Formation and electronic properties of oxide and sulphide films of Co, Ni and Mo studied by XPS

Dry O-2 oxidation up to 400 degrees C, water immersion at room temperature or H2S sulphidation at 400 degrees C forms oxide or sulphide films on polycrystalline Co and Ni foils. X-ray photoelectron spectra (XPS) of the Co 2p and Ni 2p core levels and valence band (VB) structure changes allow the identification of the chemical state of such films and their electronic properties. They are compared with the films obtained on Mo in similar conditions. Ni appears less reactive than Co during O-2 or water oxidation and is considered as a more noble metal. Dry oxidation mainly induces CoO while water immersion induces formation of CoO(OH). For Ni, phases like Ni2O3, Ni(OH)(2) and/or NiO(OH) are the most probable products, respectively. H2S sulphidation always produces a sulphur-rich Co or Ni phase. The VB response to sulphidation of the three studied metals shows that Co or Ni sulphides are potential electron-donors to MoS2. Such results an relevant to the synergy observed in hydrotreating catalysis with these sulphides. (C) 1999 Elsevier Science B.V. All rights reserved.