No abstract

A series of Ni0-W03/Al203 catalysts were studied by UV-vis diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). Both the metal content and the temperature of calcination of the catalysts were varied over a wide range. It was found that W is present as a W6+ surface phase regardless of the temperature of calcination and W content. In Ni0/Al203 samples several Ni2+ species were detected: an octahedral species located at the surface and both an octahedral and a tetrahedral species located in the A1203 support. In Ni0-W03/Al203 samples a different octahedral Ni species was also found, in which Ni is present in a mixed phase containing Ni, W, Al, and O. The Ni content has some influence on the speciation of Ni, but the temperature of calcination is the major factor which determines the location and the coordination of Ni. Calcination below 775 K results in catalysts which contain only octahedral Ni at the surface. At higher temperatures diffusion of Ni into the support is detected by XRD, and at 1175 Kan equilibrium distribution throughout the support particles is established. In the support most of the Ni is tetrahedrally coordinated, and above 925 K the distribution of Ni over tetrahedral and octahedral sites is hardly affected by a change in calcination temperature or Ni content. A model is presented which can quantitatively describe the diffusion process using independently determined parameters. It is concluded that Ni diffusion into the support is negligible under hydrodesulfurization (HDS) reaction conditions, which stresses the importance of the structure of the oxidic precursor for the structure and HDS activity of sulfided catalysts.

The sulfided form of NiO‐WO3/Al2O3 catalysts is applied for hydrotreating and hydrocracking reactions.

A comprehensive overview of the reduction behavior of sulfided Co/Al2O3, Mo/Al2O3, and Co‐Mo/Al2O3 hydrodesulfurization (HDS) catalysts is given by interpretation of temp.‐programmed reduction (TPR) studies.

026ChemInform Abstract The structure of oxidic and sulfided Mo catalysts supported on activated carbon has been investigated by XPS, temp.-programmed sulfiding (TPS), and chemical sulfur analysis, and the results are compared with those reported in the literature for Mo/Al2O3 catalysts. At Mo loadings below 3 wt.%, the oxidic Mo phase is highly dispersed on carbon as isolated or polymerized monolayer species, whereas small three-dimensional particles are present at higher loadings. Upon sulfiding particle growth occurs, although the particle size remains below 4.6 nm even at high loadings. Only Mo(IV) is detected in the sulfided samples and MoS2 is found to be the major phase present after sulfidation. The higher catalytic activity for sulfided Mo/C compared to Mo/Al2O3 is explained by the absence of strong interactions with the carbon support.