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Edge structures, thiophene adsorption and hydrodesulfurization (HDS) mechanisms are investigated on the S-edge of triangular MoS2 nanoclusters using density functional theory. The calculated formation energies for different S coverages on the S-edge suggest that the formation of coordinative unsaturated site at the vertex and edge-I (close to the vertex) sites is preferred over the edge-II (away from the vertex) sites. The adsorption of thiophene on the top site of Mo atom mainly occurs at the edge-I, whereas bridge adsorption occurs at the edge-II. The 92% and 50% S-edge coverages involve relatively larger adsorption energies (− 0.68 and − 0.79 eV) among all the possible adsorption configurations. On the S edge with 92% S coverage, the hydrogenation route is more favorable, producing 1-butene. On the S edge with 50% S coverage, the direct desulfurization route is preferred, yielding butadiene. These findings deepen the understanding of edge structures of MoS2 nanoclusters and the corresponding HDS mechanisms for MoS2-based HDS catalysts. [ABSTRACT FROM AUTHOR]

In this paper, a simple cationic exchange method was proposed to increase the Co/Mo ratio in the Evans‐Showell polyoxometalate to the desired 0.5 with both Mo and Co atoms in one molecule. This approach was proved successfully by X‐ray diffraction, X‐ray fluorescence spectrometer, infrared spectroscopy, and thermogravimetric analyzer. Then, the obtained Evans‐Showell‐type polyoxometalate was used as a superior precursor to construct efficient hydrodesulfurization catalyst, and the dibenzothiophene evaluation results showed that the hydrodesulfurization reaction turnover frequency, the rate constant, and the dibenzothiophene conversion are 1.8×10−3 s−1, 6.4×10−7 mol g−1 s−1, and 95.2 %, respectively, illustrating the excellent hydrodesulfurization performance of the catalyst. The cationic exchange approach promises the Mo and Co atoms in one molecule and the desired proximity of them, leading to a higher dispersion of MoS2 nanoparticles, a higher percent of CoMoS active phase and the excellent hydrodesulfurization performance for dibenzothiophene consequently. [ABSTRACT FROM AUTHOR]

NiMo catalysts were prepared using Waugh-type NiMo heteropolycompounds as active phase precursors and evaluated in hydrodesulfurization (HDS) of dibenzothiophene (DBT). These catalysts were compared with corresponding reference catalysts prepared from the conventional precursors (ammonium heptamolybdate and nickel nitrate). Prepared catalysts were characterized by N physisorption, XRD, FT-IR, H-TPR, DRIFT of CO adsorption and HRTEM techniques. It was found that NiMo catalysts prepared from Waugh-type NiMo HPCs showed higher performance in HDS of DBT than their counterparts. Possible reasons of this result were discussed. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Over the past decades, extensive efforts have been devoted to modulating the textural properties, morphology and microstructure of γ-Al2O3, since the physiochemical properties of γ-Al2O3 have close correlations with the performance of hydrotreating catalysts. In this work, a spongy mesoporous γ-alumina (γ-Al2O3) was synthesized using Al-based metal-organic frameworks (Al-MOFs) as precursor by two-step pyrolysis, and this Al-MOF-derived γ-Al2O3 was used as hydrodesulfurization (HDS) catalyst support, to explore the effect of support on the HDS performance. Compared with industrial γ-Al2O3, the spongy alumina displayed well-developed porosity with relatively high surface area, large pore volume, and abundant weak Lewis acid sites. Based on catalyst characterization and performance evaluation, sulfurized molybdenum and cobalt molecules were able to incorporate and highly disperse into channels of the spongy mesoporous alumina, increasing the dispersion of active catalytic species. The spongy γ-Al2O3 was also able to enhance the diffusion efficiency and mass transfer of reactant molecules due to its improved texture properties. Therefore, the corresponding catalyst presented higher activities toward HDS of dibenzothiophene (DBT) than that from industrial alumina. The spongy mesoporous γ-alumina synthesized by Al-MOFs provides a new alternative to further develop novel γ-alumina materials with different texture and various nanoporous structures, considering the diversity of MOFs with different compositions, topological structures, and morphology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient CoMoS catalysts have been successfully synthesized with TOF values up to 1.3 × 10-3 s−1 in HDS reaction, which is nearly two times higher than that of the conventional Al 2 O 3 -loaded catalysts. • The abundant CoMoS active sites on the catalyst are derived from the use of novel Co 5 Mo 10 polyoxometalate (POMs), and the intimate combination of the Co-O-Mo on the precursor ensures the generation of Co-promoted MoS 2 sites. • The high sulfidation and high dispersion of active metals is attributed to the "weakening metal-support interaction" property from the inert hollow mesoporous carbon sphere (HMCS) supports. • HMCS support with large specific surface area and appropriate pore size act as the nanoreactors facilitating the concentration of reactants within the pore channel and adequate contact with the active site. The rational design of high sulfurization and abundant CoMoS active phases catalysts is the key to drive the industrialization of hydrodesulfurization (HDS). Herein, we prepared a nano-catalyst with well-dispersed and numerous CoMoS active sites through confining Co 3 (II)[Co 2 (III)Mo 10 O 38 H 4 ] (Co 5 Mo 10) polyoxometalates (POMs) molecules with high Co/Mo ratio in hollow mesoporous carbon spheres (HMCS). On the one hand, POMs acted as pre-assembled molecular platform can build and regulate the structure of active phases by precisely adjusting the Co/Mo atomic ratio at molecular level. Meanwhile, the intimate interaction of Co-Mo on the POMs precursor also ensures that the Co species mainly exists as Co-promoted MoS 2 active phase after the sulfidation process, thus the highly efficient synergism of the bimetals can be fully utilized in the reaction. On the other hand, the mesoporous carbon sphere with homogeneous pore size and high specific surface area can effectively confine the growth of the catalyst to disperse the active metals. The weakening metal–metal interaction property of such inert support enables the S-Co 5 Mo 10 /HMCS-10 catalyst to realize higher sulfurization, shorter slab length and higher stacking number. In addition, the abundant mesopores and high pore capacity of support greatly facilitate the mass transfer process and provide sufficient space for the HDS reaction as the nanoreactor. The unique combination of POMs and HMCS enabled the S-Co 5 Mo 10 / H 10 catalyst to achieve up to 99.2% conversion of dibenzothiophene (DBT) after 4 h of HDS reaction, while obtaining a TOF value of 1.3 × 10−3 s−1 (calculated when keeping the low conversion at 42% after 0.5 h of reaction). The structural orientation of the POMs precursors to the active phases of HDS catalysts was investigated using various characterization methods, and the structure–activity relationship between the catalytic performance and the sulfide active phases was also revealed in this work. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple and environmental-friendly preparation of hydrodesulfurization catalysts. • Synchronization and riveting of MoS 2 nanoflakes in mesoporous carbon framework for efficient hydrodesulfurization catalyst. • NaCl and thiourea as hard template and sulfidizing agent, respectively. • Well-defined Evans-Showell polyoxometalate as precursor. Two new mesoporous carbon-supported Co-Mo hydrodesulfurization catalysts with different Co contents have been successfully prepared by one-step vacuum freeze-drying, followed by calcination under a nitrogen atmosphere and washing. Evans-Showell polyoxometalate (NH 4) 6 [Co 2 Mo 10 O 38 H 4 ]·7H 2 O was used as the Co-Mo precursor instead of the conventional precursors, and the obtained catalysts were structurally characterized by various technologies, including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, H 2 temperature programmed reduction, CO temperature programmed desorption and low temperature N 2 adsorption-desorption isotherm. The results show that MoS 2 particles (4.6 nm and 4.5 slabs) are homogeneously dispersed in the mesoporous carbon framework with a narrow pore size distribution centered at 3.7 nm. The catalysts were evaluated by the hydrodesulfurization of dibenzothiophene, and the results show that the dibenzothiophene conversion, overall pseudo-first order rate constant and turnover frequency can reach 95 %, 5.4 × 10−6 mol g −1 s−1 and 6.1 × 10−3 s−1 at 300 °C, respectively, indicating higher catalytic activity than previously reported catalysts. The higher proportion of the CoMoS active phase can account for the higher catalytic activity. By using in situ-produced sodium chloride crystals and thiourea as hard templates and sulfidizing agents respectively, this study opens a new avenue for the simple and environmentally friendly preparation of hydrodesulfurization catalysts with the synchronization and riveting of MoS 2 nanoflakes and 3D mesoporous carbon frameworks. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel molecular precursor of CoMo synergism was used as HDS catalyst. • Pyridine modulates the acidity of the support to weaken SMSI. • Carbonaceous deposits promote the sulfation of active metals. • POMs precursors and ligand groups together contribute to the outstanding HDS performance of S-Co x PMo 9 -py/Al 2 O 3 catalysts. Efficient CoMoS catalysts with intimate bimetallic synergy are derived from cobalt-substituted phosphomolybdate and exhibited excellent hydrodesulfurization (HDS) activity. Based on ligand protection strategy, the introduction of pyridine ligands onto the vacancies of the trivacant polyoxometalates (POMs) successfully overcame their low stability and isomerization behavior in solution. Subsequently, Co2+ was anchored in the molecular skeleton of [A-α-PMo 9 O 31 (py) 3 ]3− (PMo 9 -py) to form Co x PMo 9 -py precursors with high Co/Mo ratios, which enhanced the reducibility of Mo species and transformed them to abundant CoMoS active phase during sulfidation process. The quenching effect of pyridine molecules on the acidic sites of support and carbon deposition generated in the high temperature sulfidation weakened the strong metal-support interactions (SMSI) while improving the dispersion and sulfidation of active metals. Due to the unique structure of Co x PMo 9 -py, the CoMoS phase with high dispersion, efficient synergy and high concentration was obtained. The combination of POMs precursors and pyridine ligands enabled the S-Co x PMo 9 -py/Al 2 O 3 catalyst to achieve up to 99.5% conversion of dibenzothiophene (DBT). [ABSTRACT FROM AUTHOR]

Abstract To investigate the essential role of H 2 on thiophene removal over supported nickel catalysts, a NiO/Al 2 O 3 catalyst was prepared, and a series of desulfurization reactions were carried out with different H 2 feed concentrations. The characterization of fresh and spent catalysts indicated that reduced nickel (Ni0), which showed dependence on the H 2 feed concentration, was the key factor to the thiophene reactive adsorption desulfurization (RADS) process. The equilibrium between sulfurization and reduction of nickel species retained the activity of the catalyst. The stability of the formed nickel sulfides was related to the H 2 feed concentration. The higher H 2 feed concentration favored the RADS process for the positive auto-regeneration of the nickel species. Graphical abstract Unlabelled Image Highlights • Reduced nickel species is important to the desulfurization reactions. • H 2 concentration affects the state of nickel species. • Higher H 2 concentration favors the desulfurization reaction • Nickel sulfide can be partially reduced during the reaction with H 2. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sulfiding agent could effectively react with the supported Mo oxide to form intermediate thiosalts. • The usage of sulfiding agent could generate mononuclear and polynuclear ammonium thiosulfate. • The sulfiding conditions could modify the final morphology of active phase. • The large number of Mo nuclear would lead to the high stacking of MoS 2 slabs. • The catalyst with optimal Mo dispersion and ratios of edge sites to rim sites showed high HDS activity. Abstract The influence of sulfiding conditions in the ex-situ presulfidation process on the morphology and performances of CoMoS/γ-Al 2 O 3 catalysts was studied in details for hydrodesulfurization (HDS) of dibenzothiophene. Surface and bulk characterization using XRD, HRTEM, XPS, TPR and FT-IR confirmed that the sulfiding agent mixture of (NH 4) 2 S and elemental S effectively react with the supported Mo oxide to form intermediate thiosalts from mononuclear ammonium thiomolybdates to polynuclear ammonium thiomolybdates, namely the formed thiosalts from (NH 4) 2 MoS 4 to (NH 4) 2 Mo 2 S 12 and (NH 4) 2 Mo 3 S 13 ,which weaken the strong interaction between the γ-Al 2 O 3 support and Mo oxide, resulting in maximum sulfidation of Mo oxide species. Mo species tend to agglomerate as the number of Mo nuclear increases, which further induces significant changes in the morphology of MoS 2 particles. Such observation was further correlated with HDS activity and selectivity. The CoMoS/γ-Al 2 O 3 catalyst with (NH 4) 2 Mo 2 S 12 as intermediate exhibits suitable slab lengths and stacking numbers of MoS 2 slabs with optimal compromise between the Mo dispersion and ratios of edge sites to rim sites, and show the highest HDS activity. Therefore, a tailor-made catalyst with excellent HDS performance could be developed by adjusting the sulfiding conditions through ex-situ presulfidation method. [ABSTRACT FROM AUTHOR]

Highly active hydrodesulfurization (HDS) catalysts have been prepared successfully through a molecular approach using well-defined Strandberg P Mo Ni polyoxometalates (POMs) as superior precursors. The hand-picked POMs significantly facilitated not only the formation of highly dispersed Ni Mo species but also the formation of abundant and accessible NiMoS active sites at lower sulfidation temperatures, thereby resulting in a remarkable activity improvement in comparison with reference catalysts prepared with conventional precursors. Characterization results revealed the multidirecting effects of the POMs component and structure on the morphology and composition of the species in the NiMoS active phase and the evolution of precursors during the catalyst preparation simultaneously. The bottom-up POMs-based preparation methodology provides a better understanding of HDS catalyst structure and performance, thus further shedding light on the rational design and controllable fabrication of efficient HDS catalysts. [ABSTRACT FROM AUTHOR]

Deep hydrodesulfurization (HDS) of gas oil has become one of the most important subjects in the production of fuels, as increasingly stringent quality standards for gas oil have been introduced all around the world. We studied the technical conditions (temperature, hydrogen pressure, liquid hourly space velocity, and H 2 /oil volume ratio) for the deep HDS of fluid catalytic cracking (FCC) and coking gas oils over a highly loaded NiMoW catalyst and compared its activity and the removal of the refractory dibenzothiophenes (DBTs) with those of a commercial NiMo/γ-Al 2 O 3 catalyst and a highly loaded NiMo catalyst. The FCC gas oil, which had a lower sulfur content and simpler composition than the coking gas oil, was relatively easy to process. The coking gas oil and another FCC gas oil, of poor quality with more complex compositions, required more stringent reaction conditions. The sulfur distributions in gas oils hydrotreated to a level of 100, 50, and 10 μg/g sulfur were investigated. 4-Methyldibenzothiophene could be totally removed when the coking gas oil was hydrotreated to a level of 50 μg/g S. Only 4,6-dimethyldibenzothiophene and 2,4,6-trimethyldibenzothiophene were detected in the deep HDS to a level less than 10 μg/g S. This is attributed to the steric hindrance of substituted-alkyls at the 4 and/or 6 positions of DBT. The highly loaded NiMoW catalyst had a higher activity than a highly loaded NiMo catalyst and a commercial NiMo/γ-Al 2 O 3 catalyst, and was more suitable for the production of ultra-low-sulfur gas oils. [ABSTRACT FROM AUTHOR]

Binary NiMo, CoMo, NiW, and CoW transition-metal oxide catalyst precursors, were synthesized through a hydrothermal reaction, and highly-loaded hydrodesulfurization (HDS) catalysts were prepared by mixing the precursors with an alumina gel, calcination and sulfidation. The transition-metal oxide catalyst precursors and highly-loaded sulfide catalysts were characterized by XRD, N 2 adsorption–desorption, XRF, and HRTEM. Dibenzothiophene and fluid catalytic cracking (FCC) diesel were employed to evaluate the HDS performance. The crystalline phases of ammonium nickel (or cobalt) molybdate were detected in the NiMo (or CoMo) oxide catalyst precursors, while quasi-amorphous phases were observed for the CoW and NiW oxide precursors. In the sulfided HDS catalysts, typical MoS 2 or WS 2 phases were observed by TEM, while XRD demonstrated that Ni and Co sulfides were present, in accordance with HRTEM results. The catalytic results showed that the binary transition-metal CoMo sulfide catalyst exhibited high direct desulfurization activity and that the NiMo sulfide catalyst had higher HDS and hydrodenitrogenation activities toward the FCC diesel than the other catalysts, with conversions of higher than 99.1% and 99.7%, respectively. [ABSTRACT FROM AUTHOR]

The anchoring of Weakley-type polyoxometalate (POM) Na 7 [H 2 LaW 10 O 36 ] in mesoporous metal-organic framework (MOF) MIL-101(Cr) to prepare a novel host-guest composite is here reported for the first time. The successful encapsulation of LaW 10 into MIL-101(Cr) has been achieved via facile tandem post-synthetic modification strategy and confirmed by several instrumental techniques. The LaW 10 guests were dispersed homogeneously in MIL-101(Cr) nanocages at molecular level. The as-synthesized composite combines both the merits of the POMs (remarkable efficiency and reversible redox) and MOF (sufficient recyclability and exceptional porosity), thus displaying obvious host-guest synergistic effect. The LaW 10 O 36 @MIL-101(Cr) composite served as heterogeneous single-site catalyst for ODS process and exhibited excellent catalytic performance, with removal efficiency of 99.1, 94.5 and 84.7% for DBT, 4,6-DMDBT and BT, respectively. Thanks to the confinement effect from Cr···O W coordinative interaction, the catalyst provided outstanding recyclability and stability, and can be reused for seven times without leaching, structural alteration and deactivation. Moreover, the structure-activity relationship was investigated in detail, as well as the proposed mechanism. Image 1 • The Weakley structure POMs were encapsulated into MIL-101(Cr) for the first time. • The LaW 10 O 36 were dispersed uniformly within MIL-101(Cr) at molecular level. • The host-guest synergistic effect enhanced remarkably ODS efficiency and durability. • The confinement effect of MIL-101(Cr) on LaW 10 O 36 results in excellent ODS recyclability. [ABSTRACT FROM AUTHOR]