Dibenzothiophene Reaction Research Articles

Characterizations and HDS performances of sulfided NiMoW catalysts supported on mesoporous titania-modified SBA-15

This work studies the effect of the support modifications (SBA-15) with Ti by using a ternary system as an active phase (Ni, Mo, W). Calcined and sulfided catalysts were characterized by a variety of techniques such as XRD, SBET, TPR, TPD-NH3, DRS-UV–vis, micro-Raman spectroscopy and HRTEM. Sulfided catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene (DBT) performed in a batch reactor at 320°C and total hydrogen pressure of 800psi. This reaction was selected for the catalyst screening because DBT is a typical sulfur-containing hydrocarbon present in high-boiling petroleum fractions and coal derived liquids and the absence of any diffusion limitation for DBT molecule to entry into the porous structure of the SBA-15 supported catalysts. We observed that the incorporation of Ti did not decrease the catalytic activity in the HDS of DBT reaction except for Si/Ti=40 catalyst. UV–vis analyses show a higher amount of tetrahedral species for CAT/40TiS15 in counterpart with CAT/60TiS15 that showed a lower amount of those species however, the lower amount of Ti in the catalyst (CAT/60TiS15) showed the highest hydrogenation capability among the catalysts studied (HYD/DDS=0.81) despite the main route in the HDS of DBT reaction was the direct desulfurization (DDS) pathway (selectivity).

Influence of HZSM-5 content on behavior of CoMo/HZSM5-HMS composite catalysts in hydrodesulphurization of dibenzothiophene

CoMo-supported micro/mesoporous catalysts (CoMo/HZSM5(x)-HMS) were synthesized by varying the weight percent of zeolite (10, 20, 30 and 40 wt%). Catalytic functionalities were investigated for hydrodesulphurization reaction of dibenzothiophene over a wide temperature range of 250–400 °C. Characterization methods as XRD, XRF, FT-IR, UV–Vis DRS, NH3-TPD, H2-chemisorption, nitrogen adsorption–desorption and TGA confirmed the obtained results from these catalysts. A significant enhancement of the catalytic activity was observed for the catalysts supported on CoMo/HZSM5(20)-HMS at T = 350 °C (>97%).

Surface chemistry and catalytic properties of VOX/Ti-MCM-41 catalysts for dibenzothiophene oxidation in a biphasic system

A series of vanadium oxide supported on Ti-MCM-41 catalysts was synthesized via the incipient impregnation method by varying the vanadia loading from 5wt% to 10, 15, 20 and 25wt%. These catalysts were characterized by a variety of advanced techniques for investigating their crystalline structure, textural properties, and surface chemistry information including surface acidity, reducibility, vanadium oxidation states, and morphological features. The catalytic activities of the catalysts were evaluated in a biphasic reaction system for oxidative desulfurization (ODS) of a model diesel containing 300ppm of dibenzothiophene (DBT) where acetonitrile was used as extraction solvent and H2O2 as oxidant. ODS activity was found to be proportional to the V5+/(V4++V5+) values of the catalysts, indicating that the surface vanadium pentoxide (V2O5) was the active phase. Reaction temperature would influence significantly the ODS efficiency; high temperature, i.e., 80°C, would lead to low ODS reaction due to the partial decomposition of oxidant. All the catalysts contained both Lewis and Brønsted acid sites but the former was predominant. The catalysts with low vanadia loading (5 or 10 wt%V2O5) had many Lewis acid sites and could strongly adsorb DBT molecule via the electron donation/acceptance action which resulted in an inhibition for the reaction of DBT with the surface peroxometallic species. The catalyst with high vanadia loading (25wt%V2O5/Ti-MCM-41) showed the highest catalytic activity and could remove 99.9% of DBT at 60°C within 60min.

Characterization and HDS performance of sulfided CoMoW catalysts supported on mesoporous Al-SBA-16 substrates

In this work, the catalytic activity of ternary Co–Mo–W/Al-SBA-16 systems was investigated in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT) performed in a batch reactor at 350°C and total H2 pressure of 33.8bar. The synthesized materials were characterized by a variety of techniques (chemical analysis, N2 adsorption–desorption isotherms, XRD, TPR, TPD-NH3, FTIR of adsorbed pyridine, DRS-UV–vis, HRTEM and XPS). By applying the direct synthesis method, high surface area substrates with Al3+ incorporated into the silica framework. The activity results indicate that all CoMoW/Al-SBA-16 catalysts were active in the HDS of DBT, the largest activity was found in the catalyst with the highest Al-content. This behavior was explained in terms of its largest specific area and good dispersion of the metal sulfide phases having average size of 3.3nm (from HRTEM). Moreover, FT-IR spectroscopic study of adsorbed pyridine indicated Al incorporation into a SBA-16 substrate produces both Brønsted and Lewis acidities, which are beneficial for the HDS of DBT. All catalysts showed a high selectivity towards biphenyl indicating that HDS of DBT reaction proceeds mainly via direct desulfurization (DDS) reaction pathway.

Crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å

The dibenzothiophene (DBT) monooxygenase DszC, which is the key initiating enzyme in "4S" metabolic pathway, catalyzes sequential sulphoxidation reaction of DBT to DBT sulfoxide (DBTO), then DBT sulfone (DBTO2). Here, we report the crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å. Intriguingly, two distinct conformations occur in the flexible lid loops adjacent to the active site (residue 280-295, between α9 and α10). They are named "open"' and "closed" state respectively, and might show the status of the free and ligand-bound DszC. The molecular docking results suggest that the reduced FMN reacts with an oxygen molecule at C4a position of the isoalloxazine ring, producing the C4a-(hydro)peroxyflavin intermediate which is stabilized by H391 and S163. H391 may contribute to the formation of the C4a-(hydro)peroxyflavin by acting as a proton donor to the proximal peroxy oxygen, and it might also be involved in the protonation process of the C4a-(hydro)xyflavin. Site-directed mutagenesis study shows that mutations in the residues involved either in catalysis or in flavin or substrate-binding result in a complete loss of enzyme activity, suggesting that the accurate positions of flavin and substrate are crucial for the enzyme activity.

Effect of Organic Sulfide in Precursors on the Pore Structure of High‐Surface Area Activated Carbons

AbstractAnalogous precursors in the presence of sulfide dibenzothiophene (DBT) were employed to prepare high‐surface area activated carbons (HAC) by KOH chemical activation, in order to investigate the influence of the DBT content on the pore structure of the resultant HAC. The results indicate that the DBT in the precursor can react with and consume a certain amount of the activation agent KOH, thus reducing the actual KOH/coke ratio, which imposes a clear negative effect on the pore structure development. However, regardless of how high the DBT content is in the precursor, no residual sulfur is found in the obtained HAC. The HAC with developed porosity can also be achieved by just increasing the KOH dosage to compensate for the amount consumed in the DBT reaction during the activation process, which provides a high value‐added utilization way for organic sulfur‐containing minerals.

The use of a natural Mexican zeolite as support of NiMoW sulphide hydrotreating catalysts

In order to examine the influence of type of metal precursor on the hydrodesulfurization (HDS) activity of synthetized samples, a series of ternary Ni–Mo–W catalysts supported on a natural Mexican zeolite (clinoptilolite) were prepared by sequential wet impregnation of the zeolite support with different thiosalts of W and Mo, and Ni(NO3)2·6H2O. The synthetized samples were characterized by N2 adsorption–desorption isotherms at −196°C, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX/SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) techniques. The catalysts activity was evaluated in the HDS of dibenzothiophene (DBT) reaction performed in a batch reactor at 350°C and 3.1MPa of total hydrogen pressure. The activity tests demonstrated that the best catalyst was the NiMoW-H/zeo sample synthesized from ammonium thiosalts. The use of tetraalkylammonium thiometalates as metal precursors led to the decrease in the HDS activity. The most active catalyst in the HDS of DBT reaction showed the largest density of active phases on the support surface determined from HRTEM measurements.

Effect of gallium loading on the hydrodesulfurization activity of unsupported Ga2S3/WS2 catalysts

The effect of gallium incorporation into unsupported tungsten sulfide catalysts was investigated in dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction. The Ga/WS2 catalysts with variable gallium loadings (0.5–2.5wt%) were prepared by decomposition of W-thiosalt followed by impregnation with the Ga salt precursor. The samples were characterized by a variety of techniques: ICP-AES, N2 adsorption–desorption at −196°C, XRD, SEM, XPS, FTIR of CO chemisorbed and TPD-NH3. The last two techniques showed that gallium addition has a strong effect on the morphology of the tungsten sulfide phase by modifying the coordinately unsaturated sites (CUS) of the WS2 phase and total catalyst acidity. The HDS of DBT reaction (T=320°C, PH2=5.5 MPa) was found to proceed through two main parallel pathways: hydrogenation (HYD) and direct desulfurization (DDS), the latter being the main reaction route. With respect to Ga-free WS2 sample, all Ga-loaded catalysts showed an increase of HDS activity via hydrogenation (HYD) pathway and additional DBT cracking. The 1.5% Ga/WS2 catalyst was the most active among the catalysts studied. On the basis of the catalyst structure–activity relationship, this was linked to a homogeneous distribution of Ga species on the surface of WS2 (SEM), the largest amount of acid sites (from TPD-NH3) and the largest amount of “corner sites” on the WS2 slabs determined by FTIR-CO. For the Ga-containing catalysts, an increase of DBT transformation via HYD route was explained in terms of the formation of new CUS sites on WS2 phase as well as to an increase of the catalyst acidity. Acidity is a key requirement influencing on DBT cracking.

Role of phosphorus in carbon matrix in desulfurization of diesel fuel using adsorption process

Adsorptive removal of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from model diesel fuel with 20ppmw total concentration of sulfur was investigated on polymer-derived carbons with incorporated heteroatoms of oxygen, sulfur and phosphorus. The materials before and after exposure to model diesel fuel were characterized using adsorption of nitrogen, thermal analysis, potentiometric titration, XPS and elemental analysis. The selectivities for DBT and DMDBT adsorption were calculated with reference to naphthalene. The results indicated that the presence of phosphorus, especially in the form of pyrophosphates and P2O5, increases the capacity and selectivity for removal of dibenzothiophenes. It also affects the adsorption mechanism. Phosphorus suppresses oxidation reactions of DBT and DMDBT. Owing to a possible location of bulky phosphorus groups in pore with sizes between 1 and 3nm thiophenic molecules are strongly adsorbed there via dispersive forces. Acidic environment also enhances adsorption via acid–base interactions. Physical adsorption mechanism and stability of surface make these carbons attractive candidates for thermal regeneration.

SBA-15 as Support for Ni–MoS2 HDS Catalysts Derived from Sulfur-containing Molybdenum and Nickel Complexes in the Reaction of HDS of DBT: An All Sulfide Route

MoS2 HDS catalysts promoted with Ni supported on SBA-15 were synthesized from sulfur containing Mo (ammonium thiomolybdate, ATM, and tetramethylammonium thiomolybdate, TMATM) and a Ni complex (Nickel diethylthiocarbamate, NiDETC). The catalysts have been characterized by X-ray diffraction (XRD), N-2-physisorption and High-resolution transmission electron microscopy (HRTEM). The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P-H2 = 3.4 Mpa. In comparison with the impregnation mode, the nature of the employed thiomolybdate complex shows a stronger influence on the MoS2 morphology and consequently on the HDS activity of DBT. A similar high HDS activity to a commercial NiMo/gamma-Al2O3 catalyst despite the pronounced stacking number is shown for a Ni MoS2/SBA-15 catalyst derived from ATM. The catalysts derived from TMATM showed lower HDS activities compared to the catalysts obtained from ATM precursors due to probably the presence of closed shell structures (nano-onions) of MoS2 which offer significantly smaller amount of HDS active sites (edge sites). Moreover, the HYD/DDS ratios are interestingly higher with respect to the HYD/DDS ratio of the commercial NiMo/gamma-Al2O3 catalyst which could be ascribed to the generation of multilayered MoS2 active phase.

SBA-15 as Support for MoS2 and Co-MoS2 Catalysts Derived from Thiomolybdate Complexes in the Reaction of HDS of DBT

Molybdenum sulfide and cobalt-molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by thermal decomposition of ammonium thiomolybdate (ATM). SBA-15 was synthesized at 353 K and 413 K to obtain pore diameters of about 6 and 9 nm, respectively. The (Co)-MoS2/SBA-15 catalysts were characterized with X-ray diffraction (XRD), N2-physisorption and high-resolution transmission electron microscopy (HRTEM). HRTEM images give evidence for the presence of a poorly dispersed MoS2 phase with long MoS2 slabs and a pronounced MoS2 stacking. The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P = 3.4 MPa. The Co-MoS2/SBA-15 materials show a relatively high catalytic activity with a strong preference for the direct desulfurization (DDS) pathway. This is an interesting result in view of the significant stacking of MoS2 particles and the size of the slabs. The generation of the catalytically active CoMoS phase and a large number of coordinately unsaturated sites (CUS) may explain the high performance of Co promoted MoS2/SBA-15 catalysts in the HDS reaction. A confinement effect of the mesoporous channels of SBA-15 is observed for the unpromoted MoS2/SBA-15 catalysts. SBA-15 with 9 nm channel diameter with 11 wt.% Mo loading shows a higher selectivity for the hydrogenation pathway than SBA-15 with 6 nm channel and 16 wt.% Mo loading.

Influence of reduction temperature and metal loading on the performance of molybdenum phosphide catalysts for dibenzothiophene hydrodesulfurization

Two series of alumina-supported molybdenum phosphide (MoP) catalysts with low and high metal loadings were prepared by temperature-programmed reduction of the oxidic catalyst precursors in hydrogen to different temperatures (823, 923, 1023 and 1123 K, respectively). Effects of reduction temperature and metal loading on the surface distribution and the type of species formed were studied by TPR, SBET, XRD, HRTEM, 31P NMR, 27Al NMR and in the reaction of dibenzothiophene (DBT) hydrodesulfurization (HDS) performed in a flow reactor at 553 K and total hydrogen pressure of 3.4 MPa. HRTEM and 31P NMR confirmed formation of MoP phase on all catalysts. The 9.9 wt% Mo catalyst activated at lowest reduction temperature (823 K) was found to be most active among the catalysts studied. The presence of a low amount of Mo0 species on the surface of this catalyst does not appear to be a drawback for the catalytic activity. The increase in both metal loading (from 9.9 to 15 wt% Mo and from 3.2 to 4.8 wt% P) and reduction temperature (from 823 to 1123 K) was found to be detrimental for HDS activity due to sintering of active phase, and also to decrease in specific area and formation of phosphate species.

Effect of Al and Ti content in HMS material on the catalytic activity of NiMo and CoMo hydrotreating catalysts in the HDS of DBT

Al- and Ti-containing HMS materials, with a Si/M (Me = Al(Ti)) molar ratio equal to 40, were used as supports for preparing NiMo and CoMo HDS catalysts. The supports and catalysts were characterized by N 2 adsorption–desorption ( S BET), X-ray diffraction (XRD), UV–vis diffuse reflectance (DRS UV–vis), temperature-programmed reduction (TPR) and Raman spectroscopy. The catalysts were tested in the hydrodesulphurization (HDS) reaction of dibenzothiophene (DBT). All supported NiMo and CoMo catalysts on Al-HMS and Ti-HMS substrates showed higher catalytic activity than their Me-free counterparts. We found two interesting correlations between the structure and chemical coordination of the supported oxide precursors and catalytic activity. The differences observed in catalyst performance are attributed to the structure and specific electronic properties of the supported active species. From our results, it appears possible to optimize the Al- and Ti-loading to maximize the HDS activity.

Structure and catalytic properties of molybdenum sulfide nanoplatelets

Abstract A nanostructured form of molybdenum disulfide/dioxide was prepared by a two-step hydrothermal/gas phase reaction carried at high-temperature sulfidation of molybdenum in H 2 S/H 2 for 2 h. The material was composed of a solid MoO 2 core with MoS 2+ x crystallites nucleating on its surface. Most of the MoS 2+ x have the shape of a single stacked platelet, which are 12–30 nm long and are about one MoS 2 unit cell wide. High-resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), in high-angle annular dark-field (HAADF). Electron diffraction (EDX) in the transmission electron microscope and X-ray diffraction were used to characterize the structure of the catalysts. It is found that the sample consists of MoS 2+x nanoplatelets with unit cell thickness which are exfoliated and are free to rotate along the basal plane. In addition, the edges of the platelets become very rough increasing the number of adsorption sites. The structure–catalytic properties of MoS 2+ x for hydrogenation over sulfur removal were observed in the hydrodesulphurization (HDS) reaction of dibenzothiophene (DBT). It was found that nanoplatelets have a very high catalytic activity for HDS. The number of adsorption sites is incremented by the presence of steps and kinks at the edges of the nanoplatelets.

Hydrodesulfurization activity over supported sulfided ruthenium catalysts. Influence of the support

This work is aimed at optimizing Ru based catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) by the modification of Ru loading as well as the selection of suitable support. Zirconium doped mesoporous silica (ZrMCM-41) was used as a support of Ru catalysts with different Ru loadings (1, 3, 7 and 11wt%). The metal loading was incorporated by using the incipient wetness method, employing an aqueous solution of ruthenium(III) chloride. The catalysts were sulfided with a N2/H2S mixture (90/10%) at 400°C for 2h, and finally tested in the HDS reaction of DBT at a total pressure of 3.0MPa. An increase in activity was observed when the Ru loading was increased up 7wt%, whereas further addition of ruthenium produced a slight decrease. Once the optimum ruthenium loading (7wt%) was established, the influence of the support on the catalytic performance was studied. For this comparative study, two different materials were used as supports of the Ru catalysts with the same metal content (7wt%). These materials were a mesoporous silica (MCM-41) and a commercial γ-Al2O3. The catalyst supported on ZrMCM-41 displayed higher activity than catalysts supported on MCM-41 and Al2O3, suggesting that activity is favoured not only by the suitable textural and acidic properties of the support, but also the zirconium interaction with the ruthenium sulfide. Zirconium could act by stabilizing the Ru–S bond, an increasing its activity, thus impeding the reduction of ruthenium under the experimental conditions of the HDS reaction. This study concludes that the 7Ru–ZrMCM-41 catalyst, operating at 300°C, with WHSV=28h−1 and H2=100mlmin−1 has the best activity, giving rise to a conversion of DBT of 84%.

Surface Selective Deposition of Mo(IV) on Ni/TiO2 Particles in Aqueous Solutions

The selective depositions of MoS2 and MoO2 over Ni surfaces are demonstrated on Ni/TiO2 particles in a mild electroless deposition process. High-resolution transmission electron microscopy (HRTEM) images show the uniform distribution of 10-30 nm spherical and hemispherical Ni particles on TiO2 surface, and three to six layers of MoS2 on the surface of Ni particles. The as-prepared MoS2-Ni/TiO2 is used as a catalyst for the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT), and shows a significant increase over commercial catalysts in turnover frequencies as the result of unique distribution of active components in the binary catalyst. The selective material deposition is explained in the context of Ni catalyzed KBH4 decomposition, which produces strong reducing species responsible for the site selective deposition of Mo. The synthetic method can be potentially used to prepare bimetallic materials with similar nanostructures such as those of Mo-Co, Mo-Pd, and Mo-Rh.

Effect of sulfidation on Mo-W-Ni trimetallic catalysts in the HDS of DBT

This work presents the effect of different sulfiding agents on Mo-W-Ni trimetallic catalysts, such as “NEBULA” catalysts. The materials were prepared by direct precipitation of ammonium molybdate, ammonium tungstate and nickel nitrate, generating a trimetallic precursor designated NH 4-Ni-Mo 0.5W 0.5-O. Hydrogen sulfide (H 2S), dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) in a hydrogen atmosphere were used to sulfide the precursor at 400 °C for 2 h. The NE B H 2 S , NEB DMDS and NEB DMS catalysts obtained were evaluated in the hydrodesulphurization (HDS) reaction of dibenzothiophene (DBT). DMDS and DMS are less polluting agents than H 2S, which is indeed a highly toxic compound. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, textural properties were measured using the BET and BJH methods. NE B H 2 S and NEB DMDS catalysts present similar catalytic activities for HDS, higher than NEB DMS. However, the latter catalyst was the most selective towards biphenyl (BF). NE B H 2 S and NEB DMDS catalysts were exposed twice to the HDS reaction, they presented an improvement in catalytic activity compared to the first catalytic test.

Lathlike mesostructured γ-alumina as a hydrodesulfurization catalyst support

A mesostructured γ-alumina with a lathlike framework morphology, denoted MSU-γ, has been prepared according to previously described methods through the reassembly and crystallization of a mesostructured alumina precursor with initially amorphous framework walls and used as a support for the catalytic hydrodesulfurization (HDS) of dibenzothiophene (DBT). The alumina support was loaded with molybdenum and cobalt ions via incipient wetness impregnation methods and then converted to the active sulfide form by reaction with H 2S. HDS reactions of DBT were carried out at 400 °C and 400 psi to achieve a DBT conversion of 69–77% and a biphenyl (BP) product selectivity of 60–64% after a reaction time of 3 h, indicating that most of the DBT could undergo desulfurization while limiting excessive hydrogen consumption through aromatic hydrogenation. Although the dispersion of the active Mo/Co sulfide phase supported on lathlike MSU-γ alumina remained very high after several hours on stream, the conversions most likely were limited by a loss of surface area and porosity under HDS conditions.

Reactivity of [Ru3(CO)12] with Dibenzothiophene, Methylbenzothiophene, and Methyldibenzothiophene

The reaction of dibenzothiophene (DBT) with [Ru3(CO)12] in heptane affords the dinuclear complex [Ru2(C12H8)(μ-CO)(CO)5], derived from a double C−S bond activation−desulfurization process. The reaction of this complex with H2 under very mild conditions leads to the release of biphenyl.

Elucidation of sulfur behavior in ultra deep hydrodesulfurization using [formula omitted] radioisotope tracer methods : Part I. Hydrodesulfurization of dibenzothiophene with lower concentration over a sulfided Ni-Co-Mo/Al 2O 3 catalyst

In order to investigate the behavior of sulfur on sulfided Ni-Co-Mo/Al 2O 3 catalyst in the ultra deep hydrodesulfurization (HDS), a novel radioactive 35 S tracer method was developed. Both radioactive 35 S -labeled elemental sulfur and dibenzothiophene (DBT) were used to label the catalyst under the practical HDS, and then HDS reactions of DBT of 0.001–1.0 wt.% (content of sulfur: ca. 2–200 ppm) were carried out over the 35 S -labeled catalyst at 260 °C and under 5.00 MPa. By tracing the changes in the radioactivity of formed [ 35 S ]H 2S, the behavior of sulfur on the catalyst was determined. Either [ 35 S ]S or [ 35 S ]DBT can be used to label the catalyst well and the behavior of sulfur on the catalyst did not change with the type of 35 S agent. The release rate of [ 35 S ]H 2S from 35 S -labeled catalyst in the HDS of DBT became remarkably slow when the concentration of DBT decreased to less than 0.01 wt.%. The amount of labile sulfur participating in the HDS of DBT also decreased with decreasing the concentration of DBT. This indicates that the labile sulfur on the catalyst is not uniform and only some part but not all of labile sulfur participates in the ultra deep HDS.