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 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 krelease decreased 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. IntroductionRecently, deep desulfurization of light gas oil has been one of urgent researches in the world and much attention has been focused on the development of new catalyst for deep desulfurization1),2). Among a number of attempts made to develop the new catalyst, nonsupported3)-5) and supported6)-12) ruthenium sulfides were found to be the most active for hydrodesulfurization (HDS) of thiophenes in transition metal sulfides. Pecoraro and Chianelli3) initially reported that ruthenium sulfide is the most active for HDS of dibenzothiophene (DBT) among the transition metal sulfides. Supporting ruthenium sulfide appropriately is an attractive approach to increase catalytic activity. Harvey and With these catalysts, however, the HDS activity was rather low, probably because sulfidation of ruthenium species was incomplete and RuS2 is unstable on a support in hydrogen atmosphere. Further, these HDS reactions were performed in atmospheric pressure, and so far the activities of supported ruthenium sulfide in a pressurized flow system have not yet been clarified in comparison with those of Co-Mo/Al2O3and Ni-Mo/Al2O3. Recently, the authors reported that, in HDS of dibenzothiophene (DBT), the catalysts derived from supported metal carbonyls showed catalytic activity higher than those from conventional catalysts11),12). The cesium promoted ruthenium catalysts revealed that the activity is comparable with that of conventional Co-Mo...

Role of Cs on Hydrodesulfurization Activity of RuS2 Catalysts Supported on a Mesoporous SBA-15 Type Material

“…In this sense, the presence of cesium does not favor a good dispersion of the RuS 2 active phase, that is, less cesium atoms are close to ruthenium atoms to stabilize the Ru-S bond and therefore the amount of labile sulfur also decreases by decreasing the dispersion. 42 This is in agreement with our H 2 -TPRS experiments that show an increase of the amount of H 2 S released with a decrease of cesium content in the catalysts, indicating that sulfur lability is inhibited in the presence of a large amount of Cs on the catalyst surface. The low dispersion of the active phase and the decrease in the sulfur lability might explain the observed decrease in the catalytic activity with an increase of Cs content in the catalysts (vide infra).…”

“…While the promoter effect of cesium on γ-Al 2 O 3 is positive, on a mesoporous material such as SBA-15, the effect is negative. In this sense, the presence of cesium does not favor a good dispersion of the RuS 2 active phase, that is, less cesium atoms are close to ruthenium atoms to stabilize the Ru−S bond and therefore the amount of labile sulfur also decreases by decreasing the dispersion . This is in agreement with our H 2 -TPRS experiments that show an increase of the amount of H 2 S released with a decrease of cesium content in the catalysts, indicating that sulfur lability is inhibited in the presence of a large amount of Cs on the catalyst surface.…”

“…They reported that the location of cesium is close to the ruthenium species, and the dispersion of ruthenium species increases with an increase in the Cs/Ru ratio; furthermore, the presence of cesium in close proximity to ruthenium atoms strengthens the bond of ruthenium and sulfur, stabilizing ruthenium sulfide. In later works, , they elucidated the behavior of sulfur on the ruthenium catalysts and the role of cesium in HDS by radioisotope tracer methods, concluding 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 increased with the amount of cesium added and reached the maximum at Ru/Cs = 1:2 suggesting that the Ru species in the catalyst was successfully dispersed on alumina.…”

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

“…Further, we previously reported the structure of the active phase on sulfided Ru-Cs/Al 2 O 3 catalysts [9,23] (Fig. 15).…”