Hydrodesulfurization of sulfur-containing polyaromatic compounds in light gas oil using noble metal catalysts

Abstract

We systematically monitored the hydrodesulfurization (HDS) activity of dibenzothiophene (DBT) and groups of substituted DBTs present in a SR-LGO over various noble metal catalysts (Ru, Rh, Ru-Rh, Pt, Pd and Pt-Pd) supported on alumina. The catalytic performances were compared to those obtained over a conventional CoMo catalyst. The Pd-based catalysts exhibited excellent HDS performances, especially for desulfurizing the refractory compounds. In particular, the 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS activity over the Pd or the Pd-Pt catalyst was equivalent to that over the CoMo catalyst. This was attributed to the exceptional hydrogenation (HYD) properties of the Pd-based catalysts, which enable desulfurization of the refractory compounds by considerably minimizing the effect of the steric hindrance due to their substituents. The synergetic effect observed on the bimetallic Pt-Pd system at low temperature for all the sulfur compounds was largely attenuated in the high temperature range, probably due to shifting of the HYD/dehydrogenation equilibrium to dehydrogenation. Despite a much lower metal loading (0.25 wt.%), the performances of the Rh catalyst were superior to those of the optimized 16 wt.% Ru catalyst. A synergetic effect was observed on the Ru-Rh catalyst, on which the DBT HDS activity was significantly enhanced compared to the activity of each corresponding monometallic catalyst. Further, we recently showed that the use of SiO 2 or SiO 2-Al 2O 3 as a support allows higher optimal Rh contents, making the Rh-based HDS catalysts even more promising. In brief, we obtained encouraging results, which showed for instance that the excellent properties of the noble metal catalysts in model HDS reactions are still observed during the HDS treatment of real feeds.