THE PD NI(110) BIMETALLIC SYSTEM - SURFACE CHARACTERIZATION BY LEED, AES, XPS, AND LEIS TECHNIQUES - NEW INSIGHT ON CATALYTIC PROPERTIES/

Pd deposits on Ni(110) have been studied by low-energy electron diffra ction (LEED), Auger electron spectroscopy (AES), low-energy ion scatte ring spectroscopy (LEIS), and X-ray photoelectron spectroscopy techniq ues and their catalytic properties tested by the butadiene hydrogenati on reaction at room temperature. Their catalytic activity is greatly e nhanced by appropriate annealings, Superstructure indicative of a long range ordering of Pd atoms on Ni is evidenced for low Pd coverages ne ither before nor after annealing, For higher coverages, a LEED superst ructure appears after annealing, AES and LEIS studies reveal a sharp P d depth profile and the existence of a Pd-Ni surface alloy even at roo m temperature. The Pd 3d core level binding energy is shifted upwards by at least 0.4 eV with respect to pure Pd surface atoms and remains u nchanged in the course of annealings, Hence geometrical rearrangements have to be taken into consideration to explain the activity enhanceme nt. (C) 1996 Academic Press, Inc.