Effects of Artificial Protrusions on Self-Sustained Thermal Oscillations during Hydrogen Oxidation on Nickel

Hydrogen oxidation is studied on a series of nickel foil catalysts, some of which were flat on the scale of microns, while others were covered with micron-sized protrusions. The temperature of the protrusion-covered catalysts was found to undergo self-sustained oscillations at oxygen concentrations between 0.45 and 10% and feed temperatures between 280 and 430 °C. No oscillations are seen with untreated flat catalysts under any conditions studied. However, when 2-12-μm nickel grains are attached to the surface of the otherwise flat catalysts, thereby creating artificial protrusions, oscillations are seen. Mechanical roughening of the surface of the flat catalysts also induces oscillations. Interestingly, no oscillations are seen when nickel grains larger than 20 μm are attached to the surface of the flat catalysts. Many of the results here are in general accord with the fuzzy wire model of Jensen and Ray; however, there are some differences which need to be explored.