Higher Hydrodesulfurization Activity Research Articles

Design of active phase structure with high activity and stability in residue hydrotreating reactions

The catalyst with well-dispersed (Ni)MoS2 active phase characteristic of short slab length and low stacking numbers was designed by strengthening metal-support interaction (MSI) and metal dispersion, which displayed high activity and long-term stability in real-life residue hydrodesulfurization (HDS) reactions. Furthermore, the impacts of pseudo-boehmite and catalyst calcination temperature on surface properties were thoroughly investigated. Mo equilibrium adsorption method, Al27 NMR, XRD, Raman, UV–Vis DRS, and H2-TPR characterization showed that the hydroxyl groups concentration and tetrahedral cation vacancies increased upon reducing the pseudo-boehmite extrudates calcination temperature. Increasing calcination temperature of the catalysts further strengthened MSI, resulted in well-dispersed Mo species with enhanced MSI. Therefore, well-dispersed (Ni)MoS2 active phase was acquired on novel designed catalyst. XPS coupled with HRTEM indicated that the more potential active sites, less propensity for active phase evolution and gradual increase in sulfidation degree with processing time contributed to the high HDS performance of the designed active phase. This work can deepen our understanding toward evolution pattern of active phase during residue HDS catalysts, and give guidance for developing high performance catalyst by strengthening MSI and enhancing metal dispersion.

Simultaneous hydrodesulfurization of thiophene and benzothiophene over NiMoS catalysts supported on γ-Al2O3 composites containing ZSM-5

Alumina composites containing microporous ZSM-5 (Z-5) and mesoporous ZSM-5 (MZ-5), corresponding to xZA and xMZA, were developed by incorporating Z-5 and MZ-5 into γ - Al2O3, respectively. The two series of NiMoS/xMZA and NiMoS/xZA catalysts were prepared with these two composites as supports, respectively, and were used for the simultaneous hydrodesulfurization (HDS) of thiophene (T) and benzothiophene (BT). The results show that NiMoS/xMZA series catalysts exhibit higher HDS activity than that of NiMoS/xZA and NiMoS/γ-Al2O3, and the HDS activity of NiMoS/xMZA catalysts increases with the increase of MZ-5. The high HDS activity can be mainly attributed to the synergistic effects of the efficient diffusing pore channels, high dispersion of type II NiMoS phases, suitable acidity, and moderate Mo-support interaction. Moreover, the product distribution of HDS shows that the NiMoS/xMZA catalysts possess the dominant direct desulfurization (DDS) selectivity and the selectivity increases with the increase of MZ-5 content due to more corner sites and suitable Brønsted (B) acid sites, whereas the NiMoS/xZA catalysts perform more excellent hydrogenation (HYD) selectivity, and the selectivity increases with the increase of Z-5 content because of the existence of more edge sites. Based on this, the possible reaction network for T and BT hydrodesulfurization over the catalysts are proposed.

Unraveling the Structure and Surface Chemistry of the Phosphosulfide Phase Formed on Ni2P under Hydrodesulfurization Reaction Conditions: A DFT Study

There is experimental evidence that the actual active phase of the Ni2P catalyst under hydrodesulfurization (HDS) reaction conditions is a nickel phosphosulfide phase formed on the catalyst surface. Combining DFT calculations and an atomistic thermodynamic approach, we investigated the possibility of sulfur adsorption as well as the replacement of surface phosphorus by sulfur on the (0001) and (1010) surfaces of the Ni2P catalyst. Our DFT calculations showed that sulfur could replace up to 100% of the surface phosphorus under hydrodesulfurization (HDS) reaction conditions. We identify that possible sulfur adsorption sites on both surface terminations are arrangements of Ni trimers (Ni3 sites). We found that only the phosphosulfide phase formed on the (1010)-AB_Ni2P surface termination has coordinatively unsaturated Ni atoms available for the adsorption of organic sulfur-containing compounds. Our results suggest that the phosphosulfide phase formed on the (1010)-AB_Ni2P termination and not on the (0001)-Ni3P2 termination could be responsible for the high HDS activity of the Ni2P catalyst. Upon the replacement of P by S, the Ni3 sites undergo tensile strain, and their reactivity toward S adsorption is modified by the imposed strain. We found that the Ni–Ni bond distance is an important parameter in describing the HDS activity of the Ni2P catalyst. By analyzing the relationship among the ensemble, ligand, and strain effects, we were able to provide a better understanding of the promoting effect introduced by the formation of the nickel phosphosulfide phase.

Understanding the effects of feedstock blending and catalyst support on hydrotreatment of algae HTL biocrude with non-edible vegetable oil

The performance of cobalt-molybdenum (CoMo) on hydrotreating of algae HTL biocrude and carinata oil was investigated. Commercial CoMo/Al2O3 (CoMo/Al) and synthesized CoMo supported on Douglas fir biochar (CoMo/DF), sulfided or unsulfided catalysts, were compared for hydrodeoxygenation (HDO), hydrodenitrogenation (HDN), hydrodesulfurization (HDS) and hydrodemetallization (HDM) reactions. Results showed that there lies a synergistic effect when HTL algae biocrude and carinata oil blends are hydrotreated. The yield of the upgraded blend (UB) oils retrieved over alumina catalyst was higher than the individual hydrotreated parent oils. For example, a 9% and 5% increase in yield was noted compared to the average of individual hydrotreated parent oils. The UB produced from sulfided CoMo/Al exhibited superior HDO activity primarily by decarbonylation. This was apparent in increased heating value, carbon addition, higher octane number, and lower total acid number than the oils obtained from the biochar-supported catalysts. Sulfided CoMo/DF catalyzed cracking reactions which lowered the viscosity, followed by high HDN and HDS activity compared to the commercial catalyst. The two supports showed different sorption behaviors. Interestingly, CoMo/DF had an effective sorption mechanism that helped in higher metal removal from the oil. Additionally, presulfiding and DF support exhibited positive results in term of less coke formation. In brief, biochar supports have higher acidic sites, inorganic mineral oxides, ion exchange capacity, high surface area, pore structure and connectivity. All of these make a substantial contribution to its unique catalytic behavior.

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

CoMoS catalysts with controllable morphology are prepared by a single-source precursor hydrothermal method using sodium diethyldithiocarbamate trihydrate (DDTC) as the ligand and the sulfur source. The effects of the single-source precursor, the pH of the hydrothermal solution, and the surfactant with respect to the morphology, nanostructure, and hydrodesulfurization (HDS) activity of the CoMoS catalyst are investigated. It is revealed that the coordination between the metal atom and DDTC can effectively control the in-plane and out-of-plane crystal growth of MoS2 and promote the formation of the CoMoS active phase. The lower pH value of the hydrothermal solution facilitates the synthesis of CoMoS catalysts with improved purity, lower crystallinity, and smaller nanocrystallites, and the different surfactants would significantly change the morphologies. For HDS activity, the conversion efficiency of 4,6-DMDBT is increased from 71 to 99% by the CoMoS catalysts that have fewer stacking layers of MoS2 slabs. While the high HDS activity is maintained, a notable improvement in selectivity for the direct desulfurization (DDS) pathway is observed for the CoMoS-CTAB catalyst, where the average slab length of MoS2 is the longest.

Ultradispersed (Co)Mo catalysts with high hydrodesulfurization activity

In spite of the huge worldwide interest for single-atom and ultradispersed catalysts, metal atoms coordinated with sulfur are rarely addressed. In this work, ultradispersed molybdenum-based catalysts were obtained by adsorption of three thiomolybdates of different nuclearity (n = 1, 2, 3) on high-surface-area S-doped carbon, followed by sulfidation in H2S/H2 flow at 350 °C. Scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) attest that single atoms and few-atom clusters are predominant on the surface of the materials after adsorption, as well as after sulfidation and thiophene HDS reaction. Independently on the nature of the thiomolybdate precursor, sulfidation leads to catalysts with specific thiophene HDS activity exceeding that of a conventional supported MoS2 reference. Ultradispersed clusters were further promoted with cobalt, yielding HDS turnover frequencies 2–3 times higher than those of reported benchmark CoMoS catalysts. These findings provide new insights into the previously debated issues of structure-activity relationships for HDS catalysts and expand the range of applications of atomically dispersed catalysts.

One-step synthesis of mesoporous alumina-supported molybdenum carbide with enhanced activity for thiophene hydrodesulfurization

A new mesoporous alumina-supported molybdenum carbide (Mo2C/γ-MA) has been successfully prepared by one-step hydrolysis method without template, followed by carbonization with a mixed gas of CH4 and H2. The Mo2C particles (2.5 ± 0.3 nm) are homogeneously dispersed in the γ-alumina (γ-MA) framework and exhibit high catalytic activity and stability for thiophene hydrodesulfurization (HDS). Taking 1 wt% thiophene (3810 ppm S) as an example, the Mo2C/γ-MA exhibits 92% thiophene conversion, higher than the MoS2/γ-MA (85%), and other molybdenum carbides supported over commercial alumina and γ-MA prepared by the impregnation method. The stability test demonstrated that the Mo2C/γ-MA almost showed no deactivation during 150 h reaction, and no obvious carbon deposition and sulfurization of Mo2C species were observed over the spent Mo2C/γ-MA. The high HDS activity and stability of the Mo2C/γ-MA for HDS could be attributed to the formation of small Mo2C nanoparticles, appropriate surface acidity and the strong interaction between Mo2C species and alumina inhibiting the sulfurization of Mo2C species.

A new approach for synthesis of well-crystallized Y zeolite from bentonite and rice husk ash used in Ni-Mo/Al2O3-Y hybrid nanocatalyst for hydrocracking of heavy oil

A series of Ni-Mo/Al2O3-Y hybrid nanocatalysts were synthesized for hydrocracking of heavy oil. The well crystallized Y zeolite was synthesized from mineral bentonite and rice husk ash by a two-step synthesis method. The solution combustion method was applied to develop a fast and simple technique for preparing of alumina-supported NiMo catalyst with high hydrodesulfurization activity. Such activity may be due to the morphological and textural modification as a consequence of the release of a high amount of exhaust gases during the combustion process. The XRD analysis revealed that the P zeolite was a competitive phase presented in the obtained product that could be eliminated using a two-step synthesis method. Compared to a one-step method, the pore volume and external surface area of the synthesized zeolite by the two-step method increased by 74 and 62%, respectively. The hydrocracking results illustrated that the synthesized zeolite was able to convert 66% of heavy oil to lighter products and reduce the viscosity up to 60%. Furthermore, the amount of sulfur removal was found to be 58%. The spent catalyst characterization suggested that the type of deposited coke was hard coke with the unsaturated aromatic ring which could be responsible for the pores blockage after the cracking reaction.

HYDROTREATING AND HYDROISOMERIZATION OF OIL FRACTIONS ON MODIFIED ALUMINUM-COBALTMOLYBDENUM CATALYSTS

In this work we are given results and research of hydro refining of gasoline and diesel oil fractions on alumina catalysts CoO-MoO3-La2О3-Р2О5-ZSM-Al2O3, CoO-MoO3-Ce2О3-Р2О5-ZSM-HY-Al2O3, CoO-MoO3-La2О3-Р2О5- AAC-ZSM -Al2O3. The catalysts were prepared by impregnating a mixture of aluminum hydroxide and zeolites ZSM-5, HY with aqueous solutions of salts Co, Mo, La and phosphoric acid. Large-scale laboratory tests of the synthesized catalysts were carried out in the process of hydro processing of various types of gasoline and diesel fractions. At hydro treating of straight-run gasoline over CoO-MoO3-La2О3-Р2О5-ZSM-Al2O3 shows that in the temperature range 320 - 350оС the maximum amount of isoalkanes is formed 33.4-40.4%. The octane number of refined gasoline increases in comparison with the initial one from 78.9 to 89.3 (RON) and from 60.9 to 73.4 (MON). The sulfur content of catalysate with increasing temperature up to 400оС decreased to 0.0012 %. At hydro processing of catalytic cracking gasoline on CoO-MoO3-La2О3-Р2О5-ZSM-Al2O3 the octane number of refined gasoline is slightly reduced. The sulfur content of catalysate with increasing temperature up to 400оС decreased from initial with from 0.0134 to 0 0014 %. It was found that the lowest pour point and cloud point of hydro-refined diesel fuel is observed on the catalyst CoO-MoO3-La2O3-P2O5-ZSM-Al2O3. After hydro treating on this catalyst the pour point and cloud point are equal to minus 52.7oC and minus 40.8oC accordingly. This same catalyst has the highest hydro desulfurization activity: the sulfur content decreases from 0.5600% to 0.104%. Thus, the developed modified zeolite-containing catalysts CoO-MoO3-La2О3-P2O5-ZSM-Al2O3, CoO-MoO3-Се2О3-P2O5-ZSM-HY-Al2O3, CoO-MoO3-La2О3-P2O5-AAC-ZSM-Al2O3, exhibiting high activity at hydro treating of gasoline and diesel fractions and is able in one stage deep hydro treating, hydro isomerization and hydrocracking which allows to obtain low-sulfur, high-octane gasoline and low-sulfur and low solidifying diesel fuel which is important for operation of vehicles in winter conditions.

Synthesis, Characterization, and Hydrotreating Activity of NiW Presulfurized Catalysts Prepared via a Tetrathiotungstate-Intercalated NiAl LDH.

A tetrathiotungstate-intercalated NiAl layered double hydroxide (LDH) was synthesized and then calcined under N2 at various temperatures to prepare a series of NiW presulfurized hydrotreating catalysts. Upon calcination, WS42– in the interlayer decomposes into WS3 and then WS2, releasing sulfur to sulfurize nickel in the sheets. The property and activities of catalysts for hydrodesulfurization (HDS) of dibenzothiophene and hydrodearomatization (HDA) of tetralin are dependent on the calcination temperature. At 300 °C, WS3 can be well maintained, offering highly active hydrogenation sites S22– and superior HDA activity. As the temperature increases up to 500 °C, WS3 converts into WS2, while nickel sulfides migrate to the edge of WS2 to form NiWS phases with high HDS activity. LDH-based presulfurized catalysts can achieve fully sulfurized and well-dispersed tungsten species even at high tungsten loadings and can retain more WS3 even at high temperatures because of the peculiar properties of LDHs. Therefore, they show better HDS and superior HDA activities over an oxidic NiW LDH-based catalyst (LDO) and an alumina-supported NiWS presulfurized catalyst (NiWS/Al2O3). The optimized catalyst shows 1.59 and 1.05 times higher HDS activity than LDO and NiWS/Al2O3 while 2.05 and 1.77 times higher HDA activity than LDO and NiWS/Al2O3, respectively. It also shows better HDS and HDA activity for a real diesel than a NiCoMoW/Al2O3 commercial catalyst.

Tailoring NiMoS active phases with high hydrodesulfurization activity through facilely synthesized supports with tunable mesostructure and morphology

Nanoscaled mesoporous silicas (NMS) with tunable mesostructure and morphology were successfully fabricated using a simple modified-Stöber synthesis system. The Al modified NMS-x materials with highly ordered mesostructures were used as supports to prepare hydrodesulfurization (HDS) catalysts NiMo/Al-NMS-x. The characteristics and activity test results revealed that the dispersion and morphology of NiMoS active phases were modulated on various supports, and TOF values showed dependence on the stacking degrees and dispersion of MoS2 slabs. Moreover, diffusion properties reflected that a support with larger pore size and 3D mesochannel would alleviate restrictive diffusion. Compared to other catalysts, NiMo/Al-NMS-7 with 3D cubic mesochannel and sphere-like shape exhibited the highest catalytic activity, i.e., HDS efficiency (95%, WHSV = 20 h−1), TOF (4.8 ± 0.32 h−1), rate constant (1.4 × 10-3 mol·g−1·h−1) and De (12.8 × 106 cm2·s−1), which would be derived from the preferable diffusion performance of guest-species, especially the better dispersion and suitable stacks of active phases.

Epitaxial synthesis of Ni-MoS2/Ti3C2T x MXene heterostructures for hydrodesulfurization.

Hierarchical structures of 2D layered Ti3C2Tx MXene hold potential for a range of applications. In this study, catalysts comprising few-layered MoS2 with Ti3C2Tx have been formulated for hydrodesulfurization (HDS). The support Ti3C2Tx was derived from MAX phases (Ti3AlC2) via a liquid-phase exfoliation process, while MoS2 was obtained from synthesized aqueous ammonium tetrathiomolybdate (ATM). Furthermore, a series of catalysts with different architectures was synthesized by confinement of ATM and/or the promoter Ni in Ti3C2Tx at different mole ratios, through a thermal conversion process. The synthesized MoS2/Ti3C2Tx and Ni–MoS2/Ti3C2Tx catalysts were characterized using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction (TPR) measurements. The number of MoS2 layers formed on the Ti3C2Tx support was calculated using Raman spectroscopy. The heterostructured few-layered MoS2/Ti3C2Tx catalysts were applied in sulfur removal efficiency experiments involving thiophene. The active MoS2 sites confined by the Ti3C2Tx enhanced hydrogen activation by proton saturation, and the electron charge stabilized the sulfur atom to facilitate hydrogenation reactions, leading to predominant formation of C4 hydrocarbons. The Ni–MoS2/Ti3C2Tx showed the best activity at a promoter molar ratio of 0.3 when compared to the other catalysts. In particular, it is evident from the results that ATM and Ti3C2Tx are potential materials for the in situ fabrication of hierarchical few-layered MoS2/Ti3C2Tx catalysts for enhancing hydrodesulfurization activity in clean fuel production.

High-dispersed Ni-Mo-S active phases within hierarchical pore materials by introducing the cationic protective shell during the impregnation process for hydrodesulfurization

A highly dispersed NiMo/Beta-FDU-12 catalyst was successfully synthesized by introducing the cationic protective shell (DTA+, MTA+ and CTA+) in the impregnation process in order to achieving the optimal interaction between Mo species and the support. Based on H2-TPR, XRD, XPS and HRTEM characterization results, it could be proved that quaternary ammonium cationic salts served as effective shells to protect Mo species from aggregation in the hydrothermal treatment, thus decreasing the interaction between Mo species and support and improving the dispersion of Ni-Mo-S active phases. Compared with NiMo/BF-DTAB and NiMo/BF-MTAB catalysts, NiMo/BF-CTAB catalyst synthesized with longer alkyl-chain quaternary ammonium cationic species exhibited the best hydrodesulfurization performance of DBT, of which the conversion reached 98% at 10 h−1 WHSV. Moreover, NiMo/BF-CTAB catalyst showed higher HYD/DDS ratio, which is nearly three times than that of NiMo/BF-IWI catalyst obtained through the traditional impregnation method. The high hydrodesulfurization activity of NiMo/BF-CTAB catalyst came down to the comprehensive effects of the best dispersion of active phases (fMo = 0.32), the highest sulfidation degrees of active metals (SMo = 60.19%) and higher amounts of total acids.

Promotional effect of Co on unsupported MoS2 catalysts for slurry phase hydrocracking of vacuum residue: X-ray absorption fine structure studies

Unsupported bimetallic sulfide catalysts were obtained in situ using Mo(CO)6 and Co octoate as precursors to investigate the promotional effect of Co on the MoS2 catalyst in the hydrocracking (HCK) of vacuum residue (VR). Transmission electron microscopy (TEM) and X-ray absorption fine structure spectroscopy were used to obtain structural properties of the catalysts. The bimetallic CoMoS2 catalyst exhibited high catalytic activity in the VR HCK with respect to the H2 consumption rate and asphaltene conversion as compared with monometallic sulfides such as Co9S8 or MoS2 with the same catalyst loading of 0.113 mmol at 673 K and 9.5 MPa H2. Higher hydrodesulfurization activity was also observed for the CoMoS2 catalyst. Moreover, extended X-ray absorption fine structure and TEM analysis identified the formation of a Co–Mo–S phase in monoslab particles of average particle size 6.7 nm and the maintenance of the morphology during five times of recycle tests. These results thus suggest that the unsupported CoMoS2 catalyst has a promotional effect on VR HCK.

Sono-Assisted Synthesis and Kinetic Modeling of Nanocrystallite Silicalite-1-NiMo Catalysts for Hydrodesulfurization of Dibenzothiophene: Role of Sonication Time on Support Mesoporosity and Catalytic Activity

We report herein the sono-assisted synthesis of nanocrystallite silicalite-1 and subsequent impregnation of Ni and Mo active metals for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The effect of sonication time on the textural properties and the catalytic activity of the supported catalysts was extensively studied. The 2 h sonication time yielded the best catalyst support (SILC-2) with relatively good textural properties that remained almost intact even after the deposition of Ni and Mo metals. The SILC-2-supported NiMo catalyst demonstrated higher HDS activity than the other catalysts due to its good textural properties compared to the other catalysts. It was further discovered that high acidity and a large number of active sites are not the only criteria for high HDS activity of a catalyst.

Promotional effect of TiO2 on quinoline hydrodenitrogenation activity over Pt/γ-Al2O3 catalysts

The structural and electronic properties of Pt/γ-Al2O3 catalysts for quinoline hydrodenitrogenation were modified by introducing TiO2. The results indicated that the addition of TiO2 enhanced the reducibility of PtOx species, which increased the number of metallic Pt active sites. TiO2 facilitated quinoline hydrodenitrogenation over Pt/γ-Al2O3 catalysts, with an increase in activity from 80.6% to 91.5% at 340 °C and 3 MPa when the TiO2 content was 16.3 wt%; and improved resistance to the inhibiting effects of sulfur species, therefore the hydrodenitrogenation activity decreased less sharply. High activity in dibenzothiophene hydrodesulfurization, i.e., above 91%, was maintained with different sulfur concentrations. Density functional theory calculations confirmed that dibenzothiophene and quinoline had comparable adsorption energies on a metallic Pt surface. We propose that the partially reduced TiO2 mitigated inhibition by dibenzothiophene and enhanced the hydrogenation of quinoline via the formation of electron-rich Pt species.

Study on the modification of unsupported hydrodesulfurization catalysts by the ZSM-5 zeolite nanoclusters

The influence of ZSM-5 zeolite nanoclusters on the unsupported Ni-Mo catalyst was investigated by correlating their physicochemical properties with the hydrodesulfurization (HDS) activity of dibenzothiophene (DBT). The physicochemical properties of the catalysts before and after modification were characterized by N2 adsorption-desorption, XRD, SEM, FT-IR, H2-TPR, Py-IR, and HRTEM techniques. Results showed that the specific surface area and Lewis acid of the unsupported Ni-Mo catalyst were improved obviously after modification, which indicate that the ZSM-5 zeolite nanoclusters were successfully introduced into the unsupported Ni-Mo catalysts. Besides, DBT HDS results revealed that the catalysts Z5-NiMo-10 g and Z5-NiMo-14h exhibited high hydrodesulfurization activity (the desulfurization rate of 98.1% and 100.0%, respectively). In particular, the catalyst Z5-NiMo-10 g produced the highest isomerization rate of 68.9% due to more dispersed structure and suitable acidity.

A novel pre-sulfided hydrotreating catalyst derived from thiomolybdate intercalated NiAl LDHs

A pre-sulfided hydrotreating catalyst was prepared via thiomolybdate intercalated NiAl layered double hydroxides (LDHs) followed by calcination under N2. Upon calcination, the decomposition of thiomolybdate in the interlayer produces MoS2 and releases sulfur to react with nickel in the sheets to produce NiSx. Poorly crystallized MoS2 and NiS2 are formed at 300 °C. However, MoS2 is converted into MoO2 while NiS2 is transformed into NiS and Ni3S2 at higher temperatures. The coordinatively unsaturated sites (CUS) on catalysts and dibenzothiophene (DBT) hydrodesulfurization (HDS) activity decrease as the calcination temperature increases. The catalyst calcined at 300 °C exhibits a little higher HDS activity but 2.3 times higher activity in tetralin (THN) hydrogenation than an oxidic catalyst derived from a molybdate intercalated LDH. Moreover, it shows 2.2 times higher THN hydrogenation activity than a commercial catalyst containing more metals. This could be ascribed to the formation of CUS and non-stoichiometric sulfur species.

Effect of Additives on the Activity of Nickel–Tungsten Sulfide Hydroconversion Catalysts Prepared In Situ from Oil-Soluble Precursors

The nickel–tungsten sulfide catalysts for the hydroconversion of hydrocarbons were prepared from oil-soluble nickel and tungsten precursor compounds in situ with the use of silica, alumina, titania, zeolite Y, and amorphous aluminosilicate as additives in a vacuum gas oil medium. It was found that the catalytic activity in hydrocracking depends on the concentration of acid sites in the resulting catalyst. With the use of oxide additives, the dispersion and the promoter ratio of the in situ formed sulfide particles increased in the order SiO2–Al2O3–TiO2. It was noted that the promoter ratio of sulfide particles obtained with the use of aluminosilicate additives depended on their porous structure peculiarities. The use of titanium dioxide as a catalytic system component made it possible to reach high activity in hydrocracking, hydrodearomatization, and hydrodesulfurization, which was comparable to that of a system based on zeolite Y, a highly acidic component.

Hexamethonium bromide-assisted synthesis of CoMo/graphene catalysts for selective hydrodesulfurization

A series of CoMo/graphene selective hydrodesulfurization (HDS) catalysts were prepared using the hexamethonium bromide-assisted hydrothermal method, and the influences of the hexamethonium bromide/Mo molar ratio and the CoMoS/MoS2 ratio on the HDS activity and selectivity were investigated. The results show that the kHDS value (2.76 × 10−7 mol g−1 s−1) of thiophene and the HDS selectivity factor (13.6) over the as-prepared catalysts were 1.3 times and 1.6 times greater than those over the CoMo/graphene prepared using the conventional impregnation method. The higher HDS activity and selectivity of the as-prepared catalysts result from the higher dispersion of Mo species and the higher CoMoS/MoS2 ratio compared to the CoMo/graphene prepared by impregnation. Among all the catalysts, the catalyst with a hexamethonium bromide/Mo molar ratio of 6.0 presents the highest HDS selectivity due to its highest ratio of edge to corner Co atoms in CoMoS with a superior CoMoS/MoS2 ratio. The present investigation provides a route for developing highly selective HDS catalysts using graphene as support by adjusting the hexamethonium bromide/Mo ratio to finely tune the morphology of the active phases.