Real-time study of self-sustained oscillations in the CO oxidation rate on Pt

Abstract

The driving mechanism for self-sustained oscillations in the rate of some catalytic oxidations under steady-state conditions has remained unexplained despite numerous theoretical and experimental studies since the early 1970s. We have used reflection–absorption infrared spectroscopy to perform the first real-time analysis of a Pt foil surface during constant temperature oscillations in CO oxidation. The CO absorption capacity of the surface is shown to vary periodically during oscillations. Inverse correlation of the CO adsorption capacity with surface carbon concentration (measured with Auger spectroscopy), and demonstration that (1) carbon can diffuse from the bulk to the surface, (2) oxygen can remove surface carbon from the surface, and (3) CO can block carbon diffusion, all at oscillation temperatures, indicate that variation in surface carbon concentration may be driving the oscillations. Modeling of the phenomenon is found to account for all observations.