Role of Pd-Al bimetallic interaction in CO adsorption and catalytic properties of bulk PdAl alloy:: XPS, ISS, TDS, and SIMS study

CO adsorption on the bulk PdAl bimetallic systems has been studied using XPS, ISS, TDS, and SIMS Under UHV conditions. Pd exhibits strong interaction with Al atoms resulting in the formation of noble metal-like electronic structure of PdAl alloy. The shifts of both Pd core levels and of Pd valence d-band centroid towards higher binding energies compared to bulk Pd were observed. The surface structure of the alloy changes with temperature (Al surface segregation), ion bombardment (preferential Al Sputtering), and is also strongly affected by the presence of ambient CO. The Pd-Al bond is weakened upon the interaction with CO. which tends to dissociate or the surface even at room temperature, with carbon fraction bonding to Pd atoms and oxygen to Al. The TDS of CO spectra consisted of one to three desorption peaks, all lying lower than those from Pd foil, indicating a distinct weakening of the Pd-CO chemisorption bond. Moreover, the partial CO dissociation on PdAl was indicated both as adsorption capacity decay and CO2 and H2O production. (C) 2002 Elsevier Science B.V. All rights reserved.