Electronic and chemical properties of Pd in bimetallic systems: interaction of Pd with Rh(111)

Abstract

The nature of the metal-metal interactions in a series of Pd Rh(111) surfaces has been examined using thermal desorption mass spectroscopy, core- and valence-level photoemission, CO chemisorption, and ab initio self-consistent field calculations. A monolayer of Pd supported on Rh(111) exhibits a Pd 3 d 5 2 binding energy ∼0.2 eV higher than that of the surface atoms of Pd(100), and desorbs at ∼1390 K. The desorption temperature of CO from this Pd Rh(111) system is 50–70 K lower than those seen on Pd(111) and Rh(111), indicating a weakening of 3–5 kcal mol −1 in the strength of the CO adsorption bond. These results are compared with data reported in the literature for bimetallic surfaces that contain Pd and Rh, and general trends are explained in terms of a simple model.