Chemical oscillations in catalytic CO oxidation reaction
Temporal dynamics of a heterogeneous catalytic system, namely of the catalytic CO oxidation on Pt(110) surface at low pressures, is investigated with taking into account the adsorbate-driven structural transformations of the catalyst surface. Uniform temporal periodic chemical oscillations of the CO...
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| Опубліковано в: : | Condensed Matter Physics |
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| Дата: | 2010 |
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Інститут фізики конденсованих систем НАН України
2010
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| Цитувати: | Chemical oscillations in catalytic CO oxidation reaction / I.S. Bzovska, I.M. Mryglod // Condensed Matter Physics. — 2010. — Т. 13, № 3. — С. 34801:1-5. — Бібліогр.: 16 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859978938526203904 |
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| author | Bzovska, I.S. Mryglod, I.M. |
| author_facet | Bzovska, I.S. Mryglod, I.M. |
| citation_txt | Chemical oscillations in catalytic CO oxidation reaction / I.S. Bzovska, I.M. Mryglod // Condensed Matter Physics. — 2010. — Т. 13, № 3. — С. 34801:1-5. — Бібліогр.: 16 назв. — англ. |
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| description | Temporal dynamics of a heterogeneous catalytic system, namely of the catalytic CO oxidation on Pt(110) surface at low pressures, is investigated with taking into account the adsorbate-driven structural transformations of the catalyst surface. Uniform temporal periodic chemical oscillations of the CO and oxygen coverages, and the fraction of the surface of the 1 x 1 structure are obtained in a narrow region of phase diagram between two uniform stable states of high and low catalytic activities, respectively.
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Condensed Matter Physics 2010, Vol. 13, No 3, 34801: 1–5
http://www.icmp.lviv.ua/journal
Rapid Communication
Chemical oscillations in catalytic CO oxidation reaction
I.S. Bzovska, I.M. Mryglod
Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine,
1 Svientsitskii Str., 79011 Lviv, Ukraine
Received July 23, 2010
Temporal dynamics of a heterogeneous catalytic system, namely of the catalytic CO oxidation on Pt(110) sur-
face at low pressures, is investigated with taking into account the adsorbate-driven structural transformations
of the catalyst surface. Uniform temporal periodic chemical oscillations of the CO and oxygen coverages, and
the fraction of the surface of the 1 × 1 structure are obtained in a narrow region of phase diagram between
two uniform stable states of high and low catalytic activities, respectively.
Key words: chemical oscillations, bifurcation, catalytic oxidation, carbon monoxide, oxygen
PACS: 82.65.+r, 82.40.Bj
Since Langmuir’s pioneering studies, the oxidation of CO over Pt is a classical example of
a heterogeneous catalytic reaction. It is considered to be generic due to its apparently simple
mechanism, richness of spatio-temporal behavior, and practical relevance [1]. In particular, the
temporal behavior of the reaction, for given constant control parameters, may either be constant
(including bistability) or may become oscillatory or even chaotic [2, 3]. First kinetic oscillations
in this reaction were found by Hugo in 1970 on a supported catalyst. Later on, this phenomenon
was also observed for other types of catalysts (polycrystalline wires and single crystals) both at
ultrahigh vacuum (UHV) and subatmospheric conditions.
Based on the knowledge about individual steps forming the reaction mechanism, temporal dy-
namics (with the exception of chaotic kinetics) could be successfully modelled by the solution of
sets of ordinary differential equations (ODE’s) for the variables describing the surface concentra-
tions of the species involved [4–6]. For a close-packed Pt(111) surface, these are the coverages
for adsorbed CO and O, respectively [7]. We will study the more open Pt(110) plane where the
oscillatory behavior in the catalytic CO oxidation can be experimentally observed [8, 9].
So, the oxidation of CO on platinum is known to proceed via the classical Langmuir-Hinshelwood
(LH) mechanism (see [10–12]),
O2 + 2∗ → 2Oads ,
CO + ∗
COads ,
COads + Oads → CO2 + 2 ∗ .
(1)
Here * denotes an empty site, adsorbed species are written with the subscript ads. CO2 desorbs
immediately at the temperatures under consideration and therefore constitutes an inert product.
The other gases exhibit only small variations of their partial pressure under the applied conditions
so that they can be assumed constant.
Mathematical modelling of the experiments is conducted using a realistic model of catalytic CO
oxidation on Pt(110) first studied by Krischer et al. [13]. The model takes into account adsorption
of CO and oxygen molecules, reaction and desorption of CO molecules. For simplicity, surface
diffusion of adsorbed CO molecules, surface roughening, faceting, formation of subsurface oxygen,
and the effects of internal gas-phase coupling are not taken into account. The system of differential
c© I.S. Bzovska, I.M. Mryglod 34801-1
http://www.icmp.lviv.ua/journal
I.S. Bzovska, I.M. Mryglod
equations describing the dynamics behavior of the model is
du
dt
= F1(u, v) = pCOkCOsCO(1 − uq) − kdu − kruv, (2)
dv
dt
= F2(u, v) = pO2
kOsO(1 − u − v)2 − kruv. (3)
The variables u and v represent the surface coverage of CO and oxygen, respectively. The variables
can vary in the interval from 0 to 1. The difference between model (2)–(3) and the model considered
in our earlier paper [7] is that the precursor-type kinetics of CO adsorption is accounted for by
the exponent q = 3 in the right hand part of equation (2). It makes the model more realistic
since the inhibition of adsorption of CO and O2 is asymmetric and preadsorbed CO blocks oxygen
adsorption but not vice versa. The parameters, corresponding to Pt(110) surface, were chosen such
that the reaction was oscillatory. For explanation and values of the parameters see table 1 taken
from [14].
Table 1. Parameters of the model.
T 540 K Temperature
pCO 4.81× 10−5 mbar CO partial pressure
pO2
13 × 10−5 mbar O2 partial pressure
kCO 3.14× 105 s−1mbar−1 Impingement rate of CO
kO 5.86× 105 s−1mbar−1 Impingement rate of O2
kd 10.21 s−1 CO desorption rate
kr 283.8 s−1 Reaction rate
sCO 1 CO sticking coefficient
sO,1×1 0.6 Oxygen sticking coefficient on the 1 × 1 phase
sO,1×2 0.4 Oxygen sticking coefficient on the 1 × 2 phase
u0, δu 0.35, 0.05 Parameters for the structural phase transition
k5 1.61 s−1 Phase transition rate
Analysis of the system (2)–(3) reveals that there is a bistability in one, and a cusp in two
control parameters. It is known that in a system, the relaxation oscillations can emerge in bistable
state if the system depends on a parameter slowly varying in time. It would be a model parameter
connected with the variations of average coverages and the structural changes of the surface as a
function of time, since at the experimental conditions, depending on the CO coverage, the recon-
structed 1 × 2 Pt(110) surface may revert to the 1 × 1 structure. In this case the kinetic equation
for the surface transformation should be taken into consideration. The structural phase transition
1 × 2− 1× 1 of the Pt(110) surface is considered through a simple relaxation law [14]:
dw
dt
= F3(u, w) = k5 (p[u] − w) . (4)
The variable w denotes the local fraction of the surface area found in the nonreconstructed 1 × 1
structure.
p[u] =
1
1 + exp
(
u0 − u
δu
) (5)
is a nondecreasing and smooth function of the interval [0,1] that appears in the equation for dw/dt.
It is shown in figure 1.
The oxygen sticking coefficient sO in equation (3) was modified and taken as a linear combina-
tion of the values for the 1 × 2 − 1 × 1 structure:
sO = s1×1w + s1×2(1 − w). (6)
34801-2
Chemical oscillations in catalytic CO oxidation reaction
0,60,40,20
p
1
u
0,8
0,6
1
0,4
0,8
0
0,2
Figure 1. Function p[u] that appears in the equation for dw/dt.
The steady states of the system are defined as the time independent solutions of the kinetic
equations (2)–(4):
Fi(uss, vss, wss) = 0, i = 1, 2, 3. (7)
Linear stability analysis requires the solution of the secular equation for any given steady state:
det
∣
∣
∣
∣
∣
∣
∣
∣
λ −
(
∂(F1, F2, F3)
∂(u, v, w)
)
ss
∣
∣
∣
∣
∣
∣
∣
∣
= 0. (8)
We solve the secular equation (8) and obtain two types of stationary points, namely these are stable
nodal points, when all the roots are real and negative, and stable nodal-spirals, when one root is
real negative, and the other two are complex with negative real part. As the control parameters
are varied, we have transitions from one stability regime to another. We compute several regimes
in the phase space of partial pressures. A phase diagram in (pCO, pO2
) parameters is reproduced
in figure 2. As we see, the stable regime corresponds to the region where the partial CO pressure is
Figure 2. Phase diagram of the model of surface oscillations in the (pCO, pO2
) parameter plane.
34801-3
I.S. Bzovska, I.M. Mryglod
small compared with the O2 partial pressure. Beyond that phase space region, unstable oscillatory
regime appears. Furthermore, we obtain the surface poisoning by CO in qualitative agreement with
experimental data found previously on Pt(100) surface in the field electron microscope (FEM)
experiments [15]. In the experimental kinetic phase diagram, the region in which the Oads layer is
found at a high pO2
to pCO ratio, is separated by a region of the occurrence of kinetic oscillations
from the region of the COads layer at a lower partial pressure ratio.
The ODE system (2)–(4) exhibits uniform periodic chemical oscillations of the CO and oxygen
coverages, as well as the oscillations of the fraction of the surface of the nonreconstructed 1 × 1
structure in a narrow region of the phase diagram between two uniform stable states of high and
low catalytic activities. Examples of time series are shown in figure 3. As is seen from the figure,
u and v oscillate in strictly opposite phases, variable w reaches its maximum after u. We see that
the difference between the two cases (a) and (b) is that the oscillations have a larger period in
the latter case of higher partial pressure pCO. The similar tendency is observed in the experiment,
where the period of oscillations increases (except in the region near the right bifurcation point)
with pCO pressure increasing [16]. A decrease in T is associated with an increase of the oscillation
period as is observed in figure 3(c) at lower temperature T = 535 K.
(a) t
302515
u, v, w
10
0,6
5
0,2
20
0,8
0,4
0
0
(b) t
3025
u, v, w
0,8
1
10
0,4
0,2
20
0,6
155
0
0
(c) t
3025
u, v, w
0,8
1
10
0,4
0,2
20
0,6
155
0
0
Figure 3. Examples of oscillations obtained by integration of equations (2)–(4) for the parameter
pO2
= 13 · 10−5 mbar. Panels (a) and (b) correspond to the values pCO = 4.81 · 10−5 mbar
and pCO = 4.86 · 10−5 mbar, respectively, at T=540 K. Panel (c) corresponds to the value
pCO = 4.81 · 10−5 mbar at T=535 K. The symbols are as follows: full line for u(t), long dashes
for v(t) and dotted line for w(t).
In summary, we have investigated a kinetic model for the catalytic CO oxidation on a surface of
Pt(110) at low pressures. From the analysis of stability of stationary points of the model, a phase
diagram in the (pCO, pO2
) parameter plane has been constructed. We have found two types of
stationary points which present two different stability regimes, namely the stable and the unstable
oscillatory ones. Oscillatory regime arises due to the interplay between bistability and adsorbate-
induced surface reconstruction 1×2−1×1 exposing patches with different O2 sticking probabilities.
The proposed model is obviously capable of qualitatively describing the experimentally observed
features connected with kinetic oscillations in the catalytic CO oxidation on a Pt(110) surface at low
pressures. However, it disregards many interesting phenomena of spatiotemporal behavior of the
34801-4
Chemical oscillations in catalytic CO oxidation reaction
system such as mixed-mode oscillations, a period-doubling transition to chaos, and the formation
of stationary as well as propagating spatial patterns. A successful description of the experimentally
obtained behavior will most likely require to take spatial effects, namely diffusion of the reactants
and faceting of the surface, into account.
References
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2. Bär M., Zülicke Ch., Eiswirth M., and Ertl G., J. Chem. Phys., 1992, 96, 8595.
3. Eiswirth M., Krischer K., and Ertl G., Surf. Sci., 1988, 202, 565.
4. Chavez F., Vicente L., and Perera A., J. Phys. Chem., 2000, 113, 10353.
5. Pavlenko N., Kostrobij P.P., Suchorski Yu., Imbihl R., Surf. Sci., 2001, 489, 29.
6. Kostrobii P.P., Tokarchuk M.V., Alekseyev V.I., Phys. and Chem. of Solid State, 2006, 7, No. 1, 25.
7. Mryglod I.M., Bzovska I.S., Ukr. J. Phys., 2008, 53, No. 6, 529.
8. Meiben F., Patchett A.J., Imbihl R., Bradshaw A.M., Chem. Phys. Lett., 2001, 336, 181.
9. Chung J.-Ya., Aksoy F., Grass M.E., Kondoh H., Ross Ph. Jr., Liu Z., Mund B.S., Surf. Sci., 2009,
603, L35.
10. Grandi B.C.S. and Figueiredo W., Phys. Rev. E, 2002, 65, 036135.
11. Nekhamkina O., Digilov R., Sheintuch M., J. Chem. Phys., 2003, 119, 2322.
12. Cisternas Y., Holmes Ph., Kevrekidis I.G., Li X., J. Chem. Phys., 2003, 118, 3312.
13. Krischer K., Eiswirth M., and Ertl G., J. Chem. Phys., 1992, 96, 9161.
14. Bertram M., Mikhailov A.S., Phys. Rev. E, 2003, 67, 036207.
15. Gorodetskii V.V., Drachsel W., Applied Catalysis A: General, 1999, 188, 267.
16. Kurkina E.S., Peskov N.V., Slin’ko M.M., Physica D, 1998, 118, 103.
Хiмiчнi коливання в реакцiї каталiтичного окислення СО
I.С. Бзовська, I.М. Мриглод
Iнститут фiзики конденсованих систем НАН України, вул. Свєнцiцького, 1, 79011 Львiв, Україна
Дослiджується часова динамiка гетерогенної каталiтичної системи на прикладi реакцiї каталiтично-
го окислення СО на поверхнi Pt(110) при низьких тисках iз врахуванням перетворення поверхнi ка-
талiзатора пiд впливом процесiв адсорбцiї-десорбцiї. Отримано однорiднi часовi перiодичнi хiмiчнi
коливання покриттiв СО, кисню та частки поверхнi структури 1×1 у вузькiй областi фазової дiаграми
мiж двома однорiдними стiйкими станами високої i низької каталiтичної активностi, вiдповiдно.
Ключовi слова: хiмiчнi коливання, бiфуркацiя, каталiтичне окислення, монооксид вуглецю, кисень
34801-5
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| id | nasplib_isofts_kiev_ua-123456789-32111 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1607-324X |
| language | English |
| last_indexed | 2025-12-07T16:24:43Z |
| publishDate | 2010 |
| publisher | Інститут фізики конденсованих систем НАН України |
| record_format | dspace |
| spelling | Bzovska, I.S. Mryglod, I.M. 2012-04-08T19:28:30Z 2012-04-08T19:28:30Z 2010 Chemical oscillations in catalytic CO oxidation reaction / I.S. Bzovska, I.M. Mryglod // Condensed Matter Physics. — 2010. — Т. 13, № 3. — С. 34801:1-5. — Бібліогр.: 16 назв. — англ. 1607-324X PACS: 82.65.+r, 82.40.Bj https://nasplib.isofts.kiev.ua/handle/123456789/32111 Temporal dynamics of a heterogeneous catalytic system, namely of the catalytic CO oxidation on Pt(110) surface at low pressures, is investigated with taking into account the adsorbate-driven structural transformations of the catalyst surface. Uniform temporal periodic chemical oscillations of the CO and oxygen coverages, and the fraction of the surface of the 1 x 1 structure are obtained in a narrow region of phase diagram between two uniform stable states of high and low catalytic activities, respectively. en Інститут фізики конденсованих систем НАН України Condensed Matter Physics Rapid Communication Chemical oscillations in catalytic CO oxidation reaction Хімічні коливання в реакції каталітичного окислення CO Article published earlier |
| spellingShingle | Chemical oscillations in catalytic CO oxidation reaction Bzovska, I.S. Mryglod, I.M. Rapid Communication |
| title | Chemical oscillations in catalytic CO oxidation reaction |
| title_alt | Хімічні коливання в реакції каталітичного окислення CO |
| title_full | Chemical oscillations in catalytic CO oxidation reaction |
| title_fullStr | Chemical oscillations in catalytic CO oxidation reaction |
| title_full_unstemmed | Chemical oscillations in catalytic CO oxidation reaction |
| title_short | Chemical oscillations in catalytic CO oxidation reaction |
| title_sort | chemical oscillations in catalytic co oxidation reaction |
| topic | Rapid Communication |
| topic_facet | Rapid Communication |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/32111 |
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