Synthesis of nickel-copper-cobalt catalysts for deep oxidation of methane and optimization of their composition

Article abstract of DOI:10.1134/S1070427210010179

Possibility of fabricating catalysts based on Ni, Cu, Co, and Mn oxides by the impregnation method was examined. The samples obtained were subjected to physicochemical analysis and their catalytic activities in deep oxidation of methane were compared. The

Full text of DOI:10.1134/S1070427210010179

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 1, pp. 84−91. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © E.N. Vinogradova, A.V. Dul’nev, V.N. Efremov, E.Z. Golosman, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 1,
pp. 86−93.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Synthesis of Nickel–Copper–Cobalt Catalysts
for Deep Oxidation of Methane and Optimization
of Their Composition
E. N. Vinogradova, A. V. Dul’nev, V. N. Efremov, and E. Z. Golosman
NIAP-Katalizator Limited-Liability Company, Novomoskovsk, Tula oblast, Russia
Received July 29, 2009
Abstract—Possibility of fabricating catalysts based on Ni, Cu, Co, and Mn oxides by the impregnation method
was examined. The samples obtained were subjected to physicochemical analysis and their catalytic activities in
deep oxidation of methane were compared. The composition of the Ni–Cu–Co catalytic system was optimized.
DOI: 10.1134/S1070427210010179
The catalytic oxidation of hydrocarbons and, in
particular, methane is one of the most efficient and
cost-effective methods for purification of industrial
gases. It is preferable to perform deep oxidation, whose
technology provides conversion of a substance being
oxidized to carbon dioxide and water and precludes
formation of carbon monoxide and toxic oxygen-
containing organic substances. Compared with other
hydrocarbons, methane requires the highest temperatures
for its removal. Therefore, it has been stated [1] that, if the
required methane removal efficiency is provided under
certain purification conditions, this will be sufficient for
removing other hydrocarbons with the same efficiency.
Consequently, methane can be regarded as a key
component in gas purification to remove hydrocarbons.
highest specific catalytic activity among transition metal
oxides is observed for Co3O4. Oxides of manganese,
nickel, and copper also have high catalytic activity.
However, it has been found that the activity of complex
oxide systems in oxidation of hydrocarbons exceeds that
of individual oxides [4–7]. The authors of [8] attributed
the increased activity of cobalt spinels in full oxidation
processes to the ease of structural transformations, which
facilitates the diffusion of oxygen to a molecule being
oxidized.
Development of effective catalysts for deep oxidation
of methane without use of precious metals is a difficult
task. It can only be accomplished by an integrated
approach to the corresponding studies. The severe
operation conditions of catalysts in catalytic purification
reactors impose stringent requirements on these catalysts.
A catalyst should have a high mechanical strength,
resistance to an oxidizing medium, high and stable
activity, and low hydraulic resistance.
The maximum catalytic activity in deep oxidation
of methane is characteristic of platinum-group metals
[2]. However, their high cost and difficult availability
necessitates their replacement with nonprecious metals.
Results obtained in studies of the deep oxidation on
various oxide catalysts [11] convincingly demonstrate
that high activity is exhibited by transition metal oxides
having a mobile oxygen in their lattice. Boreskov studied
the catalytic activity of oxides of Period IV metals in
the methane oxidation reaction and demonstrated that
the oxygen binding energy on the catalyst surface is an
important factor determining the catalytic activity. The
The goal of this study was to develop supported
catalysts satisfying the above requirements, perform an
integrated study of processes occurring in their formation,
and examine the possibility of improving the catalytic
activity and thermal stability of the catalysts by varying
the ratio between their active components. In addition, it
was of interest to analyze the possibility of using various
supports for fabrication of purification catalysts.
84

SYNTHESIS OF NICKEL–COPPER–COBALT CATALYSTS
85
EXPERIMENTAL
The mechanical strength of the catalysts was measured
by the crushing method, with the load applied along the
grain generatrix. The specific surface area of the supports
and catalysts was determined by the volumetric method
from low-temperature adsorption of hydrogen, with the
BET equation used in calculations.
The catalysts were fabricated by impregnation of
ceramic supports with aqueous solutions of nickel,
copper, manganese, cobalt, and aluminum nitrates.
The impregnation was performed at 50°C for 1 h, with
subsequent drying in air for 24 h and calcination at
400°C for 4 h. To obtain the required total concentration
of the active components, several impregnations with
intermediate calcinations of the samples was performed.
Supports of NIAP-18 and NIAP-03-01, fabricated by
pelletization and slip casting, respectively, and calcined
at 1450°C were used to prepare the catalysts. The main
parameters of the supports are listed in Table 1. The
phase composition of NIAP-18 support is represented
by aluminum oxide (α-Al2O3) and calcium aluminates
The catalytic activity of the samples was studied in
purification of nitrogen to remove methane on a flow-
through laboratory installation, with chromatographic
analysis of the gas mixture. Test conditions: CH4/O2 =
0.25 ± 0.05, temperature range 300–650°C, volumetric
flow rate 10 000 h–1. The conversion of methane served
as the measure of activity. Because the maximum
sensitivity in activity determination is achieved at medium
conversions [10], the catalytic activity of the samples
under study was evaluated by the temperature at which
a 50% conversion of methane is reached, t50.
.
.
(CaO 6Al2O3, CaO 2Al2O3), and that of NIAP-03-01
support, only by corundum (α-Al2O3).
In the first stage, single-component catalysts based
on cobalt, nickel, copper, and manganese oxides were
studied. These samples were prepared by impregnation
of NIAP-03-01 support with aqueous solutions of the
corresponding nitrate salts, followed by drying and
calcination. Earlier studies of the effect of impregnation
conditions (duration and temperature of the impregnating
solution) on the total content of the active components and
on the mechanical strength of the samples have shown
that the optimal impregnation mode is that with t = 50°C
and τ = 1 h [11]. To maintain the active components in a
finished catalyst in the finely dispersed state, aluminum
nitrate was added to the impregnating solution [12].
A total of 3–5 impregnations were performed under
identical conditions, with intermediate calcinations at
400°C. The temperature at which impregnated supports
were impregnated was chosen on the basis of differential-
The chemical composition of the catalysts and
supports was determined by photoelectrocolorimetry,
complexonometry, and potentiometry. The formation
of the catalysts was studied by X-ray and integrated
thermal analyses and temperature-programmed reduction
(TPR) in a flow of hydrogen. The gaseous products
evolved in the course of catalyst reduction were
analyzed chromatographically with a heat-conductivity
detector. The X-ray analysis for determining the phase
composition, size of crystallites, and lattice parameters
of separate phases was made on DRON_2 and DRON-3
X-ray diffractometers, with CuKα radiation and graphite
monochromator. An integrated thermal analysis of
the samples was carried out on an MOM OF-103
derivatograph (Hungary) in air at a heating rate of
5 deg min–1.
Table 1. Support properties
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VINOGRADOVA et al.
thermal analyses of cobalt, manganese, nickel, copper,
and aluminum nitrates. The thermolysis of these salts is
accompanied by endothermic effects of varied intensity,
which correspond to stage-by-stage removal of crystal
hydrate water and decomposition of a salt. According to
X-ray phase analysis data, the products of decomposition
of the nitrates at 400°C are the corresponding nitrates.
The crystallite size L (Å) of the active components
in single-component cobalt, manganese, nickel, and
copper systems is in the range 200–290 Å. To provide
full decomposition of the nitrate salts, the impregnated
supports were subjected to a thermal treatment for 4 h.
Decomposition of nickel and copper nitrates at 400°C
yields the corresponding oxides; that of manganese nitrate
produces MnO2 and an insignificant amount of Mn2O3;
cobalt nitrate decomposes to a mixed oxide Co3O4.
A chemical analysis demonstrated the following content
of oxides in the samples prepared (%): Co3O4 (sample
no. 1), MnO2 14.1 (sample no. 2), NiO 14.7 (sample
no. 3), and CuO 13.8 (sample no. 4).
analyzed. Results of previous studies [11, 13–15] were
used to choose the nickel–copper system as the base
formulation for the catalyst. This system is close in its
catalytic properties to platinum [16]. It has been found
that the catalytic activity is the highest for catalyst with
a mass ratio NiO/CuO = 2.3–3.0. Samples with this
ratio were prepared on two different catalyst supports
of NIAP-18 and NIAP-03-01 brands, which show good
performance under severe working conditions. Also,
nickel–copper samples with addition of cobalt and
manganese were produced for analysis of the possibility
of additionally raising the activity of catalysts for deep
oxidation of methane. To find whether it is possible,
in principle, to lower the reaction temperature, it was
decided to limit the mass content of these additives in
multicomponent systems to about 2% in terms of oxides.
The main parameters of the starting two- and three-
component catalysts, including the phase composition,
upon their calcination at 400°C are listed in Table 2.
The total content of active components in the samples
is 11.7–17.5%.
Tests of the catalytic activity of cobalt, manganese,
nickel, and copper catalysts demonstrated that a 50%
conversion of methane on these samples is reached at
470, 520, 440, and 470°C, respectively. These parameters
are insufficient for effective purification under industrial
conditions.
According to the X-ray data in Table 2, the value of
parameter a0 for two-component nickel–copper samples
strongly differs from the tabulated parameter of the NiO
crystal lattice. The distortion of a0 may indicate that CuO
is incorporated into the crystal lattice of NiO, which
results in that an oxide copper–nickel solid solution
is formed. The formation of the nickel–copper solid
Therefore, multicomponent oxide catalytic systems
were prepared on the basis of the above elements and
Table 2. Properties of starting catalyst samples upon calcination at 400°C
a
0
,
a Tabulated lattice constants: a0NiO = 4.177 Å, a0CuO = 4.684 Å.
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SYNTHESIS OF NICKEL–COPPER–COBALT CATALYSTS
87
solution has been noted previously in studies of catalytic
solid solution occurs separately.
systems produced by mixing of nickel and copper
hydroxo carbonates in the presence of aqueous ammonia
[14]. In contrast to nickel–copper and nickel–copper-
manganese systems, in which the active components are
present as a nickel oxide phase with a distorted lattice
parameter, the X-ray patterns of the nickel–copper–cobalt
catalyst additionally show low-intensity lines of copper
oxide. Presumably, copper oxide appears in the phase
composition because of the formation of a nickel–copper–
cobalt solid solution, with the result that copper oxide is
displaced from the nickel–copper solid solution. In this
context, to make sure that solid solutions are formed
in NiO–CuO and NiO–CuO–Co3O4 systems, it was of
interest to consider the reduction of the samples under
study and X-ray diffraction parameters of the systems
produced as a result of the reduction.
The results of an X-ray diffraction analysis of samples
reduced in a flow of hydrogen at 600°C are presented
in Table 3. For nickel–copper sample nos. 5 and 6, the
calculated lattice constants of nickel strongly differ from
tabulated values. Such a distortion of a0 can be attributed
to incorporation of copper atoms into the crystal lattice
of nickel, with the result that a nickel–copper solid
solution is formed with a0Ni–Cu = 3.543–3.546 Å, which is
intermediate between a0Ni = 3.524 Å and a0Cu = 3.615 Å.
The X-ray diffraction patterns of nickel–copper–cobalt
sample no. 7 contains lines of copper, whereas no lines
of copper are observed for nickel–copper–manganese
sample no. 8. The intensity of the reflections of copper in
the nickel–copper–cobalt catalyst is low, and, therefore,
the dispersity of this phase and the lattice constant a0
could not be determined correctly. The formation of
free copper in this sample is accounted for by its partial
displacement from the nickel–copper solid solution to
give a nickel–copper–cobalt solid solution. No effect of
this kind is observed in the nickel–copper–manganese
system (sample no. 8). The distortion of the lattice
parameter of nickel indicates that solid solutions exist in
multicomponent systems: a nickel–copper–cobalt solid
solution in the catalyst with addition of cobalt and a
nickel–copper solid solution in the catalyst with addition
of manganese. No lines of manganese oxide (MnO) could
be identified because of the low concentration of this
component. The dispersity of the solid solutions in the
Figure 1 shows results of a temperature-programmed
reduction of the systems under study in a flow of
hydrogen. The reduction of nickel–copper–aluminum
systems is characterized by the presence of a single clearly
pronounced peak in the TPR curves. This indicates that
a nickel–copper solid solution is formed when catalysts
are fabricated by impregnation of supports in a solution
of a mixture of nickel and copper nitrates. A peak in
the TPR curve is observed at 210°C for nickel–copper
sample no. 5 on NIAP-03-01 support and at 240°C for
sample no. 6 on NIAP-18. Such a difference between
the characteristic reduction temperatures of the samples
prepared on two different supports can be accounted
for by the different strengths of binding of the active
components to the supports. For example, a presence of
calcium aluminates in NIAP-18 support favors a stronger
binding of the active component. The occurrence of an
insignificant effect peaked at 480°C in the curve for
sample no. 6 produced by impregnation of this support is
.
due to decomposition of the hydration products of CaO
2Al2O3 [17]. For the nickel–copper–manganese system
(sample no. 8), the peak in the TPR curve is observed at
a temperature of 210°C, as also for nickel–copper sample
no. 5. The more gently sloping run of the TPR curve for
sample no. 8 at temperatures of 220–310°C is due to the
reduction of manganese oxide, which proceeds separately
from the reduction of the nickel–copper solid solution.
The manner in which nickel–copper–cobalt systems
are reduced (sample no. 7) is somewhat more complex
because cobalt partly displaces copper from the nickel–
copper solid solution and the reduction of free copper
oxide to copper and of the oxide nickel–copper–cobalt
t, °C
Fig. 1. TPR curves for sample nos. (1) 8, (2) 6, (3) 5, and (4)
7. (t) Temperature.
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VINOGRADOVA et al.
Table 3. Results of an X-ray diffraction analysis of catalyst samples upon reduction in a flow of hydrogen at 600°C
a
0
a Tabulated lattice constants: a0Ni = 3.524 Å, a0Cu = 3.615 Å.
of the purification parameters achieved on sample nos. 5
(NIAP-03-01 support) and 6 (NIAP-18) shows that
the activity of the catalysts hardly depends on support
properties under laboratory conditions.
multicomponent systems is at the level of 160–250 Å.
The results of a study of the catalytic activity of
two- and three-component samples are presented
in Fig.2. The maximum activity is observed for the
nickel–copper–cobalt sample, for which the temperature
of 50% conversion of methane is 405°C. The activity
of the nickel–copper and nickel–copper–cobalt systems
is the same (t50 = 425–430°C). Thus, addition of cobalt
makes it possible to raise the activity of the nickel–copper
catalysts under study, whereas manganese has no effect on
the catalytic activity in the given conditions. Comparison
After it is shown that the activity of nickel–copper
catalysts can be, in principle, raised by introducing
a copper additive, it was of interest to determine the
optimal composition of a catalyst having the highest
activity in the process under study. The composition was
optimized using the mathematical method of experimental
design, named the simplex lattice technique [18]. The
suggested nickel–copper–cobalt catalytic formulation can
be regarded as a three-component system. Graphically, it
is represented as a regular simplex to each of whose points
corresponds a quite certain composition of the catalyst,
with the total weight amount of all the three components
remaining constant as the content of these components is
varied. Each composition of the simplex will have certain
properties, and, therefore, it is convenient to perform the
study by constructing composition–property diagrams.
x, %
A third-order polynomial was chosen as the
approximating model, and a design matrix was composed
for the ternary catalytic system constituted by nickel,
copper, and cobalt oxides. Samples were prepared by
impregnating NIAP-03-01 support with solutions of the
corresponding nitrate salts. The total amount of active
components in the catalysts was maintained at 15%. The
chemical composition of the catalyst was optimized on
the basis of the temperature of 50% methane conversion.
The mathematical calculations were made using MathCad
t, °C
Fig. 2. Conversion x of methane vs. temperature t for two-
component catalysts. Sample no.: (1) 5, (2) 6, (3) 7, and
(4) 8.
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SYNTHESIS OF NICKEL–COPPER–COBALT CATALYSTS
89
mathematical editor. Table 4 presents the design matrix
and characteristics of the starting and reduced samples.
cobalt oxides, respectively. The phase composition of
two- and three-component systems is represented by the
corresponding oxides with a distorted lattice constant.
For example, a0 is 4.178 Å in the single-component
nickel sample and 4.184–4.188 Å in the multicomponent
samples. A similar pattern is observed for the reduced
samples: the lattice constant is 3.531 Å for metallic nickel
in the single-component sample and 3.554–3.580 Å in
Analysis of the data in Table 4 shows that calculated
and experimental values of the chemical composition of
the samples are well correlated. With the exception of
the support phase (α-Al2O3), the phase composition of
the starting single-component nickel, copper, and cobalt
samples (nos. 1–3) is represented by nickel, copper, and
Table 4. Design matrix and characteristics of starting and reduced samples
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VINOGRADOVA et al.
Analysis of these data shows that all the single-
component samples exhibit low catalytic activity. The
temperatures of 50% conversion of methane are the
lowest for nickel–copper (sample no. 4) and nickel–
copper–cobalt systems (sample nos. 11 and 13).
copper-containing multicomponent systems. The slight
deviation of the lattice constant of nickel in nickel–cobalt
samples (nos. 8, 9) may indicate that a solid solution can
only be formed in the presence of copper. The dispersity
of the nickel active component in the starting and reduced
samples is rather high (75–205 and 120–220 Å in the
starting and reduced samples, respectively).
The experimental data and the derived regression
equation were used to calculate temperatures of 50%
conversion of methane. The adequacy of the chosen
model was verified by Student’s criterion. The regression
equation was tabulated with a computer and the data
The results obtained in a study of the catalytic activity
of the samples in oxidation of methane are presented
below:
obtained were used to construct a composition–property
diagram (Fig. 3), which enables analysis of both two- and
three-component systems. Diagrams of this kind can be
used to prognosticate and determine the catalytic activity
(t50) of catalysts with a sufficient accuracy, without
performing additional experiments. It follows from the
data in Fig. 3 that the dependence of t50 on the composition
of the catalytic system has an extremal nature. The lowest
activity is characteristic of single-component systems.
The catalytic activity increases on passing to the range
of two-component nickel–copper samples with NiO/CuO
ratios of 2 to 2.3%. The range of optimal compositions of
the catalytic system with t50 = 390–400°C is characterized
by the following component concentrations (wt %): NiO
9.0–12.5, CuO 2.5–6.0, Co3O4 0.5–3.5.
Thus, with the nickel–copper–cobalt system, the
temperature of 50% conversion of methane is 20–30°C
lower than that for nickel–copper catalysts. Nickel–
copper–cobalt catalysts on NIAP-03-01 and NIAP-18
supports were named NIAP-15-12K (brand 1) and
NIAP-15-12K (brand 2), respectively [19]. Industrial
tests of these catalysts in purification of effluent gases
at Kirovo-Chepetsk chemical combine confirmed that
palladium-containing catalyst APK-2 can be replaced
with the catalytic systems containing no precious metals,
developed in this study.
CONCLUSIONS
(1) Effective supported catalysts for deep oxidation
of methane were developed on the basis of a catalytic
formulation with nickel, copper, and cobalt.
(2) Specific features of formation of the active phase
of nickel–copper–cobalt catalysts were determined. It
was shown that solid solutions are formed.
(3) The optimal composition of nickel–copper–cobalt
catalysts with the highest activity was chosen. It has
the following component concentrations (wt %): NiO
9.0–12.5, CuO 2.5–6.0, Co3O4 0.5–3.5.
(4) Large batches of the catalyst were manufactured at
the catalyst shop of NIAP-Katalizator Limited-Liability
Company and their industrial tests were performed.
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