Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

Article abstract of DOI:10.1134/S0023158408040174

The reaction properties of Rh/TiO₂ sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of

Full text of DOI:10.1134/S0023158408040174

ISSN 0023-1584, Kinetics and Catalysis, 2008, Vol. 49, No. 4, pp. 568–573. © MAIK “Nauka /Interperiodica” (Russia), 2008.
Original Russian Text © V.I. Simagina, O.V. Netskina, O.V. Komova, G.V. Odegova, D.I. Kochubei, A.V. Ishchenko, 2008, published in Kinetika i Kataliz, 2008, Vol. 49, No. 4,
pp. 592–598.
III INTERNATIONAL CONFERENCE
“CATALYSIS: FUNDAMENTALS AND APPLICATIONS”
Activity of Rh/TiO2 Catalysts in NaBH4 Hydrolysis:
The Effect of the Interaction between RhCl3
and the Anatase Surface during Heat Treatment
V. I. Simagina, O. V. Netskina, O. V. Komova, G. V. Odegova, D. I. Kochubei, and A. V. Ishchenko
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
e-mail: simagina@catalysis.ru
Received October 15, 2007
Abstract—The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly
in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temper-
ature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy,
photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is sup-
ported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The
degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data
have demonstrated that the composition and structure of the rhodium complexes that form on the titanium diox-
ide surface during different heat treatments later determine the state of the supported rhodium particles forming
in the sodium tetrahydroborate reaction medium.
DOI: 10.1134/S0023158408040174
The necessity of developing and commercializing ium particles forming under the action of the reaction
safe and reliable power sources with a long service life medium.
has initiated R&D activities in the field of fuel-cell
Here, we will report the state of anatase-supported
power plants. The functioning of a fuel cell is impossi-
rhodium chloride studied as a function of the thermal
ble without a hydrogen generation and storage system.
pretreatment temperature by a variety of physicochem-
The catalytic hydrolysis of NaBH4 is viewed as a prom-
ical methods. We will also address the effect of heat
ising means of generating high-purity hydrogen for
treatment on the reactivity of the supported rhodium
portable power sources [1, 2].
particles forming in the NaBH4 hydrolysis medium.
Researchers are now making an intensive search for
active and stable catalysts for sodium tetrahydroborate
EXPERIMENTAL
hydrolysis. In recent publications, there has been infor-
mation concerning the high activity of supported plati-
num-metal (Pt, Ru, Rh) catalysts [3–8]. Unfortunately,
relevant data are sparse and the state of the active com-
ponent and catalyst synthesis methods have attracted
researchers’ attention only recently [9].
Catalyst Preparation
The support material for Rh/TiO2 catalysts was TiO2
powder (OOO Solikamskii Magnievyi Zavod) calcined
at 500°ë for 4 h. The specific surface area of the cal-
cined sample was 74 m2/g. According to x-ray diffrac-
tion data, the main crystalline phase of the support was
anatase (96%), which contained 4% rutile. The size of
the coherent-scattering domain (CSD) in the [101]
direction of anatase was 140 Å. Chemical analysis
revealed the following impurities (wt %): Nb, 0.04; S,
0.03; Fe, 0.22; Ca, 0.58.
The preparation of supported-metal NaBH4 hydrol-
ysis catalysts by the impregnation method consists of
two steps, namely, the interaction between the active-
component precursor and the support surface and sub-
sequent reduction. The catalyst reduction step is usu-
ally carried out directly in the NaBH4 medium since
sodium tetrahydroborate is a strong reducing agent
even at room temperature [10]. Therefore, the catalyst
A series of Rh/TiO2 catalysts was prepared by the
preparation methods should allow the properties of the incipient-wetness impregnation of titanium dioxide
catalyst to be controlled at the precursor supporting with an aqueous solution of RhCl3 (OOOAURAT). The
stage [9]. The chemistry of the support surface plays a impregnated catalysts were dried in air at 50–60°ë
significant role in the catalytic action of supported under an IR lamp and then at 110–130°ë for 2 h. Next,
rhodium catalysts [9]. It was assumed that it is the com- the catalysts were additionally calcined at 300°ë in air
position and structure of the active-component precur- for 4 h. The rhodium content was varied between 1 and
sor that determine the reaction properties of the rhod- 6 wt %.
568

ACTIVITY OF Rh/TiO2 CATALYSTS IN NaBH4 HYDROLYSIS
569
w × 10–3 (ml H2) s–1 (g Rh)–1
Physicochemical Methods
5
The Nb, Fe, and Ca contents of TiO2 were deter-
mined by atomic emission spectroscopy with induc-
tively coupled plasma on an Optima 4300DV spectro-
meter (PerkinElmer) after dissolving a titania sample in
an appropriate mixture of acids. Sulfur was quantified
in a hydrochloric acid extract from the sample.
4
3
2
1
The Rh and Cl contents of catalysts were deter-
mined by X-ray fluorescence analysis using a VRA-30
spectrometer with a Cr-anode X-ray tube.
2
1
The phase analysis of titanium dioxide was carried
out on a URD-63 diffractometer (Freiberger Präzision-
smechanik) using ëuKα radiation. The CSD size was
calculated using the Scherrer formula. Crystalline
phases in the titanium dioxide sample were quantified
using the PCW program [11].
0
1
2
3
4
5
6
7
[Rh], wt %
Diffuse reflectance electronic spectra were recorded
in air at room temperature on a Specord M-40 spectro-
photometer (Carl Zeiss Jena) equipped with a standard
diffuse reflectance attachment. The absorbance of the
support was compensated when recording the spectra.
Fig. 1. Rate of hydrogen evolution from aqueous NaBH
4
solutions as a function of the rhodium content of the cata-
lysts heat-treated in air at (1) 110–130 and (2) 300°ë.
Photoacoustic IR spectra were recorded on an MB-
102 Fourier transform spectrometer (Bomem) with an
MTEC Model 300 photoacoustic attachment.
Testing of Catalysts in NaBH4 Hydrolysis
The hydrogen generation process was studied for
sodium tetrahydroborate (98%, Sigma-Aldrich) dis-
solved in distilled water. Hydrolysis was carried out at
40°ë in a temperature-controlled glass reactor with a
magnetic stirrer at a stirring speed of 800 rpm. Sodium
tetrahydroborate (0.0465 g) was placed into the reactor,
and distilled water (10 ml) was added. Next, a catalyst
(6.2 mg) was added. The reactor was then sealed air-
tightly with a gas outlet adapter connected to a 100-ml
burette. The normalized hydrogen generation rate (w)
was determined as
Electron micrographs were obtained using a JEM-
2010 electron microscope (JEOL) with an accelerating
voltage of 200 kV and a resolving power of 1.4 Å. Peri-
odic patterns of the crystal structure were analyzed by
numerical Fourier transform methods. After NaBH4
hydrolysis, catalyst samples were isolated from the
reaction medium, washed with distilled water, dried in
air at 110–130°ë, and placed on a holey copper sub-
strate.
EXAFS spectra were recorded at the EXAFS station
of the Siberian synchrotron radiation center. The spec-
tra were obtained using aVEPP-3 booster at an electron
energy of 2 GeV and an electron current of 110 mA in
VH
2
----------
w =
,
t1/2m
the transmission mode. The spectrometer had a Si(111) where w is the reaction rate ((ml H2) s–1 (g Rh)–1), VH
2
cut-off monochromator and proportional chambers as
is the volume of hydrogen (ml NTP) released during the
reactant half-life t1/2 (s), and m is the weight of Rh (g)
in the catalyst.
detectors. Rhodium K-edge absorption spectra were
recorded in 2-eV steps. EXAFS data were processed by
a standard procedure, using the VIPER program [12] to
separate the oscillating component of the absorption
coefficient and the FEFF-7 program [13] to calculate
modeling parameters. XANES spectra were recorded
using the same procedure, but with 0.4-eV energy
steps. The catalysts were characterized both before and
after NaBH4 hydrolysis.
RESULTS AND DISCUSSION
Figure 1 plots the hydrogen generation rate per gram
of Rh as a function of the rhodium content for Rh/TiO2
catalysts subjected to different heat treatments. The
specific activity of rhodium decreases as the metal con-
tent is increased from 1 to 6 wt %. Raising the calcina-
tion temperature to 300°ë markedly enhances the spe-
cific activity of rhodium. This is particularly true for the
catalysts containing >2 wt % Rh. Further raising the
calcination temperature to 500°ë has no significant
effect on the catalytic activity. Thus, the change in the
Thermal analysis was carried out in flowing air
(25 l/h) in the temperature range 25–1000°ë at a heat-
ing rate of 10 K/min on 200-mg samples (Q 1500 D
thermoanalytical system). Heat-induced transforma-
tions in the sample were monitored by recording TG
and DTG profiles.
The specific surface area was determined from state of rhodium chloride on the titanium dioxide sur-
argon thermal desorption data.
face that is induced by raising the calcination tempera-
KINETICS AND CATALYSIS Vol. 49 No. 4 2008

570
SIMAGINA et al.
Table 1. X-ray fluorescent analysis data for the unreduced
TiO2 surface, and it was assigned to charge transfer
from oxygen to the metal [9, 15, 16]. Apparently, the
25000 cm–1 band observed in this study is also due to
the interaction of Rh3+ complexes with the surface oxy-
gen of anatase. An analysis of the diffuse reflectance
curves suggests that raising the calcination temperature
from 110–130 to 300°C results in an increase in the
total absorbance in the diffuse reflectance spectra and
in a marked strengthening of this charge-transfer band.
Therefore, the electronic state of rhodium in the unre-
duced catalysts depends on the calcination temperature.
(6 wt % Rh)/TiO2 catalyst
Thermal
Rh content, Cl content,
Rh : Cl
molar ratio
pretreatment
wt %
wt %
temperature, °C
110–130
300
5.95
5.94
6.11
5.75
4.44
1.07
1 : 2.8
1 : 2.2
1 : 0.5
500
In order to understand the changes in the diffuse
reflectance spectra caused by the heat treatment of the
catalysts, we recorded the photoacoustic IR spectrum
of supported rhodium chloride (1 wt % Rh) dried at
110–130°C and calcined at 300°C and the same spec-
trum of the initial titanium dioxide calcined under the
same conditions (Fig. 4). Clearly, the calcination of the
catalyst at 300°C causes a marked decrease in its water
content. The water content of the calcined catalyst is
ture from 110 to 300°ë results in a substantial increase
in the specific activity of supported rhodium reduced in
the NaBH4 reaction medium.
In order to study the interaction between rhodium
chloride and the titanium dioxide surface, catalyst sam-
ples were examined by various physical methods and
chemical analysis.
Table 1 lists chemical analysis data for the (6 wt %
Rh/TiO2) catalyst heat-treated in air at different temper-
atures. These data indicate that the chlorine content of
this sample decreases starting at 300°C. Note that bulk
rhodium chloride decomposes to turn into rhodium
oxide at a higher temperature (Fig. 2). The lower
decomposition temperature of supported rhodium chlo-
ride may be due to either its small particle size or its
interaction with the titanium dioxide surface.
Absorbance, %
100
Diffuse reflectance data for supported rhodium
chloride samples dried at 110–130°C and calcined at
300°C are presented in Fig. 3. According to earlier data
[9, 14], the absorption band at 19600 cm–1 is due to the
d–d transition in a hexacoordinated Rh3+ complex.
Absorption at 25000 cm–1 was observed in earlier stud-
ies of the interaction of transition metal cations with the
4
80
60
40
20
0
3
2
RhCl3 · nH2O
TG
DTG
500°ë
RhCl3
1
170°ë
920°ë
Rh2O3
32000 28000 24000 20000 16000 12000
ν, cm–1
0
100 200 300 400 500 600 700 800 900 1000
Temperature, °C
Fig. 3. Diffuse reflectance electronic spectra of the unre-
duced catalysts containing (1, 2) 1 and (3, 4) 6 wt % Rh:
(1, 3) catalysts dried at 110–130°C; (2, 4) catalysts calcined
at 300°C.
Fig. 2. Thermoanalytical curves for the decomposition of
RhCl · nH O in air.
3
2
KINETICS AND CATALYSIS Vol. 49 No. 4 2008

ACTIVITY OF Rh/TiO2 CATALYSTS IN NaBH4 HYDROLYSIS
571
5 nm
Absorbance
0.25
0.20
0.15
0.10
0.05
2
1
3
20 nm
(a)
0
4000
3500
3000
2500
2000
1500
5 nm
ν, cm–1
Rh
Fig. 4. Photoacoustic IR spectra of (1) the initial TiO cal-
2
TiO2
cined at 300°ë, (2) the unreduced (1 wt % Rh)/TiO cata-
2
lyst dried at 110–130°C, and (3) the same catalyst calcined
at 300°C.
not only below the water content of the catalyst dried at
110–130°C, but also below the water content of tita-
nium dioxide calcined at 300°C. The decrease in absor-
bance in the 3350–2270 cm–1 region suggests that both
weakly and strongly bonded water is removed from the
support surface at this temperature [17].
20 nm
(b)
Thus, both the marked strengthening of the charge-
transfer band at 25000 cm–1, which characterizes the
degree of interaction between rhodium and the titanium
dioxide surface, and the growth of the total absorbance
in the diffuse reflectance spectrum upon the calcination
of the sample at 300°C are evidence that the chemical
interaction between the rhodium complexes and the
surface sites of TiO2 is strengthened. This is accompa-
nied by strengthening of the charge transfer effect on
the d–d transitions. This is likely due to the increase in
the degree of covalence of the metal–ligand bond,
which arises from the partial replacement of chlorine
atoms by oxygen atoms in the coordination sphere of
Rh3+ and from the strengthening of the effect of the sup-
port on the state of the surface cluster.
Since, as was mentioned above, rhodium chloride
calcined at 300°C contains a smaller amount of
strongly bonded water than the support calcined under
the same conditions, it is obvious that the most likely
locations of the rhodium complex are the surface sites Rh foil
of titanium dioxide that were previously occupied by
Fig. 5. Electron micrographs of the (6 wt % Rh)/TiO cata-
2
lyst reduced in the NaBH reaction medium: (a) catalyst
4
dried at 110–130°C; (b) catalyst calcined at 300°C.
rhodium contents that the catalytic activity increases
significantly as the calcination temperature is raised
(Fig. 1). It is clear from Fig. 5a that, in the (6 wt %
Rh)/TiO2 catalyst dried at 110–130°C, the titanium
dioxide surface has metal particles of mean size 3.3 nm.
Table 2. Shift of the maximum of the first derivative of the
K-edge absorbance of rhodium (ionization of the 1s level) ac-
cording to XANES data
Sample
Shift, eV
0
RhCl3/TiO2 (6 wt % Rh), 110–130°C
RhCl3/TiO2 (6 wt % Rh), 300°C
Rh/TiO2 (6 wt % Rh), 110–130°C,
1.32
2.63
0
strongly bonded water molecules [18, 19].
According to TEM data, the degree of interaction
between the supported salt and titanium dioxide has a
considerable effect on the state of the rhodium particles reduced by NaBH4
that form in the reaction medium under the reductive
action of sodium tetrahydroborate. Figure 5 shows
images of catalysts (6 wt % Rh) that have been tested in
NaBH4 hydrolysis. As was noted above, it is at high
Rh/TiO2 (6 wt % Rh), 300°C,
1.91
3.94
reduced by NaBH4
Rh2O3
KINETICS AND CATALYSIS Vol. 49 No. 4 2008

572
SIMAGINA et al.
In order to study the charge state of the rhodium par-
Rh–Rh
ticles reduced in the sodium tetrahydroborate medium,
we measured the shifts of the maxima of the first deriv-
ative of K-edge absorbance of rhodium (ionization of
the 1s level) by the XANES method (Table 2). The zero
value was assigned to the shift observed for rhodium
foil. An analysis of the XANES data suggests that the
catalyst pretreatment temperature has an effect on the
charge state of the rhodium particles reduced in the
reaction medium, which were examined after NaBH4
hydrolysis. If, in a sample that was simply dried before
being reacted with the NaBH4 solution, the charge state
of the reduced rhodium particles is close to metallic,
additional calcination at 300°C will not result in the
complete reduction of rhodium, which will remain par-
tially oxidized (according to the EXAFS data presented
below, one-third of the introduced rhodium is in the
oxidized state). It is also possible that the rhodium
metal nanoparticles gain positive charge owing to the
presence of Rh–O bonds on their surfaces.
Rh–O
300°C
Our EXAFS data confirm the presence of oxygen in
the coordination environment of the Rh atoms in the
reduced catalysts that have been tested in NaBH4
hydrolysis. Figure 6 plots the atomic radial distribution
functions, and Table 3 lists interatomic distances (R)
and coordination numbers (N) for the nearest neighbors
of the rhodium atoms. The first coordination sphere of
rhodium in the catalyst sample that was dried at 110–
130°ë before reduction has an interatomic distance
assignable to the Rh–O bond. The four other distances
are equal to Rh–Rh distances in rhodium metal. Calci-
nation at 300°ë reduces the coordination numbers cor-
responding to the Rh–Rh distances and increases the
coordination number corresponding to the Rh–O dis-
tance.
110–130°C
0
2
4
6
8
R = δ, Å
Fig. 6. Experimental (solid lines) and calculated (dashed
lines) atomic radial distribution functions for the (6 wt %
Rh)/TiO catalyst reduced in the NaBH reaction medium
2
4
Thus, for the reduced catalyst that was calcined at
300°ë, which consists of metallic and oxide phases,
EXAFS data indicate that rhodium is either in one
charge state or in two similar charge states for which
the absorption edge shift is smaller than is observed for
Rh2O3 (Table 2). A plausible explanation of this fact is
that the reduction of the catalyst actually yields one
mixed rhodium phase in which a metal core is partially
covered by an oxide phase or is fixed to it. If this is the
case, the electronic state of the entire particle will be
averaged out. This is indicated by the absence of Rh–
after different heat treatments.
Raising the calcination temperature to 300°C decreases
the mean size of the rhodium particles in the reduced
sample to a slightly smaller value of 2.7 nm (Fig. 5b).
In addition, the rhodium particles in this sample are
completely or partially “decorated” with titanium diox-
ide. This is likely due to the strong interaction between
the support and the active component.
Table 3. EXAFS data for the (6 wt % Rh)/TiO2 catalyst reduced in the NaBH4 reaction medium
Rh–O
R, Å
Rh–Rh
R, Å
Rh–Rh
R, Å
Rh–Rh
R, Å
Rh–Rh
R, Å N
∆E0, R fac-
eV tor, %
Treatment
N
N
N
N
Heat treatment
2.01
2.02
–
0.97
2.68
2.68
5.89 3.77
4.68 3.88
4.40
4.67
4.67
2.30 5.27
1.06 5.27
3.69 –0.11 18.98
1.04 –3.09 23.95
at 110°C
Heat treatment
at 300°C
Rh metal
2.06
–
0.14
6
2.69 12
3.80
4.66 24
5.38 12
–
–
KINETICS AND CATALYSIS Vol. 49 No. 4 2008

ACTIVITY OF Rh/TiO2 CATALYSTS IN NaBH4 HYDROLYSIS
573
Rh distance peaks characteristic of Rh2O3 (2.99, 3.52,
ACKNOWLEDGMENTS
and 3.75 Å) [20] in the atomic radial distribution curve.
The nonstoichiometric oxide will possess intrinsic con-
ductivity, and the contact between the two conducting
phases will result in the formation of a single Fermi
level.
This change of the electronic properties of the metal
particles that are in chemical contact with the conduct-
ing oxides provides a plausible explanation for the
strong interaction effect well-known in the synthesis of
metal catalysts supported on transition-metal oxides.
An analysis of these results together with data of
other physicochemical methods suggests that the dif-
ference between the NaBH4 hydrolysis activities of cat-
alysts subjected to different heat treatments correlates
with the appearance of a peak due to the Rh–O distance
in the EXAFS spectra of the catalysts reduced in the
reaction medium. This is likely explicable in terms of
the composition and structure of the surface rhodium
compounds that form at the impregnation and heat
treatment stages of the supporting of rhodium chloride
on the titanium dioxide surface.
The authors are sincerely grateful to S.V. Tsybulya
for the X-ray diffraction phase analysis of titanium
dioxide, to N.N. Boldyreva and I.L. Kraevskaya for the
chemical analysis of the support and catalyst samples,
and to T.Yu. Volozhanina for testing the catalysts.
REFERENCES
1. Schlesinger, H.I., Brown, H.C., Finholt, A.E., Gil-
breath, J.R., Hockstra, H.R., and Hyde, E.K., J. Am.
Chem. Soc., 1953, vol. 75, p. 215.
2. Ross, D.K., Vacuum, 2006, vol. 80, p. 1084.
3. Amendola, S.C., Sharp-Goldman, S.L., Janjua, M.S.,
Kelly, M.T., Petillo, P.J., and Binger, M., J. Power
Sources, 2000, vol. 85, p. 186.
4. Amendola, S.C., Sharp-Goldman, S.L., Janjua, M.S.,
Spencer, N.C., Kelly, M.T., Petillo, P.J., and Binger, M.,
Int. J. Hydrogen Energy, 2000, vol. 25, p. 969.
5. Xia, Z.T. and Chan, S.H., J. Power Sources, 2005,
vol. 152, p. 46.
6. Kojima, Y., Suzuki, K., Fukumoto, K., Sasaki, M.,
Yamamoto, T., Kawai,Y., and Hayashi, H., Int. J. Hydro-
gen Energy, 2002, vol. 27, p. 1029.
CONCLUSIONS
7. Richardson, B.S., Birdwell, J.F., Pin, F.G., Jansen, J.F.,
This study has demonstrated that the conditions
under which the active-component precursor being
supported (rhodium chloride) interacts with the tita-
nium dioxide surface are a significant factor in the
NaBH4 hydrolysis activity of the Rh/TiO2 catalysts
obtained by reduction directly in the reaction medium.
Raising the heat-treatment temperature from 110–130
to 300°ë for supported rhodium chloride enhances the
activity of the Rh/TiO2 catalysts. The growth of the spe-
cific catalytic activity of rhodium is most pronounced
for the catalysts containing >2 wt % Rh. It has been
demonstrated by a variety of physicochemical methods
that, as RhCl3 is supported on the anatase modification
of TiO2, the active-component precursor interacts
strongly with the support surface. As the temperature is
raised, the interaction between the surface complexes
of rhodium and titanium dioxide strengthens. The Rh3+
complexes are likely located on surface sites that were
previously occupied by adsorbed water molecules. The
removal of water from the anatase surface at 300°ë
causes partial replacement of chlorine atoms in the first
coordination sphere of Rh3+ by oxygen atoms from the
TiO2 surface. The state of supported rhodium chloride
determines the state of the supported rhodium metal
particles in the catalysts after their reduction during
NaBH4 hydrolysis. The calcination of supported rhod-
ium chloride at 300°C reduces the mean diameter of
reduced rhodium particles. These rhodium are com-
pletely or partially decorated with titanium dioxide.
This is evidence of the strong interaction between the
support and the active component. Furthermore, the
interaction between supported rhodium chloride and
anatase exerts an effect on the electronic properties of
the reduced rhodium particles.
and Lind, R.F., J. Power Sources, 2005, vol. 145, p. 21.
8. Wu, C., Zhang, H., and Yi, B., Catal. Today, 2004,
vols. 93–95, p. 477.
9. Simagina, V.I., Storozhenko, P.A., Netskina, O.V.,
Komova, O.V., Odegova, G.V., Samoilenko, T.Yu., and
Gentsler, A.G., Kinet. Katal., 2007, vol. 48, no. 1, p. 177
[Kinet. Catal. (Engl. Transl.), vol. 48, no. 1, p. 168].
10. Mal’tseva, N.N. and Khain, V.S., Borogidrid natriya
(Sodium Tetrahydroborate), Moscow: Nauka, 1985.
11. Kraus, W. and Nolze, G., PowderCell for Windows (Ver-
sion 2.3), Berlin: Federal Institute for Materials
Research and Testing, 1999.
12. Klementev, K.V., J. Phys. D: Appl. Phys., 2001, vol. 34,
p. 209.
13. Rehr, J.J. and Ankudinov, A.L., Radiat. Phys. Chem.,
2004, vol. 70, p. 453.
14. Lever, A.B.P., Inorganic Electronic Spectroscopy,
Amsterdam: Elsevier, 1984, p. 554.
15. Odegova, G.V. and Slavinskaya, E.M., Kinet. Katal.,
2004, vol. 45, no. 1, p. 146 [Kinet. Catal. (Engl. Transl.),
vol. 45, no. 1, p. 133].
16. Komova, O.V., Simakov,A.V., Rogov,V.A., Kochubei, D.I.,
Odegova, G.V., Kriventsov, V.V., Paukshtis, E.A.,
Ushakov, V.A., Sazonova, N.N., and Nikoro, T.A., J. Mol.
Catal. A: Chem., 2000, vol. 161, p. 191.
17. Vodorodnaya svyaz’ (Hydrogen Bond), Sokolov, N.D.,
Ed., Moscow: Nauka, 1981, p. 286.
18. Nickl, J., Dutoit, D., and Baiker, A., Appl. Catal., A,
1993, vol. 98, p. 173.
19. Hadjiivanov, K.I., Klissurski, D.G., and Davydov, A.A.,
J. Catal., 1989, vol. 116, p. 498.
20. Coey, J.M.D., Acta Crystallogr., Sect. B: Struct. Sci.,
1970, vol. 26, p. 1876.
KINETICS AND CATALYSIS Vol. 49 No. 4 2008