Surface Science Approaches for the Preparation of Alumina‐Supported Hydrotreating Catalysts

Bara, Cédric; Devers, Élodie; Digne, Mathieu; Lamic‐Humblot, Anne‐Félicie; Pirngruber, Gerhard D.; Carrier, Xavier

doi:10.1002/cctc.201500436

Cited by 28 publications

(36 citation statements)

References 158 publications

(240 reference statements)

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“…The measured hexagonal structure shows a lattice constant between the one of the substrate and the one implied by the bulk oxide. As the overall crystal structure, the structures of the low index surfaces of γ -Al 2 O 3 are still discussed controversially in literature [15,54] and based mostly on theoretical work [55][56][57]. Figure 4 can be best described by subnanometer-sized γ -Al 2 O 3 nuclei.…”

Section: Methodsmentioning

confidence: 99%

“…Several further metastable phases exist, e.g., γ -, δ-, θ -, χ -, κ-, κ -, and η-Al 2 O 3 [14]. γ -Al 2 O 3 is of special technological importance, as it is the most frequently used catalyst support for hydrotreating [15]. Despite its relevance, the detailed structure of γ -Al 2 O 3 is still under debate [14,16].…”

Section: Introductionmentioning

confidence: 99%

“…Its complex unit cell contains 92 atoms with Al s bound either pyramidally or tetrahedrally, adapting a structure that cannot be clearly assigned to any bulk phase [23]. The unique structure and the nonstoichiometric nature of this 2L-alumina oxide layer recently raised questions regarding to what extent this surface oxide could be an approximant of γ -Al 2 O 3 [15]. If the thickness of the alumina film could be increased, the influence of the substrate and the interface on the surface weakens, which is expected to result in alumina films that better represent the properties of bulk Al 2 O 3 phases.…”

Section: Introductionmentioning

confidence: 99%

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From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

et al. 2017

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Oxide thin films are of fundamental importance due to their applications in materials science, optics, corrosion protection, catalysis, and microelectronics. A multistep oxidation procedure is employed to precisely tune the alumina (Al 2 O 3 ) thickness on a NiAl(110) alloy from two atomic bilayers to 1.5 nm. Structural changes are analyzed with x-ray photoelectron diffraction and low-energy electron diffraction. The long-range order does not relate to any bulk structure and is imposed by the crystallized interface. The large unit cell formed at the interface persists in thicker films. In contrast, the local order changes at a thickness above 0.5 nm from the complex structure of this prelayer under the formation of subnanometer-sized γ -Al 2 O 3 (111)-type nuclei. The band structure is monitored with angle-resolved photoelectron spectroscopy. Increasing film thickness results in a slight decrease of the work function, but does not lead to significant changes of the electronic band structure. The presented multistep procedure opens a route for the synthesis of thin film structures in general and in particular provides fundamental insight in the surface structure of spinel-based transition Al 2 O 3 .

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

et al. 2017

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“…Surface-science type studies can help resolving this issue by using planar surfaces with wellcontrolled surface structure [8]. Specific reactivity of various surface orientations can thus be studied and compared to polycrystalline industrial materials.…”

Section: Introductionmentioning

confidence: 99%

“…These authors claimed that MoS 2 slabs are oriented parallel to the support on the most predominant -Al 2 O 3 (110) surface and show the highest sulfidation degree with respect to the other (100) and (111) orientations. However, the use of thin films epitaxially grown on an oriented substrate as models for -Al 2 O 3 has been questioned [8]. More recently, we showed that -alumina single crystals can be used as a suitable model for -Al 2 O 3 since there are many analogies between the surface structure of -Al 2 O 3 , the metastable polycrystalline industrial support, and -Al 2 O 3 , the thermodynamically stable alumina polymorph from which single crystal wafers can be grown [8,11].…”

Section: Introductionmentioning

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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Ursachen der unterschiedlichen Reaktivität von [AlCeO_x]⁺ (x=2–4) gegenüber Methan in Abhängigkeit vom Sauerstoffgehalt

Zhou

Schlangen

et al. 2016

Angewandte Chemie

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Die thermischen Gasphasenreaktionen der geschlossenschaligen heteronuklearen Metalloxidcluster [AlCeO x ] + (x = 2-4) mit Methan wurden mittels FT-ICR-Massenspektrometrie und quantenchemischer Rechnungen untersucht. Während [AlCeO 2 ] + und [AlCeO 4 ] + unter thermischen Bedingungen gegenüber Methan inert sind, reagiert [AlCeO 3 ] + spontan unter Wasserstoffatomabstraktion. Unter Berücksichtigung mechanistischer Aspekte konnten die Ursachen dieser deutlich unterschiedlichen Eigenschaften der [AlCeO x ] + /CH 4 -Paare aufgedeckt werden;d ie elektronische Grundlage der beispiellosen, einfachen Wasserstoffatomabstraktion von Methan durchd en geschlossenschaligen Cluster [AlCeO 3 ] + wird diskutiert.Aluminiumund cerhaltige Metalloxide stehen wegen ihrer katalytischen Funktion in vielen großtechnischen Umwandlungsprozessen von Kohlenwasserstoffen nach wie vor im Fokus der chemischen Forschung. [1] Um Einblicke in diese Prozesse zu gewinnen, wurden zahlreiche Gasphasenuntersuchungen durchgeführt, mit denen die Reaktionsmechanismen auf strikt molekularer Ebene aufgeklärt werden konnten. [2] So kann in Modellstudien zur Methanaktivierung das aktive Zentrum eines Katalysators nachgebildet und damit die katalytische Umsetzung von Methan in der kondensierten Phase verbessert werden. Während eine Reihe von alumini-) n ]C + (n = 3-5) [10] und [Al 2 TaO 5 ] + , [11] zur thermischen Aktivierung von Methan in der Lage ist, sind nur zwei Arten von cerhaltigen Clustern, nämlich [(CeO 2 ) n ]C + (n = 2-4) [12] und [(CeO 2 ) m (V 2 O 5 ) n ] + (m = 1, 2, n = 1-5; m = 3, n = 1-4), [13] bekannt, die unter thermischen Bedingungen spontan mit Methan reagieren. Darüber hinaus gibt es unseres Wissens keine Studien zur thermischen Methanaktivierung durch heteronukleare Al/Ce-Cluster in der Gasphase;ind er konden-sierten Phase dagegen werden Al/Ce-haltige Katalysatoren fürdie Methanaktivierung bereits genutzt. [14] Hier berichten wir, dass das geschlossenschalige Oxid [AlCeO 3 ] + unter thermischen Bedingungen ein Wasserstoffatom von Methan abstrahieren kann;i mU nterschied dazu sind die beiden Kationen [AlCeO 2 ] + und [AlCeO 4 ] + gegenüber diesem Substrat inert. Darüber hinaus ist das Verhalten von [AlCeO 3 ] + auch deutlich verschieden von dem anderer geschlossenschaliger Spezies wie [OTiH] + , [15] [AuCH 2 ] + , [16] [AuC] + , [17] [OSiOH] + , [18] [XHfO] + (X = F, Cl, Br), [19] [TaO 2 ] + , [20] [TaO 3 ] + , [21] [Al 2 TaO 5 ] + , [11] [AuTi 3 O x ] À (x = 7, 8) [22] und [AuV 2 O 6 ] + . [23] Zwar kçnnen auch diese Ionen Methan unter thermischen Bedingungen aktivieren, zur einfachen Wasserstoffatomabstraktion unter Verlust eines Methylradikals sind sie jedoch nicht in der Lage.D ie Ursachen der unterschiedlichen Reaktivitäten von [AlCeO x ] + (x = 2-4) gegenüber Methan sowie die besonderen Eigenschaften von [AlCeO 3 ] + werden hier diskutiert. Setzt man massenselektierte und thermalisierte [AlCeO x ] + -Ionen (x = 2-4) der Gegenwart von CH 4 aus, reagiert nur [AlCeO 3 ] + unter Bildung von [AlCeO 3 H]C + [Abbildung 1a und Gl. (1) (t...

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Surface Science Approaches for the Preparation of Alumina‐Supported Hydrotreating Catalysts

Abstract: International audienc

Cited by 28 publications

References 158 publications

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

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

Ursachen der unterschiedlichen Reaktivität von [AlCeO_x]⁺ (x=2–4) gegenüber Methan in Abhängigkeit vom Sauerstoffgehalt

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Surface Science Approaches for the Preparation of Alumina‐Supported Hydrotreating Catalysts

Abstract: International audienc

Cited by 28 publications

References 158 publications

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

From two- to three-dimensional alumina: Interface templated films and formation of γ−Al2O3 (111) nuclei

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

Ursachen der unterschiedlichen Reaktivität von [AlCeOx]+ (x=2–4) gegenüber Methan in Abhängigkeit vom Sauerstoffgehalt

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Ursachen der unterschiedlichen Reaktivität von [AlCeO_x]⁺ (x=2–4) gegenüber Methan in Abhängigkeit vom Sauerstoffgehalt