Carbon monoxide oxidation on platinum studied by local current and emf in a solid electrolyte concentration cell

Abstract

Surface oxygen and CO concentrations ( N O and N CO) adsorbed on Pt during oxidation are determined as functions of P O 2 and p CO by local current and emf measurements for a solid electrolyte concentration cell in the region where P CO is low compared to P O 2 . The temperature range is 570 to 680 K, P O 2 is between 1 × 10 2 and 5 × 10 4 Pa, and P CO ranges from 2.5 to 1 × 10 4 Pa. The local current is measured potentiostatically using reference, counter, and working electrodes. As a result, N O is determined to be proportional to P O 2 0.0 · P CO 0.1 and N CO to P CO δ P O 2 at about 640 K, where δ increases from 1 to about 1.6 as P CO increases. At lower temperatures, such as 580 K, N O is determined to be proportional to P O 2 0.3 · P CO 0.1, and N CO to the same formula as at 640 K. The dependence of N O is considered in terms of electronic effects of adsorbed CO on the Pt surface and that of N CO in terms of the residence time of mobile CO adsorbed on Pt. It is also considered that the initiation of oscillation in CO oxidation is related to the mobility of CO adsorbed on Pt. In the region where CO is more abundant, surface concentrations cannot be determined due to the predominance of resistance polarization in the local current.