Theory of Surface Catalytic Reactions
	Objective

Catalytic surface reactions are of enormous importance in industrial (syntesis of NH3, H2SO4..., cracking and reforming processes) and environmental chemistry (catalytic control of emission CO, SO2...). For each reaction a specially adapted catalyst is very much in demand. Therefore a computer aided design of catalyst would be a great progress in optimizing the selectivity, yield and performance of  the reaction.

   Although surface reactions have been intensovely investigated in the last 20 years, surprisingly little is known about the elementary reaction steps which take place on the atomic length scale of these reactions. The CO+O2 and the CO+NO reaction systems are by far the best-explored ones both on low index single crystal and polycristalline surfaces, but experimental investigations using new spectroscopical methods are very demanding to carry out and freqently cannot resolve the individual reaction steps.

On the other hand, today's theoretical approaches do not master the complexity of most of the important reaction steps including correlations, fluctuations, formation of spatio-temporal patterns and energetic interactions both in the adsorbate layer and between the adsorbates and the surface. In this case computer simulation may be a good tool to study details of these reactions. Certain aspects of the reaction can be simulated to examine the system behavior as function of these.

Simulation of kinetic oscillations  in surface reactions on reconstructing surfaces

The occurrence of kinetic oscillations in catalytic surface reactions such as the oxidation of CO on Pt(100) and Pt(110) is a well known phenomenon and has been investigated extensively in the recent past. Experimental results show that the kinetic oscillations are closely connected with the propagation of chemical waves, i.e. with the propagation of the borders between CO and O covered regions on the catalyst surface. In the case of the Pt(100) surface adsorbed CO is abl to reverse the 1x1 -> hex surface reconstruction. As O adsorbs essentially only on the 1x1 phase, which  initiates the reaction, continuous structural transformations are propagated along with chemical waves. Gif-Animation (445 Kb)

Therefore the system of the CO + O2  reaction is in principle able to show kinetic oscillations as soon as one takes these structural transformations into account. The questions that arise are, which basic processes among the vast number of proposed reaction steps have to be included to describe the kinetic oscillations and how should these elementary reaction steps be modeled on an atomic length scale. Gif-Animation (426 Kb)

For more details see:
Kotomin E. and Kuzovkov V. Modern aspects of diffusion-controlled reactions: Cooperative phenomena in bimolecular processes, vol.34 in Comprehensive Chemical Kinetics. Amsterdam: Elsevier, 1996. - 616p.
Kortlüke O., Kuzovkov V.N. and von Niessen W. Oscillation phenomena leading to chaos in a stochastic surface reaction Model. Phys.Rev.Lett. 81, P.2164-2167 (1998).
Kuzovkov V.N., Kortlüke O. and von Niessen W. Kinetic oscillations in the catalytic CO oxidation on Pt single crystal surfaces: Theory and simulation. J.Chem.Phys.108, P.5571-5580 (1998).
Kortlüke O., Kuzovkov V.N. and von Niessen W. Simulation of kinetic oscillations in surface reactions on reconstructing surfaces. J. Chem.Phys. 110,  P.11523-11533 (1999).