Molybdenum Phosphide Research Articles

Superconductivity of MRuP and MNiP (M=Mo or W) prepared at high pressure

Ternary metal phosphides MRuP (M=Mo or W) with a Co 2P-type structure and MNiP(M=Mo or W) with a Fe 2P-type structure have been prepared at around 1600°C and 4 GPa. The electrical and magnetic properties of these compounds were studied at low temperature. The superconductivity of these compounds is observed at around 15.5 K for the molybdenum phosphides, and at 5 K for the wolfram phosphides. These are new superconductors. Both ternary molybdenum phosphides have the highest T c among the metal phosphides.

NMR Investigation of a New Superconductor MoNiP Synthesized under High Pressure

95 Mo, 61 Ni and 31 P nuclear magnetic resonance observations in a ternary molybdenum phosphide MoNiP with Fe 2 P-type structure have been carried out to investigate the mechanism of superconductivity ( T C ≃8.5 K, H C2 ≃7.4 kOe) that appears only when it is synthesized at high pressures. A large negative Knight shift of 95 Mo in the superconducting MoNiP, K =-0.155%, is indicative of a dominant d spin core-polarization interaction. The 95 Mo spin-lattice relaxation rate, ( T 1 T ) -1 =0.15 (sK) -1 , gives a large density of states at the Fermi level, N ( E F )∼1.17 states/eV. A positive Knight shift of 61 Ni, K =0.29%, on the other hand, is dominated by the Van Vleck orbital interaction. Thus it is concluded that N ( E F ) consists mainly of a narrow Mo 4 d band. In a non-superconducting MoNiP synthesized at an ambient pressure, K and ( T 1 T ) -1 of 95 Mo increase to -0.202% and to 0.19 (sK) -1 , respectively, indicating that the decrease in N ( E F ) by ∼10% induces the superconductivity, contrary to the prediction of the Bardeen-Cooper-Schrieffer theory. In MoNiP, strong electron correlations in the narrow d band of Mo are thought to be antagonistic to the electron-phonon coupling, V C ∼ V ph , and the synthesis at high pressures provides an additional screening of the Coulomb potential, which leads to the condition of V ph > V C .

Superconductivity of molybdenum phosphides prepared at high pressure

Binary molybdenum phosphides Mo 3P, Mo 8P 5 and Mo 4P 3 have been prepared at high temperatures and high pressures. The resistivity of the phosphides decreases with decreasing temperature and sharply drops at low temperatures. The superconductivity is found at around 7 K for Mo 3P, 5.8 K for Mo 8P 5 and 3 K for Mo 4P 3. The T c of the binary molybdenum phosphides decreases with decreasing density. The compounds Mo 8P 5 and Mo 4P 3 are new superconductors.

Formation, Structure, and HDN Activity of Unsupported Molybdenum Phosphide

A molybdenum phosphide catalyst was prepared from an aqueous solution of (NH4)6Mo7O24·4H2O and (NH4)2HPO4 by precipitation, calcination, and subsequent reduction in H2 at 923 K. Raman spectroscopic measurements revealed that the aqueous solution contained MoO42−, HPO42−, and P2Mo5O6−23 anions. Powder XRD measurements showed that pure molybdenum phosphide had formed after precipitation and reduction with H2. MoP crystallizes in the tungsten carbide structure in which each Mo atom is trigonal-prismatically coordinated by six P atoms. The molybdenum phosphide was tested for catalytic activity in the HDN reaction of o-propylaniline at 643 K and 3.0 MPa. The intrinsic HDN activity of the surface Mo atoms of MoP was about 6 times higher than that of Mo edge atoms in γ-Al2O3-supported MoS2. Their selectivity is comparable to that of an Ni-promoted MoS2 catalyst.

Molybdenum Phosphide: A Novel Catalyst for Hydrodenitrogenation

Abstract A single phase molybdenum phosphide, MoP, with a moderate surface area was prepared using temperature programmed reduction of an amorphous phosphate precursor and the so-prepared sample was found to be a good catalyst for hydrodenitrogenation.

95/04519 Characterization of colloidal asphaltenic particles in heavy oil

Alumina-supported molybdenum phosphide hydroprocessing catalysts, MoP/γ-Al2O3, with weight loadings from 3.5 to 39 wt% were prepared by temperature-programmed reduction of alumina-supported molybdenum phosphate precursors. The precursors were obtained by incipient wetness impregnation of the support with aqueous molar solutions of ammonium paramolybdate and ammonium phosphate (Mo/P=1/1). Effects of loading, reduction temperature, and heating rate on the catalysts were studied, and the samples were characterized by CO chemisorption, BET surface area, and X-ray diffraction (XRD) measurements. Compared to the bulk MoP and MoP/SiO2 systems (which are similar to one another), the MoP/γ-Al2O3 material showed different behavior. Whereas calcined bulk and silica-supported molybdenum phosphates form Mo–P amorphous glasses which reduce directly to MoP, for the alumina-supported phosphates at high loadings (e.g., 13 wt% MoP/γ-Al2O3), a MoO3 component is visible which reduces sequentially with temperature to MoO2 and Mo metal, and then transforms to MoP. The difference in behavior between these systems is attributed to the formation of a strongly bound amorphous phosphate surface layer on the alumina support. Alumina has a strong affinity for phosphates, and appears to initially abstract a substantial amount of phosphorus from the stoichiometric molybdenum phosphate mixture. The alumina then releases the phosphorus at high temperature, allowing it to recombine with Mo metal to form MoP and generating active sites. The MoP/γ-Al2O3 catalysts performed well in hydroprocessing of a simulated distillate containing dibenzothiophene and quinoline at conditions representative of industrial hydroprocessing (643 K, 3.1 MPa). For the 13 wt% sample the hydrodesulfurization conversion was 57% and hydrodenitrogenation conversion was 62%. Catalytic activity, based on equal chemisorption sites loaded in the reactor (70 μmol), was generally independent of the amount of MoP deposited on the alumina surface, independent of the presence of X-ray visible molybdenum phases, and was associated with a relatively high temperature reduction peak found at all loading levels of MoP/Al2O3 but not in bulk MoP. We conclude that the high-temperature peak gives rise to highly dispersed MoP which is responsible for the bulk of the CO titration sites and the catalytic activity, and that the large MoP particles visible by XRD make smaller contributions.

Spectroscopic determination of oxidation and coordination states of Mo cations in the reduced [formula omitted] catalyst

The surface sites of MoP/SiO2 catalysts and their evolution under sulfiding conditions were characterized by IR spectroscopy using CO as the probe molecule. The HDS activities of thiophene were measured on the MoP/SiO2 catalyst that was subjected to different sulfidation and reactivation pretreatments. Cus Moδ+ (0<δ⩽2) sites are probed on the surface of fresh MoP/SiO2 by molecularly adsorbed CO, exhibiting a characteristic IR band at 2045 cm−1. The surface of MoP/SiO2 is gradually sulfided in HDS reactions, as revealed by the shift of the IR band at 2045 to ca. 2100 cm−1. Although the surface of a MoP/SiO2 catalyst becomes partially sulfided, the HDS activity tests show that MoP/SiO2 is fairly stable in the initial stage of the HDS reaction, providing further evidence that molybdenum phosphide is a promising catalytic material for industrial HDS reactions. Two kinds of surface sulfur species are formed on the sulfided catalyst: reversibly and irreversibly bonded sulfur species. The MoP/SiO2 catalyst remains stable in the HDS of thiophene because most sulfur species formed under HDS conditions are reversibly bonded on the catalyst surface. A detrimental effect of presulfidation on the HDS activity is observed for the MoP/SiO2 catalyst treated by H2S/H2 at temperatures higher than 623 K, which is ascribed to the formation of a large amount of the irreversibly bonded sulfur species. The irreversibly sulfided catalyst can be completely regenerated by an oxidation and a subsequent reduction under mild conditions.

Influence of phosphate on the structure of sulfided alumina supported cobalt-molybdenum catalysts

The influence of phosphate on the sulfiding rate of alumina-supported cobalt, molybdenum and cobalt-molybdenum catalysts has been studied by means of Temperature Programmed Sulfiding (TPS). Combination of the TPS results with recently published Temperature Programmed Reduction (TPR), Mössbauer spectrometry and nitrogen oxide adsorption measurements results in a detailed picture of the sulfidic catalyst. The sulfiding of cobalt ions in phosphorus-containing alumina-supported cobalt catalysts shifted to somewhat higher temperatures with increasing phosphorus content, most likely due to the presence of “Co-AlPO4” phases. In the temperature region from 1000-1270 K, part of the cobalt sulfide species reacted with AlPO4 to cobalt phosphides. The amount of cobalt which reduced to phosphides increased strongly with increasing phosphorus content and became about 70% of the total amount of cobalt present. The sulfiding pattern of phosphorus-containing Co-Mo/Al catalysts is only slightly influenced by increasing phosphorus content below 1000 K. All components including the Co-Mo-O-P phase, present in the oxidic precursor, are relatively easy to sulfide. After sulfiding at 673 K, the Co-Mo-S phase is most likely still to be associated with the AlPO4 species. Analogous to cobalt catalysts, the major part of the cobalt in Co-Mo-P/Al catalysts ultimately reacted to cobalt phosphides above about 1000 K. The sulfiding rate of the molybdenum ions is not changed by the presence of phosphates. MoS2 does not react with the phosphates to molybdenum phosphide probably because this reaction is thermodynamically restricted. Based on the surface structures, deduced from a combination of TPR and TPS data, the striking difference between the effect of phosphates on the hydrodenitrogenation (HDN) and on the hydrodesulphurisation (HDS) reactions is discussed.

Hydroprocessing of substituted benzenes over a sulfided CoO-MoO 33/γ-A1 2O 3catalyst

The performance of titania-supported molybdenum carbide, nitride, phosphide and oxide catalysts was compared for catalytic hydrodeoxygenation (HDO) of phenol. Phenol was selected as a stable model component for lignin degradation products in fast pyrolysis bio-oil. The synthesis and formation path of the materials was evaluated by the use of complementary characterization techniques (XRD, TPR and TGA–MS). All the catalysts showed promising catalytic performance during testing in a fixed-bed reactor set-up at a temperature of 350 °C and total pressure of 25 bar, and the highest activity was achieved with 15 wt% Mo2C/TiO2. A high selectivity towards benzene was observed with all catalysts. MoP supported on TiO2 showed the strongest tendency to aromatic ring hydrogenation and also a significant selectivity (10% level) towards methylcyclopentane, indicating contributions of acidic surface chemistry. Thus, Mo based materials are active and promising materials for establishing selectivity control in HDO of bio-oils.