Hydrodesulfurization of Dibenzothiophene Catalyzed by Supported Metal Carbonyl Complexes(Part 8) Hydrodesulfurization of 35S-Labeled Dibenzothiophene on Alumina-supported Ruthenium Sulfide-Cesium Catalysts.

Abstract

In hydrodesulfurization (HDS) of 35S-labeled dibenzothiophene ([35S]DBT) catalyzed by alumina-supported ruthenium carbonyls-cesium hydroxide systems, the role of cesium was elucidated by tracing the behavior of 35S on the working ruthenium catalysts. The HDS of [35S]DBT was performed in conditions: 280-320°C, 50kg/cm2, WHSV 14h-1, H2 18l/h, DBT 1wt%, precursor Ru3(CO)12-nCsOH/Al2O3 (n=0, 3, 6 or 9). During the reaction with sulfided catalysts, the changes in the radioactivities of unreacted [35S]DBT and product [35S]H2S with reaction time were monitored. The rate constant (krelease) of release of [35S]H2S was estimated from the first order plots of the increasing and decreasing radioactivities of product [35S]H2S. The values of kreleased ecreased with increase in the amount of cesium added, indicating that the mobility of sulfur on the catalysts decreased by the addition of cesium. On the contrary, the amount of labile sulfur on the catalyst (S0), which was calculated from the maximum amount of 35S accommodated on the catalyst, increased with increase in the amount of cesium added and reached the maximum at Ru:Cs=1:2, which was kept with further addition of cesium (Ru:Cs=1:3). This shows that the active sites on the catalyst were not poisoned because S0 did not decrease with the addition of excess amount of cesium. This maximum value of S0 at Ru:Cs=1:2 corresponds to RuS1.52. Assuming that ruthenium species are present as RuS2, 76% of sulfur on the catalyst is labile. This indicates that the dispersion of ruthenium species could be significantly high. Further, it is suggested that cesium promoted the C-S bond scission of DBT and increased the activity by stabilizing Ru-S bonds for ruthenium sulfide.