Spatial and Temporal Self-organization During CO Oxidation Over Ni

Oscillatory behavior during CO oxidation over a Ni foil in a continuous-flow catalytic reactor has been discovered in the reaction mixture containing CO excess at atmospheric pressure in the temperature range of 500–630 °C. The oscillations are accompanied by propagation of the oxidation and reduction fronts which were recorded by a photo–video camera. Dark fronts of the oxidized state appear periodically in the upstream part of the catalyst and propagate to the downstream region in the direction of the gas flow. Reduction fronts move in the opposite direction. A mathematical model has been developed to simulate the oscillatory dynamics. The developed model simulates experimental data almost quantitatively. The origin of oscillations is connected with periodic oxidation and reduction of the nickel surface. It is shown that a precursor-mediated adsorption of CO on Ni surface is required to simulate the oscillations under reducing conditions.