Composition and properties of platinum-rhodium alloy surfaces.

Abstract

The use of Pt–Rh based three-way catalysts for automotive exhaust gas control stimulated us to study the surface composition and surface properties of various Pt–Rh alloy samples. In this paper we shall review our results concerning the relation of the surface structure and surface composition with the physical and chemical properties.The surface composition was studied under various experimental conditions, both in vacuum and in the presence of an atmosphere of NO, O2, CO and H2. The effect of the temperature on the surface composition will be described and discussed on the basis of thermodynamics. We shall discuss the relation of surface composition with the physical properties (Debye Temperature) and with the chemical properties of Pt–Rh alloys, in particular towards NO, CO, O2 and H2 and their reactions.Another part of the paper deals with the effect of the surface structure on the chemical properties of Pt–Rh alloys. NO dissociation, the first step in the NO reduction with CO or H2, is extremely sensitive to both the structure and the composition of the surface.