Magnifying the Morphology Change Induced by a Nickel Promoter in Tungsten(IV) Sulfide Industrial Hydrocracking Catalyst: A HAADF‐STEM and DFT Study

Gîrleanu, Maria; Alphazan, Thibault; Boudene, Zoubeyr; Bonduelle‐Skrzypczak, Audrey; Legens, C.; Copéret, Christophe; Ersen, Ovidiu; Raybaud, Pascal

doi:10.1002/cctc.201402115

Cited by 17 publications

(41 citation statements)

References 34 publications

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“…1. It is well-known that highly type II textured thin films can be grown on molten Ni promoter on sapphire substrates at high temperatures by rheotaxy which is attributed to the minimization of the film-substrate interface energy by forming molten NiS x droplets2122. In our experiments, the application of an ultra-thin Ni as a texture promoter is found to dramatically improve the crystal quality and carrier mobility of the WS 2 thin film.…”

supporting

confidence: 49%

“…Compared to type A film, carrier mobility of type B film was remarkably increased from 3.25 cm 2 /Vs to 63.3 cm 2 /Vs with the bulk carrier (hole) concentration of 7.12 × 10 16 cm −3 . The improvement in the crystallinity of the type B film is attributed to the use of Ni texture promoter which facilitates the formation of liquid NiS x phase, with a melting point of 637 °C2122, that exists at the grain boundaries during the sulfurization process. It is well known that rheotaxy is a growth technique based on a molten substrate.…”

Section: Resultsmentioning

confidence: 99%

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Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer

Fong

Wang

et al. 2016

Sci Rep

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High quality wafer-scale free-standing WS2 grown by van der Waals rheotaxy (vdWR) using Ni as a texture promoting layer is reported. The microstructure of vdWR grown WS2 was significantly modified from mixture of crystallites with their c-axes both parallel to (type I) and perpendicular to (type II) the substrate to large type II crystallites. Wafer-scale transfer of vdWR grown WS2 onto different substrates by an etching-free technique was demonstrated for the first time that utilized the hydrophobic property of WS2 and hydrophilic property of sapphire. Our results show that vdWR is a reliable technique to obtain type-II textured crystallites in WS2, which is the key factor for the wafer-scale etching-free transfer. The transferred films were found to be free of observable wrinkles, cracks, or polymer residues. High quality p-n junctions fabricated by room-temperature transfer of the p-type WS2 onto an n-type GaN was demonstrated with a small leakage current density of 29.6 μA/cm2 at −1 V which shows superior performances compared to the directly grown WS2/GaN heterojunctions.

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supporting

confidence: 49%

Section: Resultsmentioning

confidence: 99%

Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer

Fong

Wang

et al. 2016

Sci Rep

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“…Sulfide model catalysts have also been analyzed by HR HAADF-STEM in order to confirm the orientation of MoS 2 slabs determined by GI-EXAFS. In fact, with STEM in the HAADF detection mode, intensity is proportional to the squared atomic number (Z²) of the observed atoms [54,55], making feasible the detection of MoS 2 slabs oriented perpendicular to the incident electron beam and thus parallel to the surface and possibly the determination of the associated 2D morphology [56][57][58][59]. The analysis was also performed on samples sulfided at 300 °C to compare HAADF-STEM images to GI-EXAFS results.…”

Section: Support Effect On the Orientation Of Mos 2 Slabsmentioning

confidence: 99%

Surface-dependent sulfidation and orientation of MoS2 slabs on alumina-supported model hydrodesulfurization catalysts

Bara

Lamic‐Humblot

Fonda

et al. 2016

Journal of Catalysis

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The constant improvement of hydrotreating (HDT) catalysts, driven by industrial and environmental needs, requires a better understanding of the interactions between the oxide support (mostly alumina) and the MoS 2 active phase. Hence, this work addresses the supportdependent genesis of MoS 2 on four planar, single crystal -Al 2 O 3 surfaces with different crystal orientations (C (0001), R , M and A). In contrast to classical surface science techniques, which often rely on UHV-type deposition methods, the Mo is introduced by impregnation from an aqueous solution, in order to mimic the standard incipient wetness impregnation. Comparison between different preparation routes, impregnation vs. equilibrium adsorption (selective adsorption), is also considered. AFM, XAS, TEM and XPS show that the -Al 2 O 3 orientation has a clear impact on the strength of metal-support interactions at the oxide state with consequences on the sulfidation, size, stacking and orientation of MoS 2 slabs. Aggregation of molybdenum oxide particles is observed on the C (0001) plane suggesting weak metal-support interactions leading to high sulfidation degree with large slabs. Conversely, the presence of well-dispersed individual oxide particles on the R plane implies stronger metal-support interactions leading to a low sulfidation degree and shorter MoS 2 slabs. Both A and M facets, of similar crystallographic structure, display an intermediate behaviors in terms of sulfidation rate and MoS 2 size in line with intermediary metal-support interactions. Polarization-dependent Grazing-Incidence-EXAFS experiments as well as HR HAADF-STEM analysis allow us to demonstrate a surface-dependent orientation of MoS 2 slabs. A predominant basal bonding is suggested on the C (0001) plane in agreement with the existence of weak metal-support interactions. Conversely, a random orientation (edge and basal-bonding) is observed for the other planes. Generalization of these conclusions to industrial catalysts is proposed based on the comparison of the surface structure of the various model -Al 2 O 3 orientations used in this work and the predominantly exposed -Al 2 O 3 surfaces ((110), (100) and (111)).

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“…Recently, the aberration-corrected scanning transmission electron microscope (Cs-STEM) has attracted continuing interest due to its atomic-scale features [1][2][3][4][5]. The detection mode of the Cs-STEM high-angle annular dark-field (Cs-STEM-HAADF) has been proven to be extremely valuable for characterizing supported catalysts since catalytic reactions are extremely sensitive to structures.…”

Section: Introductionmentioning

confidence: 99%

Insight into the Microstructure and Deactivation Effects on Commercial NiMo/γ-Al2O3 Catalyst through Aberration-Corrected Scanning Transmission Electron Microscopy

Qiu

et al. 2019

Catalysts

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Atom-resolved microstructure variations and deactivation effects on the commercial NiMo/γ-Al2O3 catalysts were revealed by aberration-corrected scanning transmission electron microscope (Cs-STEM) equipped with enhanced energy dispersive X-ray spectroscopy (EDS). Structural information parallel to and vertical to the electron beam provides definitive insight toward an understanding of structure–activity relations. Under the mild to harsher reaction conditions, “fragment” structures (like metal single atoms, metal clusters, and nanoparticles) of commercial NiMo/γ-Al2O3 catalysts, gradually reduces, while MoS2 nanoslabs get longer and thinner. Such a result about active slabs leads to the reduction in the number of active sites, resulting in a significant decrease in activity. Likewise, the average atomic ratio of promoter Ni and Ni/(Mo + S) ratio of slabs decrease from 2.53% to 0.45% and from 0.0788 to 0.0326, respectively, by means of EDS under the same conditions stated above, reflecting the weakening of the promotional effect. XPS result confirms the existence of NixSy species in deactivated catalysts. This could be ascribed to the Ni segregation from active phase. Furthermore, statistical data give realistic coke behaviors associated with the active metals. With catalytic activity decreasing, the coke on the active metals regions tends to increase faster than that on the support regions. This highlights that the commercial NiMo/γ-Al2O3 catalyst during catalysis is prone to produce more coke on the active metal areas.

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Magnifying the Morphology Change Induced by a Nickel Promoter in Tungsten(IV) Sulfide Industrial Hydrocracking Catalyst: A HAADF‐STEM and DFT Study

Cited by 17 publications

References 34 publications

Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer

Fabrication of WS2/GaN p-n Junction by Wafer-Scale WS2 Thin Film Transfer

Surface-dependent sulfidation and orientation of MoS2 slabs on alumina-supported model hydrodesulfurization catalysts

Insight into the Microstructure and Deactivation Effects on Commercial NiMo/γ-Al2O3 Catalyst through Aberration-Corrected Scanning Transmission Electron Microscopy

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