Reaction-diffusion front propagation across stepped surfaces during catalytic oxidation of CO on Pt(100)

High-resolution microscopy studies of the removal of CO-adlayers on Pt(100) by exposure to oxygen reveal that reaction-diffusion front propagation is impeded both by mesoscopic step bunches and by monoatomic steps. The resulting "stop-and-go" nature to front propagation can be characterized in terms of a time delay for crossing each step bunch or step, at least when the separation of these defects is comparable to or exceeds the width of the front. Here, eve quantify this time delay in terms of the reduced diffusion coefficient for CO in step bunch regions and the width of these regions, or in terms of the reduced hop rate for CO across monoatomic steps. We also briefly examine front propagation across arrays of more closely spaced steps. Results facilitate assessment of terrace diffusivities from average or macroscopic front propagation velocities across multiply stepped surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.