Pd/Cu alloys as hydrodechlorination catalysts: a medium-energy ion scattering study of surface composition under exposure to chlorinated hydrocarbons

Medium-energy ion scattering (MEIS) is a surface analytical technique with the unique ability to provide layer-by-layer compositional information for crystalline materials such as the bimetallic PdCu alloy investigated here. MEIS has been used to study the segregation effects induced by the adsorpti on of trichloroethene onto a Pd0.5Cu0.5(110) single crystal; this system is a model for industrially important hydrodechlorination catalysts. The PdCu (110) clean surface is shown to be slightly Pd-rich under the preparation conditions used, with oscillatory composition going into the bulk. Adsorpti on of trichloroethene caused Cu enrichment of the first atomic layer, altho ugh this is seen to decrease with higher temperature annealing, Comparable experiments using ethene indicate that adsorbed carbon and hydrocarbon spec ies can give rise to considerable Pd segregation. The chemistry of trichlor oethene adsorption on PdCu(110) is such that considerable residual carbon a nd hydrocarbons may be present and, because this induces an opposing effect , it is probable that the effect of adsorbed Cl on Cu segregation is larger than that observed directly, Copyright (C) 2000 John Wiley & Sons, Ltd.