Macroscopic and mesoscopic characterization of a bistable reaction system: CO oxidation on Pt(111) surface

Abstract

Influence of extended interactions on the surface dynamics in the catalytic CO oxidation on Pt single crystal substrateThe catalytic oxidation of CO by oxygen on a platinum ͑111͒ single-crystal surface in a gas-flow reactor follows the Langmuir-Hinshelwood reaction mechanism. It exhibits two macroscopic stable steady states ͑low reactivity: CO-covered surface; high reactivity: O-covered surface͒, as determined by mass spectrometry. Unlike other Pt and Pd surface orientations no temporal and spatiotemporal oscillations are formed. Accordingly, COϩO/Pt͑111͒ can be considered as one of the least complicated heterogeneous reaction systems. We measured both the macroscopic and mesoscopic reaction behavior by mass spectrometry and photoelectron emission microscopy ͑PEEM͒, respectively, and explored especially the region of the phase transition between low and high reactivity. We followed the rate-dependent width of an observed hysteresis in the reactivity and the kinetics of nucleation and growth of individual oxygen and CO islands using the PEEM technique. We were able to adjust conditions of the external control parameters which totally inhibited the motion of the reaction/diffusion front. By systematic variation of these conditions we could pinpoint a whole region of external control parameters in which the reaction/diffusion front does not move. Parallel model calculations suggest that the front is actually pinned by surface defects. In summary, our experiments and simulation reveal the existence of an ''experimental'' bistable region inside the ''computed'' bistable region of the reactivity diagram ͑S-shaped curve͒ leading to a novel dollar ͑$͒-shaped curve.

Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model

“…In fact, evidence of such kind of transition has been reported in catalyzed reactions [8,9]. The occurrence of hysteretic effects around a first-order transition point has also been observed [10]. Very recently, we have performed a detailed study of the first-order IPT of the ZGB model presenting conclusive evidence of hysteretic effects [11].…”

Critical behaviour of irreversible reaction systems

“…These models exhibit many features characteristic of first-order IPT's that have also been found in numerous experiments, such as hysteretic effects [17,77] and abrupt changes of relevant properties when a control parameter is tuned around a coexistence point [17,18,19] (see also figure 2), etc. On view of these facts, special attention will be drawn to the discussion of first-order ITP's.…”

Pulsed activation in heterogeneous catalysis

“…For instance, it has been observed that oxygen and CO do not simply adsorb on random surface sites but rather they coalesce to form islands of CO and O species [58,85]. The actual reaction between CO and O is thought to take place at the edges of these islands.…”