Synergy Phenomenon in Bulk Ruthenium- Vanadium sulfides : ⁵¹V NMR and ESR studies

Abstract

For a better protection of the atmospheric environment, catalytic hydroprocessing will become increasingly important in the years to come. This is due to the need for light distillates simultaneously with a stricter environmental legislation. Since the works of Chianelli and Harris [1], it is well known that mixing two transition metal sulfides (TMS) allows developing higher activity than the ones exhibited by pure compounds in hydrotreatment reaction. From this point of view, the CoMo and NiMo conventional catalysts have been widely used. So far, an explanation for such a synergism is still matter of debate and understanding of the synergy phenomenon becomes fundamental. Our previous results [2,3] show that, rather a structural effect, we are in presence of electronic effect, which changes noticeably the environment of active site. As an example, all the iron-based mixed sulfides present, in Mossbauer spectra, only one iron species, which is Fe²⁺ low spin. Moreover, it is showed that there is a linear correlation between the hyperfine field distribution and the activity of vanadyloctaethylporphyrine hydrodeporphyrinisation. The evolution of the >HPF< at room temperature for different relative concentration of iron is due to the changes in the density of state of the d electrons at the Fermi level [4]. Magnetic resonance appears as one of the technique that can give a part of the response. As ruthenium sulfide is one of the best catalyst for hydrodesulfürisation (HDS) [5] and V is also a good candidate for the synergy phenomenon! [2], bulk RuV mixed sulfides were chosen to performed a study by solid state NMR and ESR.