Thiophene Hydrodesulfurization Reaction Research Articles

IR spectroscopy evidence of MoS2 morphology change by citric acid addition on MoS2/Al2O3 catalysts – A step forward to differentiate the reactivity of M-edge and S-edge

Citric acid was used as chelating agent to prepare a series of MoS2/Al2O3 catalysts. CO adsorption followed by infrared spectroscopy characterization (IR/CO) was employed to probe the M-edge and S-edge of MoS2 slabs on these catalysts. Addition of citric acid promotes the growth of S-edge, whereas it inhibits that of M-edge: The morphology of MoS2 is progressively modified from a slightly truncated triangle with predominately M-edge to a hexagon with both M-edge and S-edge with increasing citric acid amount. Such morphology change is of great importance to the catalytic performance as M-edge and S-edge demonstrate different reactivity in hydrodesulfurization (HDS) reactions. Indeed, IR/CO data reveal that sulfur vacancy creation occurs more easily on M-edge, whereas at room temperature, thiophene tends to adsorb more strongly on S-edge. Moreover, parallel between IR/CO study and HDS test shows that S-edge has a higher intrinsic activity than M-edge in thiophene HDS reaction.

Ultrasound Assisted Synthesis and Physicochemical Characterizations of Fluorine-Modified CoMo/Al<SUB>2</SUB>O<SUB>3</SUB> Nanocatalysts Used for Hydrodesulfurization of Thiophene

A series of CoMo/F-Al2O3 nanocatalysts with different fluorine loadings of 0, 0.4, 0.8 and 1 wt% were successfully synthesized by a sonochemical method and used for catalytic hydrodesulfurization (HDS) of thiophene. The nanocatalysts were characterized with X-ray diffraction analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), BET nitrogen adsorption Brunauer-Emmett-Teller (BET) analysis, Fourier Transform Infrared Spectroscopy (FTIR) and temperature programmed desorption of ammonia (TPD-NH3) techniques. The XRD results showed a high dispersion of the molybdenum species on the γ-Al2O3 support due to the application of sonochemical method along with fluorine addition. The CoMo/F-Al2O3 nanocatalysts had a particle size less than 100 nm. The specific surface area of the samples was slightly decreased with increasing the fluorine content. The FTIR results confirmed that with the increase of fluorine amount in the CoMo/Al2O3 nanocatalysts, it would generate more active sites. Moreover, the TPD results showed that the fluorinated nanocatalysts had higher acidity than the promoter-free nanocatalysts, because of the formation of new strong acid sites on the γ-Al2O3 support by the promoter. The catalytic activity for thiophene HDS reaction was investigated in a stirred slurry-tank reactor in the atmospheric pressure to determine the effect of fluorine amount on the nanocatalyst performance. The results of thiophene HDS reaction showed that the fluorinated nanocatalysts were more active than fluorine-free nanocatalysts and consequently, they were able to remove nearly 100% of thiophene in the initial solution. Furthermore, the nanocatalyst with the fluorine content of 0.8 wt% had the highest activity in HDS of thiophene. However, further addition of fluorine led to decrease in catalytic activity which could be attributed to the agglomerated particles formed on the nanocatalyst surface.

Hydrodesulfurization enhancement of heavy and light S-hydrocarbons on NiMo/HMS catalysts modified with Al and P

Deep hydrodesulfurization (HDS) of oil fractions is a key process in petroleum refineries due to the increasing demand for S-free diesel and gasoline fractions. In this work, a series of NiMo catalysts supported on Al- and P-modified HMS mesoporous substrate were tested in the HDS of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to evaluate the effect of Al and P additives on the catalyst response in HDS reactions (thiophene at 1bar and 4,6-DMDBT at 5.5MPa). The catalysts were characterized by a variety of techniques (XRD, N2 adsorption–desorption, TPR, TPS, FT-IR of adsorbed pyridine, UV–vis and H2 chemisorption). NiMo/Al-HMS-P catalyst containing 1.0wt.% of P exhibited the best performance in both HDS reactions as a consequence of the proper balance between the active phase dispersion and the largest hydrogenation ability among the studied catalysts. The 4,6-DMDBT HDS reaction proceeded toward direct desulfurization (DDS) and hydrogenation (HYD) reaction routes. Concerning the HDS of thiophene, the increase of the catalyst acidity led to the formation of butadiene and diminished the hydrogenation of olefins (formation of butane). At the reaction temperature of 320°C, the NiMo/Al-HMS-P1.0 catalyst exhibited the highest activity and the lowest butane formation among the catalysts studied. The isomerization of olefins in the thiophene HDS reaction did not occur, in line with the observed absence of isomerization in the 4,6-DMDBT HDS reaction.

Hydrodesulfurization of Thiophene over Few‐Layer MoS2 Covered with Cobalt and Nickel Nanoparticles

AbstractThe hydrodesulfurization reaction of thiophene has been investigated over graphene‐like few‐layer MoS2 as well as over Co‐ and Ni‐nanoparticle‐covered few‐layer MoS2. Conversion of thiophene to n‐butane over few‐layer MoS2 is superior to that over bulk MoS2; the percent conversion is approximately 64 % at 450 °C. However, over few‐layer MoS2 covered with Co or Ni nanoparticles the conversion increases to approximately 98 % at around 375 °C as a result of the smaller nanoparticles being more effective.

Preparation, characterization of Mo catalysts supported on Ni- containing calcium deficient hydroxyapatite and reactivity for the thiophene HDS reaction

Ni-containing Calcium Hydroxyapatite (NiCaHAp; 3.31 wt.% Ni) was synthesized by coprecipitation and used as catalyst support. Molybdenum was supported on NiCaHAp by impregnation using ammonium heptamolybdate. The prepared catalysts Mo(x)/NiCaHAp (x: 2 to 8 wt % in Mo) were characterized by elemental analysis, XRD, FT-IR, N2 adsorption-desorption and TEM-EDX. The catalysts were sulfided in-situ at 673 K under flowing H2S/H2 (15 Vol.% H2S) and tested in hydrodesulfurization (HDS) of thiophene at 673 K. The main XRD peaks of hydroxyapatite CaHAp phase were observed in all samples and a peak due probably to crystalline MoO3 phase was also identified from the results. However, no crystalline phase of NiO was found for the catalysts, which showed its Ni species were highly dispersed. The sulfided catalysts Mo(x)/NiCaHAp presented are active in HDS of thiophene, despite the presence of some large MoO3 crystallites and incomplete sulfidation. This activity may be due to interaction of NiO and MoO3 on CaHAp resulting in the formation of Ni-Mo-S phase under flowing H2S/H2. When the molybdenum content increased the HDS activity increasead slightly, which was caused by the agglomeration of MoO3. The Mo(8)/NiCaHAp catalyst is about two times less active for thiophene HDS than the commercial NiMoP/Al2O3.

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

SiO2-supported monometallic and bimetallic platinum–gold catalysts are prepared by deposition of metal nanoparticles stabilized by mercaptopropyltriethoxysilane (MPTES) after different aging time of the solution containing metal ions and MPTES. The materials are tested in the hydrodesulfurization (HDS) reaction of thiophene and compared with corresponding catalysts prepared by the conventional deposition–precipitation (DP) method. The monometallic Pt and the bimetallic Au–Pt prepared by DP have comparable activity. With respect to the platinum catalyst prepared by DP, the corresponding platinum catalyst prepared by MPTES particle stabilization exhibits a substantial enhancement of the activity regardless the solution aging time. On the contrary, the MPTES-assisted Au–Pt catalysts have different activities, depending on the solution aging time, with the most active being the one obtained with the 5-day-aged solution. In accord with XRD, XPS, and FTIR, the aging time of the solution, through the different interaction of Pt or Au precursors with the mercapto groups, has a crucial effect on the structure and on the surface of the catalysts. The observed differences in the catalytic activity are related to the structural and compositional changes of the bimetallic particles.

Mesoporous catalysts based on Keggin-type heteropolyacids supported on MCM-41 and their application in thiophene hydrodesulfurization

A series of tungsten and molybdenum catalysts supported on MCM-41 were prepared using Keggin heteropolyacids (H3PM12O40, M=Mo or W) as active phase sources and compared with their analogues unsupported. The physicochemical characterization was carried out by, small angle and wide angle X-ray diffraction; thermogravimetric analysis/differential scanning calorimetry; ultraviolet–visible diffuse reflectance and Fourier transform infrared spectroscopies; N2 physisorption and potentiometric titration with N-butylamine, for determination, respectively, of the structure; thermal stabilities; integrity of heteropolyacids; textural properties and superficial acidity. The solids were tested in the thiophene hydrodesulfurization reaction at 400°C, atmospheric pressure and weight hourly space velocity of 0.48h−1. In this study, it has been demonstrated the importance of supporting heteropolyacids to increase the catalytic activity. Furthermore, it was proved a correlation between surface acidity and calcination temperature with the activity and stability of these catalysts in the hydrodesulfurization reaction.

Operando Observation of Ni2P Structural Changes during Catalytic Reaction: Effect of H2S Pretreatment

Abstract In situ X-ray absorption spectroscopy was used to study the effect of H2S pretreatment on the activation of Ni2P catalysts for the thiophene hydrodesulfurization (HDS) reaction. It was found that H2S treatment produced Ni–S bonds that were slightly longer and that had higher coordination numbers than those formed during reaction. The longer Ni–S bonds formed by H2S treatment were changed to the shorter Ni–S bonds by the catalytic reaction, and these shorter bonds were associated with high activity. The work provides evidence that a NiPS phase is active in the HDS reaction.

CCl4-Assisted Preparation of Highly Dispersed Molybdenum and Tungsten Nitrides

Nanoscopic transition metal nitrides were prepared by means of a newly developed technique, using nanoparticles of scheelites (AMO4, A = Ca, Sr, Ba; M = Mo, W) as precursors. After treatment with CCl4–NH3 gas mixtures the precursor salts were transformed to mixtures of alkali earth chlorides (ACl2) and transition metal nitrides (M2N). The thermodynamic driving force of the process is the high free enthalpy of the simultaneous formation of carbon dioxide and an electropositive chloride, from the interaction between CCl4 and AMO4. As a result, the gas–solid reaction occurs at relatively low temperature (500–550 °C). After water extraction of soluble chlorides, finely dispersed solids Mo2N x C y and W2N x C y (x = 0.79–0.95, y = 0.03–0.15) were obtained, which demonstrated high specific surface areas and well developed mesoporosity. Their catalytic activity was compared in the thiophene hydrodesulfurization reaction, where the active phase is provided by MS2 sulfides formed in situ under the reaction conditions, as confirmed by temperature-programmed reduction. Due to their open porosity, the solids as obtained demonstrated high activity and increased stability as compared to the same nitrides prepared by means of other techniques. The catalytic activity of the newly prepared nitrides was evaluated in the guaiacol hydrodeoxygenation (HDO) reaction. Molybdenum nitride showed promising HDO performance and unusual selectivity, whereas the tungsten homolog demonstrated poor activity.

New HDS catalysts based on thiol functionalized mesoporous silica supports

Mesoporous silicas, SBA-15 and HMS, were functionalized with mercaptopropyl groups by the single step procedure. The organomodified silicas and the bare mesoporous silicas were used as supports for CoMo catalysts. The final materials were analysed by several techniques such as N 2 physisorption (BET), DRS UV–vis, XRD, SAXS, TPR and XPS. The catalytic activities were evaluated in the hydrodesulfurization reaction of thiophene. The effect of the two different silica textures on the catalyst activity was rather small. However a significant enhancement of the catalytic activity was observed for the catalysts supported on the functionalized silicas. Taking into account the structural and spectroscopic results, the superiority of the thiol containing catalysts is attributed to the improved dispersion and reducibility of the precursor oxide species.

Post-synthesis alumination of MCM-41: Effect of the acidity on the HDS activity of supported Pd catalysts

Siliceous MCM-41 with different amount of alumina, from 0.25 up to 4.0 wt%, were prepared by impregnation of the MCM-41 with aqueous solution of Al(NO) 3·9H 2O. The modified mesoporous silicas were then used as supports for Pd catalysts prepared by wet-impregnation from PdCl 2 precursor. Supports and corresponding Pd catalysts were characterized by XRD, XPS and NH 3-TPD. The catalytic behavior was tested in the hydrodesulfurization (HDS) reaction of thiophene. An increase of the hydrodesulfurization activity with increasing alumina amount up to 0.5 wt% was observed. On the basis of the acidity change of the support and the structural modification underwent by the deposited palladium, the improved catalytic behavior was associated to the increased acidity of the supports and also to its effect on the palladium dispersion. A bi-functional mechanism, implying that metallic palladium activates the hydrogen and the thiophene molecules are adsorbed on the acid sites of the support, could be operative. However, the increased acidity was also responsible for the larger catalyst deactivation which limited the beneficial effect up to a certain amount of alumina content.

Synthesis and characterization of W-SBA-15 and W-HMS as supports for HDS

W-modified HMS and SBA-15 mesoporous materials (Si/W molar ratio equal to 40) were synthesized using sodium tungstate as tungsten source. In order to prepare NiW catalysts these mesoporous materials were impregnated with an aqueous solution of nickel salt of 12-tungstophosphoric acid Ni3/2PW12O40. The synthesized W-HMS, W-SBA-15 materials and NiW catalysts have been characterized by SBET, XRD, UV–Vis DRS, FT-IR, TPD of NH3, 29Si MAS NMR, SEM and HRTEM. The influence of these particular supports on catalytic activity of NiW catalysts was studied in the reaction of hydrodesulfurization (HDS) of thiophene. The results from the FT-IR and UV–Vis DR spectroscopy confirm incorporation of W into the HMS and SBA-15 structures. Additionally 29Si MAS NMR measurements revealed relatively stronger effect of W ion incorporation in HMS structure on degree of silica cross-linking as compared to the effect of W ion incorporation in SBA-15 structure. The catalytic study showed that both W-HMS and W-SBA-15 materials modified with W are good supports for NiW catalysts in the HDS reaction of thiophene. The catalysts show lower selectivity for butanes than a reference NiW/γ-Al2O3 catalyst leveling of about 10% for chosen experimental conditions.

The influence of reducing and sulfiding conditions on the properties of unsupported MoS 2-based catalysts

Unsupported MoS 2 catalysts were obtained from the decomposition of ammonium tetrathiomolybdate (ATM) at variable temperatures (400–700 °C) and under different gas compositions, from pure H 2S to pure H 2. The catalysts were further studied in the non-promoted state or promoted by Ni and Co. Catalytic activity and selectivity were studied in the model reaction of thiophene hydrodesulfurization (HDS). Surface areas, crystalline phase and particle size distributions were determined by Brunauer–Emmet–Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. A comparison of average values calculated from these techniques has enabled the understanding of the morphology of the solids. The catalysts were characterized before and after catalytic tests by X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS) and temperature-programmed reduction (TPR). Comparison of catalytic activity trends with the results of the characterizations show that over-stoichiometric sulfur, present in the fresh catalysts in the form of edge-located S 2 2 - species, plays a key role for the activity of unsupported MoS 2 and for its ability to be promoted. Direct hydrogenation (HYD) of thiophene to butane occurs presumably with the participation of –SH groups, produced from the opening of S–S bridges by hydrogen. Whatever the gas atmosphere, any treatment leading to the removal of over-stoichiometric sulfur leads to a decrease in HYD selectivity. Thus, very similar catalytic properties were observed for MoS 2 annealed at 700 °C in pure H 2, H 2S or N 2 gases. Ni and Co introduced by means of reflux with acetylacetonates, gave identical promotion trends for all the MoS 2 samples. The solids treated in pure H 2S could not take up promoter atoms at the edges, whereas for the H 2-reduced samples high promotion levels were achieved. The degree of stacking does not seem to have a significant impact on the thiophene HDS activity and selectivity of the unsupported MoS 2 catalysts.

Effect of Citric Acid Addition on Co−Mo/B2O3/Al2O3Catalysts Prepared by a Post-Treatment Method

Co−Mo/B2O3/Al2O3 catalysts were prepared by a post-treatment of the calcined states with citric acid (CA) and were tested for the hydrodesulfurization (HDS) reaction of thiophene. The catalysts were characterized by LRS, UV−visible spectroscopy, Mo K-edge EXAFS, TEM, NO adsorption capacity, and surface area measurements. Catalysts obtained by simultaneous impregnation with citric acid were also prepared for comparison. Sulfided catalysts were characterized by a chemical vapor deposition (CVD) technique using Co(CO)3NO. The addition of citric acid in a post-treatment more effectively increased the catalytic activity and NO adsorption capacity than did addition by a simultaneous-impregnation method. Co-CA and Mo-CA surface complexes formed at the expense of CoMoO4 and polymolybdates. The maximum potential activity of Co−Mo/B2O3/Al2O3 was obtained by a simple post-treatment of the calcined catalyst with citric acid.

Comparing the hydrodesulfurization reaction of thiophene on γ-Al2O3 supported CoMo, NiMo and NiW sulfide catalysts

The thiophene hydrodesulfurization (HDS) reaction on γ-Al2O3 supported CoMo, NiMo and NiW sulfide catalysts was compared in order to gain insight into the promoter effect on direct desulfurization (DDS) and hydrogenation (HYD) pathways. Ni-promoted Mo (or W) sulfide catalysts favor the hydrogen transfer reactions relative to CoMo sulfide catalyst, which facilitates the direct route instead. This different performance and also the dependence of the apparent Arrhenius parameters with the catalyst formulation were attributed to the major participation of Mo (or W) edge for the Ni-containing catalysts and S edge for CoMo sulfide catalyst upon the thiophene-HDS reaction.

Relation between sulfur coordination of active sites and HDS activity for Mo and NiMo catalysts

The structure of sulfidic Type I and Type II Mo and NiMo alumina supported hydrodesulfurization (HDS) catalysts was studied using infrared (IR) analysis of adsorbed CO. The results were compared to the catalytic activity in gas phase thiophene and liquid phase dibenzothiophene HDS reactions. IR analysis confirmed the presence of MoS 2- and NiMoS-type phases. The Type II NiMo catalyst (prepared using NTA as chelating agent) had a fully promoted edge structure, whereas the Type I (calcined) NiMo catalyst exhibited both promoted and unpromoted edge sites, confirming that NTA enhances the Ni-decoration of the MoS 2 edges. The active phase in both types of catalysts exhibited a dynamic and reversible behavior in terms of sulfur coordination. The catalysts exposed a higher number and/or a higher degree of coordinative unsaturation of vacant sites under gas phase thiophene HDS conditions than directly after sulfidation. The NiMo catalysts could be fully restored to their initial state by resulfiding after thiophene HDS, whereas some sites of the Mo catalysts were irreversibly blocked. Apparently, the NiMo catalysts were able to suppress coke deposition on the active sites under the conditions applied, in contrast to the Mo catalysts. An inverse correlation was found between the gas phase thiophene HDS conversion and the number of vacant sites present on the catalyst surface. A similar trend was observed for the ratio between hydrogenation and direct desulfurization of dibenzothiophene in the liquid phase HDS reaction. These correlations show that the thiophene HDS reaction and the dibenzothiophene hydrogenation pathway are catalyzed by sulfided species on the active phase, while the direct desulfurization pathway is catalyzed by vacant sites.

Hydrodesulfurization catalysts: Promoters, promoting methods and support effect on catalytic activities

CoMoS phases supported on γ-Al2O3, TiO2 and SiO2 were prepared using various synthesis methods and Co(NO3)2·6H2O or Co(acac)2·nH2O as precursors of the promoting agent. The catalysts obtained were tested in the thiophene hydrodesulfurization (HDS) reaction at atmospheric pressure. These experiments showed that the catalysts prepared by the impregnation of supported MoS2 with cobalt precursors exhibit better HDS properties than the catalysts prepared by successive impregnation of Mo and Co salts followed by a sulfidation step. Furthermore, with γ-Al2O3 and SiO2, the use of Co(acac)2·nH2O, without any further calcination after the impregnation, allowed even better catalytic activities. With TiO2, the promoting effect is identical whatever the Co precursor used. Des catalyseurs ≪CoMoS≫ supportés sur γ-Al2O3, TiO2et SiO2 ont été préparés en utilisant différentes méthodes de synthèse et Co(NO3)2·6H2O ou Co(acac)2·nH2O comme précurseur de l'agent promoteur. Les catalyseurs obtenus ont été testés en hydrodésulfuration (HDS) du thiophène sous pression atmosphérique. Ces expériences ont montré que les catalyseurs préparés par imprégnation de MoS2 supporté avec les précurseurs de cobalt conduisaient à une meilleure activité catalytique en HDS que ceux qui étaient préparés par imprégnation successive des sels de Mo et de Co suivie d'une étape de sulfuration. Sur γ-Al2O3et SiO2, l'utilisation du Co(acac)2·nH2O, sans calcination supplémentaire après l'imprégnation, conduit aux meilleures activités catalytiques. Avec TiO2 par contre, l'effet de promotion est le même quel que soit le précurseur de Co utilisé.

12-Tungstophosphoric heteropolyacid supported on modified SBA-15 as catalyst in HDS of thiophene

NiW catalysts have been synthesized by loading a Ni salt of the 12-tungstophosphoric heteropolyacid (H 3PW 12O 40) on Al-, Ti- and W- modified SBA-15. The supports and catalysts are characterized by BET, XRD, IR, DRS, TPR and TPD of NH 3. Results from XRD and IR measurements confirm the hexagonally ordered mesoporous structure and incorporation of Al, Ti and W into the SBA-15 support. It was found that incorporation of Ti- or W- into the SBA-15 structure increases the reducibility of NiW catalysts. The catalysts are tested in the hydrodesulfurization (HDS) reaction of thiophene. The NiW catalyst supported on W- containing SBA-15 showed higher performance in the HDS of thiophene as compared to the SBA-15 modified with Al and Ti.

In situ FT-IR spectroscopy investigations of carbon nanotubes supported Co-Mo catalysts for selective hydrodesulfurization of FCC gasoline

To better understand the nature of carbon nanotubes supported Co-Mo catalysts (Co-Mo/CNTs) for selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline, studies are carried out using in situ Fourier transform infrared spectroscopy (FT-IR). The catalytic performances of Co-Mo/CNTs catalysts were evaluated with a mixture of cyclohexane, diisobutylene, cyclohexene, 1-octene (60:30:5:5, volume ratio) and thiophene (0.5%, ratio of total weight) as model compounds to simulate FCC gasoline. The HDS experimental results suggested that the HDS activity and selectivity of Co-Mo/CNTs catalysts were affected by Co/Mo ratio; the optimal Co/Mo atomic ratio is about 0.4, and the optimum reaction temperature is 260° C in situ FT-IR studies revealed that 1-octene can be completely saturated at 200° C. In the FT-IR spectra of diisobutylene, the characteristic absorption peak around 3081 cm −1 for the stretching vibration peak of =C-H bond was still clear at 320° C, indicating that diisobutylene is difficult to be hydrogenated. As for the thiophene, no characteristic absorption peak could be found around 3092 cm −1 and 835 cm −1 when the reaction temperature was raised to 280° C, indicating that thiophene had been completely hydrodesulfurized. On the basis of FT-IR results, it can be deduced that thiophene HDS reaction occurred mainly through direct hydrogenolysis route, whereas thiophene HDS and diisobutylene hydrogenation reaction over Co-Mo/CNTs catalysts might occur on two different kinds of active sites.

Hydrodesulfurization of thiophene over CoMo/AlMCM-41

In this paper the application of a series of CoMo/AlMCM-41 catalysts with different Si/Al ratios was studied in the model reaction of thiophene hydrodesulfurization. The results obtained showed good catalytic activity for the formation of H2S, isobutene, 1-butene, n-butane, 2-trans-butene-and 2-cis-butene.