SPATIOTEMPORAL TEMPERATURE PATTERNS DURING HYDROGEN OXIDATION ON A NICKEL DISK

Spatiotemporal temperature patterns on a polycrystalline nickel disk were recorded using infrared video imaging during atmospheric hydrogen oxidation and characterized by the proper orthogonal decomposition pattern analysis technique. The system was studied at two different residence times, 3.2 s and 6.4 s. At moderate feed temperatures, steady-state multiplicity and rate oscillations were found. Oscillations at a residence 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 became nonuniform, and rate oscillations occurred via traveling temperature waves which emanated from ''pacemakers '' (locally active regions) on the edge of the catalyst. During periodic oscillations, the waves were emitted synchronously from the pacemakers, while during chaotic oscillations, the pacemakers were desynchronized and emitted waves independently of each other. Nonlocal gas-phase coupling between distance surface elements caused spatial desynchronization during rate oscillations.