Search

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&z.sbnd;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&z.sbnd;Cs catalysts. We found that the heats of adsorption of DBT and H2S on the Ru&z.sbnd;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&z.sbnd;Cs catalyst on the DBT HDS activity was investigated by using 35S-tracer experiments. The results suggested that while the Ru&z.sbnd;Cs catalyst was more inhibited by H2S, the Ru&z.sbnd;S bonds were more stable on this catalyst than on the Ru catalyst. This Ru&z.sbnd;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&z.sbnd;Cs catalyst than over the Ru catalyst, despite a greater H2S inhibition on the former. [Copyright &y& Elsevier]

Alumina-supported ruthenium–cesium catalysts were presulfided using [35S]H2S pulse tracer method to evaluate their sulfidation state. Subsequently, using these previously 35S-labeled catalysts, HDS reactions of dibenzothiophene (DBT) were performed and the mobility of 35S introduced during the presulfidation stage was investigated. The results showed that the amount of labile sulfur (S0) was much smaller than the total amount of sulfur accommodated on the catalyst (Stotal). DBT conversion and Stotal increased linearly with Ru content. In a second part, labile sulfur amount was also determined under the catalyst working conditions and different results were obtained. Indeed, when the catalysts were marked with [35S] and with [35S]DBT under HDS reaction conditions, the obtained labile sulfur quantities (S0A) were significantly higher than the ones measured during the presulfidation stage (S0). These results showed that the labile sulfur is not formed on RuCs catalysts until the HDS reaction proceeds, which is quite different from that reported before for Mo, Pt, or Pd systems. [Copyright &y& Elsevier]