Novel hydrodesulfurization catalysts derived from a supported rhodium carbonyl complex

Abstract

Abstract The dibenzothiophene hydrodesulfurization (HDS) reactions were carried out over alumina, titania, silica and silica-alumina supported rhodium complex catalysts. First, a series of catalysts containing 1 wt.% Rh was prepared and tested. Whilst in the case of the Rh/Al 2 O 3 catalyst we did not observe any significant variation of the activity with the pretreatment, in the case of the titania, the silica and the silica-alumina supported catalysts, the pre-reduction treatment resulted in an activity twice as high as that obtained after the pre-sulfiding treatment. The use of the various supports slightly affected the overall HDS activity as well as the products selectivities. Whilst the Rh/Al 2 O 3 catalyst exhibited the highest biphenyl (BP) selectivity, the Rh/SiO 2 -Al 2 O 3 catalyst exhibited the highest dibenzothiophene conversion. The Rh supported on TiO 2 , SiO 2 and SiO 2 -Al 2 O 3 catalysts gave high cyclohexylbenzene (CHB) yields, indicating high hydrogenation abilities. Further, the effect of the Rh loading was studied on the titania and the silica supports. Unlike the other supports for which the activity stabilized for Rh loadings higher than 0.5–1.0 wt.%, the DBT conversions of the SiO 2 -supported Rh catalysts increased up to 4 wt.% Rh, exhibiting the highest HDS activity. To precisely elucidate the effect of the pre-activation method on the sulfidation state and on the HDS activity, the 4 wt.% Rh/SiO 2 catalyst was placed under HDS working conditions and [ 35 S ]DBT HDS tracer experiments were performed. We found that, whilst the amount of labile sulfur (S OA ) present on the surface of the prereduced catalyst was slightly lower than that observed for the presulfided catalyst, the labile sulfur atoms created on the prereduced catalyst exhibited a significantly greater mobility ( k RE ). This increase in sulfur mobility induced by the reduction pretreatment facilitated the active sites regeneration during the reaction, which led to an enhancement of the HDS catalytic activity.