Thiophene Hydrodesulfurization Activity Research Articles

Influence of ammonia on thiophene HDS at high pressures over noble metal catalysts for deep HDS applications

The thiophene hydrodesulfurization (HDS) activity of Pt/ASA, Pt/SiO 2, Ir/ASA and Ir/SiO 2 catalysts at thiophene concentrations of 300 ppm has been studied at 573 K and 20 bar. Pt/ASA showed the highest HDS activity. Nitrogen tolerance was investigated by co-feeding ammonia in gas phase concentrations from 10 to 1000 ppm. The amorphous silica alumina (ASA) supported catalysts were similarly strongly inhibited by the presence of ammonia, with even 10 ppm of ammonia causing a significant drop in activity, despite widely different dispersions. The SiO 2 supported catalysts were less severely affected by the presence of ammonia.

Sonochemical Synthesis of Nanostructured Molybdenum Sulfide

There is growing interest in nanostructured inorganic materials, in large part because they often exhibit properties distinct from those of the bulk that can prove useful in various applications, including heterogeneous catalysis.1-4 The established methods for the preparation of nanostructured inorganic materials include metal evaporation,5 reduction of metal salts,6,7 and thermal decomposition and laser pyrolysis of organometallic compounds.8,9 In addition, the sonochemical reaction of volatile organometallics is a recent and general synthetic approach to nanophase transition metal powders, alloys, carbides, and colloids.10-13 We report here a simple sonochemical synthesis of nanophase, high-surface-area molybdenum sulfide and the examination of its catalytic activity for thiophene hydrodesulfurization (HDS). MoS2 was prepared by irradiating a slurry of molybdenum hexacarbonyl and sulfur in 1,2,3,5-tetramethylbenzene (isodurene) with high-intensity ultrasound (20 kHz) under Ar.14a Elemental analysis of the purified powder indicates a stoichiometric molybdenum sulfide (S/Mo atomic ratio of 2.0) with a trace amount (<2 wt %) of carbon contamination. For comparison, a conventional molybdenum sulfide sample was also prepared by

Synergism between Brønsted acid sites and metal sulfide particles in the hydrodesulfurization of thiophene on ultrastable Y zeolite catalysts W/USY and Ni/USY

The influence of the acidity of ultrastable Y (USY) zeolite-supported tungsten or nickel sulfide catalysts, prepared at different pH values, on thiophene hydrodesulfurization activity has been studied. The acidity affects the catalysts' deactivation. The results of the initial activity clearly show a synergic effect between the metal sulfide centers and the Bronsted acid sites present in the zeolites. © 1998 SCI

Structure Effects of High Surface Area Molybdenum Nitride Powders, Macrocrystals and Nanoparticles as Catalysts for Thiophene Desulfurization

AbstractMo2N powder, macrocrystals and nanoparticles and porous Mo metal were synthesized using temperature programmed reduction of MoO3 powder and crystals with reactant feed gases consisting of NH3 N2/H2 mixtures and pure H2. The Mo-based catalysts were characterized using BET, XRD, TGA, SEM, and STM. The Mo-based catalysts were also analyzed for the hydrodesulfurization (HDS) of thiophene. The relatively lower surface area Mo2N macrocrystalline catalysts (SSA = 44 m2/g) have a greater area specific activity than that of the higher surface area Mo2N powder catalysts (SSA = 150 m2/g) for the HDS of thiophene. Mo metal catalysts have significantly lower activity for thiophene HDS than Mo 2N catalysts and the HDS selectivities of non-sulfided Mo metal catalysts are significantly different from those of Mo 2N catalysts.

Effect of Catalyst Oxidation State and Structure on Thiophene Hydrodesulfurization over Model Molybdenum Catalysts

Activity and product selectivity have been measured for thiophene hydrodesulfurization (HDS) over model silica-supported molybdenum catalysts at a pressure of 1 atm and at temperatures ranging from 398 to 673 K. The model catalysts feature isolated molybdenum atoms in the +2, +4, and +6 oxidation states and molybdenum dimers with each molybdenum atom in the +4 oxidation state. Silica-supported MoS2, prepared by deposition and decomposition of (NH4)2MoS4, was used for reference. There is a correlation between thiophene HDS activity and molybdenum oxidation state, with Mo(II) most active. Thiophene HDS activity does not show a significant structure dependence for isolated Mo(IV) versus dimeric Mo(IV) catalysts. Activation energies of 51.5 and 49.9 kJ/mol were determined for thiophene HDS over Mo(II) and MoS2/SiO2catalysts, respectively. Butane and butenes are the major products of thiophene HDS with little butadiene detected. Activity and selectivity trends suggest the HDS reaction is initiated by ηlbinding of thiophene on the supported metal catalysts.

Preparation of active HDS catalysts by controlling the dispersion of active species

It is demonstrated that the structural control of the metal ion precursors in the impregnating solution by adding the chelating agents is effective to prepare the higher active CoMo supported on alumina catalysts ( Co-Mo Al 2O 3 ) for hydrodesulfurization (HDS). Coordination structures of the Co and Mo complexes in the CoMo impregnating solution and distributions of the Co and Mo complexes were evaluated by spectroscopic characterization techniques and by using a computational calculation, respectively. An addition of a chelating agent, such as NTA (nitrilotriacetic acid) and Glu (L-glutamic acid), in the CoMo solution results in the selective formation of the Co complexes, while the amount of the Mo complex is negligibly small at the practical pH of 9.2. The addition of the chelating agent increases the thiophene HDS activity of the sulfided catalysts typically by 50%, compared with that prepared without the chelating agent. Dispersion results of Co and Mo species on both oxidic and sulfided catalysts indicate that the higher HDS activity is explained by the higher degree of surface exposure of Co sites (namely the dispersion of Co) rather than that of Mo sites. The selective formation of the Co-chelate complexes keeps Co ions stable in solution up to high concentration. Furthermore, the Co complexes are estimated to be stable on the support even in the initial step of calcination, which would depress the formation of crystalline Co compounds, such as CoAl 2O 4 and CoMoO 4. These effects result in the higher dispersion of the active Co surface species.

Thiophene Hydrodesulfurization over Alumina-Supported Molybdenum Carbide and Nitride Catalysts: Effect of Mo Loading and Phase

Alumina-supported β-Mo2C, α-MoC(1−x)(x≈0.5) and γ-Mo2N catalysts with Mo loadings in the range 1.5–20 wt% have been synthesized and characterized by X-raydiffraction and pulsed chemisorption (CO and O2) measurements. Thiophene hydrodesulfurization (HDS) activities weremeasured for the alumina-supported Mo carbide and nitride catalysts as well as sulfided Mo/Al2O3catalysts with the same Mo loadings. The HDS activities of the catalysts after 24 h at 693 K were observed to increase according to the trend: sulfided Mo≈α-MoC(1−x)<γ-Mo2N<β-Mo2C. The HDS activities of the different catalysts were found to correlate in a linear fashion with their CO and O2chemisorption capacities for the wide range of Mo loadingsinvestigated. Thiophene HDS turnover frequencies for the Mo carbide, nitride, and sulfided Mo catalysts are nearlyidentical, providing further evidence that the higher HDS activity of alumina-supported β-Mo2C and γ-Mo2N catalysts stems from ahigher density of active sites.

Chromia- and Chromium Sulfide-Pillared Clays: Preparation, Characterization, and Catalytic Activity for Thiophene Hydrodesulfurization

Chromia-pillared clay has been synthesized from naturally occurring montmorillonite through exchange of interlamellar ions with hydroxychromium polycations. Sulfidation of the heat-treated precursor with an H2S–H2mixture at 673 K results in the formation of chromium sulfide-pillared clay. The materials were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, scanning electron microscopy, electron probe microanalysis, and X-ray photoelectron spectroscopy. These methods showed that heat treatment of chromia-pillared clay under the conditions applied did not drastically change the pore structure or the chromium oxidation state and the distribution of pillars, but strongly influenced its aggregate morphology. Sulfide-pillared material has an interlamellar distance of 1.01 nm, a BET surface area of 256 m2g−1, a micropore volume of 0.082 cm3g−1, and a pore slitwidth of 1.24 nm. The sulfidation procedure does not significantly change the pillared structure or the chromium oxidation state. Sulfur is found to be present as practically uniformly distributed S2−species. The chromium sulfide phase in the finely dispersed and well-distributed state that is reached in sulfide-pillared clay is of primary importance to the high thiophene conversion over this catalyst. In the presence of this catalyst, thiophene hydrodesulfurization results exclusively in the formation of butane and butene. The distribution of hydrocarbons depends on the reaction temperature, with a higher butane yield at lower temperature.

Chromia and chromium sulfide pillared clays differing in pillar density

Chromia pillared clays differing in pillar density were synthesized from the Li-form of montmorillonite calcined in a controlled manner. These materials were characterized by XRD, TGA, AAS, nitrogen adsorption and their thiophene hydrodesulfurization activity. It is found that clays varying in cation exchange capacity pillared with Cr 12 pillar precursor ions can provide a family of catalysts that differ in surface area, porous structure and concentration of active sites. Sulfidation of the heat-treated chromia pillared clay resulted in the formation of chromium sulfide pillared derivatives with high surface area and well-developed porous structure. The activities for thiophene hydrodesulfurization and consecutive butene hydrogenation over chromium sulfide pillared montmorillonite are highest on clays with the largest pillar concentration and correlated with the total surface area. However, the activity per number of pillars increased with decreasing pillar density. Thiophene HDS predominantly results in the formation of butane and butenes, irrespective of the pillar population. The rate of deactivation is somewhat larger for catalysts that have a larger lateral pillar spacing. The chromium sulfide pillared clays exhibit a relatively high stability in thiophene HDS compared to zeolitic catalysts which is most likely due to their low protonic acidity.

Thiophene Hydrodesulfurization over Alumina-Supported Molybdenum Carbide and Nitride Catalysts: Adsorption Sites, Catalytic Activities, and Nature of the Active Surface

Mo2C/Al2O3and Mo2N/Al2O3catalysts have been synthesized and characterized by X-ray diffraction, pulsed chemisorption (CO and O2) and infrared (IR) spectroscopy, and temperature programmed desorption (TPD) measurements. Thiophene hydrodesulfurization (HDS) activities were measured for alumina-supported Mo carbide and nitride catalysts as well as a sulfided Mo/Al2O3catalyst, all with a 10 wt% Mo loading. The HDS activities (μmol Th/mol Mo/s) of the catalysts after 24 h at 693 K were found to increase according to the trend sulfided Mo<γ-Mo2N<β-Mo2C, and provide further evidence that carbide and nitride catalysts have the potential to replace sulfided Mo catalysts in commercial HDS reactors. X-ray diffraction analysis of fresh and tested 30 wt% Mo2C/Al2O3and Mo2N/Al2O3catalysts indicates that the bulk structure of the carbide (β-Mo2C) and nitride (γ-Mo2N) particles is retained, while IR spectroscopy of adsorbed CO indicates that the surface of the carbide and nitride particles becomes sulfided under reaction conditions. A model is proposed for the structure of the active catalytic surface of the alumina-supported Mo carbide and nitride catalysts in which a thin layer of highly dispersed sulfided Mo is present on the surfaces of the carbide and nitride particles.

Effect of fluoride on the structure and activity of NiW/Al 2O 3 catalysts for HDS of thiophene and HDN of pyridine

The effect of adding different amounts of fluoride to a γ-alumina used as support of NiW/Al 2O 3 catalysts was investigated using X-ray diffraction, diffuse reflectance spectroscopy (DRS), infrared spectroscopy of adsorbed NO (IR-NO), X-ray photoelectron spectroscopy (XPS), surface acidity, specific surface area and catalytic activity measurements. The catalytic activity was evaluated by two model reactions, namely thiophene hydrodesulfurization (HDS) and pyridine hydrogenation (HDN), in the temperature range 573–623 K using a flow system operated at 2 MPa (HDS) or 3 MPa (HDN) total pressure. DRS results of the oxidic precursors suggested that the effect of fluoride incorporation to the alumina support is that it increases slightly the octahedrally coordinated fractions of Ni and W. The XPS results of the sulfided catalysts showed that the dispersion of the Ni and W phases decreased progressively with increasing fluoride content. This technique also showed that these phases were only partially sulfided under the present experimental sulfiding conditions, and that the extent of sulfidation of such phases apparently tends to decrease slightly with increasing fluoride content, in contrast with the results suggested by the IR-NO spectra. The sulfur content of sulfided samples, as measured by chemical analysis, revelated that the sulfidation degree increased only slightly with increasing fluoride content. The activity for thiophene HDS was almost invariant with fluoride addition, but the subsequent hydrogenation of the intermediate products (butenes) was found to decrease linearly with the fluoride content. Possible interpretations for these changes in activity and selectivity, which reflect changes in the relative distribution of the different active sites for the two reactions, are discussed in relation with the structural variations of the active phases described above. In contrast, the activity for pyridine HDN increased considerably with the incorporation of small amounts of fluoride; this increase is mainly attributed to the increase in surface acidity which was observed with fluoride addition.

Preparation, Characterization, and Activity of Sulfided Catalysts Promoted by Co(CO)3NO Thermodecomposition

Various Co–Mo/Al2O3catalysts were prepared by deposition of Co(CO)3NO either on oxidic or sulfided Mo/Al2O3. The thermo-decomposition step was followed by IR spectroscopy, which showed that cobalt was preferentially deposited on the molybdenum phase. Thiophene hydrodesulfurization (HDS) activity was found to be higher when the precursor was deposited on sulfided Mo/Al2O3, while this catalyst was much more active than that prepared by the classical impregnation method. The nature and the amount of the surface sites of sulfided Co–Mo catalysts were assessed by Fourier transform infrared spectroscopy of adsorbed CO. Unpromoted and promoted coordinatively unsaturated Mo sites were identified on both ex-carbonyl nitrosyl and impregnated catalysts, but the ratio of the two types of sites was found to be strongly dependent on the preparation method. A good correlation was obtained between HDS activity and the integrated area of the IR band characteristic of CO adsorbed on the promoted sites. The high concentration of Co–Mo–S sites on ex-carbonyl nitrosyl catalysts may be related to the low amount of cobalt species on alumina, due to the mode of promoter introduction and to treatments subsequent to cobalt deposition which are milder on ex-carbonyl nitrosyl catalysts than on impregnated ones.

Effect of Surface Oxidation of the Support on the Thiophene Hydrodesulfurization Activity of Mo, Ni, and NiMo Catalysts Supported on Activated Carbon

The present investigation attempts to provide a better understanding of the influence of the nature of the carbon support on the HDS activity of Mo, Ni, and NiMo catalysts. For this purpose a high purity activated carbon was subjected to oxidative treatments with HNO3to modify its surface properties. NiMo catalysts supported on the resulting activated carbons were prepared and characterized by TPR, XRD, and SEM–EDX, and their activity for HDS of thiophene at 30 bars and 375°C was evaluated. The results obtained showed that oxidation of the carbon surface does not affect the HDS activity and other characteristics of the supported Mo phase. In contrast, the HDS activity of the Ni catalysts is enhanced by acid treatments of the carbon support. In this case, introduction of oxygen-containing functional groups (O(s)) leads to a strong interaction of O(s)–Ni during impregnation, which becomes essential to achieving and preserving high nickel dispersion. This effect on Ni dispersion is also reflected on the HDS activity of the bimetallic NiMo/C catalysts. The synergistic effect of the bimetallic catalysts is observed only when oxygen functional groups are present on the carbon surface, which are necessary for a good HDS activity, mainly because they enhance Ni–Mo interactions that produce the highly active Ni–Mo–S phase. A NiMoO4-like phase formed during impregnation seems to be the precursor for the active sulfide phase over the present NiMo/C catalysts.

NaY-Supported Molybdenum Sulfide Catalysts: I. Catalysts Prepared via Impregnation with Ammonium Heptamolybdate

NaY-supported molybdenum sulfide catalysts with increasing Mo loading have been prepared by impregnation with ammonium heptamolybdate and characterized by means of thiophene hydrodesulfurization (HDS), overall sulfur analysis, temperature programmed sulfidation, N2adsorption, Xe adsorption,129Xe-NMR, and high resolution electron microscopy. After impregnation nearly all Mo is located on the exterior of the zeolite particles. During calcination in air part of the Mo is redistributed, resulting in a higher amount of Mo being located in the zeolite supercages. For the sulfided catalysts an amount of Mo comparable to that after calcination is present in the supercages. At the highest Mo loadings the catalysts are incompletely sulfided, due to the presence of large “bulk-like” molybdenum oxide particles on the outside of the zeolite particles. The amount of Mo present in the supercages, as well as the thiophene HDS activity of the sulfided catalysts, increases with increasing Mo loading. The small Mo sulfide particles in the supercages contribute strongly to the thiophene HDS activity.

Thiophene hydrodesulfurization on sulfided nickel-exchanged USY zeolites. Effect of the pH of the catalyst preparation

Nickel-containing ultrastable HY zeolites prepared by ion exchange at pH 2.7, 5.6 and 11 (NH 4OH medium) were characterized in oxidic and/or sulfided state by X-ray diffraction, temperature-programmed reduction, scanning electron microscopy and energy dispersive X-ray analysis, and their thiophene hydrodesulfurization (HDS) activity and acidity were evaluated. A nickel-exchanged zeolite sample treated with a NaOH solution was also investigated. As regards to oxidic samples, significant differences in reducibility and, consequently, location of the Ni 2+ ions, which were mainly inside the zeolite cavities, were found. After sulfidation such differences were minor since most of the nickel sulfide species migrated to the mesopores of the zeolite particles. The zeolite samples having only one type of active site, either acidic (prepared at pH 2.7) or nickel sulfide species (treated with a NaOH solution), showed a low thiophene HDS activity. However, those that have both types of sites, such as the samples prepared at pH 5.6 and 11 (NH 4OH medium), exhibited a high activity for thiophene HDS and also for subsequent hydrogenation of butenes.

Catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization

A correlation exists between the number of surface acid sites and the catalytic activity of NiMo/TiO2−Al2O3 systems in thiophene hydrodesulfurization. The catalytic activity for thiophene hydrodesulfurization and surface concentration of Bronsted acid sites increase with the titania content in the TiO2−Al2O3 support.

HDS Activity and Characterization of Zeolite-Supported Nickel Sulfide Catalysts

Catalysts of nickel sulfide supported on zeolite Y have been prepared (by impregnation or ion exchange) and characterized by means of thiophene hydrodesulfurization (HDS), sulfur analysis, temperature-programmed sulfiding, 129Xe-NMR, HREM and dynamic oxygen chemisorption. The catalysts show large differences in catalytic behavior dependent on the preparation method (impregnation vs ion exchange) and the pretreatment conditions (method of sulfidation). Especially the ion-exchanged catalysts show a high initial activity, but due to the presence of acid sites deactivation is very strong. The initial activity of these catalysts can be improved significantly by drying prior to sulfidation. In all cases sulfidation results in quantitative formation of nickel sulfide, with Ni3S2 being the main product. Occasionally, also some NiS appears to be present. The major part of the nickel sulfide phase is invariably located on the outside of the zeolite particles. The fraction of nickel sulfide in the zeolite pores depends on the preparation method and the pretreatment conditions. The differences in catalytic activity are ascribed not only to variations in overall nickel sulfide dispersion but also to the acidity of the support, and the presence of very active small nickel sulfide clusters in the pores of the zeolite can have a strong influence on the thiophene HDS activity.

Influence of zeolite acidity on thiophene hydrodesulfurization activity

For H( x)NaY supported metal sulfide catalysts the intrinsic catalytic activity [thiophene hydro-desulfurization (HDS)] and the metal sulfide dispersion (dynamic oxygen chemisorption) are measured as a function of the acidity of the zeolite support (determined by ethylamine temperature-programmed desorption). The results show that the acidity can have a strong influence on both the conversion and the product selectivities. An increasing acidity results in an increase of the initial thiophene HDS activity. The increased activity is not caused by an increase in the metal sulfide dispersion, but, probably by a synergetic effect between the metal sulfide particles and the acidic zeolite support. The increase in initial thiophene HDS activity with increasing support acidity is also observed for cobalt, nickel and molybdenum sulfide catalysts prepared by impregnation using various zeolite supports (ZSM-5, Y, HUSY). The higher activity may be caused by an increase in thiophene adsorption in the zeolite pores, or by a direct effect of H + on the thiophene HDS reaction. Additionally, the acidic supports themselves also show a considerable initial HDS activity, indicating that the acid sites are able to desulfurize thiophene at reaction conditions.

In situ poisoning of the thiophene hydrodesulfurization activity of carbon-supported transition metal sulfide catalysts by phosphorus

Carbon-supported transition metal sulfide catalysts, prepared by pore volume impregnation of an activated carbon support with aqueous solutions of first, second and third row transition metal salts (Group V-VIII), drying and in situ sulfidation, were tested in thiophene hydrodesulfurization (723 K, 0. 1 MPa). In the poisoning experiments a bed of phosphorus compound-containing carbon was placed upstream of the catalyst bed. Under the sulfiding and reaction conditions the phosphorus compound was volatilized and transported to the catalyst bed where it could affect the catalytic properties of the active metal sulfide phase. This poisoning effect was different for the thiophene conversion to hydrocarbons and butene hydrogenation, and depended on the transition metal sulfide. Group VIII transition metal Sulfides were rather resistant towards the poisoning by the phosphorus compound. Only the hydrodesulfurization activity of the carbon-supported nickel catalyst was promoted in the presence of phosphorus. This beneficial effect of phosphorus on nickel might atso explain the gain in activity for the commercial Al 2O 3-supported Ni-Mo-P catalysts.

Characterization and Thiophene Hydrodesulfurization Activity of NaX Zeolite Supported Molybdena Catalysts

Abstract A series of NaX zeolite supported molybdena catalysts containing 1—15 wt% MoO3 has been prepared by impregnation method. They have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), temperature-programmed reduction (TPR), scanning electron microscopy (SEM), surface area, pore volume, Mo dispersion, and Mo extraction measurements. Zeolite crystallinity was found to be affected greatly only at 15 wt% MoO3 loading. XRD and SEM studies showed absence of any crystalline MoO3 phase. However, presence of bulk MoO3, particularly at higher loadings, was indicated by TPR and Mo extraction results. Tetrahedral surface molybdenum species are formed through strong interaction between molybdena and zeolite lattice through oxygen atoms. A direct relationship between Mo dispersion on the oxidic catalysts and their thiophene conversion activity was observed. In addition to Mo dispersion, acidity of the catalysts was also found to play an important role at high reaction temperature.