Monitoring Atomic Rearrangement in PtxPd1-x (x=1, 0.7, or 0.5) Nanoparticles Driven by Reduction and Sulfidation Processes

PtxPd1-x (x = 1, 0.7, or 0.5) nanoparticles submitted to hydrogen reduction and posterior H,S sulfidation at 150 or 300 degrees C were characterized by in situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The in situ XAS measurements allowed monitoring of short-range order changes around the Pt atoms induced by the thermal processes. The surface sensitivity and atom specific characteristics of XPS provided additional information about the chemical state of the atoms present in the outermost layers of the nanoparticles. Our experiments also indicate a Pd migration toward the surface of the nanoparticles driven by the thermal processes. We observed that the reduction process is necessary prior to the occurrence of any sulfur reaction and that the number of chemisorbed sulfur atoms is directly proportional to the quantity of Pd atoms.