Oscillatory combustion of propene during in situ mechanical activation of solid catalysts

Mechanochemical activation of solids can lead to a strong increase in their activity as catalysts in heterogeneously catalyzed reactions. In the following, we report on the effects of solid catalyst activation during ball milling that lead to oscillatory behavior in CO and CO₂ formation during propene oxidation. The oscillations arise under in situ ball milling conditions over chromium(III) oxide (Cr₂O₃) and cerium(IV) oxide (CeO₂), respectively. The experiments were conducted under continuous gas flow at ambient pressure and temperature, using both a modified steel and a tungsten carbide milling vessel. Abrasion of particles from the steel milling vessel could be eliminated as the sole cause for the oscillations through substitution by a tungsten carbide milling vessel. The intensity and frequency of oscillations are shown to be dependent on the propene-to-oxygen ratio, the milling frequency, milling ball size and metal oxide used. Overall, Cr₂O₃ shows higher activity for oscillatory propene combustion under in situ mechanical activation than CeO₂.