A Study of Strong Metal–Support Interaction Based on an Electron Spectroscopic Investigation of Nitrogen Adsorption on Simulated Ni/TiO₂, Ni/Ai₂O₃, and Related Catalyst Surfaces

Adsorption of nitrogen on Ni/TiO₂, Ni/Al₂O₃, Ni/Al, Ni–Ti alloy, TiO₂, and other surfaces prepared in situ in an electron spectrometer has been investigated by X-ray and UV photoelectron spectroscopy to understand the nature of the strong metal-support interaction (SMSI) state in the annealed Ni/TiO₂ catalyst system. The annealed Ni/TiO₂ surface has a considerable proportion of Ti³⁺ and exhibits dissociative adsorption of N₂ along with weak molecular chemisorption at 80 K just as a Ni–Ti alloy surface. This is in contrast with the nonannealed Ni/TiO₂ surface where there is only molecular chemisorption at 80 K similar to the Ni/Al₂O₃ surface. The adsorption behavior of the annealed Ni/TiO₂ surface is also different from that of TiO₂ (showing only physisorption), TiO_x (reduced surface showing physisorption and dissociation) or Ni/TiO_x (dissociation and stronger chemisorption as on Ni/TiO₂). It is suggested that the annealed Ni/TiO₂ surface may correspond to the SMSI state.