NiMoS Phase Research Articles

Effects of Second Phases on Charpy Impact Energy and Crack Propagation Behavior of Hastelloy N Sheet Using for Molten Salt Reactor

In order to obtain the effect of second phases on Charpy impact energy and crack propagation behavior of Hastelloy N sheet, Charpy notched impact toughness test have been accomplished with different directions (RD, ND) of V-notch after solution treatment. The fracture morphology and microstructure are observed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). It is shown that the dominant second phases in Hastelloy N after solution treatment includes molybdenum-riched Ni-Mo phase, which dissolve some elements such as chromium, silicon and ferrum, and a few carbides. The Charpy impact energy of sample 2# (RD) is 225J, almost twice as much as sample 1# (ND). Based on the reconstruction of morphology and distribution of second phases, the mechanism for effect of second phases on crack propagation behavior is discussed. The islands of second phase particles modify the stress triaxiality state, resulting in the propagation path of crack in 2# is totally different from that in 1#.

Peptization of alumina by ammonia to adjust catalytic properties of NiMo/B-Al2O3 hydrotreating catalysts

NiMo/B-Al2O3 catalysts for VGO hydrotreating differed in peptizing agent for supports preparation (nitric acid or ammonium solution) have been studied. The molar ratio of HNO3/Al2O3 = 0.03 and NH3aqua/Al2O3 = 0.09 and 0.15 were used. Supports and catalysts were studied by the nitrogen and mercury adsorption, IR-spectroscopy of adsorbed CO, XRD, 11B and 27Al NMR, UV–vis DRS, HRTEM, XPS. NiMo/B-Al2O3 catalyst peptized by ammonia at molar ratio of NH3/Al2O3 = 0.09 contains higher amount of NiMoS phase than catalysts peptized by nitric acid. Boron catalyst based support peptized by nitric acid is characterized by active component particles with lower slab length. Simultaneous presence of ammonia and boron results in increase of the slab length of active component, while stacking number decreases. According to the results of catalytic testing in HDS of DBT, boron-containing catalysts are more active. However, NiMo/B-Al2O3 catalyst obtained using ammonia with molar ratio of NH3/Al2O3 = 0.09 has higher activity in HDS of DBT in comparison with NiMo/B-Al2O3 catalyst obtained using nitric acid. Testing in VGO hydrotreating confirmed that utilization of ammonia as a peptizing agent for support preparation significantly improves the activity of boron catalyst in HDS and HDN reactions.

Ultradeep hydrodesulfurization of fuel over superior NiMoS phases constructed by a novel Ni(MoS4)2(C13H30N)2 precursor

Ni(MoS4)2(C13H30N)2 was synthesized and adopted for preparing a NiMoS/γ-Al2O3 hydrodesulfurization catalyst, and the as-prepared catalyst exhibits superior 4,6-dimethyldibenzothiophene hydrodesulfurization activity.

Synthesis of novel NiMo catalysts supported on highly ordered TiO2-Al2O3 composites and their superior catalytic performance for 4,6-dimethyldibenzothiophene hydrodesulfurization

Highly ordered mesoporous TiO2-Al2O3 composites with different TiO2 mass contents (MA-xTi) were successfully synthesized via an improved solvent evaporation-induced self-assembly method and the corresponding NiMo supported hydrodesulfurization (HDS) catalysts were prepared via wetness incipient co-impregnation method. The materials were characterized by means of XRD, ICP-OES, N2 physical adsorption-desorption, SEM, TEM, Py-FTIR, H2-TPR, HRTEM and XPS and the catalytic activities for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS over the prepared NiMo/MA-xTi series catalysts were investigated. The results show that the crystal forms, crystal morphologies, pore structures, pore arrangements and acidity properties of the MA-xTi samples varied with the incorporation and increase of TiO2 species; the interaction between the active metals and the support materials (MSI) can be modulated by the incorporation of TiO2 species, and TiO2 incorporation also can promote the formation of the so-called “Type II” NiMoS active phase via changing the morphology of Ni promoted MoS2 slabs, promoting the sulfidation of both Ni and Mo species and enhancing the proportion of NiMoS phase. The catalytic evaluation results show that the enhancement in the overall HDS activity of the NiMo/MA-xTi series catalysts were mainly contributed by the enhancement in the hydrogenation desulfurization (HYDS) activity. Catalyst NiMo/MA-20Ti exhibited the superior catalytic performance due to its highly ordered mesopore arrangement, proper acidity, moderate MSI, moderate stacking and high proportion of NiMoS phase which leads to more highly active “Type II” active sites.

Influence of alumina precursor on silicon capacity of NiMo/γ-Al2O3 guard bed catalysts for gas oil hydrotreating

Abstract The influence of alumina precursors on NiMo/γ-Al2O3 catalysts for silicon removal from gas oil have been studied. Alumina precursors were prepared by hydrothermal treatment of gibbsite, precipitation of aluminum nitrate by ammonia and precipitation of aluminum nitrate in autoclave. Alumina precursors, supports and catalysts were studied by XRD, nitrogen adsorption-desorption, IR spectroscopy, UV–vis, XPS, SEM, HRTEM. Series of NiMo/γ-Al2O3 catalysts differed in preparation method of alumina precursors was tested in hydrotreating of diesel fraction contaminated with decamethylcyclopentasiloxane as a model silicon compound. It was shown that prepared alumina precursors were boehmites and dawsonite, which had different particle size. The supports prepared from these alumina precursors were γ-Al2O3 with different particles size. It was shown that there was a dependence of the surface area of the support on the size of primary particles measured by XRD. The higher surface area results in the higher content of OH groups and silicon sorption capacity. Morphology of the sulfide active component also depends on the size of primary particles. The higher length of the particles, the higher slab length of NiMoS phase. The catalyst with the lowest particle size of alumina and highest length of active component had the highest HDS activity.

Study of the Promotion Effect of Citric Acid on the Active NiMoS Phase in NiMo/Al2O3 Catalysts

A series of NiMo/Al2O3 catalysts were prepared using an aqueous solution containing Ni and Mo salts and citric acid (CA). Hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD...

Nature of the Active Sites of Molybdenum-Based Catalysts and Their Interaction with Sulfur- and Nitrogen-Containing Molecules Using the Quantum Theory of Atoms in Molecules and the Molecular Electrostatic Potential

Density-functional theory (DFT), morphologic, and quantum theory of atoms in molecules (QTAIM) studies of bilayer models of nonhydrogenated MoS2, CoMoS, and NiMoS phases have been performed. The QT...

Hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiMo supported on Ga-modified Y zeolites catalysts

Y zeolites modified by gallium (Ga) via three different modification methods (impregnation, post-synthesis and in situ synthesis) were synthesized, and the synthesized supports were impregnated by NiMo precursors. Characterization techniques such as XRD, N2 physical adsorption-desorption, ICP-OES, FT-IR, 71Ga MAS NMR, Py-FTIR, H2-TPR, HRTEM and XPS were performed to determine the effects of each modification of Y zeolite by Ga on the properties of the prepared supports and catalysts. Finally, 4,6-dimenthyldibenzothiophene (4,6-DMDBT) was used as a probe to evaluate the effects of the modification of Y zeolite by Ga on the catalytic performance of the prepared catalysts. The results show that the Modification of Y zeolite by Ga affected the position of the Ga species: in the impregnation modification method, Ga species deposited on the surface of Y zeolite mainly exist as non-framework Ga2O3; in the post-synthesis modification method, Ga species are introduced to the near-surface area and mainly exist as framework Ga species; and in the in situ synthesis modification method, Ga species are introduced throughout the whole framework and exist as framework Ga species. Ga species located at the surface and near-surface area effectively prevent the formation of strong Mo-O-Al bonds, which results in both modulated acidity and weakened interactions between active metals and the support (MSI). The hydrodesulfurization (HDS) results also show that the effects of Ga on NiMoS/Y-zeolite play a very important role in the catalytic performance of the corresponding catalysts. The superior HDS performance of the catalyst NiMo/GaHY (prepared via post-synthesis method) can be attributed to the better accessibility of active sites, the modulated acidity property, the proper MSI, the higher proportion of the NiMoS phase, the higher isomerization activity and the higher matching between hydrogenation activity and hydrolysis activity.

Design and properties investigation of Ni[sbnd]Mo composite coating reinforced with duplex nanoparticles

In this study, SiC and TiN duplex nanoparticles reinforced NiMo composite coatings were designed and successfully electrodeposited on 6061 aluminum alloy. The effects of SiC and TiN duplex nanoparticles on the microstructure and properties of NiMo composite coatings were investigated. The surface morphology, element composition and phase structure of the as-prepared coating were observed and analyzed by SEM, EDS, LSCM, XRD and TEM. The results show that the most dense and uniform coating is obtained when the electrodeposition voltage is 6.5 V, and that there is a good adhesion between the coating and the substrate. The addition of the nanoparticles increases the surface roughness of the NiMo coating from 4.3 μm to 7.6 μm, and the crystallite size is decreased from 17.22 nm to 12.54 nm. The structure of the Ni-Mo-SiC-TiN nanocomposite coating is a typical FCC NiMo phase with nanoparticles dispersed uniformly. The corrosion behavior of the prepared coating was investigated in 3.5 wt% NaCl solution by Tafel polarization and immersion tests. The results show that the corrosion rates of Ni-Mo-SiC-TiN nanocomposite coating deposited at 3.8 V, 5.3 V, 6.5 V and 7.8 V are reduced by 63%, 69%, 82% and 73% respectively. The nanoparticles could further enhance resistance of the NiMo coating to the corrosive liquids. Mechanical properties are researched by the Vickers microhardness and pin-on-disc wear test. Due to the addition of SiC and TiN particles, the microhardness of the coating increased from 268 HV to 385 HV and the friction coefficient was significantly reduced from 0.35 to 0.2. The groove and adhesion effects, which existed on the Ni-Mo-SiC-TiN coating, were obviously weakened. Further, the duplex nanoparticle effect is also discussed in this paper.

Niobium modification effects on hydrodesulfurization of 4,6-DMDBT catalyzed on Ni-Mo-S active sites: A combination of experiments and theoretical study

Experiments and calculations are combined to study the Nb substitution effects on the hydrodesulfurization (HDS) performance of 4,6-DMDBT catalyzed using the Ni-Mo bimetal hydrotreating catalysts. In the experimental parts, a series of Nb post-modified NiMo/Al2O3 HDS catalysts are prepared and characterized. Then, the HDS performance of the 4,6-DMDBT is assessed using this Nb-NiMo/Al2O3. In the calculations part, the Ni-Mo-S active nanocluster model with different Nb substitution degrees for the Mo-edge and Ni-edge are established. The Nb stability on the Ni-Mo-S active sites and the Nb effects on the properties of the active sites are analyzed. Meanwhile, the key elementary reactions of the direct hydrodesulfurization (DDS) route and the hydrogenation reaction (HYD) route on the Ni-Mo-S active sites are calculated. The experiments show that the introduction of Nb leads to the agglomeration of the NiMo phase in the oxidation state. Also, the introduction of Nb will increase the length and stacking number of the NiMoS phase. Partial Nb species will convert to Nb2+ during the sulfuration process. A moderate Nb introduction will enhance the HDS conversion rate, the DDS selectivity and the TOF of the 4,6-DMDBT, whereas these factors will decrease when excess Nb is introduced. The DFT calculations show that the Nb could be stable on the S-edge and Mo-edge with various substitution rates. The Nb will spatially expand the molecular orbital on the active sites, and it has a stronger interaction with the H2S, active hydrogen, 4,6-DMDBT and its DDS intermediate in general. The partial Nb substitution enhances the C–S bond cleavage. The full Nb substitution hinders the C–S bond cleavage, but it favors the hydrogen saturation of the S-4Nb. The calculations could explain the experiments in which the DDS selectivity of the 4,6-DMDBT increases with the Nb introduction at first and then decreases as the Nb introduction continues to increase.

Kinetic and Mechanistic Analysis of Dibenzothiophene Hydrodesulfurization on Ti-SBA-15–NiMo Catalysts

MoS2-based catalysts are the most commonly used systems for the hydrodesulfurization (HDS) process on an industrial scale. Different methods were employed to enhance the efficiency of the catalysts, which include changes in catalyst support and doping agents as well as tuning the dispersion of the MoS2 phase using various synthetic techniques. In this work, we report the kinetic and mechanistic analysis of HDS of dibenzothiophene (DBT) for different NiMo-supported Ti-SBA-15 catalysts prepared by (1) direct single-pot (SP) synthesis and (2) impregnations of the NiMo phase into the Ti-SBA-15 support. Both methods were also repeated with and without the citric acid (CA) loading to achieve higher dispersion of the active metal sites. Kinetic modeling was performed to two “parallel–series” reactions of DBT, direct desulfurization (DDS) and hydrogenation (HYD), both leading to the final product of cyclohexylbenzene. Kinetic analysis reveals the considerable influence of the catalyst preparation methods to both ...

Quantum-accurate spectral neighbor analysis potential models for Ni-Mo binary alloys and fcc metals

In recent years, efficient inter-atomic potentials approaching the accuracy of density functional theory (DFT) calculations have been developed using rigorous atomic descriptors satisfying strict invariances, for example, to translation, rotation, permutation of homonuclear atoms, among others. In this work, we generalize the spectral neighbor analysis potential (SNAP) model to bcc-fcc binary alloy systems. We demonstrate that machine-learned SNAP models can yield significant improvements even over well-established, high-performing embedded atom method (EAM) and modified EAM (MEAM) potentials for fcc Cu and Ni. We also report on the development of a SNAP model for the fcc Ni-bcc Mo binary system by machine learning a carefully-constructed large computed data set of elemental and intermetallic compounds. We demonstrate that this binary Ni-Mo SNAP model can achieve excellent agreement with experiments in the prediction of Ni-Mo phase diagram as well as near-DFT accuracy in the prediction of many key properties such as elastic constants, formation energies, melting points, etc., across the entire binary composition range. In contrast, the existing Ni-Mo EAM has significant errors in the prediction of the phase diagram and completely fails in binary compounds. This work provides a systematic model development process for multicomponent alloy systems, including an efficient procedure to optimize the hyper-parameters in the model fitting, and paves the way to long-time, large-scale simulations of such systems.

Effect of preparation method of nanosized zeolite HY-Al2O3 composite as NiMo catalyst support on diesel HDS

Two NiMo catalysts using the nanosized zeolite HY-Al2O3 composite (labeled as NYA) prepared by mechanical mixing method and sol-gel method as the support were prepared and characterized by XRD, BET, TPD, HTPR, HRTEM and FT-IR spectroscopy. The former catalyst possessed larger pore volume and specific surface area, more acid amount, superior reducibility of metal phase and higher dispersion of edge and corner Mo atoms, and showed higher hydrodesulfurization (HDS) performance. Compared with the former catalyst, the latter catalyst had more MoO3 to be converted to active type-II NiMoS phase, possessed higher stacking degree and bigger length of MoS2 slabs, and showed lower active phase dispersion. Although the sol-gel method was beneficial to increase the precursor ratio of type-II NiMoS phase, the poor pore structure caused by this method inhibited this advantage and reduced the catalytic activity of the catalyst.

Titanium-Modified TUD-1 Mesoporous Catalysts for the Hydrotreatment of FCC Diesel

Titanium-modified pure aluminum-based TUD-1 (TiAT) mesoporous material with a highly active three-dimensional was successfully synthesized by using tetraethylene glycol (TEG) as a template through sol–gel method. The series catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, Raman, pyrolysis-infrared (Py-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) technologies. The characterization results indicated that Ti was incorporated into the TUD-1. In addition, the synthesized materials had large pore size (6.4 nm), high surface area (394.0 m2/g), and large pore volume (0.83 cm3/g). It was shown that Ti acting as an electronic promoter could promote the formation of Mo7O246– precursors and more type II NiMoS phases. Furthermore, Ti incorporation could bring more Bronsted and Lewis acids into the catalysts, which were beneficial to improve the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reaction processes. Catalytic performances of diffierent catalysts w...

Effects of gallium addition to mesoporous alumina by impregnation on dibenzothiophene hydrodesulfurization performances of the corresponding NiMo supported catalysts

The effects of gallium (Ga) modification on mesoporous Al2O3 (MA) were studied, focusing on the morphology changes of the active phases and the application as catalyst support for catalytic performances for dibenzothiophene (DBT) hydrodesulfurization (HDS). MA samples with wide mesopore size distribution (MA-W), double mesopore size distribution (MA-D) and single mesopore size distribution (MA-S) were synthesized from the boehmite sol–gel via a hydrothermal synthesis method. The synthesized MA-S sample was modified with Ga2O3, and the corresponding sulfide NiMo supported catalysts were prepared. The as-synthesized samples were characterized by XRD, N2 physisorption, NH3-TPD, H2-TPR, HRTEM and XPS. Superior catalytic performance was observed over the NiMo/MA-S-2Ga catalyst due to the moderate interaction between the active metals and the supports; the superior morphology for Ni promoted MoS2 crystals, the highest sulfidation degree, the largest proportion of the NiMoS phase and the enhanced hydrogenation activity caused by the introduction of Ga species.

Improved NiMoSA catalysts: Analysis of EDTA post-treatment in the HDS of 4,6-DMDBT

Abstract To optimize the performance of HDS catalysts prepared with an improved support and a chelating agent, the present work analyzes the variations in HDS activity and hydrogenation/desulfurization selectivity when different protocols are applied in the preparation of a NiMo HDS catalyst with EDTA as chelating agent and silica-modified alumina (SA) as support. It was shown that grafting 6 wt. % SiO2 on the alumina support favors the formation of Mo6+Oh and decreases the presence of Mo6+Td, which is difficult to reduce and sulfide, resulting in SA supported catalysts with increased HDS activity. The use of both SA and EDTA improves the hydrogenation rate constant and not the direct desulfurization one. Successive impregnation Ni+Mo (Mo first) leads to higher dispersion of edge sites in the MoS2 crystallites. Post-treatment of the oxide catalysts with EDTA gives rise to a better promotion associated to the removal of Ni from inactive compounds, favoring additional formation of NiMoS phase. The post-treatment is more effective in catalysts prepared by successive impregnation. The successively-prepared EDTA+Ni+Mo/SA catalyst presents the highest activity in the HDS of 4,6-DMDBT.

Influence of substituting Mo for W on solidification characteristics of Re-containing Ni based single crystal superalloy

The influence of substituting Mo for W on solidification characteristics of Re-containing single crystal superalloy was investigated via experimental analysis and thermodynamic calculation. W-rich single crystal superalloy (Alloy W) and Mo-rich single crystal superalloy (Alloy Mo) both had typical dendritic microstructure, while interdendritic precipitations of Alloy W and Alloy Mo were γ′ phase+γ/γ′ eutectic phases and γ′ phase+NiMo phase, respectively. Meanwhile, W significantly segregated to dendritic region in Alloy W, while Mo segregated to interdendritic region in Alloy Mo. Moreover, substituting Mo for W obviously decreased the microsegregation degree of Re and Al elements. The influence of substituting Mo for W on microsegregation behavior of alloying elements (e.g. Re) effectively decreased the tendency of forming freckle during solidification. Furthermore, substituting Mo for W decreased liquidus temperature and solidus temperature of single crystal superalloy.

Hydrocracking of Vacuum Gasoil on NiMo/AAS-Al2O3 Catalysts Prepared from Citric Acid: Effect of the Catalyst Heat Treatment Temperature

Ni-Mo bimetallic catalysts are prepared by impregnating a carrier containing amorphous aluminosilicate (AAS) and aluminum oxide using a solution with Ni, Mo, and citric acid. The temperature of the catalysts ranges from 120 to 550°С. The physicochemical properties of the catalysts are studied via XPS, TEM, and HCNS analysis, and they are tested in hydrocracking of vacuum gasoil. The particles of the sulfide active component (NiMoS phase) are localized predominantly on surfaces of aluminum oxide, and only some are on surfaces of AAS. When the temperature of catalyst calcination is raised, the average number of the layers in particles of the NiMoS phase grows as well, due to the removal of citric acid. This indicates strengthening of the interaction between the sulfide active component and aluminum oxide. The content of Ni-Mo massive sulfide particles also grows along with the temperature of calcination. The morphological characteristics of the sulfide active component affect the activity of the catalysts in hydrodesulfurization and hydrodenitrogenation, but not in hydrocracking. The optimum heat treatment temperature for NiMo/AAS-Al2O3 catalysts prepared with citric acid is 120°C. Recommendations are given for the heat treatment of catalysts under industrial conditions.

Active sites of sulfided NiMo/Al2O3 catalysts for 4,6-dimethyldibenzothiophene hydrodesulfurization-effects of Ni and Mo components, sulfidation, citric acid and phosphate addition

The active sites of the sulfided 5.2wt%Ni9.8wt%Mo/Al2O3 catalyst for the hydrodesulfurization of 4,6-dimethyldibenzothiophene were studied using a high-pressure flow system. The catalysts were prepared by dry sulfidation or after the calcination of four sets of NiMo precursors with and without citric acid and phosphoric acid. The dry sulfidation using the precursor of nickel carbonate and molybdenum trioxide with citric acid and phosphate produced the HDS MoO3 is considered a precursor for the hydrogenation activity, and ammonium heptamolybdate is a precursor for the direct desulfurization activity. and the highest number of active sites of the Ni2+MoS2 slab (NiMoS phase) based on the NO and XPS. The sulfidation after calcination using nickel nitrate and ammonium hexamolybdate had the highest HDS rate for the desulfurization, and the number of sites of the MoS2 (Mo4+) slab covered with Ni sulfide (Ni2+). This site was stacked with 3.3 layers and 34Å length for the 2% phosphorus catalyst and widely dispersed as multilayers, and increased when stacked by the phosphate addition and contained highly stacked slabs by the citric acid addition.

Hydrocracking of Vacuum Gasoil over NiMo/ААС-Al2O3 Catalysts Prepared with Citric Acid: The Influence of Temperature of Thermal Treatment of the Catalyst

Bimetal Ni-Mo catalysts were prepared by impregnating the support consisting of amorphous aluminosilicate (AAS) and alumina with the solution of Ni, Mo compounds and citric acid; temperature of the thermal treatment was varied from 120 to 550 °C. XPS, TEM and HCNS techniques were used for studying physicochemical properties of the prepared catalysts. The catalysts were tested for hydrocracking of vacuum gasoil. Particles of the active sulfide component (NiMoS phase) were established to reside predominantly on the alumina surface and only partially on the AAS surface. As the temperature of the catalyst calcinations rose, the average number of layers in the NiMoS particles increased due to removal of citric acid that indicated a stronger interaction between the active sulfide component and alumina. The temperature elevation also was accompanied by an increase in the proportion of bulky Ni-Mo particles. The morphology of the active sulfide component was shown to influence the catalyst activity to hydrodesulfurization and hydrodenitrogenation but not to hydrocracking. The optimal temperature of thermal treatment of NiMo/AAS-Al 2 O 3 catalysts prepared with citric acid was 120 °C. Recommendations for the thermal treatment of the catalysts under industrial conditions were provided.