HYDRODESULFURIZATION OF DIBENZOTHIOPHENE CATALYZED BY SUPPORTED METAL-CARBONYL-COMPLEXES (PART 8) - HYDRODESULFURIZATION OF S-35 LABELED DIBENZOTHIOPHENE ON ALUMINA-SUPPORTED RUTHENIUM-SULFIDE CESIUM CATALYSTS

In hydrodesulfurization (HDS) of S-35-labeled dibenzothiophene ([S-35] DBT) catalyzed by alumina-supported ruthenium carbonyls-cesium hydroxi de systems, the role of cesium was elucidated by tracing the behavior of S-35 on the working ruthenium catalysts. The HDS of [S-35]DBT was p erformed in conditions: 280-320 degrees C, 50 kg/cm(2), WHSV 14 h(-1), H-2 18 l/h, DBT 1 wt%, precursor Ru-3(CO)(12)-nCsOH/Al2O3 (n=0, 3, 6 or 9). During the reaction with sulfided catalysts, the changes in the radioactivities of unreacted [S-35]DBT and product [S-35]H2S With rea ction time were monitored. The rate constant (k(release)) Of release o f [S-35]H2S was estimated from the first order plots of the increasing and decreasing radioactivities of product [S-35]H2S. The values of k( release) decreased with increase in the amount of cesium added, indica ting that the mobility of sulfur on the catalysts decreased by the add ition of cesium. On the contrary, the amount of labile sulfur on the c atalyst (S-0), which was calculated from the maximum amount of S-35 ac commodated On the catalyst, increased with increase in the amount of c esium 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 sit es on the catalyst were not poisoned because S-0 did not decrease with the addition of excess amount of cesium. This maximum value of S-0 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 indicat es that the dispersion of ruthenium species could be significantly hig h. Further, it is suggested that cesium promoted the C-S bond scission of DBT and increased the activity by stabilizing Ru-S bonds for ruthe nium sulfide.