Effect of the metal?support interaction in Ag/CeO2 catalysts on their activity in ethanol oxidation

Article abstract of DOI:10.1134/S0023158417050056

The interaction of silver with the surface of CeO₂ in the Ag/CeO₂ catalysts prepared by coprecipitation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction, and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to formation of strong silver–support interaction and the epitaxy of silver particles (d₁₁₁ = 2.35 ?) on the surface of CeO₂ (d₁₁₁ = 3.1 ?). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetaldehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO₂ becomes the predominant direction of a catalytic reaction, and the Ag/CеО₂ catalyst obtained by impregnation technique was most active in this region as a consequence of the weaker metal–support interaction.

Full text of DOI:10.1134/S0023158417050056

ISSN 0023-1584, Kinetics and Catalysis, 2017, Vol. 58, No. 5, pp. 642–648. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © M.V. Grabchenko, G.V. Mamontov, V.I. Zaikovskii, O.V. Vodyankina, 2017, published in Kinetika i Kataliz, 2017, Vol. 58, No. 5, pp. 654–661.
Effect of the Metal−Support Interaction in Ag/CeO2 Catalysts
on Their Activity in Ethanol Oxidation
M. V. Grabchenkoa, *, G. V. Mamontova, V. I. Zaikovskiib, and O. V. Vodyankinaa
a National Research Tomsk State University, Tomsk, 634050 Russia
b Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
*e-mail: marygra@mail.ru
Received January 26, 2017
Abstract⎯The interaction of silver with the surface of CeO2 in the Ag/CeO2 catalysts prepared by coprecip-
itation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction,
and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to
formation of strong silver–support interaction and the epitaxy of silver particles (d111 = 2.35 Å) on the surface
of CeO2 (d111 = 3.1 Å). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol
at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetal-
dehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO2 becomes the predominant
direction of a catalytic reaction, and the Ag/CеО2 catalyst obtained by impregnation technique was most
active in this region as a consequence of the weaker metal–support interaction.
Keywords: Ag/CeO2 catalysts, metal−support interaction, ethanol oxidation
DOI: 10.1134/S0023158417050056
INTRODUCTION
However, the behavior of the Ag/CeO2 catalysts in
the reactions of selective oxidation is scantily known.
Earlier, it was shown [15] that interactions between Ag
nanoparticles and CeO2 on the surface of silicon diox-
ide facilitate an increase in the catalyst activity in the
oxidative dehydrogenation of ethanol. Thus, the vari-
ation of the strength of Ag–CeO2 interaction can be an
effective method for controlling the properties of sil-
ver-containing catalysts in the reactions of deep and
selective oxidation of organic substances.
The development of functional materials with
specified properties, including catalytic activity, is
currently a problem of paramount interest. The prop-
erties of a catalyst are determined in many respects by
its chemical nature, the size of particles, and the dis-
tribution of active components on the support surface.
The activity of supported nanostructured catalysts con-
siderably depends on the interaction of an active compo-
nent (metal) with the oxide support [1]. The possibility of
controlling the strong metal–support interaction at an
interface can play a decisive role in the development of
catalysts with specified properties [2].
At present, considerable attention in catalysis is
paid to ceria and materials on its basis. The ability of
the Ce4+/Ce3+ redox pair to activate gas-phase oxygen
and the defect structure of phase boundaries (oxygen
vacancy at the Ag–CeO2 interface) make a direct con-
tribution to the activity of the supported catalysts
based on ceria. The Ag/CeO2 system is a very promis-
ing catalyst for the low-temperature oxidation of
organic compounds such as formaldehyde [3], CO [1,
4–6], and soot (small carbon particles) [7–12] and for
the reduction of NOx [1]. Materials based on Ag/CeO2
are used as photocatalysts [13], and they are also used
in biochemistry due to the bactericidal properties of
ceria and silver [14].
The aim of this work was to study the role of inter-
facial metal–support interaction in the Ag/CeO2 cat-
alysts in the reaction of ethanol oxidation. Tor control
this interaction, we selected two catalyst preparation
techniques: incipient wetness impregnation (when sil-
ver was introduced into the surface of an already
formed phase of CeO2) and coprecipitation, which
included a redox reaction between Ag(I) and Ce(III)
to strengthen the interphase interaction between the
metal and the support. Temperature-programmed
reduction (TPR-H2), X-ray diffraction (XRD) analysis,
(and high-resolution transmission electron microscopy
(HR TEM) were used for studying the Ag–CeO2 inter-
action and the influence of this interaction on the
activity and selectivity of the Ag/CeO2 catalysts in a
reaction of ethanol oxidation.
642

EFFECT OF THE METAL−SUPPORT INTERACTION IN Ag/CeO2
643
EXPERIMENTAL
Synthesis of the Supports and Catalysts
For studying the phase composition and estimating
the particle sizes (coherent scattering regions, CSR) of
silver and ceria from the Scherrer equation, XRD
analysis was used. The XRD analysis was carried out
on a Rigaku Miniflex 600 diffractometer (Rigaku,
Japan) using CuKα radiation (λ = 1.5418 Å) and a Ni
filter. The phase composition was established with the
use of the PCPDFWIN database of and the
POWDER CELL 2.4 software for full profile analysis.
The CeO2 support was obtained by a precipitation
technique. An aqueous solution of ammonia (NH4OH,
25 wt %) was slowly added to 10.1 g of cerium(III)
nitrate hexahydrate (analytical grade) dissolved in
150 mL of distilled water with intense stirring to reach
pH 12. The resulting precipitate was filtered off, washed
with distilled water, dried at 80°C for 15 h, and calcined
at 500°C for 5 h.
The Ag/CeO2 catalysts with a silver content of 10 wt %
were obtained by two methods. According to the first
one, silver was supported onto CeO2 by incipient wet-
ness impregnation (imp) with the use of an aqueous
solution of silver nitrate (chemically pure). The sample
obtained was designated as Ag/CeO2 (imp). For the
preparation of a catalyst with strengthened Ag–CeO2
interphase interaction, a codeposition precipitation
technique (coDP), which included a redox reaction
between Ag(I) and Ce(III), was used [16]. For this
purpose, an aqueous solution of ammonia was slowly
poured into an aqueous solution of silver and
cerium(III) nitrates. In this case, the precipitation of
cerium(III) hydroxide occurred, and the resulting
AgOH was dissolved in an excess of ammonia, being
The structure of the samples and also the morpho-
logical and crystallographic characteristics of sup-
ported silver and ceria were studied by HR TEM on a
JEM–2200FS microscope (JEOL, Japan). The crys-
tal lattice parameters were calculated by Fourier trans-
form using the DigMicrograph (GATAN) software.
The reduction of the samples was studied by TPR-
H2 on a Chemisorb 2750 chemisorption analyzer
(Micromeritics) supplied with a thermal conductivity
detector using a gas mixture of H2 + Ar (10 vol % H2)
in a temperature range from 25 to 750°C at a gas flow
rate of 20 mL/min and a heating rate of 10 K/min.
Before each particular experiment, the samples were
subjected to oxidative pretreatment in a flow of air
(20 mL/min) under temperature-programmed oxida-
tion (TPO) conditions with heating to 500°C at a rate
of 10 K/min and keeping at this temperature for 10 min.
Ag(NH3)2+
converted into the ammonium complex
.
The catalytic properties of the samples in the oxi-
dative dehydrogenation of ethanol were studied under
flow conditions at atmospheric pressure in a tubular
U-shaped quartz reactor with a fixed bed of the catalyst.
The granule diameter of the samples was 0.25–0.5 mm,
and the sample volume was 0.5 cm3. The reaction mix-
ture containing 2 vol % C2H5OH and 18 vol % O2 in
He was passed through the catalyst bed at a rate of
60 mL/min. The concentrations of ethanol, acetalde-
hyde, acetic acid, diethyl ether, and ethyl acetate in the
reaction mixture were measured by online gas chro-
matography on a Kristall 5000.2 instrument (Khro-
matek, Russia) supplied with a Zebron Wax plus cap-
illary column (30 m × 0.32 mm) and a flame-ioniza-
tion detector at a temperature of 160°C. A metal
column packed with a Carbosieve S II polymeric
porous sorbent was used for the separation of CO and
CO2, and a thermal conductivity detector was applied.
Then, the adsorption of this complex on the particles
of cerium hydroxide occurred accompanied by the fol-
lowing redox reaction at pH ~12 [17]:
Ce(OH)3 + Ag(NH3)2ОН + 2Н2О
= Ce(OH)4 + Ag0 + 2NH4OH.
This was evidenced by a color change in the solution
to a darker color (because of the appearance of silver
nanoparticles, which absorb light in the visible
region). The sample obtained was designated as
Ag/CeO2 (coDP).
The silver catalysts prepared were dried at 80°C for
15 h and calcined at 500°C for 5 h.
Characterization of the Supports and Catalysts
The low-temperature adsorption of nitrogen was
used for measuring specific surface areas and pore-
size distributions in the support and the catalysts. The
experiments were carried out on a TriStar 3020 auto-
matic gas-adsorption analyzer (Micromeritics, the
United States).
For determining the specific surface area (Ssp), the
multipoint (10–12 points) BET method was used in a
range of the relative nitrogen pressures P/P0 from 0.05
to 0.30. The test samples were preliminarily outgassed
in a vacuum at 200°C for 120 min.
RESULTS AND DISCUSSION
The textural characteristics of the synthesized sup-
ports and catalysts were investigated by the low-tem-
perature adsorption of nitrogen. Figure 1a shows the
isotherms of nitrogen adsorption–desorption and
pore size distributions for the ceria and Ag-containing
catalysts. The isotherms can be related to type IV with
a hysteresis in the region of relative pressures of 0.45–
The pore size distribution was studied by the BJH 1.0; this fact is indicative of the mesoporous structure
method, analyzing the desorption branch of the iso- of the samples. The pore size was 2–10 nm in all of the
therm of nitrogen adsorption–desorption.
samples.
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644
GRABCHENKO et al.
The specific surface area (Ssp) of the ceria obtained
(а)
by the precipitation tecnique was 66 m2/g with a spe-
cific pore volume of 0.098 cm3/g (Table 1). Upon the
supporting of silver onto the surface of ceria by the
impregnation method, considerable changes in the
pore size distribution in the Ag/CeO2 (imp) sample
Pore volume, сm3 g–1 nm–1
Adsorption, mmol/g
1
1
3
3.0
2.5
2.0
1.5
1.0
0.5
0.02
was not observed; in this case, Ssp decreased to 33 m2/g
3
and the specific pore volume, to 0.061 cm3/g. In the
Ag/CeO2 (coDP) catalytic system, the specific surface
area and the pore volume were smaller than those in
CeO2; this fact may be indicative of the interaction of
silver precursors with ceria in the process of precipita-
tion.
2
0.01
2
0
0.2 0.4 0.6 0.8 1.0
Relative pressure
XRD analysis was used for determining the phase
composition and estimating the sizes of silver and
CeO2 crystallites. Figure 1b shows the diffractograms
of the samples based on CeO2. The ceria and Ag/CeO2
catalysts were characterized by the presence of reflec-
tions at 2θ = 28.4°, 33.8°, 47.4°, and 56.6°, which are
related to the CeO2 phase with a cubic structure. The
particle size of this phase estimated from the size of
CSR was 11–14 nm (Table 1). Weakly pronounced
reflections at 2θ = 38.1° and 44.3°, which correspond
to a silver metal phase with a crystallite size of <5 nm,
appeared in the spectra of the silver-containing sys-
tems. A decrease in the unit cell parameter of ceria in
the Ag/CeO2 (coDP) sample can indicate an increase
in the number of oxygen vacancies in the structure of
CeO2 in the presence of silver [15] or the incorporation
0
5
10
15
20
25
Pore diameter, nm
(b)
Intensity
Ag cub. (PDF 04-0783)
CeO2 cub. (PDF 02-1306)
•
∗
∗
∗
∗
∗
∗
∗
1
2
∗
∗
∗
∗
•
•
•
of Ag+ ions (according to Belov and Bokii, the ionic
radius of Ag+ is 0.88 Å) into the lattice of CeO2 (the
ionic radius of Ce4+ is 1.13 Å) [18].
•
3
•
10
20
30
40
50
2θ, deg
60
70
80
90
The reduction of the oxide states of silver and
cerium in the synthesized samples was investigated by
the TPR-H2 method. The TPR profile of the CeO2 sup-
port (Fig. 2) indicates hydrogen consumption in a range
of 350–650°C, which is related to the reduction of the
surface oxygen of CeO2. The consumption of H2 at tem-
peratures higher than 700°C can be attributed to the
reduction of the CeO2 bulk phase to Ce2O3 [19, 20].
Fig. 1. (a) Isotherms of nitrogen adsorption–desorption
and pore size distributions and (b) the diffractograms of
the samples: (1) CeO , (2) Ag/CeO (coDP), and
2
2
(3) Ag/CeO (imp).
2
oxide [21–23]. The peaks with maximums at 190 and
210°C may be attributed to the reduction of CeO2 par-
ticles, interacting with Ag particles [15, 24]. In this
case, the insignificant reduction of CeO2 surface at
temperature above 350°C was observed for the
Ag/CeO2 (coDP) and Ag/CeO2 (imp) catalyst. A sim-
The Ag/CeO2 catalysts mainly consume hydrogen
in a range of 50–350°C. In this section, it is possible to
recognize two regions of hydrogen consumption: 50–
150 and 150–280°C. Peaks with maximums at 69, 120,
and 132°C can be related to the reduction of silver
from the oxidized clusters and highly dispersed silver ilar effect of the low-temperature reduction of ceria in
Table 1. Properties of the synthesized samples
Pore volume,
Ssp, m2/g
d111 (CeO2), Å
Sample
Pore size, nm
D, nm
cm3/g
CeO2 (support)
Ag/CeO2 (coDP)
Ag/CeO2 (imp)
66
16
33
0.098
0.044
0.061
4.8
7.9
5.2
3.129
3.119
3.124
12.5
13.9
11.4
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EFFECT OF THE METAL−SUPPORT INTERACTION IN Ag/CeO2
645
The structure of the obtained catalysts and the dis-
tribution of an active constituent were investigated by
HR TEM. Figure 3a shows the TEM image of ceria
obtained by the precipitation method the CeO2 parti-
cle size distribution in this sample. It is evident that the
sample consisted of CeO2 particle agglomerates of size
5–16 nm, which have a nearly spherical shape. The
HR TEM image of the same sample (Fig. 3b) indi-
cates that the aggregated CeO2 particles were tightly
adjoined between themselves by different faces, pre-
dominantly, by the faces (111) (d111 = 3.1 Å). The HR
TEM study of the Ag/CeO2 catalyst prepared by the
coprecipitation method (Fig. 3c) showed that the
majority of silver particles were epitaxially bound to
the surface of ceria. Parallel Moiré fringes characteris-
tic of the epitaxy of particles were observed; this corre-
H2 consumption
210
120
69
190
Ag/CeO2 (imp)
132
Ag/CeO2 (coDP)
CeO2
0
100 200 300 400 500 600 700
Temperature, °C
sponds to the contact of silver nanoparticles (d111
0.23 nm) of size ~2 nm with the surface of CeO2 (d111
=
=
Fig. 2. TPR-H profiles of the catalysts based on CeO
2
2
after oxidative pretreatment at 500°C.
0.31 nm). Figure 3c shows four sections with epitaxial
contacts between the metal and ceria particles. In spite
of a significant difference in interplanar spacing in the
lattices of silver and ceria (~25%), strong interaction
between the active constituent and the support mani-
fested itself, as judged by the observed epitaxy. In this
case, the epitaxy of silver on the surface of CeO2 is most
characteristic of the crystalline metal nanoparticles of
size 2–3 nm.
Figure 3e shows the HR TEM image of the
Ag/CeO2 (imp) sample. Silver occurred in this sample
in the form of clusters with sizes from 0.5 to 3 nm. The
model of a diffraction pattern obtained with the use of
Fourier transform in the corresponding sections of
images exhibited reflections in the form of ring frag-
ments, which relate to the crystal lattice of silver
(d111 = 0.23–0.24 nm). The ring-shaped form of the
reflections can be explained by a structural disordering
with a deviation from the face-centered cubic (FCC)
lattice of silver, which is characteristic of a metal phase.
These distortions can be a consequence of the forma-
tion of metal clusters. Only a cluster state of silver was
detected in the study of a relatively large number of dif-
ferent sections in the granules of this catalyst.
the presence of noble metals was described previously
[17, 25–27]. Thus, the results of TPR make it possible
to draw the conclusion that silver partially interacts with
surface of CeO2 support. The other part of ceria surface is
free from silver. In this case, the area of uncovered surface
of CeO2 particles in the catalyst obtained by the copre-
cipitation method is greater than that in the impregnated
catalyst.
A considerable shift of the peak of surface ceria
reduction in the Ag/CeO2 (coDP) sample (a maxi-
mum at 190°C) and its higher intensity, as compared
with the peak in the profile of Ag/CeO2 (imp) (a max-
imum at 210°C), are indicative of the more intense
interaction of silver with the surface of CeO2 (possibly,
with the introduction of Ag+ ions into its crystal lat-
tice). Table 2 summarizes the amounts of hydrogen
absorbed under the TPR conditions. The area of a
peak in the region of 50–300°C in the spectrum of the
Ag/CeO2 (imp) sample corresponds to the hydrogen
absorption of 0.256 mmol/g, whereas the sample
obtained by the coprecipitation method consumed
somewhat more hydrogen (0.285 mmol/g) in this
region. This increase is explained by the stronger
interfacial interaction of silver with CeO2, which
increases the reducibility of ceria.
Properties of the Catalysts in Ethanol Oxidation
The catalytic properties of the synthesized samples
were investigated in the reaction of ethanol oxidation.
Figure 4 shows the temperature dependence of the
conversion of ethanol and selectivity for the formation
of acetaldehyde and COx on the test samples. The for-
mation of ethylene, acetic acid, diethyl ether, and
other feasible products was not detected. The CeO2
support exhibited its own activity (ethanol conversion,
10%) in the oxidation of alcohol starting from a tem-
perature of ~150°C, and the complete conversion of
ethanol on this sample was reached at ~235°C. In this
case, the high selectivity for the formation of acetalde-
hyde (more than 90%) was retained to 200°C.
Table 2. Hydrogen consumption in TPR
Н2 consumption,
Catalyst
Т, °С
mmol/g
CeO2 (support)
350–650
50–350
350–650
50–350
350–650
0.205
0.285
0.124
0.256
0.026
Ag/CeO2 (coDP)
Ag/CeO2 (imp)
KINETICS AND CATALYSIS Vol. 58 No. 5 2017

646
GRABCHENKO et al.
d111 = 3.1Å
d220 = 1.9Å
d111 = 3.1Å
(a)
dav = 13.6 nm
14
12
10
8
d200 = 2.7Å
6
4
2
d111 = 3.1Å
0
4
8
12 16 20
50 nm
5 nm
(b)
(d)
d111 = 3.1Å
Diameter, nm
0.23 nm
(c)
0.31 nm
0.23 nm
0.22 nm
0.24 nm
0.31 nm
0.23 nm
d311 = 0.16 nm
0.31 nm
0.23 nm
0.24 nm
5 nm
5 nm
0.31 nm
Fig. 3. TEM and HR TEM images of (a, b) the CeO support and the (c) Ag/CeO (coDP) and (d) Ag/CeO (imp) catalysts.
2
2
2
A 10 and 100% conversion of ethanol over the of TPR in a temperature range of 90–150°C (the
Ag/CeO2 (imp) sample was observed at a temperatures
of 110 and 170°C, respectively. Selectivity for the for-
mation of acetaldehyde remained at a level of 100% up
to 130°C. Above 130°C, along with the oxidation of
ethanol into acetaldehyde, the deep oxidation of etha-
nol into CO2 is also observed.
reduction of the oxidized states of silver). A decrease in
selectivity for the formation of acetaldehyde at tem-
peratures higher than 130°C is related to the participa-
tion of the active oxygen of ceria in the reaction at the
Ag–CeO2 phase boundary. This is consistent with the
presence of a medium-temperature peak in the region
of 100–300°C, which corresponds to the coreduction
of silver and cerium oxides, in the TPR profile. The
decrease in selectivity for the formation of the target
product can also be caused by an increase in the bind-
ing energy of adsorbed alkoxy groups, which are reac-
tion intermediates in the of oxidation of alcohol, on
the partially reduced centers of the catalyst surface;
this increases the probability of C–C bond cleavage
followed by the oxidation of the resulting C1 fragments
into CO2 [28]. Thus, the centers activated at tempera-
The Ag/CeO2 (coDP) catalyst was characterized by
higher activity at a low temperature: at 85°C, the con-
version of ethanol was 15% at 100% selectivity for the
formation of acetaldehyde. Above 130°C, this selectiv-
ity substantially decreased because of the onset of the
deep oxidation of ethanol to COx. The complete con-
version of ethanol was achieved at ~190°C.
The higher activity of the catalyst prepared by the
coprecipitation technique at relatively low tempera-
tures can be explained by an increased rate of the
recovery of active centers, as evidenced by the results
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EFFECT OF THE METAL−SUPPORT INTERACTION IN Ag/CeO2
647
(а)
Conversion of ethanol, %
(b)
Selectivity, %
100
3
2
1
3
2
1
100
80
60
40
20
0
80
60
40
20
0
10 %
3
2
1
80 100 120 140 160 180 200 220 240
80 100 120 140 160 180 200 220 240
Temperature, °С
Temperature, °С
Fig. 4. The temperature dependence of (a) the conversion of ethanol in the reaction of its oxidation on the (1) CeO , (2) Ag/CeO
2
2
(imp), and (3) Ag/CeO (coDP) samples and (b) selectivity for the formation of (solid lines) acetaldehyde and (broken lines)
2
CO . Reaction mixture, ethanol : O : He = 2 : 18 : 80; flow rate, 60 mL/min.
x
2
tures higher than 130°C are also predominantly the catalyst activity in the region of 130–170°C, as found
centers of deep oxidation.
earlier by Dutov et al. [33] in a study of the TPO of
Ag/SiO2. The Ag/CeO2 (imp) catalyst is more active
in this region. On the one hand, this can be explained
by the fact that, according to the HR TEM data, silver
in this catalyst is predominantly stabilized in the form
of clusters, which more easily undergo reoxidation
because of their small size. On the other hand, the
weaker interaction of silver with the surface of ceria
also facilitates reoxidation and, correspondingly,
imparts higher activity in the reaction of deep oxida-
tion to this catalyst, as was demonstrated using the
low-temperature oxidation of CO on the Ag/SiO2 cat-
alyst as an example [33].
Based on the experimental results, we can con-
clude that the interaction of silver with ceria at the
Ag–CeO2 interface influences the activity of the cata-
lyst in the low-temperature oxidation reactions of
organic substances, in particular ethanol. In a range of
85–130°C, ethanol is selectively converted into acetal-
dehyde; in this case, the Ag/CeO2 (coDP) catalyst,
which is characterized by the strongest metal–support
interaction, is the most active. On this basis, it is pos-
sible to assume that the strong metal–support interac-
tion, which also facilitates electron transfer between
the nanoparticles of silver and ceria, is responsible for
the more effective activation of alcohol molecules. A
pair of the Lewis acid site Agδ+ and the basic site of the
oxide surface can be formed at the Ag–CeO2 inter-
face, and this cooperation enhances effective alcohol
dehydrogenation to aldehyde with the activation of
the β-C–H bond at the Agδ+ sites and the O–H bond
at the basic sites of ceria [16, 29, 30]. The possibility of
cooperation of this kind between the silver centers and
the acid–base groups of aluminum oxide was
described based on the dehydrogenation of alcohols
on the Ag/Al2O3 catalysts as an example [31].
CONCLUSIONS
Thus, the control of the Ag–CeO2 interphase
interaction plays the most important role in the devel-
opment of highly effective silver-containing catalysts
for the selective or deep oxidation of ethanol. As
demonstrated in this work, not only the particle size of
the active constituent but also its interaction with the
support affect the activity and selectivity of a catalyst.
Stronger interaction at the Ag–CeO2 phase boundary
in the sample obtained by the coprecipitation method
increases the activity of the system in the reaction of
the low-temperature selective conversion of ethanol
into acetaldehyde. On the contrary, the relatively weak
interaction between the clusters of silver and ceria in
the Ag/CeO2 catalyst prepared by the impregnation
method decreases its activity in the reaction of ethanol
dehydrogenation to acetaldehyde and increases activ-
ity in the deep oxidation reaction of alcohol to CO2.
Above 130°C, the deep oxidation of ethanol to CO2
becomes the predominant process. This can be
explained by the fact that, according to the TPR data,
the surface oxygen of ceria is activated through the
Ag–CeO2 phase boundary at this temperature.
Because of the high mobility of the surface oxygen of
ceria, its transfer (spillover) to the Ag–CeO2 phase
boundary occurs, where the deep oxidation of alcohol
supposedly takes place [1, 32]. Above 130°C, the rate
of reoxidation of the surface of silver particles also
The regularities revealed can find use in the devel-
increases; this fact can explain a sharp increase in the opment of catalysts for high-purity acetaldehyde pro-
KINETICS AND CATALYSIS Vol. 58 No. 5 2017

648
GRABCHENKO et al.
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for the low-temperature deep oxidation of volatile
organic substances, including CO, methanol, formal-
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Moscow: Nauka, 1971.
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ACKNOWLEDGMENTS
This work was supported by a grant from the Presi-
dent of the Russian Federation (МК-2015.2017.3 in
2017) and Tomsk State University competitiveness
improvement program (grant no. 8.2.19.2017).
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Translated by V. Makhlyarchuk
KINETICS AND CATALYSIS
Vol. 58
No. 5
2017