SPATIOTEMPORAL TEMPERATURE PATTERNS DURING HYDROGEN OXIDATION ON A NICKEL DISK

Spatiotemporal temperature patterns on a polycrystalline nickel disk w ere recorded using infrared video imaging during atmospheric hydrogen oxidation and characterized by the proper orthogonal decomposition pat tern analysis technique. The system was studied at two different resid ence times, 3.2 s and 6.4 s. At moderate feed temperatures, steady-sta te multiplicity and rate oscillations were found. Oscillations at a re sidence time of 6.4 s were periodic and essentially spatially uniform. A t a residence time of 3.2 s, ho wever, the surface temperature beca me nonuniform, and rate oscillations occurred via traveling temperatur e waves which emanated from ''pacemakers '' (locally active regions) o n the edge of the catalyst. During periodic oscillations, the waves we re emitted synchronously from the pacemakers, while during chaotic osc illations, the pacemakers were desynchronized and emitted waves indepe ndently of each other. Nonlocal gas-phase coupling between distance su rface elements caused spatial desynchronization during rate oscillatio ns.