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A new analytical cell to perform liquid sulfidation of HDS catalysts in industrial conditions was developed. It enables the alternate recording of time-resolved Mo and Co K edges X-ray Absorption spectra of bimetallic catalysts under high pressure (30 bar) and temperature (350°C) during the same reaction. Thanks to this cell, a comparative study of the species formed upon gas (1 bar, 15% H 2 S/H 2) and liquid sulfidation (30 bar, H 2 /gas oil/4% DMDS) of a CoMoP/Al 2 O 3 HDS catalyst was carried out, together with a discussion on the evolution of the concentration profiles upon activation. Different Mo and Co-based chemical species are involved during gas and liquid sulfidation. On one hand, in industrial liquid sulfidation, polymolybdate species are transformed into depolymerized oxides, then into an oxysulfide, a MoS x species and finally into MoS 2. On the other hand, gas sulfidation skips the depolymerization process because of the immediate supply of H 2 S at the beginning of the process and proceeds under a stepwise transformation of oxide into oxysulfide, itself into MoS 3 species and finally into MoS 2. Cobalt species under gas sulfidation goes through a CoS 2 intermediate whereas in liquid sulfidation, it is a 4-fold coordinated Co oxide species. Irrespective to the activation route, mixture of Co 9 S 8 and CoMoS is obtained at advanced sulfidation stage (T> 200°C).

A clear description of the morphology and location, with respect to the support, of metallic subnanometric particles remains a current strenuous experimental challenge in numerous catalytic applications such as naphtha reforming and biomass conversion. High-resolution HAADF-STEM coupled with in situ and tomographic analyses have been undertaken on a platinum (Pt) active phase supported on chlorinated alumina (γ-Al2O3) with 0.3 and 1 wt % Pt loadings, highlighting the formation of flat nanoparticles (NPs) of 0.9 nm diameter and Pt single atoms (SAs) in the reduced state. While SAs and weakly cohesive clusters are predominantly observed in the oxide state, with a coordination sphere of Pt composed of O and Cl as revealed by EXAFS, the ratio between SAs and Pt NPs in the reduced state is found to be about 2.8. This ratio is the same for the two metal loadings: both the total numbers of NPs and SAs increase at a higher metal loading. Electron tomography reveals that the vast majority of NPs are located on the edges or defects (steps, kinks) of the γ-alumina support crystallites. DFT calculations further highlight the optimized structures of NPs located at the γ-Al2O3 (110)–(100) edge and near-edge with a stability competing with NPs located either on the (110) or on the (100) γ-Al2O3 facet. A mathematical analysis of the segmented volumes shows that the average geodesic distances between NPs is linked to Pt loading: 9 nm for 1 wt % Pt and 16 nm for 0.3 wt % Pt. Evaluation of support tortuosity descriptors using the nanoparticle positions confirms a uniform distribution on the support. A square network geometric model compatible with the geodesic distances between NPs reveals that one to five NPs can be present at the same time on each alumina crystallite depending on Pt loading.

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Résumé -Quantification de surface de catalyseurs sulfures de type CoMoP par spectroscopie de photoélectrons X -Relation entre activité et sites promus -Partie I : Influence du rapport Co/Mo -Ce travail est dédié à la caractérisation de catalyseurs d'hydrotraitement CoMoP/Al 2 O 3 . Afin d'identifier l'environnement du cobalt et du molybdène, la spectroscopie de photoélectrons X (XPS), la microscopie électronique à transmission (MET) et les mesures d'activité ont été utilisées. En effet une approche quantitative de la caractérisation par XPS a été développée dans le cas de catalyseurs d'hydrotraitement de type CoMoP afin d'étudier l'effet du rapport atomique Co/Mo. Nous avons quantifié les différentes espèces présentes à la surface des catalyseurs et montré que le catalyseur présentant à la fois une activité maximale en hydrogénation du toluène et une concentration maximale de phase active mixte de type CoMoS, correspond au catalyseur de rapport atomique Co/Mo nominal de 0.5. Cependant la totalité des ions cobalt n'est pas engagée dans la phase mixte CoMoS. Abstract -X-ray Photoelectron Spectroscopy Surface Quantification of Sulfided CoMoP CatalystsRelation Between Activity and Promoted Sites -Part I: Influence of the Co/Mo Ratio -This work is dedicated to the characterization of CoMoP/Al 2 O 3 hydrotreatment catalysts. In order to identify the neighboring of cobalt and molybdenum, X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and activity measurements were used. Indeed, a quantitative XPS characterization was developed to study the effect of the Co/Mo atomic ratio on