M. Lacroix

Hydrodesulphurization activity and characterization of sulphided molybdenum and cobalt—molybdenum catalysts : Comparison of Alumina-, Silica-Alumina- and Titania-Supported Catalysts

The nature of the support effect in unpromoted (Mo) and promoted (CoMo) catalysts was examined by comparing the thiophene hydrodesulphurization activities of the catalysts supported on Al2O3, TiO2 and SiO2Al2O3. Catalyst samples were prepared by the incipient wetness impregnation method and characterized by photoelectron spectroscopy (XPS) and high-resolution electron microscopy (HREM). The activity per atom of molybdenum was higher for the TiO2-unpromoted and -promoted catalysts, but the synergistic effect was higher for the Al2O3, -supported catalysts. The absence of a significant shift in the titanium and molybdenum binding energies for catalyst supported on TiO2 and Al2O3 with respect to unsupported MoS2 catalyst does not support an electronic effect as the main cause of the great differences in activity between TiO2- and Al2O3- supported catalysts. The HREM results show clear evidence of the existence of smaller MoS2 particles on the TiO2-supported catalysts. Also, the addition of the promoter leads to the formation of smaller particles on the surface of the TiO2-supported catalysts. The differences in activity and synergistic effect for the different catalysts could be explained in terms of different activities for the smaller and larger particles. It is proposed that the difference in activity between the smaller and larger particles is related to the MoS2 crystallite orientation on the surface of the support.

Hydrogenating properties of unsupported transition metal sulphides

Group VI and Group VIII transition metal sulfides (TMS) have been widely used in hydrotreating catalysis. In addition to hydrogenation reactions, these processes involve removal of sulfur (hydrodesulfurization: HDS) and nitrogen (hydrodenitrogenation: HDN). Until now, HDN has not received as much attention as HDS, probably because sulfur compounds have historically been of prime importance. As petroleum feedstocks dwindle, the need for hydroprocessing oils containing larger amounts of heteromolecules will increase and industry will require more active materials. For this purpose, researchers may either improve the current catalysts of develop a new generation of catalysts based on transition metal sulfides presenting higher activities, stabilities, and selectivities toward desired compounds. The objective of the present work is to classify the hydrogenation performances of well-defined unsupported transition metal sulfides. These catalysts have been chosen since their characterization by physiochemical techniques, mainly X-ray diffraction (XRD), is easier than that for supported materials. Actually, it has been shown in several cases that the catalytic properties are closely related to the crystalline structure and the stoichiometry of the different phases which can be encountered for a given element. The catalyst were tested in the hydrogenation of biphenyl (HN of BP) as well as in the hydrodesulfurizationmorexa0» of dibenzothiophene (HDS of DBT) in order to compare the present results to previous studies. To evaluate the hydrogenating function, the HN of BP has been chosen preferably to the consecutive HN of BP resulting from the HDS of DBT.«xa0less

Hydrogen on unsupported ruthenium sulfide: Thermodesorption and 1H NMR studies

The interaction of transition metal sulfides with hydrogen is a complex process. Understanding this process is important due to the very large number of industrial processes dealing with these systems. The main utilization of these catalysts concerns catalytic hydrotreating which involves hydrogenation reactions and C-S, C-N, and C-O bond cleavage reactions carried out in the presence of high partial pressures of hydrogen. The complexity of the interaction of hydrogen with metal sulfides is related to its double role, as reactant and as modifier of the concentration of active sites. As a matter of fact, the interaction of hydrogen with the surface of the catalyst provokes its partial reduction, leading to coordinatively unsaturated metal ions which are directly involved in the adsorptive and catalytic properties. To tackle this fundamental problem of hydrogen adsorption on ruthenium sulfide, the authors have taken the fully sulfided state as starting point and evaluated the influence of progressive desulfurization on the amount of adsorbed hydrogen. The nature of the adsorbed species was investigated using thermodesorption and [sup 1]H NMR. 20 refs., 3 figs.

Catalysts for aromatics hydrogenation in presence of sulfur: reactivities of nanoparticles of ruthenium metal and sulfide dispersed in acidic Y zeolites

Zeolite-supported ruthenium sulfide and ruthenium metal catalysts were prepared with various Si/Al ratios, with and without extra-framework Al species. They were characterized by means of NMR, HRTEM and FTIR. For the sulfided catalysts, the activity for the tetralin hydrogenation, carried out in presence of H2S was very high and roughly 10 times the activity (expressed per gram of catalyst) of an industrial hydrotreating catalyst, i.e. NiMo/Al2O3. The differences in activities within the series of zeolites were discussed in terms of dispersion of the active phase and acidity of the zeolitic support. The catalytic properties of the metal catalysts were much lower than those of the sulfided catalysts in similar testing conditions.

Catalytic properties in hydrogenation and hydrodesulphurization reactions of ruthenium sulphide solid solutions containing iron, cobalt or nickel

Solid solutions MxRu1−xS2 (M = Ni, Co, Fe) were prepared by sulphidation of mixtures of hydroxides at 673 K; their crystallographic properties were studied by X-ray diffraction. These new materials present interesting properties in biphenyl hydrogenation and in thiophene hydrodesulphurization. The catalytic properties are strongly dependent on the nature of the metal associated to ruthenium. Cobalt-ruthenium catalysts present a good activity for hydrodesulphurization but very low activity for hydrogenation, iron catalysts exhibit low activity for both reactions, and nickel catalysts possess remarkable properties in hydrogenation and hydrodesulphurization (twice the activity of pure ruthenium sulphide). A comparison has been established with the properties of molybdenum sulphide catalysts promoted by the same elements.

Deactivation of MoS2 catalysts during the HDS of thiophene

Catalytic properties of unsupported MoS2 catalysts in the thiophene hydrodesulfurization reaction were determined in the temperature range 623–653 K. The catalysts were prepared by ex situ decomposition of ammonium thiomolybdate (ATM) crystals in a mixture of 15% H2S in H2 at 673 K. Activity of catalysts decreased very rapidly before reaching a steady state after 15 h on‐stream. The thiophene conversion went down from 10–12 to 3–4% in that time. The surface area of the catalysts also decreased during the catalytic reaction from 40–50 to 8–10 m2/g. Selectivity for hydrodesulfurization, hydrogenation and isomerization reactions was affected distinctly by the deactivation process. By increasing the reaction time, double‐bond isomerization increased, hydrogenation of butenes decreased and hydrodesulfurization remained constant. Results indicate that the main cause of activity decay was surface area loss that was due to sintering of MoS2 crystallites. Selectivity variation indicates that different active sites are involved for the three reactions. A deactivation model involving diminution of active sites located in edge and rim sites of small MoS2 particles is proposed to explain the variation of product distribution.

Unsupported nickel tungsten sulfide catalysts: Part 1: Catalytic behaviour in hydrogenation and hydrodesulfurization reactions.

Abstract The behaviour of a series of unsupported nickel tungsten sulfide catalysts has been investigated in the hydrodesulfurization of dibenzothiophene and hydrogenation of biphenyl under medium-high-pressure conditions (22.5 x 10 5 Pa). The results suggest that the activity may be related to the presence of a mixed “NiWS” phase. In contrast to the “CoMoS” species, the “NiWS” entity strongly promotes the hydrogenation function. A study of the stability of these catalysts indicated that under a poorly sulfided atmosphere phase segregation occurs.

Preparation characterization and catalytic properties of unsupported and molybdenum-promoted vanadium sulfides

Hydrotreating of light and crude petroleum feedstocks involves hydrogenation of unsaturated materials and sulfur, nitrogen, or oxygen heteroatom removals. These main reactions are catalyzed by Co or Ni-promoted molybdenum or tungsten sulfides supported on alumina. Such catalysts may also be required for treating heavier feedstocks containing organically combined metals. Among the different metals present in the feed, Ni and V are the most important ones, which are mainly associated with naphtenates and porphyrins complexes. Sulfide catalysts can break up these organic complexes but unlike the heteroatom removals, the Ni and V are deposited on the catalyst surface. The hydrodesulfurization (HDS), cracking (CK), and hydrodemetallation (HDM) activities decrease as a function of the extra metal loading. This work has shown that the vanadium concentration may reach 50 wt% and despite this high metal level, the catalyst retains a non-negligible activity. Studies tend to show that the residual activity of spent hydrotreating catalyst may be related to the presence of a mixture of vanadium and molybdenum sulfides with a possible influence of a sublayer of Co or Ni chalcogenides. The aim of this work was to investigate the catalytic properties of molybdenum-promoted vanadium sulfide. Special attention was devoted to the preparation andmorexa0» the characterization of the precursor, as well as of the resulting catalysts.«xa0less

Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions

Abstract The interaction of hydrogen over unsupported MoS 2 and RuS 2 has been investigated as a function of the sulfur to metal ratio. On these solids the presence of sulfur deficient sites is required to generate an activity and to allow hydrogen chemisorption. The nature of the adsorbed species differs depending on the catalyst under investigation. On RuS 2 , two types of hydrogen were evidenced by thermoflash desorption and inelastic neutron scattering: one was assigned to hydrogen adsorbed on surface sulfur anions while the other one is retained on coordinatively unsaturated ruthenium cations. By contrast, only SH groups were detected on MoS 2 . ESR measurements have shown that a fraction of chemisorbed hydrogen induces a modification of the concentration of paramagnetic Mo(V) and Mo(III) species. Thus both solids behave differently towards an hydrogen atmosphere. RuS 2 has a pseudometallic comportment whereas for MoS 2 redox or acid base properties are involved.

X.A.F.S. study of model vanadium sulphide phases suspected to form on HDM catalyst surfaces

Abstract This paper reports on structural investigations of the vanadium and sulphur environments in vanadium sulphide phases incorporated in a calcined δ-Al2O3 support. Evidence is produced showing the formation of V=O entities coordinated to additional oxygen and sulphur ligands. Striking analogies are found with the XAFS spectra of a vanadyl hydroxythiolate species [(OH)(SH):V=O]. Combining the structural information gained from both the V* K-edge and the S* K-edge EXAFS spectra of the latter compound, we have been led to propose for it a dimeric (or even polymeric) structure with disulphide bridges. The paper also includes a report of preliminary results relative to a real NiOue5f8MoO3ue5f8Al2O3 HDM catalyst after completion of a full catalytic cycle including presulphidation, hydrogenation of toluene (HYD) and hydrodemetallation.