Article

One-step synthesis of mesoporous alumina-supported molybdenum carbide with enhanced activity for thiophene hydrodesulfurization

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Abstract

A new mesoporous alumina-supported molybdenum carbide (Mo2C/γ-MA) has been successfully prepared by one-step hydrolysis method without template, followed by carbonization with a mixed gas of CH4 and H2. The Mo2C particles (2.5 ± 0.3 nm) are homogeneously dispersed in the γ-alumina (γ-MA) framework and exhibit high catalytic activity and stability for thiophene hydrodesulfurization (HDS). Taking 1 wt% thiophene (3810 ppm S) as an example, the Mo2C/γ-MA exhibits 92% thiophene conversion, higher than the MoS2/γ-MA (85%), and other molybdenum carbides supported over commercial alumina and γ-MA prepared by the impregnation method. The stability test demonstrated that the Mo2C/γ-MA almost showed no deactivation during 150 h reaction, and no obvious carbon deposition and sulfurization of Mo2C species were observed over the spent Mo2C/γ-MA. The high HDS activity and stability of the Mo2C/γ-MA for HDS could be attributed to the formation of small Mo2C nanoparticles, appropriate surface acidity and the strong interaction between Mo2C species and alumina inhibiting the sulfurization of Mo2C species.

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... desirable electronic and magnetic properties, extreme hardness, and ionic charactericsts (Chen, 1996). However, they have additional advantages of being resistant to sintering at high temperatures, having strong interactions with nitrogen, sulfur and other heteroatoms in fuel and not causing C-C bond scission which leads to undesirable saturation of aromatics (Lin et al., 2021;Yue et al., 2021). They also have noble metal-like properties that make them effective hydrogenation catalysts (Yue et al., 2021). ...
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Ever-increasing concern on environmental impacts (e.g., sulfur pollution) by fossil fuels has triggered the research on hydrodesulfurization (HDS). In this work, Co-Mo nanoparticles were deposited on the mesoporous γ-Al2O3 support with the addition of organic compound, and the physico-chemical properties of the catalysts (Co-Mo-C/mesoporous γ-Al2O3) were then characterized by multi-techniques such as H2-TPR, HRTEM, XPS, N2 physisorption. It is found that the Co-Mo-C/mesoporous γ-Al2O3 catalyst is easier to be reduced when organic compound is added, enhancing the sulfuration. This results in better dispersion of Co-Mo-S species and more Co-Mo-S II active sites, which significantly enhance diesel ultra-deep hydrodesulfurization activity. Furthermore, this novel catalyst was also tested for HDS reaction in a 3000 kt/a industrial-scale plant. Gratifyingly, this catalyst showed effective reduction of sulfur content from 9000 to less than 10 μg/g and also high stability over 5000 h. The results are of great significance to the design and development of industrial HDS catalysts.
Article
MCM-41 was synthesized by a soft template technique. The specific surface area and pore volume of the MCM-41 were 805.9 m²/g and 0.795 cm³/g, respectively. MCM-41-supported manganese and cobalt oxide catalysts were prepared by an impregnation method. The energy dispersive X-ray spectroscopy clearly confirmed the existence of Mn, Co, and O, which indicated the successful loading of the active components on the surface of MCM-41. The structure and function of the catalysts were changed by modulating the molar ratio of manganese to cobalt. The 10%MnCo(6:1)/MCM-41 (Mn/Co molar ratio is 6:1) catalyst displayed the best catalytic activity according to the activity evaluation experiments, and chlorobenzene (1000 ppm) was totally decomposed at 270 °C. The high activity correlated with a high dispersion of the oxides and was attributed to the exposure of more active sites, which was demonstrated by X-ray diffraction and high-resolution transmission electron microscopy. The strong interactions between MnO2, Co3O4, MnCoOx, and MCM-41 indicated that cobalt promoted the redox cycles of the manganese system. The bimetal-oxide-based catalyst showed better catalytic activity than that of the single metal oxide catalysts, which was further confirmed by H2 temperature-programmed reduction. Chlorobenzene temperature-programmed desorption results showed that 10%MnCo(6:1)/MCM-41 had higher adsorption strength for chlorobenzene than that of single metal catalysts. And stronger adsorption was beneficial for combustion of chlorobenzene. Furthermore, 10%MnCo(6:1)/MCM-41 was not deactivated during a continuous reaction for 1000 h at 260 °C and displayed good resistance to water and benzene, which indicated that the catalyst could be used in a wide range of applications. © 2018 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences
Article
Four metal phthalocyanines (Pc-4, 8, 12, 16) functionalized ionic liquids were polymerized on the surface of silica gel as adsorbent materials. They were characterized by FT-IR, BET, SEM and TEM measurements. The characterization results proved that the adsorbents were prepared successfully. Their adsorptive desulfurization performances to dibenzothiophene in model oil at room temperature and atmospheric pressure were investigated in detail. The results showed that the adsorptive desulfurization effect of P-4 was best. The optimal amount of adsorbent was 10 g/100 mL model oil. The maximum amount of DBT adsorbed was 52.41 mg/g, superior to some previously reported adsorbents. The adsorption equilibrium and kinetics of this adsorbent were also examined. The adsorption behavior fitted well to Freundlich isotherm model, pseudo-second-order kinetics model and Weber and Morris kinetics model. Adsorption and regeneration by solvent processes were performed 10 times, and the adsorption capacity of the adsorbent did not decrease obviously. P-4 also had a good adsorption effect on different sulfur compounds, and the order of removal was DBT > BT > 2-MTH > TH.
Article
In this paper, a novel copper-based catalyst for FCC gasoline improving the ability of removal the sulfur and avoiding the loss of the octane number from olefin saturation by reactive adsorption desulfurization (RADS) was investigated. The series of Cu/ZnO-Al2O3 catalysts were characterized by X-ray powder diffraction (XRD), N2 adsorption analysis and temperature-programmed reduction (TPR) studies, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The experiment results showed that the catalysts had an optimum desulfurization ability with copper loading 6 wt%, which the sulfur contents of product decreased less than 10 μg/g and olefin contents decreased from 16.19% to 14.14% for the long period operation. The appropriate Cu loading content could lead to the high active and low apparent activation energy (E a). Therefore, the Cu-based catalyst may become a novel catalyst for second-generation for reactive adsorption desulfurization, which achieves the high desulfurization active and low olefins saturation to satisfy the upgrading the product.
Article
Low ash clean coal was produced from Indian coking coal through microwave irradiation or ultrasonication followed by solvent extraction in N-methyl-2-pyrollidone (NMP) containing smaller amount of Ethylenediamine (EDA) or Monoethanolamine (MEA). Pretreatment by ultrasonication followed by extraction with only NMP gave 10–15% higher clean coal yield of (56–58%) than extraction with only NMP (without pretreatment). Effect of using up to 10% EDA as cosolvent in NMP led to maximum clean coal yield. However use of EDA concentration beyond this showed decrease in clean coal yield and increase in ash contents. Clean coal yield increases because EDA is a strong polar solvent and strong base, which disrupts coal interactions and breaks bonds in coal by acid-base interactions. The extraction yield with and without pretreatment and microwave irradiation led to the enhancement in the yield of clean coal and was found to be in the range of 66–70% with microwave irradiation, which was 3–4% higher than without pretreatment. Clean coal Free Swelling Index (FSI) was improved by one unit. This was demonstrated at lab scale. Subsequently, this process was scaled up to 40 kg/batch coal mini-pilot plant.
Article
Dendritic mesoporous silica nanospheres (DMSNs) with center–radial pore structure were successfully fabricated via an anion-assisted method. Al-modified DMSNs-supported NiMo catalysts were prepared and used for hydrodesulfurization (HDS) of dibenzothiophene (DBT). The DMSNs supports and corresponding supported NiMo catalysts were characterized by SEM, TEM, N2 adsorption/desorption, electron tomography (ET), ²⁷Al NMR, NH3-TPD, UV–Vis spectroscopy, XPS, H2-TPR, Raman spectroscopy, and Pyridine-FTIR spectra. The average pore diameter of DMSNs is around 26.4 nm, which is helpful for eliminating the diffusion resistance of S-containing compounds. The center–radial pore structure of DMSNs, confirmed by ET measurement, is beneficial for enhancing the accessibility of active sites in the pore channels. The incorporation of aluminum into the framework of DMSNs can improve the acidity and modulate the metal–support interaction. Consequently, NiMo/Al-DMSNs catalysts exhibited higher HDS conversions (97.9%) for DBT than commercial NiMo/γ-Al2O3 catalyst. The superior catalytic activity of NiMo/Al-DMSNs results from a perfect combination of large center–radial pore channels, increased acidity, suitable metal–support interaction, and good dispersion/accessibility of active metals.
Article
The adsorption and dissociation of ethanol over molybdenum carbide were studied in the context of the production of H2 from alcohols. A β-Mo2C catalyst was prepared from char and Mo salts. The sample was characterized by N2 sorptometry at 77 K, temperature programmed reaction of H2, X-ray diffraction (applying Rietveld approximation) and X-ray photoelectron spectroscopy for investigating on the catalytic properties of the prepared sample. The catalyst would be active and stable for H2 dissociation at 500–600 K. The value of ethanol adsorption energy was −0.92 eV, as calculated on β-Mo2C (001) surface by means of self-consistent density functional calculations. A transfer of electron density from the surface to adsorbed ethanol was concluded from calculations. Plausible reaction pathways corresponding to ethanol dissociation to ethoxy were theoretically studied by using the Climbing Image Nudged Elastic Band (CI-NEB), which shows and activation energy value of 0.57 eV.
Article
Modification of the traditional Al2O3 support through addition of manganese to Al2O3 mixed Mn-Al oxides was herein envisaged to obtain highly active NiMo catalysts for hydrodesulfurization application. The effect of adding manganese was determined considering different Mn-Al2O3 supports synthetized using a sol–gel approach. The manganese-containing supports were furthermore impregnated with Ni(NO3)2 + (NH4)6Mo7O24 aqueous solutions at pH = 9 and characterized at their oxide state using UV–vis diffuse reflectance and Raman spectroscopies after drying and calcination steps. NiMo/Mn-Al2O3 catalysts were also characterized at the sulfide state mainly by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Finally, the sulfide catalysts were evaluated in the hydrodesulfurization of dibenzothiophene. Results show that the oxidation state of manganese species directly influences the nature of the Mo oxide species and their interaction with the Al2O3 support. At low Mn content (up to 0.5 mol% Mn as MnO), Mn²⁺ species leads to weaker interaction with the support and a higher intrinsic activity of the NiMoS species. However, these promoted sites are also formed in a lower amount than without adding Mn to the support. At too high manganese content (≥2 mol% Mn as MnO), Mn³⁺ species are formed and react with Ni to form a spinel phase decreasing the proportion of promoted phase to be formed after sulfidation. The highest activity is therefore observed at an intermediate Mn content of 1 mol% for which a higher intrinsic activity resulting from weaker support interaction and higher sulfidation rate combine together to achieve highly active NiMo HDS catalysts.
Article
The HDS activity and stability of Ni-Mo2C/AC catalysts, prepared by carbothermal hydrogen reduction (CHR) at different temperatures and with different Ni:Mo ratios, is reported. The highest HDS activity occurred for catalysts with Ni:Mo ratios of 0.38 and 0.19, when prepared at the relatively low CHR temperature of 550 and 600 °C, respectively. Partial sulfidation of the Ni-Mo2C/AC catalysts occurred rapidly upon reaction in 2 wt% dibenzothiophene (DBT) at 350 °C and 2.1 MPa H2. Uptake of S was enhanced with increased Ni content, resulting in the formation of Mo2C-MoS2 core-shell structures. The stack height of the MoS2 shell increased with increased Ni content and promoted the direct desulfurization of DBT.
Article
Ni–Ce oxides (NiO–xCeO2/γ-Al2O3) supported on mesoporous γ-alumina with various mass percentage contents of CeO2 (x = 0, 1, 2, 3, 4 and 5) were prepared through co-impregnation with citric acid. The influences of CeO2 content on the catalyst structure, surface characteristics, interaction between Ni species and the support, reducibility of Ni²⁺ ions and Ni particle dispersion were investigated in detail. The Ni–Ce oxides were highly dispersed on mesoporous γ-alumina and producing uniform Ni nanoparticles throughout γ-alumina frameworks after H2 reduction. The addition of CeO2 could lower metallic Ni particle sizes and generate oxygen vacancies. The reduced Ni–xCeO2/γ-Al2O3 catalysts were investigated for their catalytic behaviors in CO2 methanation and exhibited excellent catalytic performance at low temperature in the range of 150–350 °C. Equilibrium conversion of CO2 was achieved at a low temperature of 300 °C over the optimal CeO2 content of 3 wt%.
Article
Two series of SBA-16-supported CoMoW ternary sulfide catalysts with atomic ratio r =Mo/(Mo+W) ranging from 0.3 to 0.7 were prepared by the simultaneous impregnation of SBA-16andphosphated-SBA-16 substrates with metal precursors. The samples were characterized by a variety of techniques (chemical analysis, N2 physisorption, SEM, XRD, DRS UV-vis, TPR, TPD-NH3, Raman spectroscopy, HRTEM, XPS and coke burning). The catalytic performance was evaluated in the hydrodesulphurization (HDS) of dibenzothiophene (DBT), carried out in a batch reactor at 350Cand3.1 MPaof total H2 pressure. The maximum activity at the same atomic ratio r =0.4 was observed for the catalysts supported on SBA-16 modified with phosphorous (r =0.4(P)). HRTEM evidenced that this was because different MoS2 crystalline structures were formed: the P-free sample prepared with Mo/(Mo+W) atomic ratio of 0.6 (r =0.6) exhibited the MoS2-2Hcrystalline structure whereas the P-containing samples prepared with Mo/(Mo+W) atomic ratio of 0.4 (r =0.4(P)) exhibited the interplanar distance corresponding to (003) planes of MoS2-3R crystalline structure. Additionally, the best activity of the r =0.4(P) sulfide catalyst was linked with the enhancement of the WS2 species surface exposure accompanied with a larger sulfidation degree of W species (from XPS).
Article
Removal of sulfur from transportation fuels using zeolites as sorbents is an attractive desulfurization method, because of its low energy and cost requirements. However, diffusion limitations within the micropore structure of zeolites can reduce their adsorption capacity, especially when refractory sulfur compounds are present in fuels. Moreover, the selective adsorption of sulfur compounds from a mixture of hydrocarbons can be very challenging. The objective of this study was to address the aforementioned challenges of adsorptive desulfurization of fuels using metal-exchanged mesoporous Y zeolites. Mesoporosity was introduced in the Y zeolites by two top-down methods (desilication and surfactant-assisted). Metals, Ce and Cu, were introduced via ion-exchange. The prepared metal-exchanged mesoporous zeolites were characterized and tested in terms of their sulfur adsorption capacity using a fixed-bed column and model fuels. The strength of adsorption was determined using isosteric heat of adsorption calculations. Our results demonstrated that mesoporous Y reduced diffusion limitations and were very effective sorbents for removing sulfur compounds with high kinetic diameter, such as dibenzothiophene (DBT). Metals highly increased the selectivity toward sulfur compounds. According to experimental results, the tendency of thiophenic molecules to adsorb on the zeolites increase in the order of thiophene (TP) < benzothiophene (BT) < DBT. The results of this study revealed that metal-exchanged mesoporous Y zeolites have the potential to display remarkable sulfur removal properties since the mesopores allow access to zeolite active sites while the metal cations improve the selectivity and/or capacity for sulfur compounds.
Article
A universal strategy was developed for fabrication of highly active and durable precious-metal-free mesoporous Mo2C/graphene (m-Mo2C/G) electrocatalyst with a two-dimensional layered structural feature via a nanocasting method using glucose as a carbon source and an in-stiu assembled mesoporous KIT-6/graphene (KIT-6/G) as a template. The m-Mo2C/G catalyst exhibits high catalytic activity and excellent durability for hydrogen evolution reaction (HER) over a wide PH range, which displays a small onset potential of 8 mV, owerpotential (η10) for driving a cathodic current density of 10 mA•cm-2 of 135mV, a Tafel slope of 58 mV•dec-1, and an exchange current density of 6.31 ×10-2 mA•cm-2 in acidic media, and onset potential of of 41 mV, η10 of 128 mV, Tafel slope of 56 mV•dec-1, and an exchange current density of 4.09 ×10-2 mA•cm-2 in alkaline media, respectively. Furthermore, such m-Mo2C/G electrocatalyst also gives about 100% Faradaic yield , and shows excellent durability during 3000 cycles long-term test and the catalytic current remains stable over 20 h at fixed overpotentials, making it has great potential application prospect for energy issues.
Article
Carbothermal hydrogen reduction (CHR) of ammonium heptamolybdate impregnated activated charcoal (AC) yields a mixed Mo2C/MoOxCy catalyst. As the CHR temperature increases (from 600 to 800 ºC ) the Mo2C content increases. At 675 ºC graphite networks are generated that attach to the β-Mo2C particles and at ≥ 700 ºC agglomeration and sintering occur, all of which decrease catalyst activity. An optimal CHR temperature of ~ 650 ºC is identified based on the catalyst activity for the hydrodeoxygenation (HDO) of 4-methylphenol (4-MP) at 350 C and 4.3 MPa H2 and the high selectivity for direct deoxygenation (DDO; to yield toluene) versus hydrogenation (HYD: to yield cyclohexane). The Mo2C/MoOxCy catalysts have higher DDO selectivity than MoP, MoO2 or MoS2 when operated at similar conditions. The apparent activation energies for DDO (125 kJ/mol) and HYD (89 kJ/mol) are invariant among the catalysts with varying Mo2C content, but the rate per g Mo correlates with the CO uptake. The fact that the kinetics are not strong functions of the CHR reduction temperature and hence relative content of Mo2C versus MoOxCy, suggests that the active site of the catalyst is a result of O adsorption and/or exchange with the catalyst during reaction and these active sites occur on both Mo2C and MoOxCy during the HDO reaction.
Article
Ordered mesoporous NiMo-Al2O3 catalysts with 20.0 wt.% MoO3 and various NiO contents were synthesized by a facile one-pot evaporation-induced self-assembly (EISA) method, using P123 as structure-directing agent and anhydrous ethanol as solvent. The hydrophilic Al-, Ni-, and Mo-containing compounds surrounded the P123 micelles to form a hexagonal mesoporous structure. The NiMo-Al2O3 catalysts were characterized by a series of techniques, including N2 adsorption, XRD, XRF, TEM, SEM, FT-IR, TG-DSC (for the as-synthesized NiMo-Al2O3 precursors), and TPR. The catalytic activities were tested in hydrodesulfurization (HDS) of dibenzothiophene (DBT). Results show that calcination at 500 °C can fully remove the surfactant and solvent to form amorphous walls. Molybdenum and nickel atoms were incorporated into the channels of the ordered mesoporous alumina and highly dispersed, maintaining the hexagonal symmetry mesostructures. Incorporations of Ni promoted a transformation of molybdate from tetrahedral to octahedral sites and changed the relative intensities of the TPR peaks. Catalytic results reveal that the ordered mesoporous NiMo-Al2O3 catalysts had high activities towards DBT. Biphenyl was the abundant product in HDS reactions, and direct desulfurization was the dominant route. A high HDS activity was observed with a Ni/Mo molar ratio of 1:1, which was attributed to more easily reducible molybdate and better dispersion of the MoS2 nanoparticles. The ordered mesoporous NiMo-Al2O3 catalysts, synthesized by this facile one-pot EISA method, provide a new alternative for industrial HDS process.
Article
38% to 93% selectivity enhancement toward sulfur-free products was observed upon iridium addition to a palladium-only catalyst in the hydrodesulfurization of a refractory sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) at the same 40% conversion from a 300 ppm, S-containing feed at 5 MPa and 300 °C. Pd promoted hydrogenation to sulfurous intermediates, while Ir catalyzed C-S hydrogenolysis and also improved Pd resistance to sintering. The selectivity in the direct desulfurization path for the Ir-containing catalysts increased up to 26% versus 5% for the Pd-only catalyst. The bimetallic catalyst allowed for a decrease in S from 300 ppm to 11 ppm. It can be used at reduced pressure (3 MPa) with only a 15% decrease in hydrodesulfurization conversion as compared to the operation at 5 MPa.
Article
A highly active and stable electrocatalyst (MoSx@Mo2C) for hydrogen evolution is developed via the sulfur decoration of molybdenum carbide for the first time. Although the decoration of sulfur reduced the electrochemically active surface area and slightly enlarged the impedance resistance of Mo2C substrates, the turnover frequency was remarkably enhanced, resulting in a great improvement in the final hydrogen evolution reaction activity. More importantly, there is a synergistic effect between MoSx and Mo2C, making the MoSx@Mo2C catalyst exhibit an excellent activity with a small Tafel slope of 44 mV dec−1, which is among the best records for Mo2C-based catalysts.
Article
This work demonstrates the molecular engineering of active sites on a graphene scaffold. It was found that the N-doped graphene nanosheets prepared by a high-temperature nitridation procedure represent a novel chemical function of efficiently catalyzing aerobic alcohol oxidation. Among three types of nitrogen species doped into the graphene lattice—pyridinic N, pyrrolic N, and graphitic N—the graphitic sp2 N species were established to be catalytically active centers for the aerobic oxidation reaction based on good linear correlation with the activity results. Kinetic analysis showed that the N-doped graphene-catalyzed aerobic alcohol oxidation proceeds via a Langmuir–Hinshelwood pathway and has moderate activation energy (56.1 ± 3.5 kJ·mol–1 for the benzyl alcohol oxidation) close to that (51.4 kJ·mol–1) proceeding on the catalyst Ru/Al2O3 reported in literature. An adduct mechanism was proposed to be different remarkably from that occurring on the noble metal catalyst. The possible formation of a sp2 N–O2 adduct transition state, which can oxidize alcohols directly to aldehydes without any byproduct, including H2O2 and carboxylic acids, may be a key element step. Our results advance graphene chemistry and open a window to study the graphitic sp2 nitrogen catalysis.
Article
Mesoporous gamma-alumina (gamma-MA)-supported Ni-MgO catalysts were first prepared through one-pot hydrolysis of inorganic salts without surfactants and used for the prereformation of liquefied petroleum gas (LPG). The influence of MgO addition on catalyst structure, surface characteristics, distribution of Ni species, and reducibility of Ni2+ ions was investigated in detail. The prepared Ni-MgO/gamma-MA catalysts possessed wormhole-like mesoporous structures with large surface areas, narrow pore size distributions, and metallic Ni nanoparticles f homogeneously dispersed in gamma-MA frameworks. The results showed that MgO could improve catalyst surface basicity and lower metallic Ni particle sizes, resulting in significant enhancements in the activity, stability, and resistance to coke deposition for the prereformation of LPG. Comparative investigation of the prereformation of LPG over Ni-MgO/Al2O3 catalysts obtained by different routes revealed that the high stability and coke resistance ability were mainly due to the formation of smaller metallic Ni nanoparticles and stable support structures. (c) 2014 Elsevier Inc. All rights reserved.
Article
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.
Article
The facile synthesis of mesoporous γ-alumina is developed through the partial hydrolysis of Al(NO3)3 aqueous solution with (NH4)2CO3 without organic surfactants. In this synthesis, the stable NH4NO3/Al species (AN/Al) hybrid containing Keggin-Al13 polycations is first prepared, which is the key for the successful formation of mesoporous γ-alumina. XRD, 27Al MAS NMR, TEM, and N2 adsorption and desorption results demonstrate that the as-prepared AN/Al hybrid can be transformed to γ-alumina by treatment at 200 °C and exhibit a wormhole-like mesoporous structure with large surface area up to 450 m2 g−1, pore volume of 0.3 cm3 g−1 and narrow pore size distribution peaked at 3.9 nm after completely removing NH4NO3 at 300 °C. The obtained mesoporous γ-aluminas have high thermal stabilities up to 900 °C and excellent hydrothermal stability. The investigation shows that the synergetic effect of NH4NO3 and Al13 species promotes crystallization of Al species to γ-alumina, which may have a unique mechanism distinct from the mesoporous aluminas reported previously. CO2 adsorption measurements indicate that these mesoporous γ-aluminas have a much higher CO2 adsorption capacity than ordered mesoporous alumina synthesized by the surfactant-templating method and conventional γ-alumina derived from aluminum oxyhydroxides. We believe that this research should be useful for providing new insights into the transformation of transition alumina phases and for synthesizing mesoporous γ-alumina with promising properties for various chemical applications.
Article
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.
Article
Nanostructured beta-Mo2C on an ultrahigh surface area carbon material (>3000 m(2)/g), a kind of novel carbon material with uniform pore distribution, was prepared by the carbothermal hydrogen reduction method. The Mo precursor and Mo2C have been characterized by X-ray diffraction, nitrogen adsorption, high-resolution transmission electron microscope, and tempera Lure-programmed reduction mass spectroscopy. The data show that nanostructured beta-Mo2C can be formed on the ultrahigh surface area carbon materials by carbothermal hydrogen reduction at similar to700 degreesC. The particle sizes of beta-Mo2C increase with the increase of reaction temperatures. The carbothermal hydrogen reduction includes two successive steps: reduction of the MoO3 precursor by hydrogen and reaction between partially reduced molybdenum oxides and surface carbon atoms of carbon materials under the hydrogen atmosphere.
Article
The C-S bond cleavage of 1.33 mm Hg of tetrahydrothiophene or 1-butanethiol with 22 mm Hg of hydrogen or helium present was studied at 521°K on alumina-supported, presulfided, hydrogen-reduced catalysts containing approx. 11.5Vertical Bar3< molybdenum trioxide and 0, 3.93, and 4.93Vertical Bar3< cobalt oxide. The products from tetrahydrothiophene were 1-butene, 2-butenes, butane, and 1,3-butadiene, and their distribution resembled that previously reported for the desulfurization of thiophene. Butanethiol yielded higher proportions of butane, which suggested that no interconversion between these two sulfur compounds occurs. The results confirmed that desulfurization and hydrogenation proceed on different but related sites, and indicated that ring hydrogenation of thiophene occurs prior to C-S bond cleavage. A mechanism is proposed which involves the hydrogenation of thiophene to tetrahydrothiophene, dehydrosulfurization to 1,3-butadiene, and subsequent hydrogenation to butenes and butane. The scheme differs from mechanisms developed by other researchers and may be specific to the low pressures used in the experiments.
Article
Temperature-programmed carburization of W2N and Mo2N powders in CH4-H2 mixtures up to 1150 and 970 K, respectively, leads to metastable face-centered cubic carbide phases. The reaction is topotactic in the sense that the face-centered cubic structure of the metal atoms remains unaltered, while the nitrogen and carbon atoms exchange their interstitial positions. Thus, the product retains the structure, crystallite size, and high specific surface area of its nitride parent, namely, 55 and 185 m2 g-1 for beta-WC1-x and alpha-MoC0.45, respectively.
Article
In the presence of sucrose, hierarchical mesopores alumina was prepared and used as hydrodesulfurization catalyst support. The pore structure and acidic property of the alumina can be easily controlled by pH value and concentration of precipitator. The physical and chemical properties of catalysts are apparently changed when this novel structure alumina are introduced as support. The interaction between active component and support is decreased. The Mo species are facilely reduced and there are less acid sites on the surface of the catalysts. The unique properties make this catalysts possess higher conversion and desulfurizing ratio for 4,6-DMDBT in this study.
Article
Hydrodesulfurization is a well-documented process which has been commonly used in the refining of crude oil for over 60 years. It is a process for which interest is frequently renewed due to the requirement to use new feedstocks and the application of more severe environmental legislation, for example, the need to reduce sulfur levels in fuels. Of particular importance in achieving low sulfur levels in fuels is the problem posed by a particular class of compounds, namely hindered dibenzothiophenes, e.g. dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. Dibenzothiophenes demonstrate resilience to hydrodesulfurization using current catalyst formulations. This overview addresses the key area of hydrodesulfurization chemistry concerning the desulfurization of highly hindered sulfur containing molecules.