Inhibiting effect of H2S on the DBT HDS activity of Ru-based catalysts—effect of the Cs addition

The effect of the Cs addition on the H2S inhibition and subsequently on the DBT HDS activity over Ru-based catalysts was investigated. In good agreement with a previous study, the HDS activity over a Ru catalyst containing cesium was much higher than that over the same Ru catalyst without cesium. On the other hand, the HDS activity of the RuCs catalyst was more inhibited by H2S than that of the Ru catalyst at 260 °C. Thus, kinetic parameters were calculated using a Langmuir–Hinshelwood model to determine the mechanism of the H2S inhibition over Ru and RuCs catalysts. We found that the heats of adsorption of DBT and H2S on the RuCs catalyst were higher than on the Ru catalyst, indicating that the sulfur-containing species adsorb more strongly on the catalyst containing cesium. Subsequently, the role of cesium in the RuCs catalyst on the DBT HDS activity was investigated by using 35S-tracer experiments. The results suggested that while the RuCs catalyst was more inhibited by H2S, the RuS bonds were more stable on this catalyst than on the Ru catalyst. This RuS bond stabilization was responsible for the stabilization of the active phase, which allowed creation of a greater amount of sulfur atoms potentially labile. Thus, that explained the better HDS activity over the RuCs catalyst than over the Ru catalyst, despite a greater H2S inhibition on the former.