Behavior of iron-vanadium sulfide catalysts for hydrotreating reactions

Fe-V pure and mixed sulfides have been prepared from solutions containing iron nitrate and/or ammonium tetrathiovanadate and precipitation with ammonium sulfide. After treatment with H2S (15%)-H-2 at 673 K, they exhibit quite high surface area from 57 to 5 m(2) . g(-1). X-ray diffraction and Mossbauer spectroscopy show the existence of a continuum from the pyrrhotite phase (Fe0.85S) to a V3S4-like phase (V0.74S). The structure of the solids is not modified by the catalytic tests which consist in hydrodesulfurization (HDS) of thiophene, hydrogenation (HYD) of toluene, and hydrodeporphyrinization (HDP) of vanadyl octaethyl porphyrine. X-ray photoelectron spectroscopy characterizations indicate a surface Fe-V homogeneity in the mixed sulfides corresponding to the bulk composition and show an effective surface oxidation of the prepared or tested samples occuring during air exposure. Surface compounds like VOSO4, V2O5, Fe2O3, xH(2)O, and FeOOH have been identified. Concerning the catalytic behaviors, it is worth mentioning that bulk Fe0.85S is only active for HDP whereas bulk V0.74S has a high potential activity in HDS, HYD, and HDP by comparison with bulk MoS2. Moreover, a synergy effect is detected for about 30 atomic% in Fe which origin could be assigned to an optimal dispersion of the V active sites. (C) 1997 Academic Press.