The Influence of the Specific Surface Area of the Carbon Support on the Activity of Ruthenium Catalysts for the Ammonia-Decomposition Reaction

Article abstract of DOI:10.1134/S0023158418020015

A method for fractionation of the starting carbon composite Sibunit by density was used to obtain three samples of Sibunit with different values of the specific surface area: Sib10 at 439 m²/g, Sib13 at 389 m²/g, and Sib17 at 256 m²/g. Investigation of Sibunits using both methods, that is, X-ray diffraction analysis and combination (Raman) scattering spectroscopy, did not reveal significant differences (the parameters of the crystal lattice and the I_D/I_G ratio). The fractionated supports were used to obtain Ru-containing catalysts for ammonia decomposition reaction (0.1 MPa, 400°C). The dependence of the specific catalytic activity calculated per 1 m² of the support specific surface a for catalysts of the same composition (4.0% Ru and 13.6% Cs) has an extreme form. The authors connect this with two factors: the blocking support pores contain an active component and a change in features of ruthenium interactions with the promoter (Cs) of the catalyst.

Full text of DOI:10.1134/S0023158418020015

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 2, pp. 136–142. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.A. Borisov, K.N. Iost, V.L. Temerev, N.N. Leont’eva, I.V. Muromtsev, A.B. Arbuzov, M.V. Trenikhin, G.G. Savel’eva, N.S. Smirnova, D.A. Shlyapin,
2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 2, pp. 161–168.
The Influence of the Specific Surface Area of the Carbon Support
on the Activity of Ruthenium Catalysts
for the Ammonia-Decomposition Reaction
V. A. Borisova, b, *, K. N. Iost , V. L. Temerev , N. N. Leont’eva , I. V. Muromtsev , A. B. Arbuzov ,
a
a
a
a
a, c
a, b, c
a
d
a
M. V. Trenikhin , G. G. Savel’eva , N. S. Smirnova , and D. A. Shlyapin
a
Institute of Hydrocarbon Processing, Siberian Branch, Russian Academy of Sciences, Omsk, 644050 Russia
b
Omsk State Technical University, Omsk, 644050 Russia
c
Omsk Scientific Center, Siberian Branch, Russian Academy of Sciences, Omsk, 644024 Russia
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
d
*
e-mail: borisovtiger86@mail.ru
Received December 23, 2016
Abstract⎯ A method for fractionation of the starting carbon composite Sibunit by density was used to obtain
2
three samples of Sibunit with different values of the specific surface area: Sib10 at 439 m /g, Sib13 at
2
2
3
89 m /g, and Sib17 at 256 m /g. Investigation of Sibunits using both methods, that is, X-ray diffraction anal-
ysis and combination (Raman) scattering spectroscopy, did not reveal significant differences (the parameters
of the crystal lattice and the I /I ratio). The fractionated supports were used to obtain Ru-containing cata-
D
G
lysts for ammonia decomposition reaction (0.1 MPa, 400°C). The dependence of the specific catalytic activ-
2
ity calculated per 1 m of the support specific surface a for catalysts of the same composition (4.0% Ru and
1
3.6% Cs) has an extreme form. The authors connect this with two factors: the blocking support pores contain an
active component and a change in features of ruthenium interactions with the promoter (Cs) of the catalyst.
Keywords: Sibunit, specific surface area, ammonia decomposition, ruthenium catalysts, specific catalytic
activity, cesium promoter
DOI: 10.1134/S0023158418020015
INTRODUCTION
Ammonia is primarily needed for the preparation
this case, the equilibrium extent of the ammonia con-
version should be not less than 99.5%; this along with
adsorbents allows the ammonia concentration in
waste gases to be decreased to values that do not
of fertilizers. More than 80% of the ammonia that is
produced has been used for this purpose [1]. More-
over, one of its important uses can be as the source of
pure hydrogen in power engineering, first, in hydro-
gen fuel cells [2], because the potential hydrogen con-
tent of ammonia is 17.6 wt %. The storage of hydrogen
exceed the maximum permissible concentration
3
(
MPC) of 0.20 mg/m [5]. According to the literature
data [6], ruthenium can be the active component of
such catalysts. Ruthenium catalysts have a high level of
is a much more difficult problem than that of ammo- activity when they are applied on different supports:
nia, as the latter is in a liquid state at room temperature carbon nanotubes, MgO, TiO , Al O , ZrO , elec-
2 2 3 2
and 0.8 MPa pressure [3].
trides, zeolites, activated carbon, and graphitized car-
bon [6–9]. In order to increase the activities of cata-
lytic systems, promoters are needed: compounds of
alkaline, alkaline-earth, and rare-earth elements [10].
The key problem of hydrogen synthesis from
ammonia is the development of a stable ammonia
decomposition catalyst that is active at low tempera-
ture and pressure. Industrial nickel catalysts produced In order to prepare ruthenium ammonia decomposi-
for ammonia decomposition, such as G1-11 (BASF), tion catalysts, carbon supports are preferably used,
AD-946 and HTZ204 (China), KDA-18A (NIAP cat- because such substances appear to be the best supports
alyst, Russia), and others, function in industrial units for Ru catalysts for ammonia synthesis [11]. One of the
at temperatures of 800–1100°С and are used, as a rule, drawbacks of carbon supports is the possibility for
to solve the ecological problem of protection of the methanation of the support itself; this leads to both its
atmosphere [4]. When ammonia is used as the hydro- destruction and the deactivation of the catalyst. How-
gen source in electric vehicles, catalysts with lower ever, the use of high-surface graphite with a low-defect
operation temperature (400–600°С) are preferred. In structure allows one to overcome this limitation [12].
136

THE INFLUENCE OF THE SPECIFIC SURFACE AREA
137
Investigation of ammonia decomposition on ruthe- obtained Sibunit fractions were washed with distilled
nium catalysts on carbon supports, considering the water and dried. Support samples were characterized
influence of many factors on catalyst activity [13], by both methods: X-ray diffraction (XRD) and
showed that the activity of the catalysts for ammonia Raman spectroscopy, the specific surface area was
decomposition correlates well with the I /I ratio (the found by the BET method.
D
G
ratio of intensities of D/G bands found by the method
of Raman spectroscopy). At the same time, the role of
the specific surface area (S ) in the work above is con-
sp
X-ray Diffraction Analysis
sidered not to be essential, in spite of the fact that it
had a marked effect. It is known that the S of the sup-
X-ray diffraction analysis was performed on a D8
sp
port is due to the dispersity of supported active sub- Advance powder X-ray diffractometer (Bruker, Ger-
stances, their deficiency, the extent of contact with a many) using CuK monochromatic radiation (at a
α
promoter, and the ability to be sintered, i.e., the basic 0.15418 nm wavelength). The following measurement
catalyst characteristics, such as activity and stability. modes were used: a scanning pitch of 0.050, a signal
In order to correctly evaluate the influence of the spe- accumulation time of 2 s, the voltage and heater cur-
cific surface area of carbon supports on the catalyst rent were 40 kV and 40 mA, respectively, and the scan-
activity it is necessary to use supports with close I /I
ning interval 2θ = 10–80 grade.
D
G
values that differ in the specific surface area values.
The decryption of diffraction patterns was pro-
cessed using the ICDD PDF-2, 2006 database on
powder diffraction.
Previously [14], the influence of the S of a Sibunit
sp
support on the activity of the ruthenium catalysts for
ammonia synthesis has been studied. It has been
shown that the ruthenium dispersity does not depend
on the specific surface area; however, an increase in
Combination Scattering Spectroscopy
S leads to a decrease in the contact surface of ruthe-
sp
nium and promoter particles; therefore, the activity of
Raman spectra of starting supports were recorded
on a DXR Smart Raman dispersion spectrometer
(ThermoScientific, United States), equipped with an
attachment for registering back-scattering radiation
2
a catalyst on Sibunit (S = 542 m /g) is lower by 30–
sp
4
0% than that of samples on Sibunit (S = 231 and
sp
2
3
00 m /g).
–1
The goal of this work was to study the influence of within the 50–3500 cm range. The wavelength of the
the specific surface area of a Sibunit carbon support on exciting laser radiation was 633 nm. The laser power
the catalytic activity of supported ruthenium systems was 8 mW. The exposure time was 60 s and the number
in the ammonia-decomposition reaction.
of accumulated signals was 15. Before the Raman spectra
were recorded, the samples were made into tablets using
a hand-operated press and a special magnetic holder.
The degree of ordering of the carbon material was evalu-
ated using the procedures in [15, 16].
MATERIALS AND METHODS
Preparation of a Carbon Support
A Sibunit carbon composite with a specific surface
2
area of 326 m /g produced according to the State
Determination of Textural Parameters of the Support
Standard 38 41540-95 was used as a support. The
starting Sibunit was fractionized according to density
as follows: the sample was first placed in distilled
water. In this case particles with a density of less than
The parameters of the pore structure of the starting
supports were studied using nitrogen adsorption–
desorption isotherms at –195.7°С on a Sorptomatic-
1
(Sib10) floated to the surface; their fraction was 2%
1
900 instrument (Carlo Erba, Izrael). The calcula-
of the starting sample. The sample that remained after
the removal of floating particles was then flooded with
a Sr(NO ) solution (30.5% concentration) with a
tions of S using the BET method (S ) were per-
sp
BET
formed within the range of equilibrium relative values
3
2
of nitrogen vapors at P/P = 0.05–0.33 from the
S
density of 1.3. Sibunit particles with a density from 1.0
to 1.3 (Sib13) floated; this was 25% of the particles.
Finally, the remaining sample particles were washed
with distilled water and placed in a KJ solution (58.5%
concentration) with a density of 1.70 in; in this case no
adsorption isotherm. The total absorption pore vol-
ume (V
) was determined from the value of nitrogen
Σpore
adsorption at P/P = 0.996, with the density of adsorbed
S
nitrogen being equal to that of a normal liquid (the molar
3
Sibunit granules floated. The densities of the volume of liquid N was 34.68 cm /mol). The Sorp-
2
Sr(NO ) and KI solutions were also found using an tomatic-1900 instrument was calibrated by measuring
3
2
aerometer; these were 1.300–1.360 and 1.660– the specific surface areas of different standard disperse
3
1
.720 g/cm , respectively, (State Standard 18481-81). and porous materials. The error in measuring the spe-
Thus, the remaining sample fraction was Sibunit par- cific surface area values (Δ) of standard samples on the
ticles with ρ > 1.7 (Sib17); its yield was 73%. The instrument was ± 2.8 rel. %.
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

1
38
BORISOV et al.
Preparation of Catalysts
The procedures for preparation of both ruthenium
Table 1. The pore structure of Sibunit fractions of different
densities
3
precursors and the catalysts supported on Sibunit were
described in detail in [14]. Ruthenium catalysts were pre-
pared by impregnating the Sibunit fractions of different
densities (the particle size was 0.4–0.8 mm) with the
Ssp,
VΣ pores, cm /g DBET*,
Fraction Yield, %
2
m /g
(at P/P = 0.996) nm
s
Sib10
Sib13
Sib17
2
25
73
439
389
256
1.086
0.870
0.432
9.93
8.56
6.71
[
Ru(NH ) Cl ](OH) complex solution, dried (120°С,
3 n m p
3
h in air), and reduced in an Н flow (450°С, 4 h,
2
WH2 = 60 mL/min). The obtained Ru/Sibunit samples
*
The diameter of the Sibunit particle was calculated using the
were impregnated with a CsNO solution (the Ru : Cs
3
formula d = (4V/S ).
BET
sp
atomic ratio = 1 : 2.5), dried (120°С, 3 h in air), acti-
vated by heating in Ar (350°С, 2 h, W = 60 mL/min),
Ar
packed with Haeyesep C sorbent to separate NH and
3
reduced in an Н flow (350°С, 2 h, W = 60 mL/min),
2
H
2
N . The chromatography conditions were as follows:
2
and then blown with argon. The obtained catalysts
were characterized by the method of transmission
electron microscopy and the catalytic activity was
found.
the hydrogen carrier gas rate was 60 mL/min, the pres-
2
sure was 1 kgs/cm , the bridge voltage was 4 V, and the
column temperature was 70°С. Three parallel mea-
surements of the ammonia content of gas phase were
made for every sample, and the obtained results were
Electron Microscopy
−1
−1
averaged. The catalytic activity (in mL
g
h and
NH3 cat
The catalyst samples were studied by the method of
transmission electron microscopy (TEM) using a
JEM-2100 electron microscope (JEOL, Japan); the
accelerating voltage was 200 kV and the resolution of
the crystal lattice was 0.145 nm with an INCA-250
energy-dispersive X-ray spectrometer (Oxford Instru-
ments, Great Britain). Sample suspensions in alcohol
were preliminarily subjected to ultrasound dispersion
using an UZDN-2T instrument (Elektron, Russia)
followed by fixation on a perforated carbon film sup-
ported on a copper net. When the particle diameters
were measured, the linear sizes were calibrated using a
crystal lattice of gold particles. In this case, the error in
measuring linear sizes in the electron micrographs
−2
−1
in mL
m min ) was calculated from the chroma-
NH3
tography data.
RESULTS AND DISCUSSION
Porous Structure of Supports
The parameters of the pore structure of Sibunit
samples are listed in Table 1. According to the data
obtained all samples are mesoporous. The specific
2
surface areas of Sibunit samples were 439 ± 12 m /g
2
2
for Sib10, 389 ± 11 m /g for Sib13, and 256 ± 7 m /g
for Sib17. The total pore volume of the fraction Sib10
1.1 cm /g) was two times higher than that of the Sib17
fraction (0.43 cm /g). The change in densities of
Sibunit fractions agrees well with that in the total pore
volume: the higher the latter was, the lower the Sibunit
density was.
3
(
(
EM) was no more than 0.02 nm. The observation of
3
crystal planes within isolated nanoparticles, the deter-
mination of crystallographic parameters, and the
computer processing of EM micrographs were per-
formed using the Digital Micrograph software (Gatan,
United States). The chemical elemental analysis of the
obtained catalysts was made using an INCA-250
energy-dispersive X-ray spectrometer (Oxford Instru-
ments, Great Britain) with a resolution of 120 eV.
It is evident from Fig. 1 that the sample Sib10 has a
broad pore size distribution within the range from 5 to
3
5 nm with a relatively narrow maximum at 8 nm. The
Sib13 sample has the bimodal pore size distribution:
the first narrow maximum corresponds to ~4 nm,
while the second is wider, to ~7 nm (the shoulder in
the graph corresponds to the pore size of 5–12 nm).
Catalytic Testing
3
The Sib17 sample greater than 1.7 g/cm has a narrow,
The catalyst activity in the ammonia decomposition
reaction was tested in a flow reactor with a fixed bed at
almost monomodal pore size distribution of ~4 nm in
diameter. The average pore size calculated according
to the BET differs from this because the calculations
do not take the pore size distribution (bi- and mono-
modal) for different samples into account (Table 1).
The observed difference in both the pore volume
and the pore size distribution can be explained if some
2
0–400°С and atmosphere pressure. The weight of the
charged catalyst was 0.5 g. Pure ammonia NH was fed
3
into a reactor at a rate of 21 ± 2 mL/min. The ammonia
−
1
−1
consumption was 2500 mL
time was 1.4 s.
g
h . The contact
NH3 cat
The gas mixture in the reactor outlet was analyzed granules of the starting carbon matrix in Sibunit syn-
on a TSVET-500M chromatograph (Russia) with a thesis were subjected to an insufficient degree of com-
thermal conductivity detector; the carrier gas was paction with pyrolytic carbon or if a significant weight
hydrogen. The column had a length of 1.5 m and was loss takes place in activation and large mesopores
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THE INFLUENCE OF THE SPECIFIC SURFACE AREA
139
dV/dD
.020
fact that the mechanical strength of the low-density
Sibunit has a far lower value [18]. A higher value of the
specific surface area of low-density Sibunit can be
explained by the Sibunit activation model proposed in
0
0
0
0
0
0
.018
.016
.014
.012
.010
Sib10
Sib13
Sib17
[
19], according to which, with an increase in the
degree of burnout (activation), the entire unordered
carbon first burns out (the formation of Sib13); the
walls then become thin and large mesopores form (the
formation of Sib10). When the pore quantity decreases
per Sibunit volume unit, the pores become larger.
When the pore quantity increases per Sibunit weight
0
.008
0.006
.004
0
0
.002
unit the S also increases. Within the framework of
sp
0
5
10 15 20 25 30 35 40 45 50
the same model, one can suggest that only unordered
carbon was burned out within the granules of the Sib17
sample. The degree of activation of granules consisting
of the Sib13 sample represents the beginning of the
burnout of graphite-like carbon, while within the
Sibunit granules that the Sib10 sample consists of, the
degree of burnout of graphite-like carbon leads to
breaking of the walls between small mesopores and the
formation of large mesopores.
D , nm
av
Fig. 1. The pore-size distribution curves for Sibunit frac-
tions of different densities (D is the pore diameter).
Intensity
1325
1
595
Combination Scattering Spectroscopy and X-Ray
Diffraction Analysis
2
0
1173
2
646 2903
3195
In the Raman spectra of the studied samples (Fig. 2),
3
2
1
–1
an intense scattering band at 1595 cm is registered,
which corresponds to totally symmetrical longitudinal
stretching vibrations of C=C bonds (the G band).
Furthermore, the Raman spectrum involves the scat-
tering band at 1325 (the D band); 1173; 2646; 2903 and
–1
3
195 cm (2D band), whose origin is connected with
the defect structure of the carbon material [15, 16].
5
00 1000 1500 2000 2500 3000 3500
The ratio of the intensities of D/G bands (I /I ) in the
D
G
Wavenumber, cm–1
Raman spectra is used for the semi-quantitative eval-
uation of imperfection of carbon supports. The lower
the ratio is, the more ordered the support is.
Fig. 2. The Raman spectra of Sibunit samples that differ in
density: (1) Sib10; (2) Sib13; (3) Sib17.
The I /I ratio (Table 2) indicates that samples do
D
G
not have substantial differences, while an I /I value
D
G
greater than 1 indicates the unordered structure of the
form. According to [17], the formation of low-density
Sibunit with a high content of large mesopores, when
substantial weight is lost in activation, is considered to
studied carbon materials.
Interplanar spacings and CSR parameters obtained
be more probable. This conclusion is supported by the by the XRD method are slightly different for all the
Table 2. The XRD and Raman data for Sibunits of different densities
Interplanar spacings CSR parameters
D band
G band
I /I
for starting
support
D
G
S ,
Support
fraction
sp
2
m /g
h, rel.
h,
ν, cm–1
ν, сm–1
d002, nm d110, nm L , nm Lc, nm
a
units
rel. units
Sib10
Sib13
Sib17
439
389
256
0.348
0.348
0.346
0.212
0.211
0.211
5.1
5.0
5.3
3.5
3.5
3.4
1325
1325
1325
106
146
98
1595
1595
1595
59
85
57
1.79
1.72
1.71
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

1
40
BORISOV et al.
(b)
(а)
50 nm
50 nm
(c)
(d)
5
nm
5nm
1
nm
1 nm
Fig. 3. TEM micrographs of ammonia decomposition catalysts: 4% Ru–13.6% Cs/Sib10 (a and c); 4% Ru–13.6% Cs/Sib17 (b and d).
Sibunit samples, as the interplanar spacing does not
practically change with the growth in the support den-
Transmission Electron Microscopy
In order to determine both the morphology and the
Sibunit particle size, as well as the localization of
ruthenium and cesium, the 4%Ru–13.6%Cs/Sib10
and 4%Ru–13.6%Cs/Sib17 catalysts were studied. It
follows from analysis of the TEM results that the sam-
ples of these catalysts are Sibunit particles that contain
contrasting nanoparticles rather uniformly distributed
over the support volume. The Sibunit particles of the
sity: d0 is 0.348, 0.348, and 0.346 nm for Sib10,
02
Sib13, and Sib17, respectively. The number of carbon
layers of crystallite was ten for all samples. The peak
intensities also do not differ for all the studied samples.
From the XRD and Raman data one can state that all
the Sibunit samples have properties of the starting
Sibunit that only is different (as shown above) in the
value of the specific surface area and, to less degree,
the parameters of the pore structure. Therefore, when
4
%Ru–13.6%Cs/Sib10 (Fig. 3a) have a roundish form
close to spherical) with an envelope thickness from 5
(
the activity of the catalysts prepared using these sup- to 15 nm. The 4%Ru–13.6%Cs/Sib17 catalyst has a
ports is discussed, one can exclude the influence of all Sibunit particle form analogous to Sib10 but the enve-
factors except the specific surface area and the pore lope thickness ranges from 10 to 20 nm (Fig. 3b).
surface of the support. Because both the I /I ratio
D
G
Using greater magnification it is seen (Figs. 3c, 3d)
that the walls between pores of the 4%Ru–
and X-ray parameters of samples changed slightly, it is
likely that all of the unordered carbon burned out
during the activation of the Sibunit used in this inves-
tigation and only the graphite-like carbon remained.
Within granules consisting of the low-density sample
Sib10, a higher weight loss compared with other sam-
1
3.6%Cs/Sib10 sample are far thinner than those of
the 4%Ru–13.6%Cs/Sib17 catalyst; this also supports
the conclusion of a greater degree of Sibunit Sib10
activation. TEM micrographs of nanoparticles show the
crystal lattice with parameters of 0.214 and 0.206 nm
ples occurred because of the gasification of both unor- (Figs. 3c, 3d), which are characteristic of ruthenium
dered and graphite-like carbons. As the result, larger planes with indices (002), (101) (PDF 06-0663).
mesopores (10 nm) form than those in Sib13 (9 nm) These parameters were calculated from electron pat-
and Sib17 (7 nm).
terns obtained after the Fourier transform of images of
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THE INFLUENCE OF THE SPECIFIC SURFACE AREA
141
Table 3. The catalytic properties of the 4% Ru–13.6% Cs/Sibunit samples on different supports in the ammonia-decom-
position reaction
Catalyst activity,
Catalyst activity,
Catalyst weighed
portion, g
2
Support fraction
S , m /g
sp
−1 −1
−2
−1
mLNH3
g
h
mLNH3
m
min
cat
Sib10
Sib13
Sib17
439
389
256
0.5004
0.5007
0.5018
2288
2262
962
0.0868
0.0969
0.0625
nanoparticle crystal lattice. Differences in ruthenium
distribution over the support volume were not found.
The sizes of ruthenium particles of the 4%Ru–
−2
−1
1
3.6%Cs/Sib13 sample (0.0969 mL
m min )
NH3
was highest and was higher than for the 4%Ru–
−
2
−1
1
3.6%Cs/Sib10 sample are 3–5 nm, while they are 3– 13.6%Cs/Sib10 (0.0868 mLNH3 m min ) and
7
nm for the 4%Ru–13.6%Cs/Sib17 catalyst. X-ray
−2
−1
4
%Ru–13.6%Cs/Sib17 (0.0625 mLNH3 m min )
maps obtained in registration mode of characteristic
catalysts by 10 and 35%, respectively.
radiation of the RuL and CsL lines indicate the uni-
α
α
The data we obtained on the specific activity of the
catalysts can be explained by the influences of two fac-
tors: (1) blocking the pores of the support that con-
tained the active component with the promoter whose
fraction per 1 m was higher for the 4%Ru–
3.6%Cs/Sib17 sample with the low specific surface,
form spatial distribution of ruthenium particles on
Sibunit. According to the same X-ray maps, cesium
does not form separate particles. To determine the
cesium localization of the above catalysts, the
2
1
3.6%Cs/Sib17 sample was specially synthesized and
1
studied using the TEM and EDS methods. The anal-
ysis showed that only Sibunit particles were present in
this sample, while cesium did not form separate parti-
cles, as occurred in the 4%Ru–13.6%Cs/Sib10 and
and (2) a decrease in the interaction of ruthenium and
the promoter in the 4%Ru–13.6%Cs/Sib13 catalyst
prepared on the basis of the support with a high spe-
cific surface area. As noted above, promoter particles
were not found on the catalyst surface; however, the
hypothesis on blocking the Sibunit surface with a pro-
moter has been confirmed by previous investigations
4
%Ru–13.6%Cs/Sib17 samples. In this case, the
cesium content of the sample was ~14% according to
the X-ray microanalysis. On this basis, one can sup-
pose that cesium was uniformly distributed over the
support volume in the 4%Ru–13.6%Cs/Sib10 and
[
14, 21]. It should be noted that there are difficulties in
finding low-contrast small particles of the cesium
compound; it is evident that the size of the Cs particles
should be lower than the average pore diameter to
effectively block ruthenium in pores. The data pre-
sented in this work do not contradict such an explana-
tion of the change in the catalytic properties of the
samples when the specific surface area of the support
changes.
4%Ru–13.6%Cs/Sib17 catalysts; it is likely to be inter-
calated into the carbon lattice [20].
The TEM results indicate that significant differ-
ences in morphology of ruthenium particles do not
occur. From the data of the local elemental analysis of
several catalyst regions, the ruthenium content only
was approximately 4 wt %; this value was close to the
calculated content.
CONCLUSIONS
Catalytic properties
In order to fractionate particles of the Sibunit car-
The sample activity in the ammonia decomposi- bon composite (by density), an approach using water
3
−1
−1
(
density of 1 g/cm ) and saline solutions of different
tion reaction was evaluated in mL
g
h
and in
NH3 cat
3
densities, that is, strontium nitrate (1.30 g/cm ) and
−
2
−1
mL
m min (Table 3). It was found that the sup-
3
NH3
potassium iodide (1.70 g/cm ), was used. Three sam-
ported Ru catalysts prepared from Sibunits with a high
ples of Sibunit were obtained (designated as Sib10,
Sib13, and Sib17); the main difference between them
2
specific surface area, that is, Sib10 (439 m /g) and
2
Sib13 (389 m /g), had higher activities equal to 2288 was the specific surface area values, which were equal
−
cat
1
−1
2
to 439 ± 12 , 389 ± 11, and 256 ± 7 m /g, respectively.
and 2262 mLNH3
g
h , respectively, while the activ-
The I /I ratios, as well as the X-ray parameters of the
2
D
G
ity of the catalyst prepared from Sib17 (256 m /g) was
samples, differed insignificantly. Supported catalysts
based on the obtained supports involving 4%Ru and
−
cat
1
−1
9
62 mLNH3
g
h . The dependence of the specific
2
catalytic activity calculated per 1 m of the support 13.6%Cs were prepared and their catalytic properties
surface,
1
for
4%Ru–13.6%Cs/Sib10,
4%Ru– were studied in the ammonia-decomposition reaction
3.6%Cs/Sib13, and 4% Ru–13.6% Cs/Sib17 has an at 400°С and 1 atm. It was shown by the TEM method
extreme form. The activity of the 4%Ru– that the dispersions of active component were practi-
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

1
42
BORISOV et al.
cally equal to one another for all the catalyst samples; the
size of the Ru particles was 3–7 nm. Cesium particles were
not found in the catalysts. It was found that the depen-
dence of the specific activity of the catalyst on the textural
6. Yin, S.F., Zhang, Q.H., Xu, B.Q., Zhu, W.X., Ng, C.F.,
and Au, C.T., J. Catal., 2004, vol. 224, p. 384.
7. Yin, S.F., Xu, B.Q., Ng, C.F., and Au, C.T., Appl.
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parameters (S , pore volume and size) has an extreme
8. Xu, B.Q., Wang, S.J., Ng, C.F., and Au, C.T., Catal.
Lett., 2004, vol. 96, p. 113.
sp
−2
−1
form: the maximum (0.0969 mL
m min ) corre-
NH3
9
. Yin, S.F., Xu, B.Q., Zhu, W.X., Ng, C.F., Zhou, X.P.,
sponds to the sample based on Sib13. This is 1.1 and
.35 times higher than for the catalysts based on Sib10
and Sib17, respectively.
and Au, C.T., Catal. Today, 2004, vols. 93–95, p. 27.
1
1
0. Yin, S.F., Xu, B.Q., Zhou, X.P., and Au, C.T., Appl.
Catal., A, 2004, vol. 277, p. 1.
1. US Patent 4163775, 1979.
1
1
2. Tsyrul’nikov, P.G., Iost, K.N., Shitova, N.B., and
ACKNOWLEDGMENTS
Temerev, V.L., Catal. Ind., 2016, vol. 8, no. 4, p. 341.
The physicochemical investigations were per-
formed using instruments of the Omsk regional Center
of Collective Use of the Siberian Branch of the Rus-
sian Academy of Sciences (Omsk). This work was car-
ried out with the financial support of the FASO Russia
in accordance with the Program of Fundamental Sci-
entific Research of the State Academies of Sciences
for 2013-2020, Project No. 01201351673.
1
3. Li, L., Zhu, Z.H., Yan, Z.F., Lu, G.Q., and Rintoul, L.,
Appl. Catal., A, 2007, vol. 320, p. 166.
1
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Translated by S. Lebedev
KINETICS AND CATALYSIS
Vol. 59
No. 2
2018