Modelling of CO Oxidation

It has thus become recognized that the amplitude and variety of oscillations that can arise cannot be accounted for by simple elementary step models. This has led to a wide variety of possible extensions. These include  

A buffer species is assumed to be formed on the surface which blocks active sites but does not otherwise take part in the reaction. Formation of- 

Formation of intermediates which, again, block the active sites- 

Non-isothermal temperature effects incorporation into mass balance equations.  

Presence of two types of sites, where one type exclusively adsorbs CO, but both the gases compete for the second type of site.  

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These expressions, and also eqn. (34) make sense because (X tY/)/(X ) equals the conditional probability that there is an X t at site k if there is an X at site /. Such an easy interpretation is not possible if we have e.g. three sites that are pairwise neighbors as for a hexagonal grid. Eqn. (34) and similar equations like (38), (39), and (40) have been used before by Mai et al. in models of CO oxidation. 

There are also two factors that have already been noted in the numerical analysis of the kinetic model of CO oxidation (1) fluctuations in the surface composition of the gas phase and temperature can lead to the fact that the "actual multiplicity of steady states will degenerate into an unique steady state with high parametric sensitivity [170] and (2) due to the limitations on the observation time (which in real experiments always exists) we can observe a "false hysteresis in the case when the steady state is unique. Apparently, "false hysteresis will take place in the region in which the relaxation processes are slow. 

In the following example, we use a simple microkinetic model of CO oxidation on Pt together with the reconstructed porous catalyst to follow the evolution of local concentration profiles within the porous structure. The reaction-diffusion problem of the CO oxidation on the Pt/y-Al203 porous catalyst... 

Koci, P., Stepanek, F., Kubicek, K., and Marek, M. Modeling of CO Oxidation in Digitally Reconstructed Porous Pt/yAl203 Catalyst. Proceedings of CHISA 2004 , 22-25 August 2004, Prague, Czech Republic (2004b). 

M. Bertram and A. Mikhailov. Pattern formation on the edge of chaos mathematical modeling of CO oxidation on a Pt(llO) surface under global delayed feedback. Phys. Rev. E, 67 1-9, 2003. 

The application of Monte-Carlo simulations to non-equilibrium reaction systems in heterogeneous catalysis started by Ziff, Gulari and Barshad on the lattice-gas version of a simple Langmuir-Hinshelwood model of CO oxidation on a transition metal surface. The ZGB-model is a lattice-gas version of the Langmuir-Hinshelwood-model of CO oxidation. 

Figure 8.27. FEM-images of the oscillating CO-oxidation reaction on Pt ( (1 0 0) (E.T. Latkin, V. I. Elokhin, V. V. Gorodetskii, Spiral concentration waves in the Monte Carlo model of CO oxidation over Pd(l 1 0) caused by synchronisation via COads diffusion between separate parts of catalytic surface. Chemical Engineering Journal, 91 (2003) 123).

Liu W. and Flytzani-Stephanopoulos M. 1995. Total oxidation of carbon monoxide and methane over transition metal-fluorite oxide composite catalysts, J. Catal., 153, 304-316. Sedmak G., HoCevar S. and Levee J. 2004. Transient kinetic model of CO oxidation over a... 

Multi-Scale Modeling of CO Oxidation on Pt-Based Electrocatalysts... 

Bykov, V.I., Yablonskii, G.S., Elokhin, V.I., 1981. Steady state multiplicity of the kinetic model of CO oxidation reaction. Surf. Sci. Lett. 107, L334-L338. 

Fig. 15. Skeleton bifurcation diagram of the reconstruction model of CO oxidation on Pt(l 10) Equations (4) and of the reduced model Equations (5). Regions A and C are excitable, B oscillatory and D bistable. The latter is subdivided depending on whether one (Di) or two front solutions (Di) exist.

One concrete example of the research methods just described, is the multi-scale modeling of CO oxidation on the Ru/Ru02 catalyst at realistic ambient conditions... 

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