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The effect of the Cs addition on the H 2 S 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 RuCs catalyst was more inhibited by H 2 S 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 H 2 S inhibition over Ru and RuCs catalysts. We found that the heats of adsorption of DBT and H 2 S on the RuCs 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 RuCs catalyst on the DBT HDS activity was investigated by using 35 S-tracer experiments. The results suggested that while the RuCs catalyst was more inhibited by H 2 S, the RuS bonds were more stable on this catalyst than on the Ru catalyst. This RuS 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 RuCs catalyst than over the Ru catalyst, despite a greater H 2 S inhibition on the former. |
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