A combinatorial library of catalyst candidates, each consisting of a different metal element supported on γ-alumina, is screened for hydrogen oxidation catalytic activity. Heat liberated on the surface of active catalysts by the catalyzed reaction is detected by noninvasive IR thermography. A 16-candidate library identifies four distinctly active pellets, which correspond to active formulations known from the literature. A higher density library shows similar results, but heat and mass transport effects influence the pellet temperatures. This method may be used to screen and optimize catalyst formulations more efficiently and quickly than current methods and may also be useful for study of operational lifetime, resistance to poisons, and regenerability.

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Back-and-forth-moving temperature fronts separating regions with high and low temperatures (amplitudes up to 100 K) formed on a Pd on alumina ring during the atmospheric oxidation of carbon monoxide. The back-and-forth front movement reflects the intrinsic nonuniformity of the catalytic system and the impact of global coupling. The ignition and extinction fronts usually moved at different velocities, in agreement with theoretical predictions. Complex spatiotemporal patterns were observed due to smallamplitude temperature fronts that moved on the high-temperature region at a much higher velocity than the high-amplitude fronts. The qualitative motion features were affected by changes in the excess oxygen concentration. The nonun$orm states existed mainly for feed conditions for which the only uniform state was an extinguished one.

The atmospheric oxidation of a mixture containing 6 vol % carbon monoxide was carried out on a hollow cylindrical catalytic pellet. The catalyst was held in a conical reactor which enabled simultaneous measurement of the temperature patterns on the top and side of the pellet by an IR imager. Upon a decrease in the reactor temperature the fully ignited, high temperature state of the pellet is transformed to a nonuniform one with temperature fronts separating high and low temperature regions. The transition and the resulting states are rather intricate and are strongly influenced by the nonuniformity of the catalyst and the transport to and from it, as well as the global coupling, which stabilizes temperature fronts and patterns, which would not exist in its absence. Intricate pulse splitting and extinction were observed both on the top and the side of the pellet. Highly irregular motions and conversions were obtained following a decrease in the reactor temperature. (c) 1999 American Institute of Physics.

Stationary and spatially oscillating temperature fronts separating regions with high and low temperatures (amplitudes up to 120 K) formed during the atmospheric oxidation of carbon monoxide on a Pd on alumina ring kept in a mixed reactor. The sharp fronts bounded either one or two low temperature regions. The transition from stationary to spatially oscillating fronts occurred at a feed CO/O2 concentration ratio close to 2.0 and was independent of the reactor temperature. The net rate of local heat generation on the ring was nonuniform leading to angular variation of the temperature of the ignited state. Front motions were affected by both the nonuniformity of the system and the interaction between the catalyst and the ambient gas. The two fronts bounding a low temperature region usually moved at different velocities and their velocities increased with increasing oxygen concentration. In most cases the two fronts did not move in phase, but sometimes they moved in tandem generating a back-and-forth pulse motion. The spatial amplitude of the oscillations decreased as the slope of the net heat generation activity became steeper. The spatial variation of the standard deviation of the temperature was helpful in assessing the dynamics of the oscillating fronts.