Mo Ratio Research Articles

Sulfur exchange capacity and thiophene hydrodesulfurization activity of sulfided molybdena-alumina catalysts promoted by nickel

The capacity of sulfur exchange (i.e. S TE—the total number of exchangeable sulfur atoms) has been determined at 673 K in a circulation system with H 2S (partial pressure ∼2.5 and 25 kPa) for five sulfided catalyst samples: molybdena-alumina (Mo12), NiO/Al 2O 3 (Ni12) and three Ni-promoted molybdena-alumina with different Ni:Mo ratios [NiMo(0.X)]. A linear correlation has been found between the S TE values and thiophene hydrodesulfurization activity of the catalyst samples, containing Mo. The S TE values have been determined also in exchange between catalyst sulfur and thiophene, for three samples: Mo12, Ni12, and NiMo(0.35) for comparison of the S-exchange affinity of S in thiophene with that in H 2S. The isotope exchange capacity of sulfur bound to the catalyst ( 35S cat) with sulfur in H 2S was substantially higher than that with sulfur in thiophene, but the sequence of the S TE values was similar for the three samples, i.e., NiMo(0.35) > Mo12 > Ni12.

Water–gas shift activity of K-promoted (Ni)Mo/γ-Al2O3 systems in sulfur-containing feed

The effect of potassium additive on the catalytic activity of nickel–molybdenum alumina-supported systems has been studied by varying the molybdenum content within 5–18 mass% MoO3, reaction temperature from 180 to 400 (500)°C, and steam to gas ratio of 0.3, 0.7, and 1. It has been established that potassium reduces the activity of one-component Mo-containing samples, while, independent of molybdenum loading, nickel promotes activity within the whole temperature range studied and extends the temperature range of catalytic activity by about 70°C to lower reaction temperatures. A symbatic or additive, or antibatic catalytic behavior was observed with NiMo-containing samples depending on the atomic Ni/Mo ratio and temperature range. Potassium, being a third component in tri-component KNiMo-containing samples, enhances the water–gas shift (WGS) activity depending on the atomic K/(Ni + Mo) ratio. The activity approaches the equilibrium conversion degree in the interval of 320–500 °C. A decrease in the specific surface area of calcined and tested samples relative to the bare support shows close values indicating that the overall dispersion of the species is not changed during the catalytic test. Close examination indicated that the sample containing K2O, NiO, and MoO3 of 4.9, 2.5, and 12.7 mass%, respectively, was found to be the most suitable catalyst for water–gas shift reaction with sulfur containing feed since it attains equilibrium conversion even at 300 °C, and at a low steam to gas ratio of 0.3 atm. This catalyst demonstrates a stable and reproducible catalytic activity as inlet gas loading is increased.

Simultaneous hydrodesulfurization of benzothiophene and dibenzothiophene over CoMo/Al2O3 catalysts with different [Co/(Co + Mo)] ratios

A series of CoMo/γ-Al2O3 catalysts was prepared with [Co/(Co + Mo)] ratios of 0.3, 0.4 and 0.5 while maintaining a total metal content of 19 wt%. These catalysts were tested in a batch autoclave reactor after presulfiding with the objective of studying the influence of Co/(Co + Mo) ratio on the hydrodesulfurization (HDS) pathways of benzothiophene (BT) and dibenzothiophene (DBT). The results of this study have clearly demonstrated that the Co/Co + Mo ratio has a significant influence on the overall HDS of BT and DBT as well on the direct desulfurization (DDS) pathway, but showed no influence on the hydrogenation pathway. A Co/Co + Mo ratio of 0.4 was found to be optimum for both overall HDS as well as the HDS by DDS pathway.

ChemInform Abstract: Tunable and Rapid Crystallization of Phase Pure Bi2MoO6 (Koechlinite) and Bi2Mo3O12 via Continuous Hydrothermal Synthesis.

AbstractPhase pure nanoparticles of Bi2MoO6 and Bi2Mo3O12 are prepared in a continuous hydrothermal flow synthesis reactor from solutions of acidified Bi(NO3)3 and basic H2MoO4 with Bi:Mo ratios of 2:1, and 2:3, respectively, using supercritical water of 375—450 °C at a pressure of 24.1 MPa as a crystallization medium (82 and 86% yield of Bi2Mo3O12 and Bi2MoO6, respectively).

Catalyst development for ultra-deep hydrodesulfurization (HDS) of dibenzothiophenes. I: Effects of Ni promotion in molybdenum-based catalysts

A strong synergistic effect of nickel and molybdenum was observed for hydrodesulfurization (HDS) of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over highly active Ni-MoS 2/γ-Al 2O 3 catalysts. The surface of the most active catalyst in this study was composed by Ni:Mo = 1:3, which was determined by XPS results. In addition, catalytic behavior indicates the presence of two different adsorption models accounting for the DDS (direct desulfurization) and the HYD (hydrogenation) pathways. The structure of the NiMoS active phase appears to be identical regardless of Ni/(Ni + Mo) ratio. The reaction sequence of the DDS pathways is DBT > 4-MDBT > 4,6-DMDBT due to the steric hindrance of methyl groups located adjacent to the sulfur atom of DBT, which prevents σ-bonding of the sulfur to the active site within the NiMoS phase. The reaction rates of HYD pathways are independent of the number of methyl groups, suggesting that the alkyl groups do not interfere the π-adsorption of DBTs on the active sites.

Preparation of γ-Bi 2MoO 6 thin films by thermal evaporation deposition and characterization for photocatalytic applications

Thin films of γ-Bi 2MoO 6 were formed from γ-Bi 2MoO 6 powders by a decomposition/evaporation sequential process in a Thermal Evaporation System (TES). In order to get a controlled decomposition/evaporation of the material the deposition rate was fixed at 1.2 Å s −1. The deposited films were analyzed by XRD, TEM, SEM, and EDS. These analyses revealed the formation of Bi and Mo nanoparticles of around 10 nm in their metallic form, respectively. The EDS analysis of the deposited film showed that the atomic Bi–Mo ratio (2:1) was maintained. The thin film was treated at 550 °C under atmospheric oxygen to promote the formation of γ-Bi 2MoO 6 oxide. The XRD confirmed the formation of the γ-Bi 2MoO 6 oxide in a thin film of 200 nm of thickness. Thin films of γ-Bi 2MoO 6 showed photocatalytic activity for the bleaching of rhodamine B under visible-light irradiation.

Interaction affinity of nickel promoted molybdena alumina with C, H and S in some catalytic conversions

The activation energy values of cyclohexane dehydrogenation and hydrogenolysis on alumina supported Ni, MoOx and three NiMoOx samples of different Ni:Mo ratio have been determined. Applying these values and the activation energies determined before for thiophene hydrodesulfurization on these catalysts, the C-Cat, H-Cat and S-Cat bond strengths were calculated. The bond strengths C-Cat and S-Cat are significantly higher for the samples of higher catalytic activity [NiMo(0.35) and NiMo(0.6)] in comparison with those of the less active ones [NiMo(0.15) and Ni12]. Compensation plots between Arrhenius constants indicate equal site distribution for the three reactions.

Effect of oxidation on abrasive wear behaviour of titanium carbide based composites in silica medium

The aim of the study was to investigate the effect of oxidation on the behaviour of TiC- based cermets with Ni-Mo binder under low intensity wear conditions in silica sand medium. Three types of material performance maps were constructed: oxidation rate map, wear rate map and map showing the effect of oxidation on wear. Discussion on the performance of cermets is based on oxidation, wear, SEM, EDS and XRD results. It is shown that cermets behaviour is highly influenced by microstructure (Ni, Mo content and Ni:Mo ratio) and oxidation kinetic. The paper should facilitate the optimization of TiC-Mo2C-Ni cermets selection for room and high temperature wear applications.

RHENIUM-RICH MOLYBDENITE AND RHENIITE IN THE PAGONI RACHI Mo-Cu-Te-Ag-Au PROSPECT, NORTHERN GREECE: IMPLICATIONS FOR THE Re GEOCHEMISTRY OF PORPHYRY-STYLE Cu-Mo AND Mo MINERALIZATION

The porphyry-type Pagoni Rachi Mo–Cu–Te–Ag–Au prospect, in northern Greece, is a porphyry-epithermal system hosted by an Oligocene dacite porphyry and quartz–feldspar porphyry dikes. The rare mineral rheniite (ReS2) and molybdenite, with very high contents of Re (up to 4.7 wt% Re), occur in quartz veins along with Fe–Cu sulfides, Pb-, Sn-, and Cl-bearing oxides, hematite, ilmenite and tellurides of Bi; these veins are spatially related to sericitic and transitional sericitic–sodic–potassic alteration. Earlier-formed gold-bearing quartz and magnetite veins with sodic–potassic–calcic alteration and late precious-metal telluride-rich carbonate–quartz veins with argillic alteration contain only minor amounts of molybdenite. The composition of rheniite ranges from almost pure, stoichiometric rheniite with low Mo content to rheniite with up to 5.99 wt% Mo. Petrographic, scanning electron microscope, and structural studies suggest that the high Re content of molybdenite from Pagoni Rachi is the result of the isovalent Re-for-Mo substitution in molybdenite. This fact is corroborated by the progressive shortening of the Mo–S mean bond-distance (from 2.414 A in pure molybdenite to 2.355 A), as well as by the isotropic decrease of the unit-cell values with the increase of the Re:Mo ratio. The structural analysis of four molybdenite crystals, with the highest Re content ever reported in nature, demonstrates that they crystallize as the 2 H polytype and not the 3 R polytype, as previously hypothesized, thus suggesting that Re concentration does not correlate with a specific polytype. The fluid inclusions in quartz in the Re-bearing molybdenite–rheniite veins at Pagoni Rachi show that they homogenize to either the liquid or vapor phases (354 to 428°C) or by halite dissolution at 317 to 585°C, which equates to salinities of 40 to 59 wt% NaCl equiv. Rheniite and molybdenite likely precipitated as temperatures fell below 400°C during phase separation under relatively oxidizing conditions, at elevated chlorine activity, and from relatively acid hydrothermal solutions. However, the presence of Pb oxides, Sn-bearing minerals and tellurides is compelling evidence that rheniite and Re-rich molybdenite may have formed directly from the vapor as sublimates, in a manner similar to the way they are deposited at the Kudriavy volcano, Kurile Islands.

Effects of Transition-Metal Composition of Protonated, Layered Nonstoichiometric Oxides H1−xNb1−xMo1+xO6 on Heterogeneous Acid Catalysis

Protonated, layered transition-metal oxides H1−xNb1−xMo1+xO6 with various Nb and Mo ratios were examined as solid acid catalysts. The effects of transition-metal composition on layered crystal structure, solid acid proprieties, and catalytic activities were investigated. X-ray diffraction (XRD) patterns revealed that a layered crystal structure was maintained in the range of x = −0.15 to 0.15. Beyond this range, the oxides did not form a layered structure, which resulted in negligible acid catalytic activity. The acid strength and acid amount determined by ammonia temperature-programmed desorption measurements indicated that increasing Mo concentration enhanced the acid strength. On the other hand, an increase in Nb concentration increased the acid amount. These layered oxides possess intercalation availability for benzyl alcohol, determined by XRD and thermogravimetric analysis, where the amount of intercalated benzyl alcohol tended to correspond to the acid amount of the layered metal oxides. Layered Nb−Mo oxides exhibited remarkable catalytic activity in Friedel−Crafts alkylation of toluene with benzyl alcohol, exceeding that of niobic acid, ion-exchange resins, and H-type zeolites, and this was attributed to the intercalation behavior. The alkylation activity over layered Nb−Mo oxides increased with increasing Nb concentration, which was related to the acid amount rather than the acid strength. For hydrolysis of cellobiose and esterification of lactic acid, on the other hand, the acid catalytic activity increased with increasing Mo concentration, H0.9Nb0.9Mo1.1O6 > HNbMoO6 > H1.1Nb1.1Mo0.9O6, indicating that the acid strength was more important in these reactions.

Synthesis of hybrid (Ni-Mo)carbides/carbon-coated mesoporous materials and their catalytic properties for hydrocracking of intermediate paraffins (n-C 8)

This work explores the structure and physical chemistry of hybrid materials formed by casting of carbon precursors ( i.e., acrylonitrile, AN) in mesoporous MCM-41 type siliceous materials. After polymerization and carbonization hollow carbonaceous fibers were formed and these were impregnated with Ni and Mo salts, i.e., 2.8 atoms Mo/nm 2 and Ni/(Ni + Mo) ratio equal to 0.5. The supported metal carbides were characterized by XRD, BET, NH 3-TPD and HRTEM and evaluated for the catalytic hydrocracking of intermediate straight chain model paraffins (i.e. n-octane) at 673 K, P = 1 atm. The overall activity and selectivity of the NiMoC/PAN-P catalysts for n-C 8 hydrocracking were distinct with respect to other catalysts of reference, i.e., NiMo/Al 2O 3. In particular, carbon nanofibers and lower hydrocarbons ( i.e., from propane to n-heptane) are the products formed by the successive dehydrogenation, cracking and carbon atoms diffusion through the metal particles.

Highly active CoMoS phase on titania nanotubes as new hydrodesulfurization catalysts

A series of CoMoS on nanotubular TiO2 (NT) catalysts were prepared by incipient impregnation at Mo=3–5atoms/nm2 and Co/(Co+Mo)=0.2–0.4. A nanotubular TiO2 (NT) of 5.5nm inner diameter, 236m2/g surface area and 0.5cm3/g total pore volume was prepared and used as support. The CoMoS/NT catalysts were characterized mainly by Raman and XPS spectroscopies, HRTEM and HAADF (high angle annular dark field) detector. The sulfided catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene at 320°C and 56kg/cm2. Inorganic fullerene-like MoS2 and/or CoMoS particles, made up of 2–6 structural layers, depending on the Co/(Co+Mo) ratio, were observed, smeared along the nanotubes. An estimation of CoMoS phase surface density (δ), after taken into account all sulfided species quantified by XPS spectra, indicated that highest HDS activity (43×10−4m3/kgMos) is attained when Mo=5atoms/nm2 and Co/(Co+Mo)=0.3. In comparison, at a lower (0.2) or higher (0.4) Co/(Co+Mo) ratio, either segregated MoO3 or Co9S8 phases were detected, respectively, with Co sulfidability decreasing 60–42%, respectively, and HDS activity being considerably lower.

Is it possible to counterbalance deficiencies or imbalances in cobalt, copper and/or molybdenum in forage based diets by including more and other plants?

To investigate whether species other than perennial grasses may contribute to a more balanced trace element supply for livestock, three studies have been conducted in coastal areas of Norway. From two series of field trial samples of green fodder crops were collected. Fodder vetch, broad beans and lupin may improve the supply of Co but do not solve severe deficiencies. None of the investigated species appeared to have the potential to counterbalance severe deficiencies in Cu and/or Mo. In a third study, samples of common dicotyledonous forbs and leaves from trees were collected from semi-natural pastures. Rumex species and tree leaves were high in Co (0.39–1.1 mg Co kg DM−1) and may be good sources for Co to grazing animals. Ranunculus repens was relatively high in Cu (10–13 mg kg DM−1) whereas the Cu:Mo ratio was not consistently high. Tree leaves on the other hand, would counterbalance a low Cu:Mo ratio.

Studies on mixed metal oxides solid solutions as heterogeneous catalysts

In this work, a series of perovskite-type mixed oxide LaMo xV1-xO3+δ powder catalysts (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0, with 0.5 < δ < 1.5), prepared by the sol-gel process and calcined at 750ºC, provide an attractive and effective alternative means of synthesizing materials with better control of morphology. Structures of resins obtained during the gel formation process by FT-IR spectroscopy and XRD analysis showed that all the LaMo xV1-xO3+δ samples are single phase perovskite-type solid solutions. The surface area (BET) between 2.5 - 5.0 m²/g (x = 0.1 and 1.0 respectively) increases with increasing Mo ratio in the samples. They show high purity, good chemical homogeneity, and lower calcinations temperatures as compared with the solid-state chemistry route. SEM coupled to EDS and thermogravimetric analysis/differential thermal analyses (TGA/DTA) have been carried out in order to evaluate the homogeneity of the catalyst. Finally, the experimental studies show that the calcination temperature and Mo content exhibited a significant influence on catalytic activity. Among the LaMo xV1-xO3+δ samples, LaMo0.7V0.3O4.2 showed the best catalytic activity for the topic reaction and the best activity and stability for ethane reforming at 850ºC under 8 bar.

Synthesis of polymolybdenophenylsiloxane

Polymolybdenophenylsiloxane containing Mo(V) atoms and preserving the Si : Mo ratio equal to that in the starting mixture was prepared by the reaction of molybdenum(V) oxychloride dimethyl sulfoxide crystal solvate with sodium polyphenylsiliconate in the presence of dimethyl sulfoxide. The influence of the reaction conditions on the nature and yields of products was examined. Experiments on thermal oxidative degradation of polymolybdenophenylsiloxane showed that it is more stable compared to the previously studied polymetalloorganosiloxanes containing various d elements with the stoichiometric Si : metal ratio.

Sulfur uptake determination on Ni containing molybdena-alumina samples by radioisotope tracer technique

Five solid oxides, used as hydrodesulfurization catalysts (Al 2O 3 supported Ni, MoO x , Ni–MoO x -s of different Ni:Mo ratio) were sulfided by [ 35S]H 2S. Amounts of the total, reversible and irreversible sulfur uptakes were determined measuring the change of gas phase radioactivity during exposure [ 35S]H 2S to the oxides, and compared with the amounts determined measuring radioactivity of the sulfided samples. The S/(Ni+Mo) values determined by X-ray photoelectron spectroscopy (XPS) were in satisfactory agreement with the results obtained by radiosulfur. Significantly different sulfur uptakes were observed for the different samples.

Effect of Mo and Co loading in HDS catalysts supported on solvo-thermally treated ZrO 2–TiO 2 mixed oxides

Molybdenum (at 2.8, 3.3, 4.0 and 4.7 atoms nm −2) and cobalt (Co/(Co + Mo) ratios of 0.3, 0.4 and 0.5) were impregnated on wide-pore ZrO 2–TiO 2 mixed oxides (30–70) prepared with solvo-thermal treatment (80 °C, 1 day). Materials characterization comprised N 2 physisorption, XRD, thermal analyses, and UV–vis DRS, Raman, and IR spectroscopies. For impregnated dried materials (non-calcined) at concentrations beyond 3.3 atom nm −2 and activated by sulfiding (H 2S/H 2, 400 °C) no further improvement in activity in dibenzothiophene (DBT) hydrodesulfurization (HDS) (at 5.59 MPa, T = 320 °C) was observed. Thus, monolayer Mo dispersion was assumed at that content. The aforementioned formulation was chosen to be promoted by Co at different concentrations, the maximum HDS activity being found for sulfided catalyst with Co/(Co + Mo) = 0.4. Nevertheless, the promotion observed by Co addition was small (by a factor of ∼3.2). The activity trends observed in the DBT HDS were well confirmed in the hydrotreatment of a real feedstock (straight-run gasoil). Dibenzothiophene reliably represented the behavior of organo-sulfur compounds present in the middle distillate, at the reaction conditions used in this study where sterically hindered compounds remained unreacted in the hydrotreated gasoil.

Aging of Co(Ni)MoP/Al 2O 3 catalysts in working state

The deactivation behavior of Co(Ni)MoP/Al 2O 3 catalysts during diesel fuel hydrotreatment is investigated by means of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). XPS measurements performed on aged Co(Ni)MoP/Al 2O 3 catalysts show that the promoter quantity on the edges of MoS 2 nano-crystallites decreases with increasing lifetime. TEM coupled with energy dispersive X-ray spectrometry (EDX) indicates that the Co(Ni)/Mo ratio inside crystallites changes without any modification over MoS 2 layers (size and stacking). Moreover toluene hydrogenation activity loss on aged catalysts is found to be linearly correlated to the XPS promotion rate decrease during deactivation. These experimental results have been analyzed in the light of recent density functional theory (DFT) calculations on the thermodynamic stability of Co(Ni)MoS phases in sulfo-reductive working conditions. It is shown that the destabilization of the mixed phase may be partially attributed to the reaction conditions (high temperature and reductive environment). In addition, the role of the coke cannot be excluded to explain the promotion rate decrease revealed by XPS spectra. The experimental results combined with DFT results are used to propose an origin of the active phase modifications in working state.

Environmental risks of farmed and barren alkaline coal ash landfills in Tuzla, Bosnia and Herzegovina

The disposal of coal combustion residues (CCR) has led to a significant consumption of land in the West Balkan region. In Tuzla (Bosnia and Herzegovina) we studied previously soil-covered (farmed) and barren CCR landfills including management practises, field ageing of CCR and the transfer of trace elements into crops, wild plants and wastewaters. Soil tillage resulted in mixing of cover soil with CCR. Medicago sativa showed very low Cu:Mo ratios (1.25) which may cause hypocuprosis in ruminants. Total loads of inorganic pollutants in the CCR transport water, but not pH (∼12), were below regulatory limits of most EU countries. Arsenic concentrations in CCR transport water were <2 μg l −1 whereas reductive conditions in an abandoned landfill significantly enhanced concentrations in leachates (44 μg l −1). The opposite pattern was found for Cr likely due to large initial leaching of CrVI. Public use of landfills, including farming, should be based on a prior risk assessment due to the heterogeneity of CCR.

Bismuth molybdates model catalysts with controlled crystallinities spin-coated on Si (1 0 0)

The possibility of spin-coating crystalline multi-element oxide model catalysts using citrate complexes of Bi 3+ and Mo 6+ solutions was studied. The characterization of obtained thin films was performed by XRD, Raman spectroscopy, SEM and XPS. XRD and confocal Raman data indicated that Bi 2O 3–MoO 3 mixed systems behaved as dictated by the composition of the starting solutions, and pure α-Bi 2Mo 3O 12, β-Bi 2Mo 2O 9, and γ-Bi 2MoO 6 phases were obtained without any heterogeneity. XPS confirmed that Bi:Mo ratios at the surface of the films never differed from those in the bulk, namely that of the starting co-solutions. SEM revealed that the thickness of the films could be tuned in the range 40–140 nm via adjustment of the spin-rate (2, 3, or 5 krpm) and the concentration of the precursors solution (0.24 or 0.48 M in Mo), without any disturbance of crystallinity, the Bi:Mo ratio or the homogeneity of the films. Performed studies suggested that spin-coating of mixed citrate complexes appears as a versatile and easy route to prepare homogenous films of multi-element transition metal oxides with controlled formulation and crystalline structure.