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A detailed kinetic model was proposed to analyze experimental data obtained from indole hydrodenitrogenation (HDN) over γ-Al2O3 and amorphous silica-alumina (ASA)-supported NiMo catalysts. The goal was to investigate the support acidity effects on indole HDN and compare with a recent study on quinoline HDN. Similarly to quinoline HDN, indole HDN occurred via hydrogenation of the aromatic ring, followed by N-ring opening and exocyclic C-N bond breaking. The high support acidity of NiMo(P)/ASA exhibited a promoting effect for N-removal steps and adsorption of nitrogen compounds. However, in contrast to quinoline HDN, it did not clearly induce a positive effect for the hydrogenation step. The acidic function of ASA also favored the formation of byproducts such as toluene, cyclohexane, dimer, and trimer of indole. Catalytic conversion of a quinoline and indole mixture revealed a strong inhibiting effect of quinoline on indole HDN, whereas the inhibiting effect of indole on quinoline HDN was weak. The inhibition was weaker over NiMo(P)/Al2O3 than over NiMo(P)/ASA. This result is in agreement with a relative ranking of apparent adsorption constants of quinoline, indole, and their products on NiMo(P)/Al2O3 and ASA. [ABSTRACT FROM AUTHOR]

A detailed kinetic study of the hydrodenitrogenation (HDN) network of quinoline was carried out over Ni-promoted MoS 2 catalysts supported either on γ-Al 2 O 3 or on amorphous silica alumina (ASA), the objective is to identify the role of the support acidity in HDN reactions. The kinetic data obtained from catalytic tests in a batch reactor were analyzed by a model including the liquid-vapor mass transfer. The adsorption constants of all intermediates and the kinetic constants of all elementary steps were estimated. We found that the NiMo(P)/ASA exhibited a higher rate constant in the hydrogenation of tetrahydroquinoline, which was the rate determining step of the main reaction pathway, and in exocyclic carbon-nitrogen bond cleavage reactions, than the NiMo(P)/Al 2 O 3 . Characterization data by Infra-Red spectroscopy of CO suggested that this result might be related to the modification of the electronic properties of promoted NiMoS phase due to higher acidity of ASA. However, the stronger self-inhibiting effect due to stronger adsorption of nitrogen compounds over NiMo(P)/ASA and its lower content of NiMoS phase decreased its global catalytic activity. [ABSTRACT FROM AUTHOR]

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 support-dependent genesis of MoS 2 on four planar single-crystal α-Al 2 O 3 surfaces with different crystal orientations (C (0 0 0 1), R ( 1 1 ¯ 0 2 ) , M ( 1 0 1 ¯ 0 ) , and A ( 1 1 2 ¯ 0 ) ). In contrast to classical surface science techniques, which often rely on UHV-type deposition methods, Mo is introduced by impregnation from an aqueous solution in order to mimic standard incipient wetness impregnation. Comparison between different preparation routes, impregnation vs. equilibrium adsorption (selective adsorption), is also considered. Atomic force microscopy, X-ray absorption spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy show that the α-Al 2 O 3 orientation has a clear impact on the strength of metal–support interactions in the oxide state with consequences for the sulfidation, size, stacking, and orientation of MoS 2 slabs. Aggregation of molybdenum oxide particles is observed on the C (0 0 0 1) plane, suggesting weak metal–support interactions leading to a high sulfidation degree with large slabs. Conversely, the presence of well-dispersed individual oxide particles on the R ( 1 1 ¯ 0 2 ) plane implies stronger metal–support interactions, leading to a low sulfidation degree and shorter MoS 2 slabs. Both A ( 1 1 2 ¯ 0 ) and M ( 1 0 1 ¯ 0 ) facets, of similar crystallographic structure, display intermediate behavior in terms of sulfidation rate and MoS 2 size, in line with intermediate metal–support interactions. Polarization-dependent grazing-incidence-EXAFS experiments, as well as high-angle annular dark-field (HAADF) scanning transmission electron microscopy analysis, allow us to demonstrate a surface-dependent orientation of MoS 2 slabs. Predominant basal bonding is suggested on the C (0 0 0 1) 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 comparison of the surface structure of the various model α-Al 2 O 3 orientations used in this work and the predominantly exposed γ-Al 2 O 3 surfaces ((1 1 0), (1 0 0), and (1 1 1)). [ABSTRACT FROM AUTHOR]

• VGO from conversion processes have a very different distribution of neutral nitrogen species than straight run VGOs. • Transition of neutral to basic N-species was observed for heavy coker gas oil. • DBE shift in basic nitrogen species depends on the number of the carbon atoms. • Neutral species with high DBE convert into carbazoles, which are "refractory". • Isomeric characterization is necessary for the selection of the reactivity descriptors. This paper is a part of a study on reactivity descriptors in vacuum gas oil hydrotreatment (VGO HDT). It aims to understand the differences in feeds of various process origins and the corresponding hydrotreated effluents on a molecular level. Four different vacuum gas oils were hydrotreated over a sulfided NiMo/Al 2 O 3 catalyst at a wide range of temperatures and residence times in order to collect HDT effluents at a broad range of hydrodenitrogenation (HDN) conversions. Vacuum gas oils and HDT effluents have been analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) in positive ESI(+) and negative ESI(-) electrospray ionization modes to characterize the basic and neutral nitrogen-containing species and the subtleties of HDT transformations depending on the feedstock type. [ABSTRACT FROM AUTHOR]

The role of the oxide support on the structure of the MoS2 active phase (size, morphology, orientation, sulfidation ratio, etc.) remains an open question in hydrotreating catalysis and biomass processing with important industrial implications for the design of improved catalytic formulations. The present work builds on an aqueous-phase surface-science approach using four well-defined a-alumina single crystal surfaces (C (0001), A (1120), M (lOlO), and R (1102) planes) as surrogates for y-alumina (the industrial support) in order to discriminate the specific role of individual support facets. The reactivity of the various surface orientations toward molybdenum adsorption is controlled by the speciation of surface hydroxyls that determines the surface charge at the oxide/water interface. The C (0001) plane is inert, and the R (1102 ) plane has a limited Mo adsorption capacity while the A (1120) and M (1010) surfaces are highly reactive. Sulfidation of model catalysts reveals the highest sulfidation degree for the A (1120) and M (1010) planes suggesting weak metal/support interactions. Conversely, a low sulfidation rate and shorter MoS2 slabs are found for the R (1102) plane implying stronger Mo-O-Al bonds. These limiting cases are reminiscent of type I/type II MoS2 nanostructures. Structural analogies between α-and γ-alumina surfaces allow us to bridge the material gap with real Al203-supported catalysts. Hence, it can be proposed that Mo distribution and sulfidation rate are heterogeneous and surfacedependent on industrial γ-Al203-supported high-surface-area catalysts. These results demonstrate that a proper control of the γ-alumina morphology is a strategic lever for a molecular-scale design of hydrotreating catalysts. [ABSTRACT FROM AUTHOR]

New developments and breakthroughs in the design of hydrotreating (HDT) catalysts for complying with fuel specifications and reduced sulfur contents ask for a continuous improvement in the molecular scale description of the active phase both at the oxide and sulfide states. HDT catalysts are mainly based on alumina-supported molybdenum nanophases and the present contribution is dedicated to review the surface science approaches that have helped gain a molecular-scale insight into the structure of the active-phase (mainly molybdenum) and the role of metal-support (mainly alumina) interactions through the use of well-defined surfaces and surface sensitive analysis techniques. The main focus of this Review is placed on model systems that can bridge the gap with industrial catalysts, that is, oxide-supported active phases prepared in aqueous conditions, as opposed to more traditional surface-science studies that consider metal-supported nanophases prepared in UHV conditions. The synthesis and structure of well-defined alumina surfaces (thin films and single crystal wafers) is first presented before discussing aqueous-deposition of Mo precursors on flat surfaces. The detailed role of the oxide support is then addressed with an emphasis on the genesis and structure of the MoS2 phase namely sulfidation rate, stacking, and orientation. [ABSTRACT FROM AUTHOR]

Review: 158 refs. [ABSTRACT FROM AUTHOR]