Jung Joon Lee

Hydrodesulfurization of DBT, 4-MDBT, and 4,6-DMDBT on fluorinated CoMoS/Al2O3 catalysts

CoMoS/Al2O3 catalysts containing different amounts of fluorine have been tested for the hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT), and the results have been analyzed based on three fundamental reactions involved in the HDS mechanism: hydrogenation of the aromatic ring, hydrogenolysis of the C–S bond, and migration of methyl groups in the ring structure. Fluorine addition to the catalyst promotes all of these three reactions due to the enhancement of two factors: the metal dispersion and the catalyst acidity. The extents that the HDS rates are improved by fluorine addition increase in the order of DBT<4-MDBT<4,6-DMDBT. Product distributions change in characteristic trends with fluorine addition depending on the individual reactants. That is, in DBT HDS, CHB obtained by the ring saturation is enhanced more than BP produced by the direct desulfurization, while the opposite trend is observed in 4-MDBT HDS. 4,6-DMDBT HDS shows an intermediate trend: products of both types are promoted to similar extents on fluorinated catalysts. The migration of methyl groups in the reactant ring structure due to the catalyst acidity, which reduces the steric hindrance to the C–S bond, is responsible for the characteristic trends in the product distribution observed with the individual reactants.

Performance of CoMoS catalysts supported on nanoporous carbon in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Abstract A new type of nanoporous carbon with a large surface area and mesoporosity was prepared and used as a support for a hydrodesulfurization (HDS) catalyst. The overall activity of CoMoS catalysts for the HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) is affected by the type of support used for preparing the catalyst and decreases in the order of CoMo /( nanoporous carbon )> CoMo /( activated carbon )> CoMo / Al 2 O 3 . The surface area of activated carbon is the largest among these three types of supports but is significantly lowered after metal loading during the preparation of the catalyst. On the other hand, the surface areas of the other two supports are largely preserved after metal loading. The intrinsic activity of the catalysts, estimated by dividing the overall HDS rate by the amount of NO adsorbed on the catalyst, shows a trend that is different from that for the overall activity, and follows the order of CoMo /( nanoporous carbon )≈ CoMo / Al 2 O 3 > CoMo /( activated carbon ) . The low intrinsic activity of CoMo/(activated carbon) compared to that of the other two catalysts, particularly in the case of 4,6-DMDBT HDS, is obtained because the diffusion of reactants into the catalyst pores is significantly limited. This is not observed with other catalysts supported on nanoporous carbon and alumina. From the results of this study, we conclude that nanoporous carbon is a promising support for HDS catalysts, compared to conventional supports such as alumina and activated carbon, because it has a large surface area and a high mesoporosity, both of which are beneficial to the preparation of highly dispersed metal catalysts without significant pore blocking due to the dispersed metal particles.

Performance of NiMoS/Al2O3 prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Different types of NiMoS/Al2O3 catalysts were prepared by a combination of sonochemical synthesis and chemical vapor deposition (CVD) methods. The performance of the prepared catalysts in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was compared with that of catalysts prepared using the impregnation method. Ni that was selectively added to the MoS2 surface by CVD promoted the HDS activity to a greater extent than Ni added by impregnation, particularly for the direct-desulfurization (DDS) route of the reaction. This was attributed to the former method allowing an intimate interaction between the added Ni and the MoS2 surface, as confirmed by the XPS analysis of the catalysts. NiMoS/Al2O3 prepared by a combination of two methods, sonochemical and CVD, showed improvement in activity over the catalyst prepared by impregnation. Moreover, the hydrogenation (HYD) activity of the former catalyst was significantly higher than that of the latter due to the dominant effect of sonochemical synthesis on the activity. The improvement in activity was greater for the HDS of 4,6-DMDBT than for the HDS of DBT.

Properties of sonochemically synthesized, highly dispersed MoS2/Al2O3 catalysts for the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

The sonochemical decomposition of molybdenum hexacarbonyl in the presence of sulfur and alumina generated a highly dispersed MoS 2 /Al 2 O 3 catalyst. The catalysts were tested for the hydrodesulfurization (HDS) of dibenzothiophene and 4,6-dimethyldibenzothiophene. This sonochemically synthesized catalyst prepared by the direct sonication of molybdenum hexacarbonyl and sulfur exhibited superior HDS and hydrogenation activity compared to that of the catalysts prepared by other methods. The nitric oxide chemisorption studies of the catalysts revealed that the enhanced HDS activity resulted from the improved dispersion of the active species on the support. Temperature programmed reduction indicated that the poisoning of catalytically active sites by hydrogen sulfide did not occur on the sonochemically prepared catalysts. On the other hand, the catalysts prepared by the calcination and sulfidation of sonochemically generated Mo 2 C/Al 2 O 3 showed low HDS activity due to the agglomeration of the surface particles during the heat treatments.

66 Hydrodesulfurization of dibenzothiophene and 4, 6-dimethyldibenzothiophene using fluorinated NiMoS/Al2O3 catalysts

A series of fluorinated NiMo/Al2O3 catalysts containing different amounts of fluorine were prepared and their activity with respect to the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was examined. The addition of fluorine modified two properties of the catalyst, namely the dispersion of metal and the acidity of the catalyst. In the HDS of DBT, the catalytic activity increased with added fluorine up to 0.5 wt.%, and then decreased with further fluorine addition due to the decrease in the surface area of the catalyst. In the HDS of 4,6-DMDBT, catalytic activity increased in proportion to the fluorine content up to 5.0 wt.%. This is possibly due to the increased surface acidity that results from the addition of fluorine.