Mo Precursor Research Articles

Synthesis, characterization and spectrochemical studies on a few binuclear µ-oxo molybdenum(V) complexes of pyrimidine derived Schiff base ligands

Ten new binuclear singly oxo-bridged molybdenum complexes (complexes 1–10) were prepared using five pyrimidine derived Schiff base ligands and two Mo(V) precursors (NH4)2MoOCl5 and (NH4)2MoOBr5. The ligands are prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicylaldehyde (for HL1), o-hydroxy acetophenone (for HL2) and substituted salicylaldehydes (for HL3, HL4 and HL5) respectively. These ligands are already reported as good donors for Mo(VI) state. The µ-oxo Mo(V) complexes reported here bears a distorted octahedral geometry around each Mo atom with either N2O2Cl or N2O2Br chromophores. Fine variations in the spectroscopic behaviour of the complexes are observed in accordance with the varying electron donating properties of the ligands. All the complexes are unstable in solution and X-ray quality crystal of complex 1 could be isolated. All the complexes are characterized by IR and UV-Vis spectra.

Formation of heteropolymolybdates during the preparation of Mo and NiMo HDS catalysts supported on SBA-15: Influence on the dispersion of the active phase and on the HDS activity

Mo and Ni–Mo sulfides in SBA-15 and Al-SBA-15 catalysts were prepared by incipient wetness co-impregnation of molybdenum and nickel precursors followed by thermal treatment under He at 823 K and sulfidation under 10% H 2S/H 2 at 673 K. Only incipient wetness impregnation of Mo on pure silica SBA-15 led to a high dispersion of the MoS 2 phase and a high catalytic activity for dibenzothiophene (DBT) hydrodesulfurization (HDS). For the other samples, we observed a poor dispersion of the sulfide phase together with a low activity for HDS of DBT (Mo/Al-SBA-15) and 4,6-dimethyl-dibenzothiophene (NiMo/(Al-)SBA-15). In order to rationalize these results, i.e. to understand the reasons for the poor sulfide phase dispersion, we have investigated the chemical phenomena occurring during the process of co-impregnation of Ni and Mo precursors on (Al-)SBA-15. The formation of two Anderson heteropolymolybdates [X(OH) 6Mo 6O 18] n − (X = Al(III) or Ni(II)) during impregnation was demonstrated by XRD and 27Al MAS-NMR. 27Al and 95Mo liquid-state NMR were also used to gain more insight into the formation and respective stability of these heteropolyanions (HPA) in aqueous solutions containing either Mo and Al, or Mo and Ni, or Mo, Al and Ni precursors. The dispersion of the Mo and NiMo phases in the oxide and the final sulfide phases, were shown to be strongly dependent upon the formation of these Anderson HPA species.

Effect of sulfidation temperature on the intrinsic activity of Co–MoS 2 and Co–WS 2 hydrodesulfurization catalysts

The effect of presulfidation temperature on the magnetic property, local structure, and intrinsic hydrodesulfurization activity of Co–Mo(W)–S has been studied with SiO 2-supported Co–Mo and Co–W sulfide catalysts prepared by exposing presulfided MoS 2/SiO 2 and WS 2/SiO 2, respectively, to a vapor of Co(CO) 3NO. A TPS study shows that complete sulfidation of Mo(W) precursors to Mo(W)S 2 particles is required for the formation of Co–Mo(W)–S Type II. The intrinsic activity of Co–W–S Type II is 1.6 times as high as that of Co–Mo–S Type II. The Co K-edge EXAFS analysis of Co–Mo(W)–S confirms the formation of dinuclear Co sulfide clusters on Mo(W)S 2 edges. The intrinsic activity of Co–Mo–S is correlated with the Co–S–Co antiferromagnetic interaction strength, suggesting modifications of the electronic state and local structure of Co–Mo–S by MoS 2–O-support interactions, in conformity with the EXAFS analysis.

Atomic-Scale Structure of Mo6S6 Nanowires

We have studied the atomic-scale structure of the Mo6S6 nanowires using scanning tunneling microscopy and spectroscopy (STM and STS) and density functional theory (DFT). A novel synthesis route based on metallic Mo precursors is presented for the selective formation of elementary pure Mo6S6 nanowires. The Mo6S6 nanowires selectively organize as trimer bundles, and each of the Mo6S6 nanowires consists of an electrically conducting Mo backbone dressed with a sulfur exterior cap. The Mo6S6 nanowires may thus be of interest as novel building blocks in nanoelectronics because the Mo6S6 nanowires exist in a robust, singular structural conformation with uniquely defined electrical (metallic) properties.

Impact of preparation method and support modification on the activity of mesoporous hydrotreating CoMo catalysts

Abstract This work seeks to optimize CoMo/HMS-Ti catalysts for the hydrodesulphurization (HDS) of dibenzothiophene (DBT) by support modification with phosphorous, as well as select a suitable catalyst preparation method. The Ti-loaded hexagonal mesoporous silica ((HMS)-Ti material prepared with Si/Ti molar ratio of 40) was modified varying the phosphorus amount (0.2–1.0 wt%) and used as support to deposit oxide Co and Mo precursors by simultaneous and successive impregnation methods. Structural features of the pure supports and oxide CoMo-loaded materials have been revealed by different techniques including specific surface area ( S BET ), X-ray diffraction, temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS UV–vis) and micro-Raman spectroscopy. Activity–structure correlations showed that the number of irregular oxide Mo 6+ particles, as determined by Raman spectroscopy, influenced the final catalytic response of sulphided systems. All catalysts prepared by simultaneous impregnation showed larger HDS activity than their counterparts prepared by successive impregnation, and this was linked, in part, to a higher specific surface area of the former systems. All P-containing catalysts recorded greater activity than their P-free counterparts because the presence of phosphorus on the support surface forced the formation of octahedral Co 2+ species and irregular oxide Mo 6+ particles. From the activity–structure correlation, the optimum P-loading was archived at 0.64% of P 2 O 5 .

Effect of the preparation method on the structural stability and hydrodesulfurization activity of NiMo/SBA-15 catalysts

Defined hexagonal cylindrical pore structure SBA-15 material was synthesized as support for hydrotreating catalysts. The stability of the mesoporous material under acid and basic environments commonly used to prepare hydrotreating catalysts was investigated. The effects of the acid and basic treatments on the stability of SBA-15 and NiMo/SBA-15 catalysts were evidenced by different characterization techniques such as N 2 adsorption–desorption, X-ray diffraction (XRD), Raman Spectroscopy and high resolution transmission electron microscopy (HRTEM). Supported NiMo/SBA-15 catalysts prepared by pore volume co-impregnation in acidic, neutral and basic solutions of the Ni and Mo precursor salts were characterized to evaluate the textural and structural changes caused by the method of preparation. Characterization of the support after accelerated stability tests indicates large deterioration of the SBA-15 structural order at basic pH. The characterization results of oxide and sulfided catalysts indicate, for the catalysts prepared at high pH, an increasing presence of β–NiMoO 4 phase in the oxide catalysts, and a relatively lower population of MoS 2 in the sulfided catalysts. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalysts prepared at low pH.

Comparisons of Phosphorus Ligation Properties in P(CH2NR)3P

Bicyclic P(CH2NMe)3P was synthesized, and its reactions with MnO2, elemental sulfur, p-toluenesulfonyl azide, BH3.THF, and W(CO)5(THF) were shown to furnish a variety of products in which the PC3 and/or the PN3 phosphorus are oxidized/coordinated. In contrast, reactions of the previously known P(CH2NPh)3P with Mo(0) and Ru(II) precursors were shown to afford products in which only the PC3 phosphorus is coordinated. The contrast in reactivity of P(CH2NR)3P (R = Me, Ph) with the aforementioned reagents is discussed in terms of steric and electronic factors. The new compounds are characterized by analytical and spectroscopic (IR, 1H, 31P, and 13C NMR) methods. The results of crystal and molecular structure X-ray analyses of the previously known compounds P(CH2O)3P and P(CH2NPh)3P and 6 of the 14 new compounds obtained in this investigation are presented. Salient features of these structures and the analysis of the Tolman cone angles calculated from their structural parameters are discussed in terms of the effects of constraint in the bicyclic moieties. Evidence is presented for greater M-P sigma bonding effects on coordination of the PC3 phosphorus of P(CH2NR)3P (R = Me, Ph) than are present in PMe3 analogues of group 6B metal carbonyls. From 1JBP data on the BH3 adducts of P(CH2NMe)3P, it is suggested that the free bases MeC(CH2NMe)3P < P(CH2NMe)3P < (Me2N)3P < P(MeNCH2CH2)3N increase in Lewis basicity at the PN3 phosphorus in the order shown. Substantial differences in 31P chemical shifts in the bicyclic compounds discussed herein relative to their acyclic analogues do not seem to be associated with the relatively small bond angle changes that occur around either the PN3 or the PC3 trivalent phosphorus atoms.

Deposition of bismuth-titanate films with liquid-delivery spin MO-CVD

A vertical liquid-delivery metal-organic chemical vapour deposition (MO-CVD) reactor was used to deposit Bi 4Ti 3O 12 films on SrTiO 3(1 0 0) substrates. Depending on the growth conditions the films show a pure Bi 4Ti 3O 12 phase or additionally a Bi poor phase. Well-ordered, (0 0 1)-oriented, epitaxially grown Bi 4Ti 3O 12 films were obtained at a growth temperature of 700 °C, a Bi excess of 25%, and a substrate rotation between 500 and 750 rpm. The Bi deficiency can be influenced by the concentration of MO precursor in the liquid solution. Depositions on NdGaO 3(1 1 0) also result in epitaxial (0 0 1)-oriented Bi 4Ti 3O 12 films, but the structural quality was slightly poorer.

Fabrication of molybdenum carbide catalysts over multi-walled carbon nanotubes by carbothermal hydrogen reduction

Molybdenum carbide catalysts were successfully prepared using original multi-walled carbon nanotubes (MWCNTs) and nitric acid treated ones as support and carbon source by carbothermal hydrogen reduction from 580 °C to 700 °C. Ammonium heptamolybdate was used as Mo precursor and the effects of oxygen functional groups on MWCNT surface were investigated. TEM and XRD results show that oxygen functional groups act as anchor sites to interact with the Mo oxyanion species during impregnation, which promote the dispersion of Mo precursors. Due to the relatively strong interaction between Mo precursors and MWCNTs, the agglomeration of Mo carbide particles is prevented even when the treatment temperature is as high as 700 °C. Moreover, as the support, modified MWCNTs exhibit better thermal resistances. The temperature (580 °C) for Mo2C formation over MWCNTs is much lower than that over conventional carbon supports using carbothermal hydrogen reduction. The methylcyclohexane dehydrogenation was used as a probe reaction to test the catalytic performances of the Mo2C catalysts obtained.

Low Temperature ALD MoN for Applications in Nanoscale Devices

A low temperature plasma enhanced atomic layer deposition (ALD) process has been developed for the growth of ultra thin MoN films. An optimized process was identified by performing a systematic study of film growth rate as a function of Mo precursor pulse and purge times, N2 and H2 pulse time and heater temperature. Subsequent chemical and microstructural analysis shows that the as-deposited MoN film has a stoichiometric composition, a resistivity of 1280 mW, an atomically smooth surface and amorphous structure. Copper diffusion barrier performance measurements show that MoN films between 2.5 and 15 nm thick could prevent copper diffusion after a 1-hour anneal at 600{degree sign}C.

Influence of double promotion on HDS catalysts prepared by urea-matrix combustion synthesis

The stringent environmental regulations in the US, Japan and Europe are requiring significant improvement in the quality of transportation fuels. A new strategy based on urea-matrix combustion method for the synthesis of alumina-supported molybdate-based mixed oxides (i.e., bimetallic and trimetallic oxides) has been applied. This permits to control the alumina–mixed oxide interaction and therefore the HDS catalytic behaviour. The oxidic and sulfurized states of the HDS catalysts were characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), temperature-programmed reduction (TPR) and high resolution transmission electron microscopy (HRTEM). Catalyst performance was evaluated using a tubular fixed-bed reactor and the hydrodesulfurization of thiophene under normal pressure as model reaction. It has been found that Ni-promoted alumina-supported MoO 3 catalyst precursor presented a non well-ordered structure of Ni–Mo phase supported on alumina surface. However, when cobalt was added to Ni–Mo precursor the β-isomorph stability was significantly improved and the formation of alumina-supported β-Co 0.5Ni 0.5MoO 4 was observed. The activation treatments markedly affect the catalyst structure and hence the HDS catalytic performance. The catalyst series pretreated in H 2S–H 2 was 2–3 times more active than those C 4H 4S–H 2-pretreated catalysts and ca. 2–10 times more active than the pre-reduced samples. A significantly greater HDS activity of H 2S–H 2-pretreated Co 0.5Mg 0.5MoS x /γ-Al 2O 3 catalyst was observed, which is attributed to the fact that both promoters are into the same network interacting directly with the molybdenum. This feature hinders not only the segregation of cobalt sulfide, but also the formation of long MoS 2 slabs.

Highly active, selective and stable Mo/Ru-HZSM-5 catalysts for oxygen-free methane aromatization

Highly active, selective and stable catalysts for oxygen-free methane aromatization were prepared by using ion-exchange and vapor deposition techniques rather than the conventional metal impregnation methods. Ruthenium (0.15 wt%) was incorporated first to ZSM-5 as a promoter by ion-exchange at room temperature. Then 1–3 wt% of Mo was loaded using Mo(CO) 6 as a Mo precursor. High benzene yields of 4.0–4.2% using a 1.5–2 wt% Mo catalyst were achieved at 600 °C with methane flow rate of 270 cm 3/g h and 1 atm pressure. Effect of changes in the pretreatment conditions (carburization time) was also investigated. Slower heating rates decreased the induction time and improved benzene yield. Mo loading beyond 2.5 wt% led to lower methane conversions. Temperature-programmed oxidation technique was used to characterize the nature of coke formed on spent catalysts. The amount of coke formed was negligible, resulting in high catalyst performance.

Unilineage monocytopoiesis in hematopoietic progenitor culture: switching cytokine treatment at all Mo developmental stages induces differentiation into dendritic cells

We have developed a new culture system whereby human hematopoietic progenitors purified from adult peripheral blood extensively proliferate and gradually differentiate into >95% pure monocytic (Mo) cells. At all developmental stages treatment with interleukin (IL)-4+granulocyte-macrophage colony-stimulating factor or IL-4+c-Kit-ligand+FLT-3 ligand switched the Mo precursors into dendritic cells (DCs). The switching capacity decreased only at the end of the culture, when most Mo cells matured to macrophages. Moreover, the Mo precursors were highly susceptible to transduction with lentiviral vectors: once switched to DCs, they maintained the transgene expression, as well as the phenotype and function of the DC lineage. Our results provide new insight into the potential role of the Mo lineage as a reservoir of DCs in vivo. Furthermore, the methodology for transduction of Mo precursors provides a tool to generate genetically modified, normally functioning DCs potentially useful for immunotherapy.

Characterization and Reactivity of the Tetrametallic Pd2-Mo2 Complex Ph(Bu)P(η5-C5H4)Mo(CO)3Pd(μ-I)2PdMo(CO)3(η5-C5H4)P(Ph)Bu and Its Use to Model Pd-Catalyzed Cross-Coupling Reactions Leading to M−C⋮C Bonds

The mechanism of the Pd-catalyzed cross-coupling reaction between tributyltin acetylides and metal iodides has been investigated with the use of a model Mo precursor bearing a ligand with appropriate steric and electronic properties. This study has allowed us to intercept the tetrametallic Pd2-Mo2 complex Ph(Bu)P(η5-C5H4)Mo(CO)3Pd(μ-I)2PdMo(CO)3(η5-C5H4)P(Ph)Bu, which is a precursor to the catalytically active solvento complex Ph(Bu)P(η5-C5H4)Mo(CO)3PdI(DMF). Both complexes play a key role in Pd-catalyzed cross-coupling reactions between tributyltin acetylides and metal iodides, leading to metal-σ-alkynyls. The catalytic cycle for such a reaction has been further elucidated, especially with regard to the role of the ligands in the metal iodide for the stabilization and/or detection of the intermediates as well as for the formation of the M-alkynyl product.

The Identification of Different Active Sites on Mo/Al2O3 Metathesis Catalysts

Mo/Al2O3 catalysts prepared via fixation of Mo(η3-C3H5)4 on Al2O3 or by conventional impregnation (2.2 or 2.9 wt% Mo) have been compared with regard to their catalytic behavior in the metathesis of propene in different temperature ranges (293-323 K, 473 K). Different active sites have been distinguished. A site derived from a Mo(VI) precursor by thermal activation in inert gas exhibits stable activity, with a propene reaction order near 1. Other sites that are derived from a reduced Mo precursor, probably Mo(IV), are of higher activity but unstable with time-on-stream and also at elevated temperatures (>323 K). These sites support the metathesis at a propene reaction order of 0.5 and with activation energies between 10 and 25 kJ/mol depending on unknown structural details. Due to their instability, they cannot contribute to the high-temperature (T > 373 K) metathesis activity observed with Mo/Al2O3 catalysts. The latter is supported by Mo(VI)-derived sites or, at after reduction of catalysts with higher Mo contents, by Mo(IV)-derived sites that are different from those identified in the present study.

Silicate interface formation during the deposition of Y2O3 on Si

ABSTRACTThe interface behaviour during PE-MOCVD deposition of Y2O3 thin films on Si/SiO2 (8 Å) substrates has been investigated by XPS, TEM and OES analysis. The deposition process involves the sequential injection of MO precursors into the CVD chamber and is assisted by an O2 plasma. The injection frequency greatly influences the interface behaviour in terms of thickness and composition. The O2 plasma and the solvent also greatly affect substrate oxidation, and subsequently interface formation during deposition. Several mechanisms are discussed to account for substrate oxidation in view of a careful control of interface formation.

XANES Mo L-Edges and XPS Study of Mo Loaded in HY Zeolite

Molybdena-containing ultrastable (HY) zeolites, prepared using several Mo precursors and activation procedures, were characterized by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Combined XANES Mo L-edge and XPS results revealed that the Mo 4d electronic level is not strongly influenced by the preparation procedures but that it is clearly modified by the presence of Pd. The splitting of 2.4−2.6 eV obtained in the white line at both Mo LII,III-edges clearly indicated that Mo was tetrahedrally coordinated in all dehydrated catalysts. The Mo oxidation state, evaluated by the energy shift in the absorption edge, was also independent of the synthesis process. The Mo LII-edge is discussed for the first time as a very sensitive probe to determine the nature of Mo species. Even the XANES LIII-edge relative intensity of the maximum at the split white line depends on the Mo coordination; at the LII-edge, intensities do not depend on Mo coordination alone. This aspect shou...

Nanostructured β-Mo2C Prepared by Carbothermal Hydrogen Reduction on Ultrahigh Surface Area Carbon Material

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.

Encapsulating the electroluminescent phosphor micro-particles using a pulsed metal-organic chemical vapor deposition process in a fluidized bed

The protective coating efficiency of illuminated phosphor micro-particles has been investigated. The coating was performed by a pulsed feeding metal-organic chemical vapor deposition (MOCVD) in a fluidized bed using aluminum tri-sec-butylate or aluminum isopropoxide as a precursor. This pulsed MOCVD process in a fluidized bed shows excellent performance for encapsulating micro-particles. The pulsed feeding and the fluidization minimize the agglomeration between the phosphor micro-particles during the MOCVD process. Coating thickness is also precisely controlled up to the range of a few angstroms in thickness. Furthermore, by feeding the explosive aluminum MO precursor separately with oxygen gas, the coating process has been performed more safely in the pulsed MOCVD process.

Atomic Layer Deposition of High-k Gate Dielectrics Using MO Precursor and Cyclic Plasma Exposure

ABSTRACTWe have successfully achieved an ALD like deposition of ZrO2 or HfO2 by using a MO precursor. The MO precursor used in this study was zirconium tetra-tert-butoxide (ZTB) Zr(t-OC(CH3)3)4 and hafnium tetra-tert-butoxide (HTB) Hf(t-OC(CH3)3)4. Because MO precursors are very sensitive to H2O, we used oxygen plasma as an oxidizer instead of H2O in order to reduce background H2O pressure and suppress the background reaction. As a result, we successfully achieved an ALD-like deposition proved by a self-limiting adsorption of MO precursor. The carbon content in the films was suppressed due to highly reactive oxygen plasma. The leakage current of the film with plasma oxidation is much lower than that of film with H2O oxidation. Thus, MO-ALD using a plasma oxidation is a promising candidate for the high-k gate deposition process.