Characterization of new catalysts based on uranium oxides

Article abstract of DOI:10.1134/S0023158407040076

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al₂O₃ catalysts were synthesized. The uranium ox

Full text of DOI:10.1134/S0023158407040076

ISSN 0023-1584, Kinetics and Catalysis, 2007, Vol. 48, No. 4, pp. 511–520. © MAIK “Nauka /Interperiodica” (Russia), 2007.
Original Russian Text © Z.R. Ismagilov, S.V. Kuntsevich, V.V. Kuznetsov, N.V. Shikina, M.A. Kerzhentsev, V.A. Rogov, V.A. Ushakov, 2007, published in Kinetika i Kataliz, 2007,
Vol. 48, No. 4, pp. 544–553.
MECHANISMS
OF CATALYTIC REACTIONS
Characterization of New Catalysts Based on Uranium Oxides
Z. R. Ismagilov, S. V. Kuntsevich, V. V. Kuznetsov, N. V. Shikina,
M. A. Kerzhentsev, V. A. Rogov, and V. A. Ushakov
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
e-mail: zri@catalysis.ru
Received November 21, 2006
Abstract—Catalysts based on uranium oxides were systematically studied for the first time. Catalysts contain-
ing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni–U/Al2O3 catalysts
were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the
low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction
with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physico-
chemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and car-
bon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a cata-
lyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature meth-
ane oxidation. For the Ni–U/Al2O3 catalysts containing various uranium amounts (from 0 to 30%), the
introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam
reforming and partial oxidation.
DOI: 10.1134/S0023158407040076
INTRODUCTION
The 10 mol % U3O8/SiO2 supported catalyst was
studied in the publications cited above. Hutchings et al.
demonstrated that the supporting of U3O8 on SiO2
increased the temperature of complete VOC conversion
by approximately 50 K, as compared with that on pure
U3O8. Nevertheless, in this case, the activity of the cat-
alyst remained higher than that of Co3O4. The introduc-
tion of transition metal (Co, Cu, Cr, etc.) oxides as
modifying additives increased the activity of supported
Uranium oxides form the basis of fuel elements;
they are also successfully used in other areas of science
and technology [1]. The unique properties of the U–O
system are also highly attractive to catalysis. Uranium
is characterized by a number of oxidation states. Many
polymorphic modifications and solid solutions occur in
the U–O system; there are a variety of compounds with
variable composition and metastable phases. The uranium catalysts to the level of bulk U3O8. In this case,
occurrence of at least 10 uranium oxides and 14 of their selectivity for CO2 increased to almost 100%. This
effect was most pronounced in the case of the addition
of Cu [6, 9].
An analysis of the patent literature over the past
40 years allowed us to conclude that a great number of
chemical processes effectively occur with the participa-
tion of catalysts based on uranium oxides.
Uranium-containing catalysts are active in the fol-
lowing processes: the hydrotreatment of hydrocarbon
raw materials [19, 20]; the Fischer–Tropsch synthesis
of hydrocarbons [21–24]; the steam reforming of
hydrocarbons [25, 26]; the synthesis of liquid hydro-
carbons from methanol [27]; and the manufacture of
CO, CH4, and H2 from higher hydrocarbons [28–30].
Because mixed multicomponent uranium oxide cata-
lysts with the specified strengths of oxygen bonds can
be synthesized, they are successfully used in the
industrial processes of ammoxidation and partial oxi-
dation [31–36].
modifications was reported [2, 3].
Hutchings et al. [4–16] studied the catalytic proper-
ties of uranium oxides in the low-temperature catalytic
oxidation of volatile organic compounds (VOCs),
including organochlorine compounds. Thus, Hutchings
et al. [6] demonstrated the possibility of almost com-
plete (99.9%) VOC conversion on uranium oxide cata-
lysts at 100% selectivity for ëé2 over the temperature
range 300–400°C depending on VOC composition. For
comparison, analogous results were obtained on Co3O4,
which is the most active catalyst of well-known cata-
lysts for VOC oxidation [17], at 600°C. Moreover,
unlike all of the well-known catalysts, including Co3O4
and catalysts based on noble metals [18], uranium
oxide catalysts were found to exhibit uniquely high
resistance to the poisonous effect of halogens. Accord-
ing to the preliminary data of Hutchings and coworkers,
uranium oxide catalysts retained high activity in the
presence of sulfur-containing impurity compounds and
water vapor. Their enhanced thermal stability was also
noted.
The development of new catalysts based on uranium
oxides is of considerable current interest in the pro-
cesses of hydrogen energetics, petroleum refining,
511

512
ISMAGILOV et al.
petroleum chemistry, fine organic synthesis, and gas
The XRD analysis was performed on an HZG-4
purification for the removal of harmful impurities instrument with CuKα radiation over the 2θ angle range
including halogen- and sulfur-containing VOCs.
20°–80° at a scanning rate of 1 deg/min. Phases were
identified using the JCPDS XRD database.
This work is the first publication of a series of sys-
tematic studies initiated in the past few years. It is
The TPR experiments with catalyst samples were
devoted to the synthesis and characterization of cata- performed in a flow reactor. The catalyst samples were
lysts containing individual uranium oxides and mixed trained in a flow of oxygen at 500°C immediately
compositions with transition metal oxides supported before experiments. In the TPR measurements, the
onto alumina. Catalytic activity was measured for com- samples were heated from 40 to 900°C at a rate of
paratively simple reactions: deep hydrocarbon oxida- 10 K/min. The flow rate of a working mixture was
tion, steam and carbon dioxide reforming of methane, 40 ml/min. The composition of the mixture was 10%
and the partial oxidation of methane to synthesis gas.
hydrogen in argon or 10% CO in helium. The reduction
products (water or CO2) were frozen in a low-tempera-
ture trap. A thermal-conductivity detector (TCD) was
used for the detection of hydrogen or CO consumption.
EXPERIMENTAL
Synthesis of Catalysts
Catalytic Activity
The uranium oxide catalysts supported on alumina
were prepared by the incipient wetness impregnation of
a spherical γ-Al2O3 support (particle size of 1.0–1.6
mm), which was prepared by hydrocarbon–ammonia
molding [37], with aqueous solutions of uranyl nitrate
(UO2(NO3)2 · 6H2O). The catalyst after impregnation
was dried at 100°C and calcined at 600, 800, and 900°C
for 4 h or at 1000°C for 3 h. The uranium content of the
UOx/Al2O3 oxide catalysts was calculated as the
amount of uranium element in wt %. For convenience,
the samples containing 5 and 15 wt % U are referred to
as 5U/Al2O3 and 15U/Al2O3, respectively.
The catalytic activity in the deep oxidation reactions
of methane and butane was studied in a quartz tube flow
reactor. The reactor temperature was varied from 200 to
700°C in the case of CH4 or from 100 to 700°C in the
case of C4H10. The catalyst loading was 1 cm3. The ini-
tial reaction mixture containing 1 vol % CH4 in air was
supplied to the reactor at a rate of 16.7 cm3/min, which
corresponded to a space velocity of 1000 h–1. The reac-
tion mixtures before and after the reactor were analyzed
on an LKhM-8MD chromatograph with a TCD. The
gas mixtures were separated on a NaX column at room
temperature.
The nickel–uranium catalysts were prepared by the
impregnation of U/Al2O3 catalysts calcined at 500 and
1000°C with a solution of nickel nitrate, which was
taken in an amount required for 10 wt % Ni in the
mixed catalyst. For comparison, a 10% Ni/Al2O3 cata-
lyst was prepared by the impregnation of the support
with a solution of nickel nitrate. The catalysts were cal-
cined at 850°C in air. The uranium contents of the pre-
pared catalysts were 0, 4.3, 13, and 26 wt %. Hence-
forth, the concentration of uranium (in wt %) before the
stage of supporting nickel and the temperature of calci-
nation after impregnation are specified in catalyst des-
ignations, for example, Ni–5U(500)/Al2O3; that is, Ni
was supported on a uranium–alumina catalyst contain-
ing 5% U and calcined at 500°C.
The reactions of methane steam and carbon dioxide
reforming were performed in a flow reactor in a labora-
tory setup over the temperature range 700–850°C. The
synthesized Ni–U/Al2O3 catalysts were tested in the
reactions of methane steam (CCH = 20 vol %, CH O
=
4
2
60 vol %, CAr = 20 vol %, and space velocity of 50000 h–1)
and carbon dioxide reforming (CCH = 20 vol %,
4
C
= 20 vol %, CAr = 60 vol %, and space velocity of
CO2
50000 h–1).
The catalytic activity in the reaction of partial meth-
ane oxidation to synthesis gas was studied in a flow
setup (CCH = 20 vol %, CO = 10 vol %, CAr = 70 vol %,
4
2
space velocity of 50000 h–1, and reactor temperature of
550–800°C). The reaction mixtures were analyzed on a
Kristall 2000M gas chromatograph equipped with a
thermal-conductivity and a flame-ionization detector.
Catalyst Characterization
The synthesized catalysts were characterized by the
thermal desorption of argon, the low-temperature
adsorption of nitrogen, X-ray diffraction (XRD) analy-
sis, and temperature-programmed reduction (TPR)
with hydrogen and CO.
RESULTS AND DISCUSSION
The specific surface areas (Ssp, m2/g) of samples
were measured using the thermal desorption of argon.
Individual Uranium Oxides Supported
on Alumina (U/Al2O3)
The pore structure of catalysts was studied on an
Physicochemical properties of U/Al2O3 catalysts.
ASAP-2400 instrument using nitrogen adsorption at Tables 1 and 2 summarize the main physicochemical
−196°C.
properties (Ssp; phase composition) of catalyst samples
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

CHARACTERIZATION OF NEW CATALYSTS BASED ON URANIUM OXIDES
Table 1. Dependence of the properties of the 5U/Al2O3 catalyst on the conditions of thermal treatment
Conditions of ther-
513
Ssp, m2/g
XRD data
Catalyst color
mal treatment
Support
γ-Al2O3 (a = 7.920 Å)
Catalysts
550°C in air
170
White
500°C in air
600°C in air
600°C in H2 + Ar
800°C in air
900°C in air
160
167
154
110
78
γ-Al2O3 (a = 7.920 Å)
Yellowish orange
Yellowish orange
Gray
"
"
γ-Al2O3
δ-Al2O3
γ-Al2O3
Yellowish brown
Yellowish brown
1000°C in air
1100°C in air
40
33
θ-Al2O3, α-U3O8 (31-1424)*; α-UO3.01 (46-947)*
or α-UO2.92 (46-948)* can occur
Gray with beige spots
Greenish gray
θ-Al2O3, α-Al2O3 (traces), α-U3O8 (31-1424)*;
α-UO3.01 (46-947)* or α-UO2.92 (46-948)* can occur
* Compound number in the JCPDS database.
Table 2. Dependence of the properties of the 15U/Al2O3 catalyst on the conditions of thermal treatment
Conditions of ther-
Ssp, m2/g
XRD data
Catalyst color
mal treatment
Drying in air
600°C in air
800°C in air
–
γ-Al2O3
Yellowish orange
Yellowish orange
Yellowish green
122
60
"
γ-Al2O3, α-U3O8 (31-1424)*; α-UO3.01 (46-947)* or
α-UO2.92 (46-948)* can occur
900°C in air
43
32
δ-Al2O3, α-U3O8 (31-1424)*; α-UO3.01 (46-947)* or
α-UO2.92 (46-948)* can occur
Dark green
Dark green
1000°C in air
θ-Al2O3, α-U3O8 (31-1424)*; α-UO3.01 (46-947)* or
α-UO2.92 (46-948)* can occur
* Compound number in the JCPDS database.
containing 5 and 15% U supported on alumina and cal-
cined at various temperatures.
Table 3 summarizes the effect of calcination temper-
ature on the pore volume and specific surface area of
the 5U/Al2O3 catalyst (600, 1000, and 1100°C) as stud-
ied using the low-temperature adsorption of nitrogen
Tables 1 and 2 show changes in the specific surface
areas of catalyst samples depending on thermal treat-
ment conditions. The results suggest that the specific
surface area of catalysts decreased with calcination
temperature in the samples of both 5U/Al2O3 and
15U/Al2O3. It is most likely that, as the calcination tem-
perature was increased to 800°C, the specific surface
area of catalysts decreased because of changes in the
pore structure of the support due to the observed phase
transformations of alumina. After thermal treatment at
1000°C, the decrease in the specific surface area was
also due to the agglomeration of the uranium oxide
phase.
Table 3. Dependence of the texture properties of 5U/Al2O3
catalyst samples on the temperature of calcination (Tcalcin
)
Ssp (Ar),
Ssp (N2),
Vpore (N2),
Tcalcin, °C
m2/g
m2/g
cm3/g
600
800
167
110
40
165
116
48
0.42
0.41
0.35
0.13
1000
1100
33
30
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

514
ISMAGILOV et al.
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
(‡)
(b)
1
2
1
2
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
(c)
(d)
1
1
2
2
100
Pore diameter, Å
1000
100
Pore diameter, Å
1000
Fig. 1. Pore-size distribution in the samples of (1) the support and (2) the 5U/Al O catalyst calcined at (a) 600, (b) 800, (c) 1000,
2
3
and (d) 1100°C.
and argon. Figure 1 shows pore-size distributions (as was different. In the catalyst sample calcined at 600°C,
pores of size from 30 to 100 Å mainly occurred. As the
calcination temperature was increased to 1000°C, fine
pores disappeared, particles that formed the catalyst
framework became coarser, and pores of size from 200
to 1000 Å appeared. The total pore volume decreased
only slightly, whereas the specific surface area, which
depends on the amount of fine pores, dramatically
decreased (Table 3). Thermal treatment at 1100°C
resulted in the agglomeration of coarse pores; the spe-
cific surface area decreased to a lesser extent, whereas
the pore volume decreased considerably, as compared
with corresponding changes over the calcination tem-
perature range 600–1000°C.
differential functions) at various temperatures of calci-
nation of the catalyst and the parent support. The spe-
cific surface area characteristics are consistent with
data obtained by the thermal desorption of argon
(Table 3). The pore structure of catalysts changed as the
calcination temperature was increased. The dynamics
of changes in the specific surface area and pore volume
Intensity
* α-U3O8
*
*
Figures 2 and 3 show the diffraction patterns of cat-
alysts from the 5U/Al2O3 and 15U/Al2O3 series. The
samples of 5U/Al2O3 calcined at 600°C (Fig. 2) exhib-
ited only lines due to the γ-Al2O3 support. This can be
related to the fact that, at a ≤5% uranium content of the
catalyst, uranium oxide occurred as a highly dispersed
phase with a particle size smaller than 5.0 nm, and it
was not detected by XRD analysis, which was used in
this study.
*
*
*
*
*
*
*
*
5
4
3
2
1
As the calcination temperature was increased to
900°C, polymorphic transformations occurred in the
support. Because of this, the diffraction pattern exhib-
ited lines due to δ-Al2O3 (the most characteristic region
35°–37°) in addition to the lines of γ-Al2O3. At 1000–
1100°C, the lines of a practically pure θ-Al2O3 phase
10
20 30 40 50 60 70 80 90
2θ, deg
Fig. 2. Diffraction patterns of (1) the support and 5U/Al O
catalyst samples calcined at (2) 600, (3) 900, (4) 1000, and
(5) 1100°C.
2
3
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

CHARACTERIZATION OF NEW CATALYSTS BASED ON URANIUM OXIDES
515
Intensity
Conversion of CH4, %
100
*
*
* α-U3O8
*
1
80
2
3
4
5
*
60
40
*
*
6
5
4
20
0
3
1
2
10
20 30 40 50 60 70 80 90
200
300
400
500
600
700
2θ, deg
Temperature, °C
Fig. 4. The temperature dependence of methane conversion
Fig. 3. Diffraction patterns of (1) the support and
15U/Al O catalyst samples (2) dried and calcined at (3)
in the deep oxidation reaction on the 5U/Al O catalyst cal-
2
3
2
3
cined (1) in a flow of 30 vol % H + Ar at 600°C or in air at
600, (4) 800, (5) 900, and (6) 1000°C.
2
(2) 600, (3) 900, (4) 1000, and (5) 1100°C.
and uranium oxide appeared. It is most likely that the
latter is U3O8 (31-1424), whose characteristic lines
appear at the angles 25° and 30°. The other lines of the
U3O8 phase appear at the angles 30.92°, 39.61°, 40.11°,
51.16°, 53.37°, 54.59°, 59.77°, 60.60°, 60.91°, and
68.81°. Table 1 shows other conceivable uranium oxide
compounds; however, the final identification of these
compounds is difficult to perform because of the over-
lapping of support and uranium oxide lines.
The diffraction patterns of 15U/Al2O3 samples
(Fig. 3) are analogous to those of 5U/Al2O3 samples
and consistent with the polymorphic transformations of
alumina, which occur in the course of the thermal treat-
ment of catalysts at 900°C or higher. In the 15U/Al2O3
samples, lines corresponding to uranium compounds
appeared after calcination at 800°C.
An increase in the calcination temperature above
1000°C for 5U/Al2O3 samples or 800°C for 15U/Al2O3
samples resulted in a dramatic increase in the intensi-
ties of uranium oxide lines. The effect observed can be
due to the agglomeration of the highly dispersed active
component of a catalyst at high temperatures with the
formation of a coarsely dispersed phase of uranium
oxides with a particle size greater than 50 nm.
Catalytic activity of U/Al2O3 in the deep oxida-
tion of methane. Figures 4 and 5 show the temperature
dependence of the degree of methane conversion. The
effect of thermal activation was observed in catalysts
with a low uranium content (5 wt %) (Fig. 4). The activ-
ity of a catalyst increased as the calcination temperature
was increased from 600 to 1000°C. The catalyst cal-
cined at 1000°C exhibited the highest activity. A further
increase in the calcination temperature to 1100°C
resulted in a considerable decrease in catalytic activity.
This change in catalytic activity can be explained by the
occurrence of the optimum particle size of the active
component formed upon a moderate agglomeration of
highly dispersed particles. As the calcination tempera-
ture was increased to 1100°C, the subsequent agglom-
eration with the formation of coarse particles of ura-
nium oxides resulted in deactivation.
In catalysts with a high uranium content (15 wt %)
(Fig. 5), the catalysts calcined at 600 and 800°C were
most active. That is, particles with an optimum size
were formed at lower temperatures, whereas an
increase in the calcination temperature to 900 or
1000°C resulted in a decrease in catalytic activity.
Catalytic activity of U/Al2O3 in the deep oxida-
tion of butane. The samples of U/Al2O3 catalysts con-
taining 5 and 15% U calcined at 600 and 800°C were
studied in the reaction of deep oxidation of butane. For
comparison, the samples of bulk U3O8, which were pre-
pared by precipitation from aqueous solutions of uranyl
nitrate [38] and calcined at 600 and 800°C, were also
studied (Fig. 6). A comparison between data obtained
Conversion of CH4, %
100
1
80
2
3
4
60
40
20
0
200
300
400
500
600
700
Temperature, °C
Fig. 5. The temperature dependence of methane conversion
in the deep oxidation reaction on the 15U/Al O catalyst
2
3
calcined in air at (1) 600, (2) 800, (3) 900, and (4) 1000°C.
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

516
ISMAGILOV et al.
100
80
60
40
20
0
(‡)
(b)
3
3
1
1
2
2
200 250 300 350 400 450 500
200 250 300 350 400 450 500
Temperature, °C
Temperature, °C
Fig. 6. The temperature dependence of butane conversion in the deep oxidation reaction on catalysts calcined at (a) 600 and
(b) 800°C: (1) bulk U O , (2) 5U/Al O , and (3) 15U/Al O .
3
8
2
3
2
3
1.2
1.0
8.0
6.0
4.0
2.0
0
(‡)
(b)
800°ë
900°ë
1000°ë
600°ë
1000°ë
900°ë
1100°ë
600°ë
200
400
600
800
200
400
600
800
Temperature, °C
Temperature, °C
Fig. 7. TPR-H curves for the samples of (a) 5U/Al O and (b) 15U/Al O catalysts calcined at various temperatures (specified in
2
2
3
2 3
the figure).
in bulk and supported catalysts allowed us to conclude
TPR studies of U/Al2O3 catalysts. To explain the
that the catalytic activity of supported samples in the effect of the conditions of thermal treatment of sup-
ported uranium oxide catalysts on their activity in the
deep oxidation of methane, we performed studies using
TPR with hydrogen and CO.
reaction of butane oxidation was close to the activity of
U3O8 or higher than the activity of the bulk sample.
Figure 7 shows the TPR curves obtained in
5U/Al2O3 and 15U/Al2O3 samples calcined at various
temperatures. The test catalysts were characterized by
hydrogen absorption peaks in the temperature range
200–600°C. The positions and intensities of these
peaks depended on the amount of supported uranium
and the temperature of sample calcination. An increase
in the calcination temperature resulted in a decrease in
the temperature of hydrogen absorption for samples
containing either 5 or 15% uranium; that is, oxygen
species that were more reactive appeared, and these
species were removed by hydrogen at 300°C. However,
the behavior can be additionally complicated because
of changes in both the valence state of uranium in an
oxide and the dispersion of particles, as well as due to
the occurrence of phase transformations and interac-
tions.
Absorption of CO, arb. units
0.6
600°ë
0.5
0.4
0.3
900°ë
1000°ë
1100°ë
0.2
0.1
0
–0.1
200
400
600
800
Temperature, °C
Fig. 8. TPR-CO curves for the samples of 5U/Al O cat-
alysts calcined at various temperatures (specified in the
figure).
2
3
The samples of the 5U/Al2O3 catalyst calcined at
various temperatures were studied using the TPR of
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CHARACTERIZATION OF NEW CATALYSTS BASED ON URANIUM OXIDES
517
Table 4. Properties of Ni–U/Al2O3 catalysts
Catalyst composition Ssp, m2/g
XRD data
Ni/Al2O3
120
80
Solid solution based on the γ-Al2O3 structure (α = 7.960 Å)
Solid solution based on the γ-Al2O3 structure (α = 7.956 Å)
Ni-5U(500)/Al2O3
Ni-30U(500)/Al2O3
25
γ-Al2O3 + δ-Al2O3 (traces); solid solution based on the γ-Al2O3 structure (α = 7.960 Å);
α-U3O8 (J25 = 420)*
Ni-5U(1000)/Al2O3
Ni-15U(1000)/Al2O3
33
19
γ-Al2O3 + δ-Al2O3 (traces); solid solution based on the γ-Al2O3 structure (α = 7.950 Å)
γ-Al2O3 + δ-Al2O3 (traces); solid solution based on the γ-Al2O3 structure (α = 7.960 Å);
α-U3O8 (J25 = 300)*
Ni-30U(1000)/Al2O3
12
γ-Al2O3 + δ-Al2O3 (traces); solid solution based on the γ-Al2O3 structure (α = 7.960 Å);
α-U3O8 (J25 = 450)*
* Phase amount estimated from the integrated intensity of a line at θ = 25° in a diffraction pattern in arbitrary units.
CO. Figure 8 shows the TPR-CO curves obtained in the amounts of uranium oxides (<5%), the phase of α-U3O8
samples calcined at 600, 900, 1000, and 1100°C.
was not observed; it was detected only at a uranium
content of the sample higher than 15%. Although the
nickel content of the catalysts was high (10 wt %), the
presence of NiO oxide phases and Ni metal was not
detected. The high temperature of catalyst calcination
(850°C) facilitated the incorporation of nickel into
solid solutions based on the γ-Al2O3 structure; this was
observed in diffraction patterns.
In a region from 110 to 450°C, all four curves exhib-
ited a group of peaks. As the temperature of catalyst
calcination was increased from 600 to 1000°C, the peak
maximums of CO absorption were shifted toward low
temperatures or toward increasing temperature in the
sample calcined at 1100°C (Fig. 4).
A broad peak was observed in the region 450–
850°C; the area of this peak decreased with increasing
calcination temperature. It is most likely that the reduc-
tion of uranium oxides over a wide temperature range
and the occurrence of several absorption peaks in dif-
ferent temperature regions suggest the occurrence of
the active component of the catalysts (uranium) in var-
ious oxidation states.
Table 5. Activity characteristics of catalyst samples (yields
of H2, CO, and carbon) in the carbon dioxide reforming of
methane
Reaction tem-
perature, °C
Catalyst
Characteristic
800
850
Ni–U/Al2O3 Mixed Catalysts
Physicochemical properties. Table 4 summarizes
data on the specific surface areas and phase composi-
tions of nickel–uranium catalysts calcined at 850°C
depending on the uranium content of the samples and
the temperature of calcination after the stage of sup-
porting uranium. An increase in the uranium content of
the samples from 0 to 30% resulted in a considerable
decrease in the specific surface areas of the catalysts:
the Ssp of the 15% Ni/Al2O3 sample containing no ura-
nium additives was 120 m2/g, and it decreased by an
order of magnitude to 12 m2/g as the amount of ura-
nium was increased to 30%. An increase in the temper-
ature of calcination of a U/Al2O3 sample before the
stage of introducing nickel from 500 to 1000°C also
resulted in a decrease in the specific surface area of the
final catalyst.
Ni/Al2O3
Yield of H2, %
18
18
14
11
12
5
22
17
14
17
16
7
Yield of CO, %
Yield of carbon, %
Ni–5U(1000)/Al2O3 Yield of H2, %
Yield of CO, %
Yield of carbon, %
Ni–15U(1000)/Al2O3 Yield of H2, %
Yield of CO, %
5
17
23
1.5
22
26
0.4
10
0
Yield of carbon, %
Ni–30U(1000)/Al2O3 Yield of H2, %
Yield of CO, %
8
Changes in the phase composition of Ni–U/Al2O3
catalysts are analogous to those of the samples of indi-
vidual uranium oxides supported on alumina. At small
13
0
Yield of carbon, %
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

518
ISMAGILOV et al.
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
700°C
750°C
1
2
H2
CO
1
3
H2
2
CO
3
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
800°C
850°C
1
1
2
H2
2
3
H2
CO
3
CO
0
5
10 15 20 25 30
0
5
10 15 20 25 30
Concentration of U, %
Concentration of U, %
Fig. 9. Dependence of (1) the conversion of methane and the yields of (2) hydrogen and (3) CO in the steam reforming of CH on
4
the concentration of uranium in Ni–U/Al O catalysts calcined at 850°C. The reaction temperatures are specified in the figure.
2
3
Catalytic activity of Ni–U/Al2O3 in the steam increased the catalytic activity. In this case, the higher
reforming of methane. The results of testing catalysts the uranium content of the catalyst, the higher the activ-
that contained 10% Ni supported on U/Al2O3 samples ity. In a sample containing 30% U, activity increased
with various uranium contents (0–30%) and calcined at with reaction temperature to reach a maximum value at
1000°C in the steam reforming of methane (Fig. 9) 850°C (the conversion of CH4 was 77%). The catalysts
indicate that the presence of uranium in a Ni catalyst calcined at 1000°C after supporting uranium exhibited
Table 6. Activity characteristics of catalyst samples (methane conversion and the yields of H2 and CO) in the partial oxida-
tion of methane
Reaction temperature, °C
Catalyst
Ni/Al2O3
Characteristic
550
37
600
40
700
60
750
66
800
60
XCH , %
4
Yield of CO, %
30
20
32
25
48
40
54
47
50
40
Yield of H2, %
X
, %
Ni–5U(1000)/Al2O3
54
60
72
76
80
CH4
Yield of CO, %
Yield of H2, %
46
46
51
50
65
58
70
61
73
63
Ni–15U(1000)/Al2O3 XCH , %
17
35
64
73
85
4
Yield of CO, %
Yield of H2, %
, %
8
16
27
33
52
42
60
50
68
14
X
Ni–30U(1000)/Al2O3
20
40
61
71
79
CH4
Yield of CO, %
Yield of H2, %
12
16
23
31
37
50
44
58
50
65
–1
Reaction conditions: CCH = 20 vol %; CO = 10 vol %; C = 70 vol %; CH /O = 2 : 1; space velocity, 50000 h
.
Ar
4
2
4
2
KINETICS AND CATALYSIS Vol. 48 No. 4 2007

CHARACTERIZATION OF NEW CATALYSTS BASED ON URANIUM OXIDES
519
higher activities, as compared with the catalysts pre- on the Ni–30U/Al2O3 catalyst were 77 and 42%,
pared from U/Al2O3 samples calcined at 500°C (the respectively.
conversion of CH4 was 47% at 850°C).
In the reaction of the carbon dioxide reforming of
methane, an increase in the uranium content of the cat-
alyst resulted in a decrease in coke formation. The addi-
tion of 30% U as a catalyst constituent almost com-
pletely inhibited coke formation (at 850°C, the yield of
carbon was ~0.4%), whereas the yield of carbon on the
commercial analogue was 14% at 850°C.
The catalysts containing uranium oxides and the
mixed nickel–uranium catalysts were tested in the par-
tial oxidation of methane. The introduction of uranium
as a constituent of traditional nickel-based catalysts for
partial oxidation allowed us to increase the yield of
hydrogen. The yield of hydrogen on uranium-contain-
ing catalysts at 800°C was as high as 65% against 40%
for an analogue of a commercial Ni/Al2O3 catalyst
under the same conditions.
Catalytic activity of Ni–U/Al2O3 in the carbon
dioxide reforming of methane. Table 5 summarizes
the results of testing the catalyst in the carbon dioxide
reforming of methane.
It is well known that the main problem in the devel-
opment of catalysts for the carbon dioxide reforming of
methane is catalyst deactivation as a result of coke for-
mation. In Table 5, it can be seen that the addition of
uranium as a constituent of a Ni-containing catalyst sig-
nificantly decreased coke formation at a comparable
value of the yield of hydrogen. The yield of carbon
observed at 800°C decreased from 14% for the catalyst
free of uranium additives to 0% for the catalyst contain-
ing 30% uranium.
Catalytic activity of Ni–U/Al2O3 in the partial
oxidation of methane. Table 6 summarizes the results
of testing the Ni–U/Al2O3 catalysts in the reaction of
partial methane oxidation.
ACKNOWLEDGMENTS
This work was supported by the International Sci-
ence and Technology Center (project no. 2799r).
As the temperature was increased from 550 to
800°C, the activity of all of the catalyst samples
(0−30 wt % U) increased. The sample with 5% uranium
exhibited a higher activity at reaction temperatures of
550–750°C, as compared with samples with high ura-
nium contents and a sample containing no uranium. As
the reaction temperature was increased to 800°C, the
maximum conversion of methane (85%) and the maxi-
mum yield of hydrogen (68%) were reached on a cata-
lyst containing 15% U.
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