Interaction of Zinc with Transition-Metal Surfaces: Electronic and Chemical Perturbations Induced by Bimetallic Bonding

Abstract

The addition of zinc can induce significant changes in the chemical and catalytic properties of a transition-metal surface. The properties of a series of bimetallic surfaces that combine Zn with Rh or group 10 elements (TM = Ni, Pd, or Pt) have been examined using thermal desorption mass spectroscopy, core- and valence-level photoemission, CO chemisorption, and ab initio self-consistent-field calculations. The deposition of Zn on Rh(111) or polycrystalline surfaces of group 10 metals leads to the formation of alloys. These surface alloys decompose at high temperatures: 600−800 K, ZnNi; 650−850 K, ZnRh; 750−950 K, ZnPt; 850−1000 K, ZnPd. In the alloys, the core levels and valence d band of the transition metals exhibit positive binding energy shifts, while negative shifts are observed for the Zn 2p levels and 3d band. For CO/ZnRh and CO/ZnTM surfaces, the CO adsorption bond is weaker than for CO/Rh and CO/TM surfaces: 1−2 kcal/mol on ZnNi; 4−5 kcal/mol on ZnRh; 4−8 kcal/mol on ZnPt; and 12−16 kcal/mol on...