Self-sustained Oscillations in Oxidation of Propane Over Nickel: Experimental Study and Mathematical Modelling

The regular reaction rate oscillations were observed by mass-spectrometry in the oxidation of propane over the Ni foil. CO, CO₂, H₂, and H₂O were detected as products. The oscillations of products and reactants in the gas phase were accompanied by the oscillations of the catalyst temperature. It was shown by using isotopic labeling ¹⁸O₂ that CO and CO₂ formed simultaneously by the propane oxidation when the catalyst was in the highly active state. The non-isothermal model of a continuous stirred-tank reactor based on a microkinetic scheme including 50 reaction steps was developed. The model takes into account periodic oxidation and reduction of nickel and formation of main products. Using the method of quasi-steady-state approximations, it was shown that the observed self-sustained oscillations are associated with periodic changes in the coverage of the Ni surface by adsorbed oxygen and carbon as well as nickel oxide species. It was shown that the microkinetic scheme coupled with a continuous stirred-tank reactor model qualitatively describes the experimental data if the model also considers the periodic processes of oxidation and reduction of the Ni bulk.