Effect of molybdenum and tungsten on Co/MSU as hydrogenation catalysts

A zirconium-doped mesoporous silica (MSU) was used as a support for Co, CoMo, and CoW catalysts with varying Mo and W loadings. Their activity was tested in the hydrogenation and hydrogenolysis/hydrocracking of tetralin under varying temperatures, experimental conditions, and concentrations of dibenzothiophene (DBT) in a high-pressure, fixed-bed, continuous-flow stainless steel catalytic reactor operating at a pressure of 6.0 MPa. Textural, structural, and metallic properties were studied by XRD, XPS, H2-TPR, NH3-TPD, and N2 adsorption–desorption isotherms. The results indicate that the addition of a promoter, such as W and Mo, improves their catalytic properties in hydrogenation reactions with or without DBT in the feed compared with catalysts containing only cobalt as an active phase. The hydrogenation yield is higher in the case of molybdenum- and tungsten-promoted catalysts, but the molybdenum-promoted catalysts enhances the yield most significantly; with a catalyst containing 5 wt% of Mo at 315 °C with a contact time of 3.6 s and an H2:tetralin molar ratio of 15, the hydrogenation yield is 93.5%, whereas a catalyst containing 15 wt% of Co gives a yield of 74.0%. The yield of hydrogenolysis/hydrocracking is lower for the promoted catalysts, although those containing tungsten exhibit an intermediate behavior between those containing only cobalt or cobalt and molybdenum as active phases. However, catalysts with molybdenum as a promoter agent have very good thiotolerant properties. With 15 wt% of cobalt and 5 wt% of molybdenum, when 850 ppm of DBT is added to the feed, the conversion of tetralin is nearly 52.0% with a 44.0% yield of hydrogenation products after 6 h on stream; for a catalyst with 15% of cobalt, these values are only 13.1 and 0.9%, respectively, after 5 h on stream.