Kinetic oscillations

P. Moller, K. Wetzl, M. Eiswirth, G. Ertl. Kinetic oscillations in the catalytic CO oxidation Computer simulations. J Chem Phys 55 5328-5334, 1986. 

V. N. Kusovkov, O. Kortluke, W. von Niessen. Kinetic oscillations in the catalytic CO oxidation on Pt single crystal surfaces Theory and simulation. J Chem Phys 705 5571-5580, 1998. 

Ertl G, Norton PR, Riistig J. 1982. Kinetic oscillations in the platinum-catalyzed oxidation of CO. Phys Rev Lett 49 177. 

ImhM R, Cox MP, Ertl G, Muller H, Brenig W. 1984. Kinetic oscillations in the catal34ic CO oxidation on Pt(lOO) Theory. J Chem Phys 83 1578. 

Kurtanjek, A., Sheintuch, M., and Luss, D. Surface state and kinetic oscillations in the oxidation of hydrogen on nickel. 

We demonstrate the use of Matlab s numerical integration routines (ODE-solvers) and apply them to a representative collection of interesting mechanisms of increasing complexity, such as an autocatalytic reaction, predator-prey kinetics, oscillating reactions and chaotic systems. This section demonstrates the educational usefulness of data modelling. 

Ortho-para deuterium, 27 25, 50 Ortho-para hydrogen conversion, 27 23 Oscillatory catalytic reactions, 37 213-215, 271-272 see also Platinum catalytic CO oxidation on Pt(l 11) and Pt(llO) surfaces COj formation, 37 216-217 kinetic oscillation mechanism, 37 220-228... 

PbOj anode, 40 155-156 oxygen evolution, 40 109-110 PCE, catalytic synthesis of, l,l,l-trifluoro-2,2-dischloroethane, 39 341-343 7t complex multicenter processes of norboma-diene, 18 373-395 PdfllO), CO oxidation, 37 262-266 CO titration curves, 37 264—266 kinetic model, 37 266 kinetic oscillations, 37 262-263 subsurface oxygen phase, 37 264—265 work function and reaction rate, 37 263-264 Pd (CO) formation, 39 155 PdjCrjCp fCOljPMe, 38 350-351 (J-PdH phase, Pd transformation, 37 79-80 P-dimensional subspace, 32 280-281 Pdf 111) mica film, epitaxially oriented, 37 55-56... 

Hj Dj exchange on, 26 39-43 heteropolyanion-supported, 41 230-231 high MiUer index, 26 12-15,35,36 -H-USY zeoUte, 39 186-187 hydrocarbons adsorption, 38 229-230 reactions of cyclopropane, cyclohexane, and n-heptane, 26 51-53 structural effects, 30 25-26 hydrogen adsorption on, 23 15 hydrogenation, 30 281-282 olefins, in ethanol, 30 352-353 in hydrogenation reaction, 33 101 -iron alloys, 26 75 isomerization, 30 2-3 isotope, NMR properties, 33 213,274 kinetic oscillations, 37 220-228 ball models of densely packed surfaces, 37 221-222... 

Scanning LEED, oscillatory reactions, 39 69 Scanning photoemission microscopy, kinetic oscillations, Pt(lOO), 37 250-253 Scanning photoemission spectroscopy oscillatory reactions, 39 69... 

Exotic Kinetics Oscillating Reactions in the Troposphere (J. Phys. Chem. A 2001, 105, 11212-11219. "Steady State Instability and Oscillation in Simplified Models of Tropospheric Chemistry")... 

At the present time, the fruitful cooperation of a biophysicist and a mathematician (Zhabotinskii and Korzukhin) has led to the decoding of kinetic oscillations. Certainly, a happy combination of various fruits in one personality is also possible, an example of such a person being Van t Hoff. ("This double inclination to mathematics on the one hand and to chemistry on the other manifested itself in all my scientific interests .) Franck-Kamenetskii, Horiuti, Semenov and Temkin are also examples of such a combination. ... 

Mechanistic studies with real catalysts near atmospheric pressure conditions are complicated by several factors the surface structure and composition will be inhomogeneous and hence also the reactivity may be spatially different. In addition, the heat released by the reaction may change the (local) temperature, and as a consequence, kinetic oscillations are frequently associated with strong nonisothermal effects. These prob-... 

More generally, the surface can (for certain sets of parameters) be in two states, with either predominant CO or O coverage. Upon variation of one of the partial pressures, for example, a more or less abrupt transition between these states occurs, whereby the system may also show pronounced hysteresis effects—it exhibits bistability. Figure 2 reproduces corresponding experimental data for Pt(110), where the stationary work function change A4> (oxygen coverage) is plotted as a function of pco at fixed p0, and for various temperatures (24). Kinetic oscillations are ob-... 

The qualitative features of the r( pco) curve of Fig. 1 are the same for all types of platinum metal surfaces and will serve as a guide for exploring the mechanisms of kinetic oscillations occurring with this reaction. The shape of this curve can be modeled quite easily on the basis of the underlying reaction mechanism (8, 25). These equations are nonlinear in nature and can, for example, describe hysteresis effects observed in the transition region between high and low reactivity, but they will not produce sustained temporal oscillations. The latter require additional processes for which numerous suggestions and speculations can be found in the literature (S). 

Figure 4 shows a typical example of sustained kinetic oscillations occurring for particular conditions (pc0, p0r and T) during the catalytic CO oxidation on a Pt(llO) surface (40). The measurements were performed with an UHV system acting as flow reactor, where the C02 partial pressure is directly proportional to the rate. The simultaneously recorded CO pressure oscillates with the same period and with amplitudes of about 1%, whereby pco shows a minimum whenever the reaction rate is maximum. The work function A varies parallel to the rate R. This quantity is essentially determined by the oxygen coverage. Because under oscillatory conditions the rate is determined by oxygen adsorption (see above), it becomes plausible why A and R vary in phase. 

Once the external parameters (pco, p0,- and T) have been established to initiate autonomous kinetic oscillations, these can usually be sustained for periods of time as long as desired, provided that the surfaces are prevented from becoming contaminated (in particular by carbon, originating from spurious traces of hydrocarbons in the feed gas mixture) and that the partial pressures are not drifting off (31). With Pt(l 10) a complication may arise insofar that during the course of the reaction the surface struc-... 

Fig. 13. Kinetic oscillations during the CO/O reaction on Pt(110) at I = 540 K, />0, = 7.5 x 10-5 torr, and for varying pm. (From Ref. 71.) (a) pco = 3.90 x 10 lorr constant behavior (fixed point), (b) pt0 = 3.K4 x I0"5 torr onset of harmonic oscillations with small amplitudes (Hopf bifurcation), (c)pco = 3.66 x 10 5 torr harmonic oscillation with increased amplitude, (d) pc0 = 3.61 x I0-5 torr first period doubling, (e) pc0 = 3.52 x 10 torr second period doubling, (f) pco = 3.42 x 10 5 torr aperiodic (chaotic) behavior.

The formation of facets may take place under conditions for which kinetic oscillations also occur, and of course the latter will be affected,... 

Fig. 26. LEED intensity distributions over a 4 x 7-mm2 Pt(IOO) sample from spots characterizing the CO c2 x 2 structure (left) and the hex structure (right) during kinetic oscillations, illustrating the propagation of waves of structural transformations across the surface. (From Ref. JO.)...

Fig. 27. Spatial pattern formation within a 1.5 x 1-mm2 area of a Pt( 100) surface during kinetic oscillations as recorded by scanning photoemission microscopy. (From Ref. 138.)... 

The mechanism of the kinetic oscillations occurring with the CO + 07 reaction on clean Pt( 100) and Pt( 110) surfaces was based on the reversible transformation of the surface structure by the presence of adsorbed CO and by an associated variation of the oxygen sticking coefficient that increased upon CO-induced lifting of the reconstruction of the clean surface. The most densely packed Pt(lll) surface is not reconstructed and its structure is also not affected by CO adsorption. Accordingly, kinetic oscillations with a clean Pt(lll) surface (i.e., for partial pressure <10 3 torr) could never be observed (13, 26, 27, 38). Again no reconstruction... 

Fig. 34. Development of kinetic oscillations with the CO/O, reaction on Pt(2IO). After establishing the indicated conditions at point C, the system slowly evolved oscillations with continuously changing periods and amplitude. (From Ref.. . )...

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