Hydrodesulfurization Activity Research Articles

Reactivity of Olefins and Thiophenes in Hydrodesulfurization of FCC Gasoline

The reactivity of olefins and S-compounds and their distributions in different catalyst-bed lengths were experimentally evaluated with a FCC gasoline in a high-pressure fixed-bed continuous flow pilot unit over the CoMoS/γ-Al2O3 catalyst. The evaluation results demonstrated that the increased steric hindrances around the double bond (C=C) and that to the thiophene molecules could suppress the hydrogenation of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. Meanwhile, the reaction temperatures could influence the acidic property of the CoMoS active phase confirmed by FT-IR analysis, and thus induced the different reactions. It was found that the isomerization of terminal olefins to internal olefins was promoted by the Brønsted acid sites (-SH) at low temperatures, as well as the skeletal isomerization by the strong Lewis acid sites occurred to a minor extent at high temperatures. Besides, the distributions of olefins and S-compounds in different catalyst-bed lengths showed that the removal of S-compounds reached 80% of its maximum conversion at the first 40% of the reactor length, however, the saturation of olefins increased linearly as the reactor length increased. Therefore, a new catalyst-loading method was developed, i.e., the upper 40% of the reactor length filling with catalyst of high HDS activity and the bottom 60% with catalyst of low olefin saturation activity, respectively. The evaluation results showed that the graded catalyst loading process showed higher selectivity in HDS of FCC gasoline.

Comparison of nitrogen tolerance of PdMo/Al2O3 and CoMo/Al2O3 catalysts in hydrodesulfurization of model compounds

Pd promoted Mo/Al2O3 sulfide catalysts were tested in hydrodesulfurization (HDS) of thiophene and benzothiophene in the presence of different amounts of basic nitrogen compounds (pyridine, quinoline) and compared with CoMo/Al2O3. The Pd promoted catalysts were in both HDS reactions more nitrogen tolerant than CoMo/Al2O3. In thiophene HDS in the presence of pyridine, the PdMo catalysts were more active than CoMo. This was explained by the higher C–N bond hydrogenolytic activity of the adsorbed intermediate piperidine, allowing its removal by hydrodenitrogenation (HDN) and the recovery of the catalyst surface. In HDS of benzothiophene in the presence of quinoline, the PdMo catalysts were comparable to the CoMo catalysts. The HDN intermediate, tetrahydroquinoline, was formed easily on all catalysts. This compound is strong inhibitor as quinoline and much less reactive than piperidine. The higher C–N bond cleavage activity of PdMo catalysts observed in the reaction of pyridine was not sufficient to break this adsorbed intermediate. This impeded the recovery of catalytic sites needed for HDS and resulted in HDS activity comparable to CoMo/Al2O3.

A general approach to the synthesis of metal phosphide catalysts

A simple and efficient approach to the preparation of hollow or porous metal phosphide nanoparticles was presented. Bulk and supported Ni2P, CoP, FeP, and Cu3P were successfully synthesized by reducing metal pyrophosphate precursors in flowing hydrogen. The structural properties of these samples are investigated using X-ray powder diffraction, transmission electron microscopy, inductively coupled plasma and X-ray photoemission spectroscopy. The Ni2P/SiO2 catalysts were used for the gas phase catalytic hydrodesulfurization of dibenzothiophene. The hydrodesulfurization activity of the catalyst reached 99% when the reaction temperature was 340°C. In the paper, a possible reaction mechanism was discussed to form Ni2P, CoP, FeP, and Cu3P. The route and mechanism could also be applied to the preparation of other metal phosphides.

Hydrogenation of Model Compounds Catalyzed by MCM-41-Supported Nickel Phosphide

MCM-41 supported nickel phosphide (Ni2P/MCM-41) was prepared by temperature-programmed reduction of the corresponding phosphate. The catalyst activity for hydrodeoxygenation (HDO), hydrodearomatization (HDA), hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) was investigated in a fixed bed reactor. O-cresol HDO, 1-methylnaphthalene HDA, quinoline HDN, dibenzothiophene HDS and simultaneous HDO, HDA, HDN, HDS were respectively tested at different temperatures with constant pressure (6.0 MPa), liquid hourly space velocity (3.0 h-1), hydrogen-to-oil volume ratio (600:1). The results indicate that Ni2P /MCM-41 catalyst has great performance on HDO, HDA, HDN, HDS in single model compound reactions. O-cresol and DBT are almost completely transformed at 375°C, while 1-methylnaphthalene and quinoline reach the highest conversion at 300°C. In the simultaneous reactions, quinoline shows higher conversion by competitive adsorption on the catalyst hydrogenation sites, leading to conversion decrease of o-cresol, 1-methylnaphthalene and DBT.

Microwave-assisted synthesis of MoS2/graphene nanocomposites for efficient hydrodesulfurization

This work presents a facile and rapid approach for the preparation of graphene sheet (GS) decorated by nanometer scaled molybdenum disulfide (MoS2) with effective hydrodesulfurization activity for carbonyl sulfide conversion at low temperature (<300°C). Using functionalized GS as microwave susceptor and ammonium tetrathiomolybdate as the precursor of MoS2, nanocomposites consisting of MoS2 nanoparticles and GS was prepared through a solvent-free microwave-assisted route. The synthesized MoS2 and GS hybrid (M-MoS2/GS) was characterized by X-ray diffraction, Fourier transform infrared spectrometry, Raman spectrometry, scanning and transmission electron microscopies as well as low temperature nitrogen adsorption. Compared to MoS2/GS and MoS2/activated carbon catalysts made by conventional thermal decomposition, the M-MoS2/GS composite shows excellent performance for the hydrodesulfurization of carbonyl sulfide. The high catalytic efficiency over M-MoS2/GS composite demonstrates that microwave irradiation is helpful for the preparation of graphene-based catalysts with enhanced catalytic activity. The low-cost synthesis procedure paves the way for the exploitation of the presented hybrid materials as catalysts for the hydrodesulfurization of coal-based gas.

Preparation of novel mesoporous Ce-Ni2P/SBA-15 catalysts and their catalytic performance for hydrodesulfurization of dibenzothiophene

Ni2P/SBA-15 precursors with Ni2P loadings of 25 wt% and initial P/Ni of 0.8 were prepared using nickel nitride as nickel source, diammonium hydrogen phosphide as phosphorus and mesopore molecular sieve SBA-15 as support. Then Ce was introduced into the Ni2P/SBA-15 precursor. The novel mesoporous Ce-Ni2P/SBA-15 catalysts were prepared after temperature-programmed reduction in flowing H2. The structure was characterized by X-ray diffraction, N2 adsorption–desorption isotherms, NH3 temperature-programmed desorption and X-ray photoelectron spectroscopy. The catalytic activities for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were evaluated. The results showed that only Ni2P phase was formed in Ce-Ni2P/SAB-15 catalysts with Ce loadings of 0–5 wt%. Ni2P and Ni12P5 phases were existed in 7 wt% Ce-Ni2P/SBA-15 catalyst. The surface area and pore volume increased when Ce was added to Ni2P/SBA-15 catalyst. The strength of the acid sites and total acid amount of Ce-Ni2P/SBA-15 catalysts increased with increasing Ce loadings. Ce existed in the form of Ce3+and Ce4+, Ni existed in the form of Ni2+ and Niδ+, and P existed in the form of Pδ− and P5+. The addition of Ce to the Ni2P/SBA-15 catalyst decreased Niδ+ concentration in Ni2P/SBA-15 catalyst. The activity for HDS of DBT over Ni2P/SBA-15 catalysts was affected by the addition of Ce at 300–340 °C. The catalysts exhibited a good catalytic performance of deep hydrodesulfurization of dibenzothiophene and the conversion of DBT can reach 98.9 % at 380 °C. Biphenyl was the main product over Ce-Ni2P/SBA-15 catalysts and cyclohexylbenzene was the main product over Ni2P/SBA-15 catalyst at 380 °C.

Relationship between active phase morphology and catalytic properties of the carbon–alumina-supported Co(Ni)Mo catalysts in HDS and HYD reactions

Effects of activated carbon of a carbon-coated alumina support and active phase morphology of transition metal sulfide (TMS) catalysts in hydrotreatment (HDT) of S-containing compounds were studied. The catalysts were synthesized from Anderson-type heteropoly compounds and characterized with multiple methods: X-ray powder diffraction, N2 physisorption, temperature-programmed desorption of ammonia, pyridine-adsorbed Fourier transform infrared spectroscopy, H2 temperature-programmed reduction, and high-resolution transmission electron microscopy. The catalysts were tested in hydrodesulfurization (HDS) of thiophene, dibenzothiophene and HDT of diesel. The results suggest that the catalytic activity in HDS and hydrogenation reactions depends on the shape of crystallites of the active phase. The results are interpreted using recently proposed concept of interlayer dynamics. This concept is helpful in establishing structure–activity relations for TMS.

A new preparation approach for NiCoP/SiO2 catalyst by solid phase reaction of nickel and cobalt cations with potassium dihydrogen phosphate

A NiCoP/SiO2 catalyst was fabricated by solid phase reaction of nickel chloride (NiCl2) and cobalt chloride (CoCl2) with potassium dihydrogen phosphate (KH2PO3). The structure and properties of NiCoP/SiO2 were characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis and Brunauer–Emmett–Teller in detail. A mechanism was postulated based on the results of thermal gravimetric analysis. The as-prepared NiCoP/SiO2 catalyst had excellent hydrodesulfurization activity, as indicated by using dibenzothiophene as the reactant. Hydrodesulfurization occurred sequentially following hydrogenation of dibenzothiophene and desulfurization in the presence of NiCoP/SiO2.

Novel Binary Promoter NiCoMo Layered Molybdate Catalyst: Synthesis, Characterization and Hydrodesulfurization Property

A novel binary promoter NiCoMo layered molybdate was synthesized as potential hydrodesulfurization (HDS) catalyst precursor by chemical precipitation from a solution containing nickel nitrate, cobalt nitrate and ammonium heptamolybdate. NiMo and CoMo layered molybdates were also prepared for comparison by the same method. The NiCoMo, NiMo and CoMo layered molybdates were characterized by means of N2 physisorption, XRD, FT-IR, TG–DSC–MS, SEM and HRTEM, and catalytic properties were evaluated in the continuous HDS of dibenzothiophene (DBT) and straight-run gas oil. The characterization results indicated the three precursors were endowed with the same structure of ammonium nickel molybdate, and catalytic results showed that the NiCoMo catalyst exhibited higher HDS activity towards DBT and straight-run gas oil, which might be more attractive for industrial applications.

Synthesis, Characterization, and Hydrodesulfurization Activity of Diatomite-Dispersed NiMoW Composition

Diatomite-dispersed NiMoW composition was synthesized by deposition-precipitation method. Diatomite was employed to disperse active metals for full utilization of active components. BET analysis showed diatomite-dispersed NiMoW composition had a higher surface area (97.0 m2/g) and pore volume (0.24 mL/g) in comparison with pure NiMoW composition. Sulfided diatomite-dispersed NiMoW composition exhibited excellent catalytic activity in hydrogenation test transmission electron microscopy images indicate the main reason for this result should be the different stacking numbers and the curvature of MoS2 or WS2.

Effect of morphology properties of NiW catalysts on hydrodesulfurization for individual sulfur compounds in fluid catalytic cracking diesel

Three catalysts NiW/Al2O3, NiW–P/Al2O3 and NiW–CA/Al2O3 with different morphologies but similar pore structures and acidity properties were prepared for studying the effect of morphology properties on the hydrodesulfurization (HDS) activity for individual sulfur compounds in fluid catalytic cracking (FCC) diesel. The morphology properties of the selected catalysts in oxidation and sulfidation states were characterized and the contents of individual sulfur compounds were determined by gas chromatography–pulse flame photometric detector (GC–PFPD). The results showed that NiW–P/Al2O3 possessed the highest edge density of WS2 phase and NiW–CA/Al2O3 had the highest stacking degree of multilayered WS2 phase. The HDS assessment showed that NiW–CA/Al2O3 demonstrated positive effects on the HDS of refractory sulfur compounds like 4,6-dimethyldibenzothiophene (4,6-DMDBT) or dibenzothiophene (DBT) with alkyl substitutes containing 3 carbons (C3DBT) but slight negative effects on the HDS of simple sulfur compounds such as benzothiophene (BT) with alkyl substitutes containing 1~5 carbons (C1~C5BT) and DBT with alkyl substitutes containing 1 carbon (C1DBT); while NiW–P/Al2O3 favored for the HDS of simple sulfur compounds. The present results indicated that the morphology of WS2 phase has a great influence on the HDS selectivity for different structured sulfur compounds.

Synthesis of a Ni2P catalyst supported on anatase–TiO2 whiskers with high hydrodesulfurization activity, based on triphenylphosphine

A solution method for preparing a Ni2P catalyst supported on anatase–TiO2 whiskers (Ni2P–PPh3) based on low cost triphenylphosphine (PPh3) is described. This approach suppressed the formation of the TiPO4 phase. The synthesis temperature is modest (603K). The Ni2P–PPh3 catalyst did not modify the anatase–TiO2 phase in any way, and it showed much higher hydrodesulfurization activity than the same catalyst prepared by the conventional TPR method.

A new multi–metallic bulk catalyst with high hydrodesulfurization activity of 4,6–DMDBT prepared using layered hydroxide salts as structural templates

Layered multi–metallic bulk catalysts NixZnyMoW with different Ni/Zn molar ratios were prepared based on the NiZn–layered hydroxide precursor by co–precipitation method and well characterized by various technologies including XRD, SEM, HRTEM and Raman spectroscopy. HRTEM images illustrated that both the slab sizes and stacking layers of sulfided catalysts were changed with different Zn contents. These catalysts were tested for hydrodesulfurization (HDS) of 4,6–dimethyldibenzothiophene (4,6–DMDBT) from model diesel. Hydrodesulfurization (HDS) reaction of 4,6–dimethyldibenzothiophene showed that all the catalysts NixZnyMoW with layered structure exhibited high HDS activity and the sulfur content in the model diesel can be reduced from 517ppm to less than 10ppm under mild reaction conditions of 3.0MPa of H2 pressure, 300°C, a LHSV of 9h−1, and H2/oil ratio of 800Ncm3/cm3. The catalysts NixZnyMoW have shown much higher specific HDS activity than that of the commercial catalyst CoNiMoW/Al2O3. However, ZnMoW without Ni has shown relatively low activity. The higher HDS activity of NixZnyMoW could be ascribed to high contents of active metals and the layered structure. Meanwhile, the synergism between Ni/Zn and Mo/W plays an important role in achieving the excellent HDS performance of catalysts NixZnyMoW.

The use of a natural Mexican zeolite as support of NiMoW sulphide hydrotreating catalysts

In order to examine the influence of type of metal precursor on the hydrodesulfurization (HDS) activity of synthetized samples, a series of ternary Ni–Mo–W catalysts supported on a natural Mexican zeolite (clinoptilolite) were prepared by sequential wet impregnation of the zeolite support with different thiosalts of W and Mo, and Ni(NO3)2·6H2O. The synthetized samples were characterized by N2 adsorption–desorption isotherms at −196°C, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX/SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) techniques. The catalysts activity was evaluated in the HDS of dibenzothiophene (DBT) reaction performed in a batch reactor at 350°C and 3.1MPa of total hydrogen pressure. The activity tests demonstrated that the best catalyst was the NiMoW-H/zeo sample synthesized from ammonium thiosalts. The use of tetraalkylammonium thiometalates as metal precursors led to the decrease in the HDS activity. The most active catalyst in the HDS of DBT reaction showed the largest density of active phases on the support surface determined from HRTEM measurements.

Effect of different preparation methods of MoO3/Al2O3 catalysts on the existing states of Mo species and hydrodesulfurization activity

Effect of different preparation methods of MoO3/Al2O3 catalysts on the existing states of Mo species and hydrodesulfurization activity was investigated. A series of supported Mo catalysts were prepared by equilibrium adsorption method (at 298K or at 373K) and incipient wetness impregnation method, with ammonium heptamolybdate as Mo precursor, γ-alumina and pseudo-boehmite as initial support. The results of pre-hydrothermal treatment and XRD characterization showed that different preparation methods can greatly influence the dispersion of Mo species. The results of LRS, TPR, XPS and HRTEM characterization clearly indicated that the existence of Al(OH)6Mo6O183- anions can hinder the reduction or sulfidation of Mo species. The HDS tests showed that the catalyst prepared by incipient wetness impregnation method exhibits the highest HDS activity for 4,6-DMDBT, owning to the predominance of well-dispersed polymolybdate species and the absence of Al(OH)6Mo6O183- anions.

Design and Synthesis of Metal Sulfide Catalysts Supported on Zeolite Nanofiber Bundles with Unprecedented Hydrodesulfurization Activities

Developing highly active hydrodesulfurization (HDS) catalysts is of great importance for producing ultraclean fuel. Herein we report on crystalline mordenite nanofibers (NB-MOR) with a bundle structure containing parallel mesopore channels. After the introduction of cobalt and molybdenum (CoMo) species into the mesopores and micropores of NB-MOR, the NB-MOR-supported CoMo catalyst (CoMo/NB-MOR) exhibited an unprecedented high activity (99.1%) as well as very good catalyst life in the HDS of 4,6-dimethyldibenzothiophene compared with a conventional γ-alumina-supported CoMo catalyst (61.5%). The spillover hydrogen formed in the micropores migrates onto nearby active CoMo sites in the mesopores, which could be responsible for the great enhancement of the HDS activity.

Effect of the amount of citric acid used in the preparation of NiMo/SBA-15 catalysts on their performance in HDS of dibenzothiophene-type compounds

In the present work, NiMo catalysts supported on SBA-15 were prepared with the addition of different amounts of citric acid (CA) in the impregnation solutions. The aim of this study was to inquire into the effect of the amount of citric acid on the activity and selectivity of the NiMo/SBA-15 catalysts in deep hydrodesulfurization (HDS). Catalysts were prepared by coimpregnation of Ni and Mo species from acidic aqueous solutions containing citric acid without further adjusting the solution's pH. The amount of citric acid used in the catalyst preparation was varied from CA:Mo molar ratio 0.5 to 2.0. In addition, a reference NiMo/SBA-15 catalyst was prepared without citric acid. After the impregnation, catalysts were dried (100°C, 6h) and calcined (500°C, 4h). The prepared catalysts were characterized by nitrogen physisorption, small-angle and powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), high resolution transmission electron microscopy (HRTEM) and tested in simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in a batch reactor at 300°C for 8h. XRD, DRS and TPR characterizations showed that Ni and Mo oxide species were well dispersed in all catalysts prepared with CA. In contrast, a NiMoO4 crystalline phase was detected by XRD in the reference NiMo/SBA-15 catalyst prepared without citric acid. Addition of citric acid to the impregnation solutions used for the catalyst preparation also resulted in an increase in the degree of sulfidation and in the dispersion of catalytically active MoS2 phase (elemental analysis, HRTEM). In accordance with this, HDS activity of the NiMo catalysts prepared with the addition of citric acid resulted to be significantly higher than that of the reference NiMo/SBA-15 sample for both sulfur-containing compounds tested (DBT and 4,6-DMDBT). It was found that the optimum amount of citric acid, which allows achieving the highest catalytic activity, corresponds to CA:Mo molar ratio equal to 1. Further increase in the amount of citric acid resulted in a slight decrease in the HDS activity. Regarding selectivity, addition of small amounts of CA, in general, resulted in an increase of the hydrogenation ability of the NiMo/SBA-15 catalysts. However, some differences in the selectivity of the catalysts were observed with different amounts of citric acid used.

An Efficient Approach to Produce Clean Diesel Fuel: Development of Catalysts With Ultra-High Hydrogenation Performance

The sulfur specification for diesel fuel has been tightened exponentially over the years. To help resolve this question, the authors aimed to develop a novel unsupported Ni-Mo sulfide catalyst with ultra-high hydrogenation performance, for the production of clean diesel fuel. This catalyst was prepared directly with ammonium tetrathiomolybdate and basic nickel carbonate as the catalyst precursors through the low-temperature solid-state surface reaction. XRD and HRTEM characterization results indicate that the stacking number of MoS2 layers is very high in the unsupported Ni-Mo sulfide. The evaluation results of model compound (dibenzothiophene) and FCC diesel fuel demonstrate that the unsupported Ni-Mo sulfide catalyst has excellent hydrodesulfurization activity and ultra-high hydrogenation performance, which can be attributed to the high stacking number of MoS2 layers.

Mesoporous Matrix Encapsulation for the Synthesis of Monodisperse Pd5P2 Nanoparticle Hydrodesulfurization Catalysts

The synthesis of monodisperse 5-10 nm Pd5P2 catalytic particles by encapsulation in a mesoporous silica network, along with preliminary data on hydrodesulfurization (HDS) activity, is reported. Precursor Pd-P amorphous nanoparticles are prepared by solution-phase reaction of palladium(II) acetylacetonate with trioctylphosphine at temperatures up to 300 °C. Direct crystallization of Pd5P2 in solution by increasing the temperature to 360 °C leads to sintering, but particle size can be maintained during the transformation by encapsulation of the amorphous Pd-P particles in a mesoporous silica shell, followed by treatment of the solid at 500 °C under a reducing atmosphere, yielding Pd5P2@mSiO2. The resultant materials exhibit high BET surface areas (>1000 m(2)/g) and an average pore size of 3.7 nm. Access to the catalyst surface is demonstrated by dibenzodithiophene (DBT) HDS testing. Pd5P2@mSiO2 shows a consistent increase in HDS activity as a function of temperature, with DBT conversion approaching 60% at 402 °C. The ability to control particle size, phase, and sintering is expected to enable the fundamental catalytic attributes that underscore activity in Pd5P2 to be assessed.

HDS and HDN on SBA-supported RuS2 catalysts promoted by Pt and Ir

Simultaneous hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions over RuS2/SBA and the effect of feed composition and the presence of Pt or Ir in the catalyst formulation have been studied. Activity tests were carried out in a flow reactor under a hydrogen pressure of 3.0MPa and WHSV 32h−1. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption desorption isotherms at −196°C, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy of adsorbed CO at low temperature. Characterization results reveal that under the presence of noble metals the dispersion of the RuS2 phase is not affected, the RuS2 coordinatively unsaturated sites (CUS) are in a very sulfided ambient and their population increases; while the noble metals are poorly sulfided and undergo reduction upon reaction. The evaluation of HDN and HDS activity for RuS2/SBA when both (dibenzothiophene) DBT and (quinoline) Q were present in the feed has highlighted the high activity of the RuS2 phase in hydrotreating. The HDS reaction is hardly affected by the presence of Q molecules, with only the hydrogenation (HYD) sites responsible for cyclohexylbenzene (CHB) formation being anyhow altered. HDN results improve in the presence of DBT, even showing high HDN conversion when Q is present in great quantities. These catalytic results strongly suggest that the HDN and HDS reactions must take place on different sites. CO-FTIR spectroscopy results have evidenced that N-containing molecules block the CUS sites responsible for CO adsorption although when S-containing molecules are present, N-containing molecules should be easily transformed since CO-adsorption sites are again available. The addition of small quantities of iridium and platinum to ruthenium sulfide improves the catalytic behavior of the RuS2 catalyst. This is probably due to the greater number of CUS sites and Ir and Pt acting as active hydrogen suppliers. Moreover, these noble metals can act as real active sites where the DBT HDS reaction takes place.