Control of catalytic surface reactions by local laser heating

Utilizing a focused laser beam manipulated through computer-controlled mirrors, and capable of "writing" spatiotemporal temperature fields on a surface, we explore the fundamental impact of localized spatiotemporal perturbations on a simple reaction-diffusion system (1). Our two-dimensional model system is the low-pressure catalytic oxidation of CO on Pt(110), a reaction exhibiting well-understood spatiotemporal patterns. In the simplest case the laser spot causes the ignition of a reaction wave by a single critical "kick" at a selected surface location. The cooperativeness between two local sub-critical perturbations separated in time and/or space is then explored (2). A temperature heterogeneity moving along a line may ignite waves along its path, or can drag preexisting pulses. In particular, we studied how a traveling chemical pulse is ''dragged'' by a localized, moving temperature heterogeneity as a function of its intensity and speed. The acceleration and eventual ''detachment'' of the wave from the heterogeneity is explored through simulation and stability analysis (3). Additionally we demonstrated how pulses, the basic building blocks of chemical patterns, can be modified, guided, and erased and how the overall reaction rate can be increased through localized actuation. Computational studies supplement and rationalize these experimental findings. Finally we studied ultra thin (~200 nm) Pt(110) metal single crystals enables, which small thermal capacity allowed the exploration of catalytic reaction energetics at low pressures. We discovered a new chemo-thermo-mechanical instability in this regime, in which catalytic reaction kinetics interact with heat transfer and mechanical buckling to create oscillations (4). These interacting components are separated and explored through experimentation, mathematical modeling, and scientific computation, and from their synthesis an explanation of the phenomenon emerges.

1. J. Wolff, A. G. Papathanasiou, I. G. Kevrekidis, H. H. Rotermund, G. Ertl, Science 294, 134-137 (2001).
2. J. Wolff, A. G. Papathanasiou, H. H. Rotermund, G. Ertl, M. Katsoulakis, X. Li, I. G. Kevrekidis, Phys. Rev. Lett. 90, 148301-4 (2003).
3. J. Wolff, A. G. Papathanasiou, H. H. Rotermund, G. Ertl, X. Li, I. G. Kevrekidis, Phys. Rev. Lett. 90, 018302 1-4 (2003).
4. Fehmi Cirak, Jaime E. Cisternas, Alberto M. Cuitino, Gerhard Ertl, Philip Holmes, Ioannis G. Kevrekidis, Michael Ortiz, Harm Hinrich Rotermund, Michael Schunack, Janpeter Wolff, Science 300, 1932 (2003)