Structural characterization of W-Ni-Al₂O₃ catalysts

A series of W/Ni/Al₂O₃ catalysts was prepared by coprecipitation of nickel and aluminum and impregnation of tungsten. The samples were characterized by XRD, XPS and XAS techniques. XRD measurements detected two phases: NiO as the main phase and NiAl₂O₄ in lower amount; no phase containing tungsten was detected. XPS measurements indicated the presence of Al₂O₃, NiAl₂O₄, and Al₂(WO₄)₃ phases on the catalyst surfaces. The XANES spectra of catalysts were rather similar for all of the samples. According to the EXAFS results, at the short range level, tungsten does not form any bound with Ni atoms. The nickel first coordination shell in the catalysts containing tungsten is similar to that encountered in COP 1 catalyst without tungsten. The lower Ni-Ni coordination number observed for all catalysts, when compared to the NiO phase, can be attributed to the nickel-aluminum interaction.