Changes in the surface structure of Pd/Ta2O5 by oxygen and CO studied using X-ray Photoelectron Spectroscopy (XPS)

Abstract

Behaviors of Pd structures with different thicknesses supported by Ta2O5/Ta in the reaction with oxygen and CO were studied by XPS and SEM. For the sampleswith a Pd thickness of 3 nm, a new low-binding-energy component appeared in the Pd 3d level upon O-2 exposure at similar to 200 degrees C and was reduced in intensity after a subsequent CO exposure at 150 and 200 degrees C. The change in the Ta 4f state could also be found upon oxygen and CO exposure, indicating that both Pd and the Ta-oxide substrate participate in the chemical reactions. For the sample with a higher Pd thickness, a positive shift in the Pd 3d level due to the oxidation of Pd was observed after exposure to O-2 at a higher temperature (280 degrees C). A subsequent CO exposure at similar to 150 degrees C could not reduce Pd-oxide layers, as confirmed by the unchanged Pd 3d spectra after CO treatment, i.e. Pd-oxide was not reactive for CO oxidation. Copyright (C) 2010 John Wiley & Sons, Ltd.