HDS, HDN and HYD activities and temperature-programmed reduction of unsupported transition metal sulfides

Several transition metal sulfides have been shown to exhibit high catalytic activities in various hydrotreating reactions. The simultaneous catalytic activities for hydrodesulfurization of dibenzothiophene, hydrodenitrogenation of indole and hydrogenation of naphthalene have been studied using high surface area bulk sulfides: NbS2, MoS2, ReS2, RuS2 and Co9S8. The metal-sulfur bond strengths have been assessed by temperature-programmed reduction of H2S-pretreated sulfides, and it is demonstrated that this pretreatment is necessary to obtain reliable TPR data for the sulfides. The catalytic HDS activity is shown to follow the trend in the metal-sulfur bond strengths estimated by this improved method. Furthermore, the metal-sulfur bond strengths determined this way follow the trend estimated previously from theory. The TPR data suggest that a large number of sulfur vacancies exist in active catalysts under industrial reaction conditions. Such vacancies have recently been observed on model catalysts by use of STM.