Compatibility of field emitter studies of oscillating surface reactions with single crystal measurements: catalytic CO oxidation on Pt

Abstract

Kinetic oscillations in catalytic CO oxidation on Pt have been studied on large (millimeter size) single crystal planes of Pt as well as on a Pt field emitter tip that exposes different crystal facets of nanometer size. In order to examine the compatibility of results from the two types of experiments, the regions of different dynamical behavior (bifurcation diagram) have been mapped out in p CO, T-parameter space using a field electron microscope (FEM) and a field ion microscope (FIM). The comparison with the results of single crystal measurements shows that in the case of applied electrostatic fields less than 5 V nm −1 (FEM), the field-induced effects are negligible, but they are significant for fields exceeding 12 V nm −1 (FIM). The field-induced shift of the bifurcation diagram toward lower p CO values, observed with FIM, is explained in terms of a field-modified interaction of CO and O 2 with Pt studied here with field ion appearance energy spectroscopy. With coadsorbed lithium (submonolayer coverage), the existence range for rate oscillations is shifted toward higher p CO values. This shift is attributed to a redistribution of the electron density at the surface induced by alkali metal co-adsorption.