ON THE REACTIVITY OF 2D PD SURFACE ALLOYS OBTAINED BY SURFACE SEGREGATION OR DEPOSITION TECHNIQUE

Two-dimensional Pd surface alloys can be obtained by two different met hods: either by surface segregation or by deposition followed by contr olled annealing. For a similar Pd surface concentration, Pd-Ni samples , prepared by these two ways, exhibit similar activity towards the hyd rogenation of 1,3-butadiene and are more effective than pure Pd. Diffe rent UHV techniques allow us to think that the same catalytic behaviou r is due to the same chemical composition and atomic arrangement at th e very surface. Moreover, XPS measurements show similar electronic pro perties of the active site which might be a Pd pair modified by surrou nding Ni atoms.