BULK AND SURFACE CHARACTERIZATION OF SOME HETEROPOLYMOLYBDATES AND THE PRODUCTS OF THEIR REDUCTION AND SULFIDATION

[CoMo6O24H6](NH4)3.7H2O Anderson-type hexamolybdate (as prepared, supported on gamma-alumina and after thermal treatment in hydrogen or in a thiophene/hydrogen mixture) has been characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal analysis and X-ray photoelectron spectroscopy (XPS). The Anderson phase also contains Co3+ and Mo6+ species at the surface. After thermal treatment at 773 K in hydrogen and exposure to air at room temperature, MoO3 and CoMoO4 are formed. The XP spectrum of the Anderson phase supported on gamma-alumina showed the presence of two Mo6+ species, probably due to the coexistence of the molybdenum contained in the structural framework of the Anderson phase and a species derived from the interaction of the hexamolybdate with gamma-alumina. The XP spectrum of the supported Anderson phase after sulfidation revealed the presence of two molybdenum species which could be due to the coexistence of sulfide and oxisulfide phases; in addition, the Mo:Al atomic ratio was increased by sulfidation, suggesting a good dispersion of the MoS2-like layered structure with small crystallite sizes. [AlMo6O24H6](NH4)3.7H2O treated in hydrogen at 1073 K was also characterized and its XRD pattern showed the presence of metallic molybdenum.