Abstract
With the growing demand for high quality diesel fuels more and more severe environmental regulations are imposed to the refineries. In order to meet the new stringent specifications, the development of new efficient catalysts is required while making efforts to elucidate the reaction mechanism. Previous research showed that for the second row the highest HDS activity was obtained over ruthenium sulfides for unsupported catalysts, and rhodium sulfides for transition metal (TM) sulfides supported on carbon. Such TMs exhibit high intrinsic HDS activity that can be enhanced by using appropriate carriers, preparation and pre-activation methods. On the other hand, in order to achieve deep hydrodesulfurization it is important to examine the reactivity of refractory sulfur compounds, such as 4,6-dimethyl- dibenzothiophene (4,6-DMDBT). Therefore, in the present study, we investigated the HDS of dibenzothiophene (DBT) over various metals (Co, Mo, Ni, Cr, W, Pd, Pt, Ru, Rh, Re, Ir) supported on alumina. For the TM catalysts showing the highest HDS activity, the effects of carrier, metal loading and preactivation methods on DBT and 4,6-DMDBT HDS activity and product selectivity were examined. The results showed that the alumina-supported rhodium catalyst exhibited the highest HDS activity of the 2nd row. Especially, Rh/Al2O3 catalysts exhibited a superior HDS performance compared with a conventional CoMo alumina catalyst (based on the specific activity per metal atom). In addition, the HDS activities of such catalysts could be further increased for instance by changing the support or the preactivation method. The behavior of sulfur on the working catalyst using 35S tracer was also introduced.
