Molybdenum Oxynitride Research Articles

Cobalt Molybdenum Oxynitrides: Synthesis, Structural Characterization, and Catalytic Activity for the Oxygen Reduction Reaction

A non-noble metal electrocatalyst has been developed for the oxygen reduction reaction. Carbon-supported cobalt molybdenum oxynitride was simply prepared by impregnation followed by thermal ammonolysis. The oxynitride electrocatalytic activity nearly matched that of platinum in 0.1 M KOH solution. The catalyst structure and valence have been characterized using complementary local and bulk probes. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Nanoporous transition metal oxynitrides as catalysts for the oxygen reduction reaction

Nanoporous molybdenum oxynitride has been synthesized and studied for the first time as an oxygen reduction catalyst in a 0.1M KCl aqueous solution (pH 5.6). Modified electrodes containing the oxynitride catalyst, TIMCAL Super P™ Li carbon as a conducting carbon additive and polyvinylidene fluoride as a binder were prepared, and the ratios of the different components were studied in detail to yield the optimum composition. The oxygen reduction reaction mechanism has been analyzed by the Koutecky–Levich equation using a rotating disk electrode and is in concordance with a four-electron pathway for the molybdenum oxynitride catalyst. Rotating ring-disk electrode experiments have further confirmed the electrocatalytic performance of such oxynitrides toward oxygen reduction, determining an average production of H2O2 of just 2.35%. Finally, we have also compared the performance of vanadium and tungsten oxynitrides under the same conditions as the optimal molybdenum oxynitride.

Graphene–molybdenum oxynitride porous material with improved cyclic stability and rate capability for rechargeable lithium ion batteries

A graphene-molybdenum oxynitride (GMON) hybrid porous material was prepared by a thermal decomposition method and investigated as an anode material in lithium ion batteries. In the thermal decomposition reaction, a chemically homogeneous complex formed by ammonium molybdate and hexamethylenetetramine was used as the precursor for the synthesis of molybdenum oxynitride (MON), and graphene oxide was thermally reduced into graphene. Meanwhile, the graphene sheets were nitrogen doped by the ammonia generated during the thermal reaction. The GMON hybrid porous materials were characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. Nitrogen sorption analysis showed that GMON possesses an enhanced porosity compared with the MON prepared in the same method. Owing to the improvement in the porosity and the conductivity, the GMON anode exhibited a reversible capacity of about 960 mA h g(-1) at a current density of 100 mA g(-1), furthermore, the rate performance and the cycling stability of the GMON anode were dramatically enhanced in comparison with thermal reduced graphene oxide and MON.

Surface characterization of Mo oxynitride films obtained by RF sputtering at various N2 ratios

Molybdenum oxynitride (MoNxOy) thin films were deposited on p-type Si(100) wafer by rf magnetron sputtering method at various nitrogen gas ratios. The surface characteristics of deposited thin films were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The thickness of films decreased down to 70 from 1000 nm and the roughness was varied with increasing N2 gas ratio. The formation of MoNxOy was confirmed by existence of Mo species between Moδ+ and Mo5+ oxidation state and ON bond in XP spectra. At 0% of N2 gas ratio, metallic simple cubic Mo structure was observed. As the N2 gas ratio increased, Mo nitrate and Mo silicate phases were appeared.

Synthesis of nitrided MoO2 and its application as anode materials for lithium-ion batteries

Nitrided MoO2 has been synthesized by hydrothermal processing followed by post-nitridation with NH3 and investigated as alternative anode materials for rechargeable lithium batteries. Characterization data reveal the presence of molybdenum nitride (γ-Mo2N and δ-MoN) and molybdenum oxynitride (MoOxNy). The nitrided MoO2 exhibits a capacity of >420mAh/g after 100cycles and good rate capability. The improved electrochemical performance of the nitrided MoO2 compared to that of molybdenum oxide (MoO2) is attributed to high electrical conductivity provided by nitrogen doping/or substitution in the oxygen octahedral site of MoO2 structure.

Electrical and materials properties of AlN/ HfO 2 high- k stack with a metal gate

In this study, aluminum nitride (AlN) was grown by molecular layer deposition on HfO 2 that had been deposited on 200 mm Si (100) substrates. The AlN was grown on HfO 2 using sequential exposures of trimethyl-aluminum and ammonia (NH 3) in a batch vertical furnace. Excellent thickness uniformity on test wafers from the top of the furnace to the bottom of the furnace (across the furnace load) was obtained. The equivalent oxide thickness was 16.5–18.8 Å for the AlN/HfO 2 stack on patterned device wafers with a molybdenum oxynitride metal gate with leakage current densities from low 10 − 5 to mid 10 − 6 A/cm 2 at threshold voltage minus one volt. There was no change in the work function with the AlN cap on HfO 2 with the MoN metal gate, even with a 1000 °C anneal.

Effect of thermal treatments on the structure of MoN xO y thin films

MoN x O y films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure molybdenum target, varying the flow rate of reactive gases. X-ray diffraction (XRD) results revealed the occurrence of cubic MoN x and hexagonal (δ-MoN) phases for the films with high nitrogen flow rates. The increase of oxygen content induces the decrease of the grain size of the molybdenum nitride crystallites. The thermal stability of a set of samples was studied in vacuum, for an annealing time of 1 h, for temperatures ranging from 500 to 800 °C in 100 °C steps. The results showed that pure molybdenum nitride films changed their structure from a meta-stable cubic MoN to hexagonal δ-MoN and cubic γ-Mo 2N-type structures with increasing annealing temperatures. The samples with molybdenum nitride films evidenced a good thermal stability, but those with molybdenum oxynitride coatings showed a tendency to detach with the increase of the annealing temperature.

Nanosized Titanium Oxynitride and Molybdenum Oxynitride Particles Assembled in Mesoporous Silica MCM-41

Titanium oxynitride and molybdenum oxynitride assembled in the pores of mesoporous materials were achieved by nitriding titania-modified MCM-41 and molybdena-modified MCM-41 at 800°C for 3 hours under flowing NH3 atmosphere. XRD, XPS and N2 adsorption-desorption isotherms were employed to characterize the structure of the composite materials. The results showed that the nanosized TiOxNy and MoOxNy particles were assembled in mesoporous silica MCM-41 with the restrict mesopores. The hexagonal periodicity of the parent MCM-41 materials was maintained upon assembly at the provided nitridation temperature. The exact formation was TiO0.4N0.8 in MCM-TiOxNy, and MoO1.7N0.57 in MCM-MoOxNy, which were calculated from the data in XPS spectra of Ti 2p and Mo 3d.

Synthesis and Characterization of the Oxynitride Y2Mo2O4.5N2.5 Pyrochlore: A Neutron Diffraction and Magnetic Study

Abstract A new molybdenum oxynitride Y2Mo2O4.5N2.5 with cubic pyrochlore structure (a = 10.3350(2) Å, space group Fd3̅m, Z =8) has been synthesized by heating the parent Y2Mo2O7 oxide in flowing ammonia at 898 K. The polycrystalline sample has been characterized by thermal analysis, X-ray and neutron diffraction (NPD), and magnetic susceptibility measurements. The analysis of high resolution NPD data, based on the contrast existing between the scattering lengths of O and N, shows that both atoms are distributed at random at the anion substructure; the refined crystallographic formula implies an oxidation state of +5.25 for Mo cations. The thermogravimetric curve shows a weight gain of 7.5% at 1000 K in air, corresponding to the complete elimination of N2 and oxidation to Mo(VI) oxide, in good agreement with the proposed composition. The magnetic susceptibility exhibits a Pauli-like, temperature-independent term which derives from the partial delocalization of Mo electrons on Mo-(O,N) bands with a broader bandwidth, as a consequence of the significant opening of the Mo-(O,N)-Mo angle and strengthening of the Mo-(O,N) interactions with respect to the parent Y2Mo2O7 oxide. As in this oxide, a reminiscent spin-glass behaviour is observed at low temperature.

Properties of MoN xO y thin films as a function of the N/O ratio

The main purpose of this work is the preparation of single layer films of molybdenum oxynitride, MoN x O y . The films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure Mo target and varying the flow rate of reactive gases. This allowed tuning of the crystallographic structure between insulating oxides and metallic nitrides and consequently changes in the electronic, mechanical and optical properties of the material. X-ray diffraction (XRD) results revealed the presence of molybdenum nitride for the films with low oxygen fraction: face-centered cubic phases (γ-Mo 2N) for low nitrogen flow rate or cubic MoN x and hexagonal phase (δ-MoN) for high nitrogen flow rate. The increase of oxygen content induces an amorphization of the nitride phases and the appearance of MoO 3 phases. The increase of the oxygen fraction in the films induces also a high decrease in the film's hardness. Residual stresses were compressive, in the range of very few tenths of GPa to − 2 GPa. These results will be presented as a function of the deposition parameters, the chemical composition and the structure of the films.

The preparation of molybdenum oxynitride by hydrazine reduction of MoO3 at moderate temperature and its application in the selective hydrogenation of long-chain linear alkadienes

Molybdenum oxynitride was prepared by hydrazine reduction of MoO3 at moderate temperatures. The anhydrous condition was favorable to production of amorphous molybdenum oxynitride, and the presence of hydrogen favored the reduction of Mo6+ and Mo4+ species to Moδ+ (0 < δ < 4) species. These molybdenum oxynitrides exhibited activity for hydrogenation which depended on the amount of Moδ+ (0 < δ < 4) species produced under reaction conditions. The amorphous molybdenum oxynitride MoO1.83N0.36 catalyst showed a good catalytic activity, selectivity, and resistance to poisoning of H2S for liquid-phase hydrogenation of longer-chain alkadienes.

Synthesis and characterization of the oxynitride pyrochlore - Sm 2Mo 2O 3.83N 3.17

Sm 2Mo 2O 3.83N 3.17, the first molybdenum oxynitride pyrochlore, was synthesized by heating the Sm 2Mo 2O 7 pyrochlore in flowing ammonia at 625°C for 24 hours. Sm 2Mo 2O 3.83N 3.17 forms with the cubic pyrochlore structure, space group Fd3m (a = 10.4975 Å). The sample is semiconducting and the temperature-dependent magnetic susceptibility follows Curie-Weiss behavior. X-ray absorption near-edge spectroscopy measurements indicate that in the oxynitride, molybdenum has a formal oxidation state significantly larger than 4+.

Preparation, Characterization, and Catalytic Behavior of Molybdenum Oxynitrides Supported on EMT Zeolite (NaEMT and HEMT) Catalysts

EMT zeolite-encaged molybdenum oxynitride clusters were prepared byseveral methods, leading to different dispersions of the molybdenumspecies. HRTEM and EDX measurements indicated that, when the molybdenumspecies were inside of the zeolite porosity, they werehomogeneously dispersed in the form of clusters whose diameters were less than 10 Å. Depending on the preparation, it was shown by X-raydiffraction and specific surface area measurements that the EMTzeolite crystallinity was affected to different extents followingammonia treatments used for nitridation. The catalytic behavior ofthese nitrided compounds was studied in then-heptaneconversion. Supported on NaEMT, the encaged molybdenum oxynitrideshowed a reactivity of a bulk material. The most active catalystwas the low-temperature (523 K) catalyst, then-heptaneisomerization appearing as the main reaction. In contrast, for thecatalysts supported on acidic HEMT,n-heptane cracking wasmainly observed and the deactivation of the Mo-oxynitride supportedcatalysts was lowered compared to that of HEMT alone.

NEXAFS Characterization and Reactivity Studies of Bimetallic Vanadium Molybdenum Oxynitride Hydrotreating Catalysts

The surface and bulk compositions of vanadium molybdenum oxynitride (V{sub 2}MoO{sub 1.7}N{sub 2.4}), prepared by temperature-programmed reaction (TPR) of vanadium molybdenum oxide (V{sub 2}MoO{sub 8}) with ammonia, have been characterized using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS data were recorded at the K-edges of nitrogen and oxygen, the L-edge of vanadium, and the M-edge of molybdenum. The nitrogen K-edge region of V-Mo oxynitride shows the characteristic NEXAFS features of early-transition-metal nitrides, although these features are different from those of either VN or Mo{sub 2}N. Furthermore, comparison of the electron yield and fluorescence yield measurements also reveals that the oxidation state is different for vanadium near the surface region and for vanadium in the bulk, which is estimated to be 2.8 {+-} 0.3 and 3.8 {+-} 0.3, respectively. The oxidation state of bulk molybdenum is also estimated to be 4.4 {+-} 0.3. The X-ray diffraction pattern shows that the bulk phase of the bimetallic oxide is different from the pure monometallic oxide phases but the oxynitride has a cubic structure that resembles the pure vanadium and molybdenum nitride phases. The V-Mo oxide as prepared shows a preferential orientation of [001] crystallographic planes which is lost during the nitridationmore » process. This shows that the solid state transformation V{sub 2}MoO{sub 8} {yields} V{sub 2}MoO{sub 1.7}N{sub 2.4} is not topotactic. 27 refs., 8 figs., 1 tab.« less

Modification of the surface composition of molybdenum oxynitride during hydrocarbon catalysis

With an oxygen containing molybdenum nitride catalyst, the rate of hydrogenation of propylbenzene increases with time. This is attributed to the carburization of surface during reaction. Both surface reactivity in chemisorption and superficial chemical composition change during the activation of the catalyst.

Preparation and Characterization of New Molybdenum Nitride or Oxynitride Phases

ABSTRACTSeveral methods of synthesizing molybdenum nitride or oxynitride fine powders are presented.We have prepared a γ-Mo2N type oxynitride phase by reacting ammonia with MoO3. The surface area and morphology of the oxynitride powders depend on the synthesis conditions. Characterization of the solids by elemental analysis, X-ray and neutron diffraction, and thermogravimetric analysis shows dramatic modification of the stoichiometry of conventional Mo2N nitride. Aging at room temperature under air results in decreasing the material surface area. The initial surface area can be recovered be fine tuning of experimental conditions. MoCl5 and Ca3N2 are reacted in a molten CaCl2 medium leading to a new Mo2N structure type.The reaction between molybdenum sulfide and NH3 produces two different phases depending on the reaction conditions. They are structurally related to δ-MoN.

Preparation, Characterization and Catalytic Activity of Niobium Oxynitride and Oxycarbide in Hydrotreatment

ABSTRACTOxynitride and oxycarbide of niobium present metallic and acidic catalytic functions as evidenced by molecular probe reactions: isomerization of cyclohexane and hydrodenitrogenation of 1–4 tetrahydroquinoline. The proximity of the two functions leads to the concept of “dual site” by selective inhibition of the metallic and acid sites. Substitution of nitrogen of the oxynitride by carbon to form the oxycarbide produces a large enhancement of the metallic character of the surface. The oxynitride was shown to present a more acidic and a less hydrogenating activity as compared to the activity of the oxycarbide. Both compounds of niobium have been compared to molybdenum oxynitride.