Electronic and chemical properties of Pt, Pd and Ni in bimetallic surfaces

The electronic properties of a series of bimetallic surfaces that combine Group-10 elements (Pt, Pd or Ni) with transition and s,p metals have been examined using ab initio self-consistent-held (SCF) calculations and cluster models. By analyzing the results of these theoretical studies together with the results of experimental techniques (photoemission, L-edge X-ray absorption fine structure, work function measurements, CO chemisorption, etc.), one can obtain a general idea of the nature of the bimetallic bond in these systems. A Group-10 adatom in contact with the surface of a s,p or early-transition metal exhibits large perturbations in its electronic and chemical properties. Zn this type of system, there is an important redistribution of charge that shifts d electrons from around the Group-10 metal into the interface region between the admetal and substrate, producing an accumulation of electrons around the bimetallic bonds. This redistribution of charge affects the stability of the core levels and valence d band of the Group-10 metal. The larger the movement of d electrons from the Group-10 metal toward the admetal-substrate interface, the stronger the bimetallic bond, and the lower the ability of the Group-10 metal to bond CO through pi-backdonation. Among the Group-10 metals, Pd shows the strongest electronic and chemical perturbations, while Ni exhibits the weakest (Ni<Pt<Pd).