A series of Pd-Cu/KL zeolites with varying Pd:Cu ratios have been studied by a combination of FTIR and XANES. XANES indicates that only one PdCu alloy is formed for all samples and that the bulk of the alloy is not modified by extended periods under CO/H-2 at elevated temperatures. A combination of low temperature adsorption studies and in situ high temperature/high pressure FTIR indicates that an adsorbate induced surface segregation of Pd occurs following exposure of the bimetallic catalysts to a CO/H-2 reaction mixture under hydrogenation conditions, A progressive loss in Pd three-fold adsorption centres is observed as a function of time in contact with the reaction mixture.