders after DRM.
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No. 3
2018

SYNTHESIS GAS PRODUCTION BY PARTIAL OXIDATION OF METHANE
213
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ACKNOWLEDGMENTS
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The authors thank S.A. Chernyak (Moscow State
University) for assistance in SEM studies. This work
was supported by the Russian Science Foundation,
project no. 14-13-01007P (catalyst synthesis, catalytic
tests, pore structure analysis); the Ministry of Educa-
tion and Science of the Russian Federation (basic part
of the state task “Organization of Scientific
Research,” application form no. 1422); and the Pre-
sidium of the Russian Academy of Sciences.
12. J. Estephane, S. Aouad, S Hany., et al. Int. J. Hydrogen
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PETROLEUM CHEMISTRY Vol. 58 No. 3 2018