Reaction paths of the formation and consumption of nitroorganic complex intermediates in the selective catalytic reduction of nitrogen oxides with propylene on zirconium dioxide according to in situ Fourier transform IR spectroscopic data

Article abstract of DOI:10.1134/S0023158406040161

Nitrate, acetate, and nitroorganic complexes were detected on the surface of ZrO₂ under the reaction conditions of nitrogen oxide reduction with propylene using Fourier transform IR spectroscopy. The nitroorganic complex was formed in the reaction between acetate and nitrate complexes by the replacement of the carboxyl group in the acetate complex by the nitro group. Monodentate nitrate was the most reactive species in this process. The adsorption of various nitroorganic substances was studied. It was found that the nitroorganic complex was structurally analogous to the nitromethane molecule bound to the surface through the nitro group. The experimental data led us to a conclusion that nitroorganic compounds were subsequently consumed in reactions with nitrate complexes. In this surface reaction, monodentate nitrate was also the most reactive species. The presence of oxygen had no effect on the consumption of the nitroorganic complex. MAIK Nauka/ Interperiodica , 2006.

Full text of DOI:10.1134/S0023158406040161

ISSN 0023-1584, Kinetics and Catalysis, 2006, Vol. 47, No. 4, pp. 593–602. © MAIK “Nauka /Interperiodica” (Russia), 2006.
Original Russian Text © V.A. Matyshak, V.F. Tret’yakov, K.A. Chernyshev, T.N. Burdeinaya, V.N. Korchak, V.A. Sadykov, 2006, published in Kinetika i Kataliz, 2006, Vol. 47,
No. 4, pp. 610–619.
Reaction Paths of the Formation and Consumption
of Nitroorganic Complex Intermediates
in the Selective Catalytic Reduction of Nitrogen Oxides
with Propylene on Zirconium Dioxide According
to In Situ Fourier Transform IR Spectroscopic Data
a
b
a
b
V. A. Matyshak , V. F. Tret’yakov , K. A. Chernyshev , T. N. Burdeinaya ,
a
c
V. N. Korchak , and V. A. Sadykov
a
Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 117977 Russia
b
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 117912 Russia
c
Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia
Received January 25, 2005
Abstract—Nitrate, acetate, and nitroorganic complexes were detected on the surface of ZrO under the reaction
2
conditions of nitrogen oxide reduction with propylene using Fourier transform IR spectroscopy. The nitroor-
ganic complex was formed in the reaction between acetate and nitrate complexes by the replacement of the car-
boxyl group in the acetate complex by the nitro group. Monodentate nitrate was the most reactive species in this
process. The adsorption of various nitroorganic substances was studied. It was found that the nitroorganic com-
plex was structurally analogous to the nitromethane molecule bound to the surface through the nitro group. The
experimental data led us to a conclusion that nitroorganic compounds were subsequently consumed in reactions
with nitrate complexes. In this surface reaction, monodentate nitrate was also the most reactive species. The
presence of oxygen had no effect on the consumption of the nitroorganic complex.
DOI: 10.1134/S0023158406040161
INTRODUCTION
[21, 24]. Surface isocyanates are the most stable and,
consequently, most often detectable decomposition
products of N-containing compounds.
The selective catalytic reduction (SCR) of nitrogen
oxides with hydrocarbons in an excess of oxygen is a
promising method for the removal of NO from indus-
trial waste gases and automotive exhaust emissions [1].
A great number of publications were devoted to the
mechanistic studies of this process [2–18].
Isocyanates, as well as surface cyanides, readily
react with a mixture of NO + O and/or NO even at
x
2
2
room temperature to be converted into molecular nitro-
gen and N O [26, 28, 29, 31–33].
2
Thus, the reduction of surface nitrates with hydro-
carbons primarily results in the appearance of nitrogen-
containing organic compounds, which either directly
Currently, it is well established that nitrate com-
plexes participate in the reaction. As a result of many
studies on the role of nitrite–nitrate structures in SCR,
the concept of the interaction of nitrate complexes
interact with NO + O to form SCR products or decom-
x
2
–
–
and/or NO (their degradation product) with hydrocar- pose to substances containing NC and OCN anions. In
2
an excess of oxygen, the undesirable oxidation of nitro-
gen-containing organic compounds can occur to result
in the formation of a superequilibrium concentration of
bons and/or their partial oxidation products has been
most widely developed. This interaction causes the for-
mation of nitrogen-containing substances, primarily,
nitroorganic compounds O N–C H and organic
NO [24]:
2
2
m
n
nitrites ONO–C H [19–28].
m
n
C H NO + é
NO + CO + H O.
2 2 2
m
n
2
2
At elevated temperatures, these compounds react
with NO + O /NO to form molecular nitrogen. At an
2
2
As follows from the published data cited above,
common properties of surface nitroorganic compounds
have been determined to date. At the same time, there is
insufficient amount of an oxidizing agent and at tem-
peratures higher than 200–300°C, nitrogen-containing
–
organic compounds can decompose to form OCN [26, no information on the steps of the formation of these
–
2
8] and NC anions [28, 29], organic nitriles [21], cyan- complexes, on the structure of organic moieties, on the
ogen [30], hydrocyanic acid [30, 31], or even ammonia mechanism of conversion of a nitrate complex into
5
93

5
94
MATYSHAK et al.
molecular nitrogen, and on the roles of oxygen and
The interaction of NO with the surface of ZrO was
x 2
nitrogen oxides in this process. Information on the role also studied using temperature-programmed desorption
of the nature of the catalyst in the above surface reac- (TPD). The TPD under flow conditions in a reactor cell
tions is of paramount importance from the standpoint of was combined with the measurement of the IR spectra
SCR process activity and selectivity control.
of surface complexes. Before performing a thermal-
desorption experiment, the sample of ZrO was treated
In this context, the aim of this study was to deter-
2
mine the reaction paths of formation and consumption with nitrogen at 400–500°C immediately in the IR cell.
of nitroorganic complex intermediates in the SCR of Unless otherwise specified, the samples were cooled to
nitrogen oxides with propylene in the presence of cata- room temperature in a closed cell (without a flow of
lysts based on zirconium dioxide with the use of in situ
N ); thereafter, the adsorption of 0.2% NO/N was per-
2 2
Fourier transform IR spectroscopy. The ZrO -contain- formed for 20 min. An excess amount of NO was dis-
2
ing systems are promising low-temperature catalysts placed with a flow of nitrogen for 25 min. Thermal des-
for the SCR of NO with hydrocarbons in an excess of orption was performed with continuous analysis for
x
NO and NO in a gas phase before and after the reactor
oxygen; they exhibit good hydrothermal properties and
resistance to sulfur poisoning [34, 35]. Here, we report using a Beckman 951A chemiluminescence NO/NO
the results of a study of the properties of nitroorganic analyzer (nitrogen was a carrier gas; the heating rate
x
x
compounds on the surface of zirconium dioxide.
was 5 K/min). In the course of thermal desorption, the
spectra of surface compounds were measured. Each
particular spectrum provided information on changes in
the surface state upon heating by 20°C.
EXPERIMENTAL
–
1
ZrO was synthesized in accordance with a pub-
2
The gas flow rate was 9000 h in all of the experi-
lished procedure [36]. A freshly prepared 1.5 M aque- ments. All of the gases were purified with the use of
ous solution of ZrO(NO ) was aged for 15 h and then traps containing anhydrone and Ascarite. The base
3
2
hydrolyzed in excess aqueous ammonia with intense composition of the mixture was 0.2% NO +
stirring; pH ~ 9.5 was adjusted. The resulting zirconium 0.2% C H + 2.5% O /N . In a study of the effect of the
3
6
2
2
hydroxide in the mother liquor was hydrothermally composition of the mixture on the properties of surface
treated in an autoclave at 90°C for 24 h and at 110°C for compounds, the concentrations of NO, C H , and O
3
6
2
8
h.
ZrO + éç
The resulting ZrO · nH O was filtered off, washed
were varied from 0 to 0.5, 1.0, and 4.0%, respectively.
The analysis of gases before and after the reactor cell
2
–
–
Zré (Oç)
ZrO · nç é.
was performed using a Beckman 951A NO/NO chemi-
c
d
2
2
x
luminescence analyzer and a Beckman 590 HC/CO
infrared analyzer.
2
2
with 0.1 M NH OH, dried at 110°C, and then calcined
4
at 500°C for 2 h (the sample designated as ZrO (500)).
2
RESULTS AND DISCUSSION
The X-ray diffraction (XRD) analysis of samples was
According to XRD data, the resulting samples of
zirconium dioxide were a mixture of two phases, mon-
oclinic (m-ZrO ) and tetragonal (t-ZrO ); the latter was
performed on a DRON-3 diffractometer (CuK (λ =
α
1.54178 Å), 2θ step of 0.1°, and exposure time of 2 s).
All of the calculations, including the evaluation of
interplanar distances, were performed in accordance
with standard procedures. The phase composition anal-
ysis was performed by comparing with data in the
JCPDS File.
2
2
predominant. The average size of the coherent-scatter-
ing region (CSR) was evaluated from the half-width of
a reflection corresponding to the (111) face of m-ZrO2.
The TPD spectra of NO after the adsorption of NO
x
The interaction of reaction components and their on the surface of ZrO (500), which mainly contained a
2
mixtures with sample surfaces was studied in the course tetragonal phase, consisted of two broad peaks with
of reaching a steady state using transmission Fourier Tmax = 240 and 490°C (Fig. 1). Both of the peaks corre-
transform IR spectroscopy (Spectrum RX I FT-IR Sys- sponded to the release of NO and NO molecules into a
2
tem spectrometer from Perkin-Elmer). Before measur-
gas phase; as a rule, the thermal-desorption maximums
2
ing the IR spectra, ZrO pellets (10−20 mg/cm ) were of these oxides did not coincide. The thermal-desorp-
2
treated in a flow of N at 400°C. The design of IR reac- tion curves shown in Fig. 1 suggest that low-tempera-
2
tor cells, which allowed us to measure the spectra at ture desorption was primarily related to the release of
elevated temperatures, was described elsewhere [37]. NO, whereas the amount of NO molecules formed in
2
The intensities of absorption bands in transmission the high-temperature region predominated over the
spectra were measured in absorbance units (A).
release of NO.
The IR spectra were obtained by subtracting the
The IR spectra measured in the course of the above
spectra of a sample in a flow of nitrogen from the spec- thermal-desorption experiments mainly exhibited
tra of sample ZrO (500) in a flow of a reaction mixture absorption bands due to nitrate (~1610, 1587, and
2
–
1
–1
under the same conditions.
1568 cm ) and nitrite (~1505 and 1291 cm ) com-
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

REACTION PATHS OF THE FORMATION AND CONSUMPTION
595
Concentration, vol %
the TPD spectrum. The decrease in the intensity of
absorption bands due to bridging nitrite complexes
0
0
0
0
0
0
.06
.05
.04
.03
.02
.01
–
1
(
1530 and 1180 cm ) in the course of desorption corre-
NOx
sponds to the peak with Tmax = 230–240°C (Fig. 1).
Steady-Sate Spectrokinetic Data
NO
Figure 2 shows the IR spectra obtained upon the
interaction of binary mixtures with the surface of ZrO2
and the spectrum of a mixture of NO + C H + O .
3
6
2
Spectrum 1 (a mixture of 0.2% NO + 2.5% O /N ) con-
2
2
sists of absorption bands due to nitrate and nitrite com-
plexes. Bands corresponding to nitrosyl complexes
were not observed under these conditions. The assign-
ment of absorption bands was performed based on
well-known published data [39–44] (Table 2).
0
100
200
300
400
500
600
T, °C
Fig. 1. TPD spectrum of NO after the adsorption of NO on
x
the surface of ZrO (500).
Spectrum 2 (a mixture of 0.2% C H + 2.5% O /N )
2
3
6
2
2
includes low-intensity absorption bands due to carbon-
ate–carboxylate structures. Table 3 summarizes the
assignment of absorption bands [39]. Note that the
plexes. Matyshak et al. [38] found that the intensity of
absorption bands due to nitrate complexes decreased intensity of these absorption bands passed through a
upon desorption over the range 400–500°C, whereas maximum as the temperature was increased.
the intensity of absorption bands due to bridging nitrite
Spectrum 3 for a mixture of 0.2% NO + 0.2%
–
1
complexes (1505 and 1291 cm ) decreased over the
range 200–300°C. A comparison between spectro-
scopic and TPD data showed that the decrease in the
intensity of absorption bands due to nitrate complexes
in the course of desorption corresponds to the high-
C H /N is similar to spectrum 2 in the occurrence of
3
6
2
absorption bands due to nitrate and nitrite complexes.
The difference consists in the presence of absorption
–1
bands at 1360–1380 and 1560–1570 cm in spectrum 3.
In accordance with published data [25–28, 45, 46],
temperature peak of NO release (T = 430–480°C) in these bands can be attributed to symmetric and anti-
x
max
A, arb. units
0
0
0
0
0
0
0
0
0
0
.19
.18
.16
.14
.12
.10
.08
.06
.04
.02
0
1
587
4
1
610
1
568
1
383
363
1
1
1226
1
550
1
008
12911243
322
1
505
1
1031
1
436
9
65
1
174
1058
930
5
2
–
–
0.02
0.04
3
1
800
1700
1600
1500
1400
1300
1200
1100
1000
900
ν, cm–1
Fig. 2. IR spectra obtained upon the interaction of (1) 0.2 vol % NO + 2.5 vol % O /N (T = 250°C), (2) 0.2 vol % C H + 2.5 vol %
2
2
3 6
O /N (T = 250°C), (3) 0.2 vol % NO + 0.2 vol % C H /N (T = 300°C), and (4) 0.2 vol % NO + 0.2 vol % C H + 2.5 vol % O /N
2
2
3
6
2
3
6
2
2
(T = 300°C) mixtures or (5) nitromethane (T = 300°C) with the surface of ZrO2.
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

5
96
MATYSHAK et al.
Table 1. Characteristics of sample ZrO (500)
symmetric vibrations of the nitro group in a nitroor-
2
ganic surface complex. This assignment was also sup-
ported by the fact that these absorption bands were not
observed in the absence of NO or C H from a gas
2
S , m /g
CSR, Å
195
I (111)/I (111), arb. units
t m
sp
3
6
1
16
1.4
phase, as well as by special experiments on the adsorp-
tion of various nitroorganic compounds under analo-
gous conditions (Fig. 3). For comparison, Figure 2
Table 2. Assignment of absorption bands in spectra after the
interaction of a 0.2 vol % NO + 2.5 vol % O /N gas mixture
with the surface of ZrO at 150°C
(spectrum 5) shows the spectrum of nitromethane
2
2
adsorbed under identical conditions. Konin [47]
reported additional TPD and IR- and EPR-spectro-
scopic data on the formation of nitroorganic complexes
in this system. The presence of absorption bands due to
acetate complexes in the spectra is also possible.
Table 4 summarizes the assignment of absorption
bands [25–28, 45, 46].
2
Absorption bands, cm–1
Complex
Bridging nitrate
1610
1
1
226
031
Spectrum 4 was obtained upon the interaction of a
Bidentate nitrate
1587
ternary reaction mixture of 0.2% NO + 0.2% C H +
3
6
2
.5% O /N with the surface of ZrO . This spectrum
1
1
243
058
2 2 2
consists of several closely spaced absorption bands due
to nitrite, nitrate, acetate, and nitroorganic complexes.
In order to find the temperature dependence of the
intensity of an absorption band due to a particular com-
plex, the total spectrum was decomposed into constitu-
ents with the use of standard programs assuming
Lorentzian or Gaussian shapes of absorption bands.
Figure 4 shows how absorption band intensities (1–9)
and the activity of ZrO in the SCR of NO with propy-
lene (10, 11) vary as the sample temperature in the flow-
ing reaction mixture is increased. An analysis of these
data provides support for the assignment of absorption
bands observed under reaction conditions to vibrations
Monodentate nitrate
1580
1
1
226
008
Monodentate nitrite
Bidentate nitrite
1505
291
1531
174
1
2
x
1
Table 3. Assignment of absorption bands in spectra after the in a nitroorganic complex, two nitrates (bridging and
interaction of a 0.2 vol % C H + 2.5 vol % O /N gas mix- bidentate), nitrite, and acetate complexes. As the tem-
3
6
2
2
ture with the surface of ZrO at 250–350°C
perature was decreased, the surface concentration of
these complexes either increased or passed through a
maximum. Moreover, an increase in catalytic activity
with temperature is accompanied by a decrease in the
intensity of absorption bands due to surface com-
pounds. Note that absorption bands due to a nitrite
complex (curves 8, 9) disappeared from the spectra at a
lower temperature than the absorption bands of other
surface compounds.
2
Absorption
bands, cm
Absorption
Complex
–1
Complex
Acetate
–1
bands, cm
Monodentate
carbonate
1560
1550
1445
1
1
250
133
In order to study the effect of the composition of a
reaction mixture, spectroscopic measurements were
performed at 250, 300, and 350°C. Data obtained at
Table 4. Assignment of absorption bands in spectra after the
interaction of a 0.2 vol % NO + 0.2 vol % C H /N gas mix-
3
6
2
2
50°C are considered below. An increase in the O con-
2
ture with the surface of ZrO at 250°C
2
tent of the reaction mixture resulted in a monotonic
increase in the concentrations (intensities of corre-
sponding absorption bands in the spectra) of all of the
Complex
Bridging nitrate
Absorption bands, cm–1
above complexes with a plateau at 2–2.5% O . An
1610, 1226, 1031
1587, 1243, 1058
1568, 1228, 1008
1560, 1383, 1363
1505, 1291
2
increase in the concentration of NO in the reaction mix-
ture to 0.4% was characterized by an increase in the
concentrations of all of the complexes.
Bidentate nitrate
Monodentate nitrate
Nitroorganic complex
Monodentate nitrite
Acetate
The most interesting results were obtained with
increasing propylene concentration (0–0.4%) in the
reaction mixture (Fig. 5). The addition of a small
amount of propylene to the flow of a mixture of 0.2%
NO + 2.5% O /N resulted in a considerable increase in
1550, 1445
2
2
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

REACTION PATHS OF THE FORMATION AND CONSUMPTION
A, arb. units
597
2
0
0
0
0
0
.018
.016
.014
.012
.010
1
380
1
346
1
465
1143
1057
025
1
675
3
1
4
0
0
0
0
.08
9
66
9
31
.06 2200
1455
.04
2080
1
363
.02
0
1
282
1
571
1315
1
1
549
1
438
2
200 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900
2
3
0
0
0
0
.016
.012
.008
.004
0
3
650
1
–
–
–
–
0.004
0.008
0.012
0.016
3
334
2
963
2
4
936
2
734
2
860
4
000
3800
3600
3400
3200
ν, cm–1
3000
2800
2600 2500
Fig. 3. IR spectra measured in the course of the interaction of (1) nitromethane, (2) nitroethane, and (3) nitropropane at 300°C or
4) nitromethane at 250°C with the surface of ZrO2.
(
the intensities of absorption bands due to bridging and observed. The observed changes can be explained
bidentate nitrates (curves 1 and 2) and a decrease in the based on the assumption that monodentate nitrates
intensities of absorption bands due to monodentate most efficiently react with propylene to form nitroor-
nitrates up to the disappearance of these bands (curve 3). ganic complexes. This assumption was also supported
As the concentration of propylene in the mixture was by the fact that the absorption bands of monodentate
increased, the concentration of bridging nitrates complexes were not observed under reaction conditions
decreased, whereas the concentration of bidentate (Fig. 3). In this case, a portion of oxygen sites on the
nitrates remained unchanged. Simultaneously, an surface became free. An additional amount of bridging
increase in the surface concentrations of nitroorganic and bidentate nitrates was formed at these sites. It is
(curve 4) and acetate (curve 5) complexes was likely that surface nitrite complexes were a source for
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

5
98
A, arb. units
MATYSHAK et al.
A, arb. units
0.6
Conversion, %
100
0
.20
.16
.12
.08
.04
*
2
0
0
0
0
80
60
40
20
0
0.5
1
1
0
0
0
0
0
.4
.3
.2
.1
2
5
3
1
*
11
0
1
*
00 150 200 250 300 350 400 450 500
3
4
0
0
0
0
0
.25
.20
.15
.10
.05
0
0.2
0.4
0.6
0.8
1.0
4
[C3H6], vol %
Fig. 5. Changes in the intensities of absorption bands as
functions of propylene concentration in the reaction mix-
ture: (1) bridging nitrate (1610 cm ), (2) bidentate nitrate
1587 cm ), (3) monodentate nitrate (1568 cm ),
4) nitroorganic complex (1383 cm ), and (5) acetate com-
plex (1550 cm ); T = 250°C.
5
–1
–
1
–1
(
(
–
1
–
1
0
1
00
150
200
250
300
350
400
0
0
0
0
0
0
.12
.10
.08
.06
.04
.02
drawn based on analogous experiments at 300 and
3
50°C.
6
In order to refine the structure of the nitroorganic
complex, we performed the adsorption of various nitro-
9
8
organic compounds on ZrO (T = 250 and 300°C;
2
7
nitromethane, nitroethane, and nitropropane concentra-
tions in a flow of nitrogen were 3%). Figure 3 shows the
results of such experiments. The spectra obtained upon
the interaction of a sample with a flow of nitropropane
and nitroethane were similar, and they were character-
0
1
00
150
200
250
300
350
400
T, °C
Fig. 4. Changes in the activity of ZrO and in the intensities
of absorption bands due to nitroorganic ((1) 1560, (2) 1383,
and (3) 1363 cm ), nitrate ((4) 1610 and (5) 1587 cm ),
acetate ((6) 1550 and (7) 1445 cm ), and nitrite ((8) 1505
and (9) 1291 cm ) complexes as a function of reaction tem-
perature: (10) C H conversion and (11) NO conversion
(
2
ized by the presence of intense absorption bands at
–1
1
440 and 1550 cm (spectra 2 and 3). In contrast to
–
1
–1
–1
this, absorption bands at 1560–1570 cm and a doublet
–
1
–1
at 1380 and 1363 cm were the main components of
–
1
the spectra of adsorbed nitromethane (spectra 1 and 4).
3
6
x
An analogous spectrum obtained upon nitromethane
a mixture of 0.2 vol % NO + 0.2 vol % C H + 2.5 vol %
3 6
adsorption on Pt/SiO [25] is consistent with spectrum
2
O /N ).
2
2
5
, which was observed under reaction conditions, in
Fig. 2. This similarity allowed us to state that the struc-
ture of the nitroorganic complex observed under reac-
tion conditions is close to the structure of adsorbed
nitromethane. A comparison of the position of absorp-
tion bands due to adsorbed nitromethane with the posi-
tion of absorption bands due to nitromethane molecules
in a gas phase demonstrates that the symmetric vibra-
the formation of nitrates. A decrease in the concentra-
tion of bridging nitrates as the concentration of propy-
lene in the mixture was increased can also be explained
by their interaction with propylene to form nitroorganic
complexes.
The experimental data suggest that nitrates are tions of the NO group underwent the greatest low-fre-
2
among the surface reagents yielding nitroorganic com-
plexes; the rates of their reactions with propylene
decreased in the following order: monodentate, bridg-
ing, and bidentate. We failed to identify the surface pro-
pylene species that participate in the formation of nitro-
organic compounds based on the experimental data.
–1
quency shift (~40 cm ). By this is meant that NO
bonds of the nitro group participated in the formation of
a bond between the complex and the surface.
The interaction of nitromethane with the surface of
ZrO resulted not only in its adsorption but also in its
2
The only propylene species on the surface is an acetate conversion, as evidenced by the appearance of an
–
1
complex. If it participates in the formation of nitroor- absorption band at 1675 cm (Fig. 3, spectrum 4) in the
ganic complexes, their structure should be close to the spectra; this band was due to vibrations in a nitritoor-
structure of nitromethane. Analogous conclusions were ganic complex [19–28]. Moreover, the spectra exhib-
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

REACTION PATHS OF THE FORMATION AND CONSUMPTION
599
ited absorption bands due to CH groups (2936 and
A, arb. units
2
–
1
–1
2
860 cm ), NO (2080 and 2200 cm ), and NH (931
ads 3
0.030
–
1
and 966 cm ); this is indicative of deeper degradation
of the nitromethane molecule.
2
0
0
0
0
.025
.020
.015
.010
Note that nitritoorganic complexes are thermally
less stable than nitroorganic surface compounds
1
(
Fig. 3, spectra 1 and 4). By this is meant that the par-
3
4
ticipation of nitritoorganic complexes in reaction would
be expected at lower temperatures, as compared with
nitroorganic surface compounds.
0.005
0
The experimental data suggest that the surface com-
plex of nitromethane is formed by the interaction of
surface acetate and nitrate complexes via the replace-
ment of the COO group of acetate by the NOO group of
the nitrate complex.
5
10
15
20
25
30
Time, min
Fig. 6. Changes in the intensities of absorption bands in the
spectra obtained with increasing time of purging the reactor
cell with a flow of nitrogen: (1) bridging nitrate (1610 cm ),
–
1
The above data exhibit an additional interesting
property of the test system. Upon the combined adsorp-
tion of C H , NO, and O or upon the addition of a third
–
1
(
2) bidentate nitrate (1587 cm ), (3) monodentate nitrate
–
1
–1
(1568 cm ), and (4) acetate complex (1550 cm ); T =
50°C.
3
6
2
3
component to a flow of two reagents, the amount of sur-
face complexes dramatically increased, as compared
with the individual adsorption of the reagents. In partic-
ular, the concentration of surface nitrates increased
upon the addition of propylene to a flow of NO + O2
A, arb. units
0
0
0
0
0
.045
.040
.035
.030
.025
(
Fig. 4); the concentration of surface acetates increased
2
upon the addition of NO to a flow of C H + O . It is
3
6
2
likely that surface properties were changed upon the
adsorption of a reagent; this facilitated the adsorption
of other reagents.
0.020
0
0
0
.015
.010
.005
3
1
Non-Steady-State Measurements
Figures 6–8 illustrate the results of non-steady-state
measurements. Strongly bound acetate (Fig. 6, curve 4)
and nitrate complexes (Fig. 6, curves 1–3) were formed
0
5
10
15
20
25
30
Time, min
upon the interaction of C H + O /N or NO + O /N
3
6
2
2
2
2
Fig. 7. Changes in the intensities of absorption bands in the
mixtures with the surface of ZrO . At 350°C, these
spectra obtained with increasing time of purging the reactor
2
cell with a flow of a 0.2 vol % NO/N mixture: (1) nitroor-
complexes were not removed from the surface after
blowing the catalyst with an inert gas flow. This result
is consistent with data on the thermal desorption of NO
2
–
1
–1
ganic complex (1383 cm ), (2) bridging nitrate (1610 cm ),
and (3) acetate complex (1445 cm ; T = 350°C.
–
1)
(Fig. 1).
The study of the reactivity of surface acetate com- compounds in reactions with NO or NO , which were
2
plexes demonstrated that earlier formed acetate com- released in the degradation of surface nitrates, with the
plexes were consumed upon the addition of a flow con-
taining NO (Fig. 7, curve 3), whereas the concentration
of nitroorganic compounds and nitrate complexes
formation of reaction products.
passed through a maximum (Fig. 7, curves 1 and 2). Table 5. Rate constants of consumption of nitroorganic
(
k(I)) and nitrate (k(II)) complexes on the surface of ZrO2
Simple evaluations demonstrated that the intensity of
absorption bands due to a nitroorganic compound was
approximately proportional to the product of the
absorption band intensities of nitrate and acetate com-
pounds. Consequently, the nitroorganic compound was
formed by the interaction of nitrate and acetate surface
complexes. The additional decrease in the absorption
band intensity of nitroorganic compounds can be
explained by the subsequent consumption of these
k(I), min–1
k(II), min–1
T, °C
383 cm–1 1568 cm–1 1587 cm–1 1610 cm–1
1
250
0
0
0
0
3
3
00
50
0.021
0.042
0.019
0.045
0
0
0.012
0.010
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

6
00
MATYSHAK et al.
A, arb. units
absorption bands due to a nitroorganic compound was
also approximately proportional to the product of the
concentrations of nitrate and acetate compounds.
0
0
0
0
0
0
.030
.025
.020
.015
.010
.005
(
a)
Figures 8b and 8c show plots that characterize the
consumption of nitroorganic compounds. These com-
pounds were formed on the surface by the interaction of
a mixture of propylene, NO, and oxygen with the cata-
lyst surface. In this case, nitrate and acetate complexes
were formed on the surface in addition to the nitroor-
ganic complex. As the duration of purging the cell with a
flow of nitrogen was increased (Fig. 8), a decrease in the
concentration of the nitroorganic compound (curve 1)
and nitrate complexes (curves 2–4) was observed at a
constant concentration of surface acetate complexes
1
2
3
4
5
0
5
10
15
20
25
30
0
0
0
0
0
.025
(curve 5). Because the nitrate and acetate complexes
(
b)
individually occurring on the surface were not desorbed
in a flow of nitrogen (Fig. 6), this fact unambiguously
indicates that nitroorganic compounds were consumed
in the interaction with nitrate complexes. In this case,
monodentate nitrate was the most reactive species
.020
.015
.010
.005
(curve 4).
Figure 8c shows changes in the intensities of
adsorption bands due to surface compounds with
increasing duration of purging the cell with a flow of a
mixture of oxygen and nitrogen. It can be seen that the
rate of decrease of the concentration of a nitroorganic
compound (curve 1) and nitrate complexes with time
does not depend on the presence of oxygen in a gas
phase (cf. Figs. 8b and 8c). Therefore, the nitroorganic
0
5
10
15
20
25
30
0
0
0
0
0
0
0
.035
.030
.025
.020
.015
.010
.005
(c)
complex on the surface of ZrO almost does not react
2
with oxygen.
Analogous experiments were also performed at 300
and 250°C. The results of these experiments allowed us
to evaluate the rate constants and activation energy of
the interaction of a nitroorganic compound and a mon-
odentate nitrate complex on the surface of ZrO2
(Table 5).
0
5
10
15
20
25
30
Time, min
Data given in Figs. 3 and 4 and Table 5 indicate that,
at 250°C, nitroorganic complexes were formed but
almost not consumed. This fact is consistent with the
Fig. 8. Changes in the intensities of absorption bands in the
spectra obtained with increasing time of purging the reactor
cell with a flow of (a) a 0.2 vol % C H + 2.5 vol % O /N
fact that ZrO did not exhibit detectable activity at
2
3
6
2
2
2
50°C (Fig. 3, curves 10, 11).
mixture, (b) nitrogen, or (c) a 2.5 vol % O /N mixture:
2
2
–
1
(
(
1) nitroorganic complex (1383 cm ), (2) bridging nitrate
The equality of the rate constants of consumption of
–
1
–1
nitroorganic and monodentate nitrate complexes sup-
ports the fact that the interaction between them is the
main surface reaction that leads to the formation of
SCR products. This conclusion is supported by the esti-
mated activation energies of the consumption of nitro-
1610 cm ), (3) bidentate nitrate (1587 cm ), (4) mono-
–
1
dentate nitrate (1568 cm ), and (5) acetate complex
–
1
(
1445 cm ); T = 350°C.
Figure 8a shows the results of an analogous study of organic and monodentate nitrate complexes. The esti-
the reactivity of surface nitrate complexes. It can be mated values were found approximately equal to
seen that, upon the addition of a mixture of propylene 60 kJ/mol and close to the activation energy of the over-
and oxygen, previously formed nitrate complexes were all SCR of NO
consumed (Fig. 8a, curves 2–4), whereas the concentra-
tion of nitroorganic compounds passed through a max-
imum (curve 1). Note that monodentate nitrate exhib-
found previously [47].
CONCLUSIONS
x
ited the highest reactivity (curve 3). The intensities of
Under the reaction conditions examined, nitrate,
absorption bands due to acetate complexes increased acetate, and nitroorganic complexes occurred on the
(curve 5). In this case, as estimated, the intensity of surface of ZrO . Surface reaction between nitrate and
2
KINETICS AND CATALYSIS Vol. 47 No. 4 2006

REACTION PATHS OF THE FORMATION AND CONSUMPTION
601
acetate complexes resulted in the formation of a nitro-
organic compound. A monodentate nitrate complex
was most reactive in this process; this was likely
because its structure was most capable of forming an
NOO group upon activation. Based on the experimental
results obtained in this work, we can state that the
replacement of the carboxyl group in an acetate com-
plex by this group is the main surface reaction of the
formation of a nitroorganic complex. The participation
of an acetate surface complex in the formation of a
nitroorganic compound was also reported by Shimizu
et al. [12].
Nitroorganic compounds are usually identified by
the occurrence of vibrations of the nitro group. The
structural identification of the organic moiety of a nitro-
organic complex is very difficult to perform. For exam-
ple, Chi and Chuang [28] assumed the structure of a
nitroorganic complex to be identical to that of adsorbed
nitropropane without experimental justification.
Haneda et al. [17] interpreted the fact that the sets of
reaction products were identical with the use of propy-
lene and nitropropane as reducing agents in favor of a
structural similarity between the nitroorganic complex
and nitropropane.
3. Iwamoto, M, Proc. 10th Int. Zeolite Conf., Garmisch–
Partenkirchen, 1994, p. 1395.
4. Iwamoto, M., Catal. Today, 1996, vol. 29, nos. 1–4,
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8
9
. Walker, A.P., Catal. Today, 1995, vol. 26, p. 107.
. Burch, R., Catal. Today, 1997, vol. 35, p. 27.
. Ansell, G.P., Diwell, A.F., Goloinski, S.F., Hayes, J.W.,
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1
1
1
1
1
1
0. Tanaka, T., Okuhara, T., and Misono, M., Appl. Catal., B,
1994, vol. 4, p. 1.
1. Satsuma, A., Cowan, A.D., Cant, N.C., and Trimm, D.L.,
J. Catal., 1999, vol. 181, p. 165.
2. Shimizu, K., Shibata, J., Yoshida, H., Satsuma, A., and
Hattori, T., Appl. Catal., B, 2001, vol. 30, p. 151.
3. Chi, Y. and Chuang, S.S.C., J. Catal., 2000, vol. 190,
p. 75.
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Korchak, V.N., J. Catal., 1997, vol. 171, p. 245.
5. Sadykov, V.A., Beloshapkin, S.A., Paukshtis, E.A.,
Alikina, G.M., Kochubei, D.I., Degtyarev, S.A., Bulga-
kov, N.N., Veniaminov, S.A., Bunina, R.V., Kharla-
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In this study, we attempted to determine the struc-
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scopic study of the interaction of various nitroorganic
substances with the surface of ZrO under analogous
2
reaction conditions. The results of this study (Figs. 2, 3)
indicate that the spectrum of the nitroorganic complex
measured under reaction conditions is similar to the
spectrum obtained upon the interaction of a sample
with nitromethane. It is believed that the nitroorganic
complex is a nitromethane molecule bound to the sur-
face through the nitro group.
1
1
6. Sadykov, V.A., Lunin, V.V., Matyshak, V.A., Pauk-
shtis, E.A., Rozovskii, A.Ya., Bulgakov, N.N., and
Ross, Dzh., Kinet. Katal., 2003, vol. 44, no. 3, p. 412.
7. Haneda, M., Joubert, E., Menezo, J.-Ch., Duprez, D.,
Barbier, J., Bion, N., Daturi, M., Saussey, J., Lavalley, J.-C.,
and Hamada, H., J. Mol. Catal. A: Chem., 2001,
vol. 175, p. 179.
Data obtained in this work (Figs. 8b, 8c) suggest
that nitroorganic compounds are further consumed in
reactions with nitrate complexes; a monodentate nitrate
complex is also most reactive in this process.
Note that the rate of decrease of the concentration of
a nitroorganic compound with time does not depend on 20. Yokoyama, C. and Misono, M., Catal. Today, 1994,
1
1
8. Tret’yakov, V.F., Burdeinaya, T.N., Zakorchevnaya,Yu.P.,
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vol. 54, p. 4379.
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no. 1, p. 71.
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2
x
2
structure of the nitroorganic complex explains the fact
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2
6. Sumiya, S., He, H., Abe, A., et al., J. Chem. Soc., Fara-
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