Formation and Conversion of Surface Compounds upon Interaction of Ethanol with Cu/CeO2 Catalyst According to in situ IR Spectroscopy

Article abstract of DOI:10.1134/S0023158418030114

In the conditions of ethanol conversion on the surface of a 5%Cu/CeO₂ catalyst, the method of in situ IR spectroscopy reveals ethoxy groups, acetate and formiate complexes, and consolidation products. Acetaldehyde, acetone, croton aldehyde, butadiene, hydrogen, CO, and CO₂ are observed in the reaction products. As the temperature of the experiment increases, the concentration of acetaldehyde passes through a maximum at T = 250°C. This product is formed due to the interaction of ethoxy and hydroxyl surface groups. The concentration of acetone, croton aldehyde, and butadiene also passes through a maximum in the 350–400°C range. These products are associated with the decomposition of the consolidation products. The concentration of hydrogen, CO and CO₂ steadily increases with temperature and only these reaction products are left at T > 400°C. A mechanism of hydrogen formation based on the conversion of the highest temperature formiate surface complex is discussed.

Full text of DOI:10.1134/S0023158418030114

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 3, pp. 320–327. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.A. Matyshak, O.N. Sil’chenkova, V.Yu. Bychkov, Yu.P. Tyulenin, 2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 3, pp. 324–331.
Formation and Conversion of Surface Compounds
upon Interaction of Ethanol with Cu/CeO Catalyst
2
According to in situ IR Spectroscopy
a,
a,
a
a
V. A. Matyshak *, O. N. Sil’chenkova **, V. Yu. Bychkov , and Yu. P. Tyulenin
a
Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: matyshak@polymer.chph.ras.ru
*
*e-mail: son1108@yandex.ru
Received June 22, 2017
Abstract⎯ In the conditions of ethanol conversion on the surface of a 5%Cu/CeO catalyst, the method of in
2
situ IR spectroscopy reveals ethoxy groups, acetate and formiate complexes, and consolidation products.
Acetaldehyde, acetone, croton aldehyde, butadiene, hydrogen, CO, and CO are observed in the reaction
2
products. As the temperature of the experiment increases, the concentration of acetaldehyde passes through
a maximum at T = 250°C. This product is formed due to the interaction of ethoxy and hydroxyl surface
groups. The concentration of acetone, croton aldehyde, and butadiene also passes through a maximum in the
3
50–400°C range. These products are associated with the decomposition of the consolidation products. The
concentration of hydrogen, CO and CO steadily increases with temperature and only these reaction products
2
are left at T > 400°C. A mechanism of hydrogen formation based on the conversion of the highest temperature
formiate surface complex is discussed.
Keywords: ethanol, hydrogen, intermediate compounds, in situ molecular spectroscopy
DOI: 10.1134/S0023158418030114
INTRODUCTION
does not favor the formation of hydrocarbons, because
this leads to the loss of hydrogen in adverse reactions.
Ethanol is a promising reagent for the production
of a wide range of industrially important products.
Olefins С –С and aromatic hydrocarbons, which are
used as components of motor fuels and petrochemi-
cals substrates, are produced by the catalytic conver-
sion of ethanol [1, 2].
Two-component catalytic systems containing Rh,
Pd, or Pt are the most suited to the criteria mentioned
above in the reforming conditions [5, 6]. From the
viewpoint of hydrogen production from ethanol in the
reaction of partial oxidation, the promising catalysts
are oxide systems based on CeO and CeZrO ,
4
12
2
2
Another promising process of ethanol conversion is
the production of hydrogen, which is used as an energy
source in fuel cells. Several reactions of the synthesis
of hydrogen from ethanol are known: steam reforming
because they have a high oxygen capacity and are
highly active in dissociating molecules such as ROH
(
alcohol and water). Modification by the noble (Pt,
Pd, Ru, Rh, Au) and transition (Co, Ni) metals is used
to increase the activity, selectivity, and stability of
these catalysts [7–20].
(
1), partial oxidation (2), and oxidative steam reform-
ing (3) [3, 4].
C H OH + 3H O → 2CO + 6H ,
(1)
2
5
2
2
2
To establish the nature of the activity and mecha-
C H OH + 1.5O → 2CO + 3H ,
(2) nism of the process, the surface compounds were also
2
5
2
2
2
studied by the method of IR spectroscopy in the con-
C H OH + 2H O + 0.5O → 2CO + 5H .
(3)
2
5
2
2
2
2
ditions of ethanol conversion. According to the data of
The implementation of one or another reaction numerous studies of very different catalysts [12, 15–
route depends on the reaction conditions and the 19], the formation of the ethoxy group is the initial
choice of the catalyst. An effective catalyst for produc- stage of the interaction of ethanol with the surface.
ing hydrogen from ethanol should satisfy at least three The oxidized forms were also observed, including
conditions: (1) it breaks the carbon–carbon bond in adsorbed acetaldehyde, croton aldehyde, formic and
ethanol at the lowest possible temperature, preferably acetate complexes, and adsorbed CO molecules [15–
below 300°C; (2) it does not cause the formation of 23]. According to [21], the stability of carboxylate
CO under the optimal reaction conditions; and (3) it complexes depends on the nature of the catalyst. In
320

FORMATION AND CONVERSION
321
particular, acetate particles on ZnO at 750 K are OmniStar GSD 301 mass spectrometer (Pfeiffer, Ger-
decomposed into CO and CH [22] and on CeO at many).
4
2
7
50 K into CO, CH , and CO [23].
The technique of unsteady spectra-kinetic studies
consists of simultaneously measuring the concentra-
tion of the surface compounds by in situ IR spectros-
copy and the formation rate of the reaction products
by the chromatographic method in the process of
establishing the stationary regime of the ethanol con-
version reaction or upon the exclusion of ethanol from
the flow of the reaction mixture.
4
2
The surface compounds formed by the interaction
of ethanol with oxide catalysts are clearly character-
ized in the literature; however, the role of these com-
plexes in the formation of different products of the
process is not clear. In this regard, the main purpose of
this work was to study the properties of the surface
compounds and routes of their conversion into prod-
ucts in the interaction of ethanol with the surface of
CeO and Cu/CeO .
2
2
RESULTS
Stationary Measurements
EXPERIMENTAL
Figure 1 shows the IR spectra recorded during the
ethanol conversion on a sample of 5%Cu/CeO at dif-
Experimental Technique
2
ferent temperatures. The spectrum obtained at 150°C
2
Cerium oxide with a specific surface S = 73 m /g
sp
exhibits absorption bands in the region of the С–О
was obtained by decomposing nitric acid salt
–1
vibration of the linear (1116 cm ) and bridge
Се(NO ) ⋅ 6H O in air at 500°C for 2 h. The specific
–1
3
4
2
(1057 cm ) ethoxy groups [15, 19, 20]. The absorp-
surface area was determined by the BET method by
the low-temperature adsorption of argon. Samples of
CuO/CeO were prepared by impregnating CeO with
–1
tion band at 1380 cm (δ vibration of СН ) also
s
2
belongs to ethoxy groups. The increase in the tem-
perature leads to an abrupt decrease in the intensity of
2
2
an aqueous solution of nitric acid salt (based on apply-
ing 5.0 wt % of CuO).
–1
the 1116 cm absorption band and the appearance of
–
1
a 1095 cm absorption band belonging to yet another
type of linear ethoxy group. At a temperature above
In the reaction of ethanol conversion, a 7% mix-
ture of ethanol in helium was used as the initial mix-
ture. The He gas used in the work contained up to
1
50°C (Fig. 1, spectra 3, 5) the IR spectra are domi-
nated by the absorption bands of acetate complexes at
0
.2% oxygen as an admixture.
–1
1
555 and 1440 cm [15]. As the temperature is
The spectro-kinetic measurements in the condi- increased to 300–350°C, the absorption bands of the
tions of the ethanol conversion reaction were carried acetate complexes become broader and more complex
out according to the method described in [24]. The in shape. Such changes indicate the appearance of the
experimental setup included a Spectrum RX I FT-IR absorption bands of other surface compounds in this
System IR Fourier spectrometer (Perkin Elmer, spectral region. The nature of these compounds will
United States) or IFS-45 (Brucker, Germany), a be discussed below.
3
heated flow cuvette-reactor (V = 1 cm ), a gas prepa-
For comparison, Fig. 1 also shows the spectrum
ration unit, and a system for product and reagent anal- (curve 1) recorded in similar conditions on the carrier.
ysis. The intensity of the absorption bands in transmis- As is seen, the set of absorption bands on the carrier
sion spectra was measured in units of optical density (A). and the catalyst is the same except some difference
–1
The typical number of scans was 64 and the resolution (1–5 cm ) in the frequencies of the corresponding
was 4 s/m.
A sample in the form of a tablet with a weight of 20
absorption bands.
Figure 2 shows how the temperature affects the
2
to 30 mg and an area of 2 cm was placed in a cuvette, concentration of the ethanol conversion products
which simultaneously served as a catalytic flow reac- (Fig. 2b), as well as the intensity of the absorption
tor. Before the measurements, the sample was treated bands (Fig. 2a).
in an flow of an inert gas (He) at 450°C for an hour,
cooled to the required temperature in a He flow, and
then the reaction mixture flow (30 mL/min) was
turned on.
According to Fig. 2b, the formation of H and CO
2 2
on the copper-containing catalyst (curves 1, 3) begins
at Т > 150°C and steadily grows with temperature. The
formation of acetaldehyde (curve 2) and acetone
The weight change during the reaction of ethanol (curve 6) begins at T > 200°C. The temperature depen-
with Cu/CeO was studied in a SETSYS Evolution dences of their concentrations pass via a maximum at
2
3
20–330°C. Trace amounts of ethylene (curve 5), as well
termoweight (Setaram, France). A fresh sample
as CO, butene, and croton aldehyde (curves 4, 7, 8),
(
85 mg) was pretreated in a He + O flow at 400°C and
2
were found at T > 300°C. Above 450°C the reaction
then cooled to 30°C in a He flow. Ethyl alcohol was
products are mainly H , CO, and CO .
added through a bubbler purged by He at a rate of
2
2
1
4 mL/min. The sample was heated to 500°C at a rate
Note that the products formed during the conver-
of 10°C/min. The exhaust gas was analyzed using an sion of ethanol are more numerous than for methanol
KINETICS AND CATALYSIS Vol. 59 No. 3 2018

3
22
Absorption, arb. units
MATYSHAK et al.
(a)
Absorption, arb. unit
.0
Absorption, arb. unit
21
1555
1
7
0.1
0
.9
1560
1440
1545
0
0
0
.8
.7
.6
16
11
6
6
5
1057
0.5
0
.4
5
4
1095
0.3
0.2
1
1
3
0
.1
2
4
0
–4
5
0
100
150
200
(b)
250
300
350
3
2
1116
1340
7
8
Ion current × 10 , A
1.5
Ion current × 10 , A
1380
1
5.0
3
1
.4
.3
1.2
.1
.0
4
.5
4.0
.5
3.0
.5
1
1
600 1500 1400 1300 1200 1100 ν, cm–1
2
4
1
3
1
Fig. 1. IR spectra obtained (1) in conditions of ethanol
0.9
0.8
0.7
0.6
0.5
conversion (7 vol % in He) on CeO carrier at 200°С;
2
2
(
2) in similar conditions on 5%Cu/CeO sample at 150,
2
5
8
(
3) 200, (5) 350°С; (4) C H OH + H O (1 : 1) mixture on
2.0
1.5
1.0
2
5
2
5
%Cu/CeO sample at 200°С.
2
6
0
0
0
.4
.3
.2
1
7
0.5
[
24]. In the latter case, the only observed product is
0.1
0
0
methylformate.
5
0
100 150 200 250 300 350 400 450 500
Figure 2c shows the temperature dependence of the
sample weight measured in the reaction conditions. It
is important to note the increase and subsequent loss
of the sample weight in the 170–350°C range. As can
be seen, the decrease in the intensity of the absorption
bands of the ethoxy groups (Fig. 2a, curves 1, 2) is
accompanied by an increase and subsequent decrease
of the intensity of the absorption bands of the acetate
complexes (Fig. 2a, curves 5, 6). In turn, the decreas-
ing intensity of the absorption bands of ethoxy groups
and acetate complexes is due to the formation of reac-
tion products. As the temperature increases, these
absorption bands shift towards low frequencies. Such a
behavior of the absorption bands is associated with the
partial restoration of the catalyst surface [25].
(
c)
Weight, mg
38.6
38.5
3
3
3
8.4
8.3
8.2
3
8.1
8.0
7.9
7.8
7.7
7.6
3
3
3
3
3
5
0
100 150 200 250 300 350 400 450 500
T, °C
Curve 7 in Fig. 2a represents the total range of
absorption bands of the valent C–H vibrations. The
reason for the rather complex temperature dependence
of the total area is that the decrease in the intensity of the
C–H vibrations of the ethoxy groups is accompanied by
the growth of the intensity of the C–H vibrations of the
acetate complexes. The complex shape of the absorption
bands of the acetate complexes does not exclude the
presence of formate and carbonate complexes or con-
solidation products on the surface.
Fig. 2. Temperature dependence of (a) intensities of
absorption bands at (1) 1057, (2) 1100, (3)1117, (4) 1340,
–1
(5) 1437, (6) 1558, and (7) 2890 cm ; (b) concentrations
of ethanol conversion products (1) H , (2) acetaldehyde
2
CH –CH=O, (3) CO , (4) CO, (5) ethylene, (6) acetone,
3
2
(
7) croton aldehyde, and (8) butene; (c) weight of
5
%Cu/CeO sample during reaction.
2
Non-Stationary Measurements
After attaining stationary concentrations of the sur-
face compounds (in a flow of helium with 7% of etha-
nol) and exclusion of ethanol from the reaction mix-
ture, the isothermal desorption of the surface com-
A comparison of the spectral and catalytic data
(
Figs. 2a, 2b) shows that the formation of the reaction
products occurs in the same temperature interval as
the conversion of the ethoxy groups and acetate com-
plexes.
KINETICS AND CATALYSIS
Vol. 59
No. 3
2018

FORMATION AND CONVERSION
Absorption, arb. unit
323
Absorption, arb. unit
Absorption, arb. unit
0.016
0
.30
0.25
.20
0
0
.014
.012
0.010
0.008
.006
.004
.002
0
0
0
0
0
0
.7
.6
.5
.4
.3
.2
1545
1427
2
0
4
0
.15
.10
1
0
0
0
0
0
0.05
3
1
0
5
10
15
20
25
30
t, min
1095
1019
2
4
0
.1
Fig. 4. Time dependences of intensity of absorption bands
at (1) 1050,(2) 1080, (3) 1357, (4) 1437 cm– . T = 250°С.
5
1356
370
3
1
1
1
600 1500 1400 1300 1200 1100 1000
ν, cm–1
with time. At T > 200°C (Fig. 4, curve 4), the intensity
of absorption bands belonging to acetates remains
almost constant for a long time and decreases only
when the concentration of the ethoxy groups becomes
negligible (Fig. 4, curves 1, 2). The initial rates of ace-
tate consumption were determined from the end parts
of the kinetic curves.
Fig. 3. IR spectra recorded at different times after change-
over from ethanol flow (7 vol % in He) on 5%Cu/CeO
2
sample to He flow: (1) spectrum in ethanol; (2) 15; (3) 22;
(4) 25; (5) 30 min. T = 250°С.
pounds was carried out in an He flow or in a flow of an
He mixture with water vapor. The absorption bands of
the acetate complexes, as well as the bridge and linear
ethoxy groups, were monitored in the IR spectra. Fig-
ure 3 shows the spectra obtained in a typical spectra-
kinetic experiment. It is seen that as the absorption
bands of the acetate complexes decrease, the absorp-
tion bands of formic complexes emerge in the spectra.
Figure 4 shows the results of a spectra-kinetic
experiment after data processing. The first and second
order equations are not sufficient for describing the
time dependence of the intensity of the bands belong-
ing to the bridge and linear ethoxy groups (Fig. 4,
curves 1–3) and acetate complexes (Fig. 4, curve 4) in
the process of isothermal desorption. Apparently, the
reason for this is that the linear and bridge ethoxy
Similar experiments were carried out in the 150– groups are consumed along several routes. The con-
300°C range. The absorption bands of ethoxy groups version process of the surface compounds in this case
disappear more rapidly as the temperature increases. was characterized using the initial conversion rates.
The time-dependence of the absorption bands of ace- The corresponding values are given in Table 1. The
tate complexes at different temperatures is complex. data in Table 1 also shows that the conversion rate of
Acetate complexes are formed at low temperatures and the surface compounds is virtually constant in the
the intensity of their absorption bands does not change presence of water vapor (3%).
Table 1. Initial rates of surface compound conversion in conditions of ethanol conversion reaction on CeO2
Initial rate of surface compound conversion, arb. units
Acetate formation
acetate,
band at 1020 cm–1
ethoxy group,
band at 1046 cm
ethoxy group,
band at 1090 cm
–1
constant k, min
band at 1340 cm )*
–1
–1
Т, °С
–1
(
standard
in presence
standard
in presence
standard
in presence
n = 1
conditions of water vapor conditions of water vapor conditions of water vapor
1
50 No absorption No absorption
0.017
0.017
0.043
No absorption
0.042
band band
band
2
00
0.0
0.083
0.01
0.081
0.025
0.14
0.024
0.15
0.143
0.28
0.150
–
–
2
50
No absorption
band
300
0.127
0.13
0.1
0.104
No absorption No absorption
–
band
band
*
Constant is calculated from intensity of absorption band at 1340 cm–1
.
Dashes mean that process of acetate formation is not observed at given temperature.
KINETICS AND CATALYSIS Vol. 59 No. 3 2018

3
24
MATYSHAK et al.
the observed complexes are formed on the surface of
DISCUSSION
CeO , which is free from copper oxide particles. However,
2
Model of an Active Surface
–1
some shift (±2–5 cm ) of absorption band frequencies
can be
cess, the spectra of the 5%Cu/СеО and СеО sam- explained by the dissolution of copper oxide in the sur-
In the conditions of the ethanol conversion pro- relative to the values observed for CeO
2
2
2
ples exhibit the same set of absorption bands. The face layer of CeO when applying copper [25]. The
2
absorption bands of ethoxy groups have approximately obtained data confirm the active surface model of the
equal intensities (Fig. 1, spectra 1, 2). This means that catalyst which we proposed earlier [24].
H
C
O O
H
C
C H
2
5
H
O
Cu
O
O O
Cu
Cu + CeO2
CeO2
The model is also supported by the TPR-H data
A comparison of the IR spectra at 200°C (at this
2
temperature the classic acetate spectrum is observed)
and at 350°C (Fig. 1, spectra 3, 5) shows that the shape
and half-width of the acetate bands varies consider-
ably as the temperature increases. Figure 5 shows the
result of subtracting the spectrum of acetate complexes
from the spectrum at 300°C recorded in the reaction
conditions. It is seen that the difference spectrum exhib-
for Cu/СеО [26, 27], according to which the TPR-H
2
2
spectra exhibit two peaks of hydrogen absorption in
the 100–200°C range. The first (low-temperature)
2+
peak corresponds to the recovery of Cu ions local-
ized in the surface layer of the CeO lattice and the
2
second peak corresponds to the recovery of the CuO
particles on the CeO surface. It should be noted that
–1
2
its a broad absorption in the 1350–1650 cm region with
in the spectra, at low temperatures, the absorption
bands of formiate complexes can be observed against
the background of the relatively low intensity of the
absorption bands of the acetate complexes (Fig. 1,
spectrum 2). As the temperature increases, the formi-
ate bands are masked by the intense bands of the ace-
tate complexes (Fig. 1, spectrum 3).
–1
separate bands at 1590, 1524, 1460, and 1380 cm .
The bands in this region are related to vibrations of
–1
conjugate double bonds (1600–1590 cm ) and the
–1
–
C–H-bond (1380 cm ), as well as in COO com-
–1
plexes (1460, 1524 cm ) [28].
According to thermogravimetric analysis (TGA) in
the reaction conditions (Fig. 2c), the sample weight
increases in the specified temperature range. Based on
this and the published data [29], the bands in the
Absorption, arb. unit
–1
1
350–1650 cm region (Fig. 5, spectrum 3) can be
1440
confidentially assigned to vibrations in the consolida-
tion products (CPs).
0.05
As a result, it can be argued that in the reaction
conditions there are ethoxy groups, acetate and formi-
ate complexes, as well as consolidation products, on
the catalyst surface.
1550
1340
Conversion of the Surface Compounds
2
Ethoxy group. The formation of ethoxy groups
1
1524
upon the interaction of ethanol with the CeO surface
2
1460
1
380
1590
is accompanied by a decreasing intensity of the
3
–1
hydroxyl group bands (3600, 3640 cm ). This means
that they are formed according to the classical scheme
with the participation of hydroxyl groups on the sur-
face [30]. The linear and bridge ethoxy groups are
formed with the participation of the terminal and
bridge hydroxyl groups, respectively. At the same time,
the formation of ethoxy groups can be accompanied
by a rupture of both th H–H and C–O bonds in the
2
375 220020001900 1800 1700 1600 1500 1400 1300 1200
ν, cm–1
Fig. 5. IR spectra of ethanol on 5%Cu/CeO sample at
1) 300, (2) 200°С and (3) their difference.
2
(
KINETICS AND CATALYSIS
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2018

FORMATION AND CONVERSION
325
alcohol molecule depending on the basicity or acidity Table 2. Initial rates of ethoxy groups consumption and for-
mation of acetates in conditions of ethanol conversion reac-
of the hydroxyl groups.
tion on CeO at 150°C
2
Acetate complexes. The IR spectra recorded in the
reaction conditions for the 5%Cu/CeO sample (Fig. 1)
Initial
Initial
2
exhibit bands which are characteristic for vibrations in
Surface
compound
consumption rate formation rate
–1
–1
–1
surface acetate complexes (1560, 1440, and 1340 cm ).
The decreasing intensity of the ethoxy group bands is
accompanied by the growing intensity of the acetate
group bands (Fig. 2). This suggests that the ethoxy
k, min
k, min
n = 1
n = 1
Linear ethoxy group
groups are the formation source for acetates. The data (1116 cm )
0.02
–**
–1
obtained on the carrier confirm this conclusion. Table 2
shows the initial rates of the ethoxy group consump-
tion, which were calculated in the present work, and
Linear ethoxy group
0.01
0.01
–*
–**
–**
–1
(
1097 cm )
Bridge ethoxy group
the acetate formation rates for CeO . As can be seen,
2
–1
the sum of the initial consumption rates of the ethoxy (1057 cm )
groups coincides with the initial rate of acetate forma-
tion. This also proves that the ethoxy groups are the
source of acetate formation. In this case, the initial
rates could be compared because the molar extinction
coefficients for acetates (A = 1.7 × 10 cm/mole-
cule) and the ethoxy group (A = 1.15 × 10 cm/mol-
ecule) are quite close to each other [31].
Acetate (1340 cm–1)
0.040
Dashes indicate that in specified conditions consumption reac-
tion (*) or formation reaction (**) of given surface compound is
not observed.
–
17
0
–
17
0
their formation. Ethoxy groups probably play the key
role in this, since the formation of CPs is terminated in
the absence of ethoxy group on the surface (Fig. 2). As
follows from the data in Fig. 5 (spectrum 3), the CPs
Another indication that acetates are formed from
ethoxy groups was obtained in the experiments on the
isothermal desorption of the surface compounds at
–1
contain conjugate double bonds (~1600 cm ), C–H,
250°C. As can be seen from Fig. 4, the intensity of the
–1
and C–O bonds (1550–1380 cm ), as well as acetate
complexes.
acetate absorption bands (Fig. 4, curve 4) remains virtu-
ally unchanged until the complete consumption of all the
ethoxy groups (Fig. 4, curves 1, 2). This is possible if the
loss of acetates (filling all the places reserved for them) is
replenished by the conversion of the ethoxy groups. It is
very likely that the ethoxy groups are localized at the
centers on the currier, since both the intensities of the
absorption bands and their frequencies are almost
identical on the currier and on the catalyst.
Formation of Products
Acetaldehyde. The concentration of acetaldehyde
passes through a maximum as the temperature
increases (Fig. 2b, curve 3). This type of dependence
can be explained by the formation of acetaldehyde
from ethoxy groups with the participation of hydroxyl
groups, the content of which decreases with tempera-
ture (Fig. 2a, curve 7). The formation of acetaldehyde
should be accompanied by the release of an equivalent
amount of hydrogen. However, the recorded amount
of hydrogen is much smaller (Fig. 2b, curve 1). A pos-
sible explanation of the hydrogen deficiency can be its
consumption for regenerating the catalyst with the for-
mation of water in accordance with the following
stages:
Formiate complexes. Formiate complexes (absorp-
–1
tion bands at 1356 and 1370 cm ) can be observed in
the nonstationary experiments against the background
of acetate absorption bands whose intensity decreases
(
Fig. 3). It is not easy to establish the sources of formi-
ate formation in this case—they could be both the
ethoxy groups and the acetate complexes. By analogy
with the adsorption of methanol on this catalyst [24],
it can be assumed that formiates are localized both on
the carrier and on the copper clusters. It should be
noted that formiate complexes are characterized by a CH
−CH −OH +ZOH → CH −CH −OZ + H O, (4)
2 3 2 2
3
higher thermal stability in comparison with acetate
complexes.
CH −CH −OZ + ZOH → CH −CH=O + H O. (5)
3
2
3
2
Acetone, butene, croton aldehyde. As follows from
Fig. 2, the aforementioned products are formed by the
conversion of the consolidation products. As men-
tioned above, the appropriate particles for this are
available on the surface. It should be noted that in the
literature the formation of these products is described
with the help of schemes without taking into account
the possible presence of CPs on the surface [15].
Consolidation products. The intensity of acetate
absorption bands at 200°C (Fig. 5, spectrum 2) corre-
sponds to the maximum (monolayer) filling of the cat-
alyst surface. At 300°C the intensity is greater than at
2
00°C (Fig. 5, spectrum 1) with the other conditions
remaing the same. This means that the surface filling
in these conditions is much higher than one mono-
layer. This is a strong indication of the formation of
consolidation products (CPs). Any of the surface
Hydrogen, methane, CO , CO. The formation of
2
complexes mentioned above can be the sources of simple products of the ethanol conversion reaction is
KINETICS AND CATALYSIS Vol. 59 No. 3 2018

3
26
MATYSHAK et al.
explained by the scheme given below. The scheme
takes into account that an acetate complex is obtained
from an ethoxy group. In turn, the acetate complex
can be decomposed with the release of methane and
ACKNOWLEDGMENTS
The work was supported by the Russian Founda-
tion for Basic Research, grant no. 18-03-00627А.
CO , and it can also be converted into formiate and its
2
coproduct ethylene:
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Translated by V. Alekseev
KINETICS AND CATALYSIS Vol. 59 No. 3 2018