CHARACTERIZATION OF UNSUPPORTED FEMOS CATALYSTS - STABILITY DURING REACTION AND EFFECT OF THE SULFIDING TEMPERATURE

Unsupported iron, molybdenum and iron-molybdenum sulfides were prepared by the Homogeneous Sulfide Precipitation (HSP) method. They were investigated by surface area, XRD, MAS (Mössbauer Absorption Spectroscopy), electrophoretic migration, and XPS measurements; various temperature-programmed methods have also been used. Catalytic activity in the simultaneous hydrodesulfurisation of thiophene and hydrogenation of cyclohexene at 3 MPa and 573 K has been measured. It has been verified that the HSP method gives samples containing a high proportion of the Fe species giving the signal attributed to the so called "FeMoS" species, together with a noncrystalline phase possibly corresponding to FeS 2 (pyrite) and some pyrrhotite (Fe 1-x S). When the final reduction- sulfidation (15% H 2 S in H 2 ) temperature of the HSP precipitate is increased (from 673 to 1073 K), FeS2 and the iron of FeMoS transform to troilite (FeS). Samples sulfided above 873 K no longer contain FeMoS. The FeMoS "phase" decomposes extensively during the catalytic reaction. Catalytic activity does not correlate with the quantity of FeMoS present in the samples, but seems to vary in parallel with the amount of FeS 2 remaining in the working catalyst. © 1992.