Deep hydrodesulfurization of 4,6-dimethydibenzothiophene over CoMoS/TiO2 catalysts: Impact of the TiO2 treatment

Abstract

Mesostructured titania as support for the CoMoS active phase in deep hydrodesulfurization (HDS) of 4,6-dimethydibenzothiophene (4,6-DMDBT) leads to an increase of the intrinsic HDS activity and a higher selectivity for direct desulfurization (DDS) for HDS reaction in contrast with the conventional CoMoS/alumina catalyst. The temperature treatment of the mesostructured TiO 2 support, modifies the catalyst's activity for the transformation of 4,6-DMDBT. The higher total and HDS activities were obtained after treatment at 380°C corresponding to the higher specific surface area and to a mesostructured TiO 2 material with a semi-crystalline anatase framework. Beyond 550°C, the specific surface area decreases strongly corresponding to a complete crystallization of the mesopores walls into anatase structure. Moreover, the temperature under which the support is treated prior its impregnation has no impact on the selectivity of the transformation routes of the sulfur compound.

Effect of Mesostructured Zirconia Support on the Activity and Selectivity of 4,6-Dimethydibenzothiophene Hydrodesulfurization

“…However, the same tendency was noted for the activity per atom of Mo; we can thus assume that the difference in activity and selectivity may have been due to a modification of the active sites which are the molybdenum atoms. This involved different interactions with the support because of the presence of the amorphous phase, which will lead to modifications of the electronic properties, as already observed with TiO 2 [20]. Indeed, in a recent study [29], we showed that the prepared amorphous mesostructured ZrO 2 exhibited a high thermal stability up to 400 • C. We can thus assume that the change in selectivity was mainly due to the presence of this amorphous phase, which likely modified the intermediates of reaction by favoring the ones involved in the direct rupture of the C-S bond [5], and/or by modifying the properties of the active phase.…”

“…Amorphous mesostructured ZrO 2 was prepared according the procedure described in reference [29]. The wet impregnation used CoN 2 O 6 , 6H 2 O, 99.00% Si (Sigma-Aldrich Chemie S.a.r.l., Saint-Quentin Fallavier, France) and (NH 4 ) 6 Mo 7 , 6H 2 O, 99.98% (Sigma-Aldrich Chemie S.a.r.l., Saint-Quentin Fallavier, France) precursors and was performed under the same conditions as the ones reported in Reference [20].…”

“…As reported in previous papers [20], the catalyst was sulfided in situ before the catalytic reaction, in the presence of hydrogen by the hydrogen sulfide, resulting from the decomposition of dimethyl disulfide (DMDS). The sulfurizing charge consisted of a mixture of n-heptane and DMDS (5 by weight).…”

“…Ishihana et al [19] highlighted the role of Ti 3+ , which could have an electronic effect on the active phase. More recently, by comparison with conventional catalysts, we have shown that a change of selectivity for the hydrodesulfurization (HDS) of 46DMDBT is obtained when the active phase is dispersed on mesostructured titania [20]. This behavior has been correlated for one part of the intrinsic properties of the mesostructured titania [20].…”

Controllable Synthesis of Defect-Rich CoMoS Catalysts with Different Morphologies for the Ultradeep Hydrodesulfurization of 4,6-Dimethydibenzothiophene

“…The production of sulfur-free fuel oil from petroleum materials, especially from low-grade diesel, has been a pressing mission because of increasingly stringent standards on the maximum sulfur content of diesel fuel. − However, the production of ultraclean diesel is limited by the refractory sulfur compound 4,6-di­methyl­di­benzo­thio­phene (4,6-DMDBT) with alkyl groups at the 4 and 6 positions that resulted in the space-shield effect. , Industrially, hydrodesulfurization (HDS) is the most effective and widely used desulfurization technology to reduce the sulfur concentration of fuel oil to below 10 ppm. Co­(Ni)­MoS supported over Al 2 O 3 is a commonly used HDS catalysts in the petroleum refining industry.…”