Surface characterization of bulk Fe–Mo mixed sulphide catalysts

Difference of work function potential measurements and X-ray photoelectron spectroscopy (XPS) were used to characterize bulk Fe–Mo mixed sulphides. Thiophene hydrodesulphurization (HDS) and toluene hydrogenation (HYD), at high pressure, were used as catalytic tests. A clear synergetic effect is observed for both reactions. According to difference of work function potential values, mixed sulphides are not a mixture of Mo and Fe sulphides but rather Fe–Mo bimetallic sulphides. They also suggest electron enrichment around the Fe atom for mixed sulphides.     

Sintering and microstructure of mullite–Mo composites

Mullite–Mo composites of different compositions (0–100 vol.% Mo) were sintered to near theoretical density by pulse electric current sintering (PECS). The densification behaviour and the microstructure of mullite–Mo composites as a function of Mo content were studied. The addition of 10 vol.% Mo significantly enhanced the strength and toughness of monolithic mullite to 556 MPa and 2.9 MPa m^1/2, respectively. SEM observations revealed the modification of discrete isolated Mo particles to continuosly interconnected network with the increase in the Mo content. Mo grains were located at the grain boundaries as well as inside the mullite grains. The addition of Mo to monolithic mullite led to a change in the fracture mode.     

Hydrodesulfurization of tetrahydrothiophene over evaporated Mo, Co and Mo–Co model catalysts

The hydrodesulfurization (HDS) of tetrahydrothiophene was studied over model catalysts prepared by deposition of Co and Mo thin films on a stainless‐steel foil covered with graphite. There are three main findings: (1) the nominal turnover rate for the HDS reaction is approximately constant and independent of the Co to Mo ratio, (2) the main product was 1,3‐butadiene for cobalt and 1,3‐butadiene and 1‐butene for molybdenum, and (3) the reaction is not poisoned by sulfur. The surfaces were characterized by Auger electron spectroscopy (AES) before and after reaction. The reactions were carried out under 2.6 kPa of tetrahydrothiophene and 100 kPa of H₂ at 613 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-temperature sintering and microstructure control of mullite–Mo composites

Dense mullite–Mo (45 vol%) composites with homogeneous microstructure have been obtained by plasma activated sintering of a mixture of Mo and mullite precursors at a relatively low temperature (1350 °C) and a pressure of 30 MPa. The mullite precursor was synthesized by a sol–gel process followed by a heat-treatment at 1000 °C. The influence of different mullite precursors on the densification behavior and the microstructure of mullite–Mo composites has been studied. The precursor powder heat-treated at 1000 °C with only Si–Al spinel but no mullite phase shows an excellent sintering activity. Following the sintering shrinkage curves, a two-stage sintering process is designed to enhance the composite densification for further reducing the sintering temperature. The study reveals that viscous flow sintering of amorphous SiO₂ at low temperatures effectively enhances the densification. Moreover, microstructure of these composites can be controlled by selecting different precursors and sintering temperatures.     

High strength,low modulus and biocompatible porous Ti–Mo–Fe alloys

Porous Ti–10Mo–xFe (x = 2–5) alloys were prepared by powder metallurgy using ammonium hydrocarbonate (NH₄HCO₃) as the space-holder. When 7 wt% NH₄HCO₃ is added, the porosity of the Ti–Fe and Ti–Mo–Fe alloys is about 20 %. It was found that Fe has a significant strengthening effect on the Ti-based alloys, while Mo is effective in stabilizing the Ti–10Mo–xFe alloys into β-phase. The inherent better ductility of β-phase than that of the α-phase and the efficient strengthening effect Fe provide a good combination of strength and ductility to the Ti–10Mo–xFe alloys. The compressive yield strength of the porous Ti–10Mo–xFe alloys is from 500 to 800 MPa, much higher than that of the Fe–10Mo alloy (about 260 MPa) and human bone (about 130–180 MPa). Elastic modulus of the alloys is <10 GPa. The alloys also have corrosion resistance similar to that of pure Ti. Cytotoxic tests show that the L929 cell RGR values of the Ti–10Mo–xFe alloys are over 80 % at day 1, day 4 and day 7. The cells grew in good condition on the seventh day. The results indicate that the porous Ti–10Mo–xFe alloys have superior mechanical properties, good corrosion resistance, and excellent biocompatibility, and are promising candidates for bone substitute materials.     

Oxidative desulfurization of dibenzothiophene over Fe promoted Co–Mo/Al_2O_3 and Ni–Mo/Al_2O_3 catalysts using hydrogen peroxide and formic acid as oxidants

This work reports the enhancing effect of a highly cost effective and efficient metal, Fe, incorporation to Co or Ni based Mo/Al_2O_3 catalysts in the oxidative desulfurization(ODS) of dibenzothiophene(DBT) using H_2O_2 and formic acid as oxidants. The influence of operating parameters i.e. reaction time, catalyst dose, reaction temperature and oxidant amount on oxidation process was investigated. Results revealed that 99% DBT conversion was achieved at 60 °C and 150 min reaction time over Fe–Ni–Mo/Al_2O_3. Fe tremendously enhanced the ODS activity of Co or Ni based Mo/Al_2O_3 catalysts following the activity order: Fe–Ni–Mo/Al_2O_3 NFe–Co–Mo/Al_2O_3 NNi–Mo/Al_2O_3 NCo–Mo/Al_2O_3, while H_2O_2 exhibited higher oxidation activity than formic acid over all catalyst systems. Insight about the surface morphology and textural properties of fresh and spent catalysts were achieved using scanning electron microscopy(SEM), X-ray diffraction(XRD), energy dispersive X-ray(EDX)analysis, Atomic Absorption Spectroscopy(AAS) and BET surface area analysis, which helped in the interpretation of experimental data. The present study can be deemed as an effective approach on industrial level for ODS of fuel oils crediting to its high efficiency, low process/catalyst cost, safety and mild operating condition.     

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO₄ · 7H₂O and CrCl₃ · 6H₂O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.     

Investigation of Alumina Wetting by Fe–Ti,Fe–P and Fe–Ti–P Alloys

Abstract

The wetting of alumina substrates by Fe–Ti, Fe–P and Fe–Ti–P alloys has been investigated using sessile drop experiments conducted under an inert gas atmosphere in the temperature range of 1550 to 1620°C. The surface and interfacial structures have been explored by scanning electron microscopy and energy dispersive X-ray spectroscopy. Substantial additions of titanium are known to induce steel melts to wet alumina due to the formation of a Ti-rich reaction product at the alloy/ceramic interface, but the present work has shown that even low Ti concentrations can induce a reactive wetting process leading to an improvement of the wettability of alumina by Fe alloys. The contact angle of molten steel containing phosphorus on alumina decreased with increasing P content. The improvement of the wetting behaviour in this system was attributed solely to the adsorption of P onto the surface of the Fe melt. The addition of P as a ternary alloying element to the system Fe–Ti proved to be beneficial to the wetting behaviour. The measured contact angles were much lower than those in the binary systems Fe–Ti and Fe–P. This effect was related to the fact that P enhances the activity of Ti in the Fe melt. According to experimental observations, it turns out that the wettability of liquid Fe-based alloys, when an Al2O3 surface is present, is not only a property of the metal/oxide couple but is also dependent on the oxygen partial pressure, whereas temperature variations bring about a comparatively small effect. This work is of interest in understanding the phenomena pertaining to inclusion engineering and steel– refractory interactions, such as the clogging of submerged entry nozzles by agglomerated alumina particles during the continuous casting process.     

Fe－Mo非晶态合金电沉积工艺研究

研究了Ｆｅ－Ｍｏ非晶态合金电沉积的工艺条件、镀液中各成分的含量及添加剂对镀层成分和结构的影响。结果表明：控制适当的工艺条件，可获得２０μｍ以上厚度的非晶态Ｆｅ－Ｍｏ镀层；镀液中Ｍｏ￣（６＋）／（Ｍｏ￣（６＋）＋Ｆｅ￣（２＋））比值的提高、电流密度的增加、温度的升高及ｐＨ值的提高均使镀层中钼含量增加；其中对钼含量影响最大的是ｐＨ值；镀层的钼含量不随电镀时间的增加而变化；在镀液中加入适量的三乙醇胺、酒石酸钾钠后仍可得到非晶态Ｆｅ－Ｍｏ镀层，且镀层中钼含量增加；镀层的耐蚀性不及不锈钢可能是由于镀层有微裂纹所致。     

Fe—Mo非晶态合金电沉积工艺研究

研究了Ｆｅ－Ｍｏ非晶态合金电沉积的工艺条件，镀液中各成分的含量及添加剂对镀层成分和结构的影响，结果表明：控制适当的工艺条件，可获得２０μｍ以上厚度的非晶态Ｆｅ－Ｍｏ镀层；镀液中Ｍｏ＾６＋／（Ｍｏ＾６＋＋Ｆｅ＾２＋）比值的提高，电流密度的增加、温度的升高及ｐＨ值的提高均使镀层中钼含量增加；其中对钼含量影响最大的是ｐＨ值，镀层的钼含量不随电镀时间的增加而变化，在镀液中加入适量的三乙醇胺、酒石酸钾钠后仍     

Synthesis of 3-fluorobenzaldehyde by gas-phase selective oxidation on Fe–Mo oxide/boralite catalysts

The gas-phase selective synthesis of 3-fluorobenzaldehyde from 3-fluorotoluene over bulk iron molybdate and Fe–Mo oxide in a host boralite sample is described. The latter samples, prepared by adding Fe and Mo by chemical vapor deposition to the boralite, show high selectivity in oxidation, making yields of 3-fluorobenzaldehyde of over 40% possible. The pretreatment of the zeolite to eliminate extra-framework boron improves behavior, and secondary post-addition of molybdenum by CVD to increase the Mo/Fe ratio in the catalyst has a similar enhancing effect. The behavior of Fe–Mo/boralite samples proves significantly better, in terms of both specific activity (per mass of active phase) and selectivity, than bulk Fe₂(MoO₄)₃, but at high conversion lower selectivities are found probably due to the presence of limitations in the backdiffusion of 3-fluorobenzaldehyde. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis, Characterization and HDS Activity of Carbon-Containing Ni–Mo Sulfide Nano-Spheres

Ni-promoted tetramethylammonium tetrathiomolybdate precursor was prepared by the aqueous solution precipitation method using (NH₄)₂MoS₄, (CH₃)₄NBr and NiCl₂.6H₂O as raw materials. Carbon-containing Ni–Mo sulfide nanospheres, namely Ni/C₁–MoS₂, were obtained by ex situ thermal decomposition of the precursor under N₂ atmosphere. Energy dispersive X-ray spectroscopy (EDS), low temperature N₂ adsorption (BET method), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) techniques were employed to characterize these as–synthesized sulfide particles. The results showed that the average size of solid Ni–Mo sulfide nanospheres, with surface composition MoNi₀.₄₀S₀.₇₃C₁.₄₃, is 75 nm and the solid structure leads to low surface area of Ni/C₁–MoS₂. In addition, the introduction of methyl chain improved the dispersion of nickel phases and resulted in C/Mo ratio, 1.4. By comparison with catalytic performance of the Ni/MoS₂ catalyst counterpart, Ni/C₁–MoS₂ revealed lower HDS activity but higher direct desulfurization (DDS) selectivity. Lower stacking number of MoS₂ slabs (5 layers) and shorter slabs length of MoS₂ slabs (6 nm) explained higher DDS selectivity satisfactorily. The formation of carbon-containing Ni–Mo sulfide nanospheres was possibly due to surfactant effect of tetramethylammonium cations and the potential measure to increase their surface area was discussed as well in this work.     

Mössbauer Spectroscopy Study of Macromolecular Complexes of Polycarbosilazane Coordinated with Fe(II), Fe(III) and Mixed Valence Fe(II-III) Chlorides

A series of iron-polyethylenediaminecarbosilazane (PEDCSZ-Fe) macromolecular chloride macromolecular complexes were prepared by the reaction of Fe(II), Fe(III), and mixed valence Fe(II-III) chlorides with polyethylenediaminecarbosilazane matrix in toluene under inert atmosphere. The mixed valence macromolecular complexes composed of three different ratios of Fe(II)/Fe(III) (1:2, 1:1, and 2:1). Mössbauer spectra were recorded for the samples at room temperature. The spectra of the PEDCSZ-Fe(II) and PEDCSZ-Fe(III) macromolecular complexes showed pure paramagnetic phase, whereas, the spectra for the mixed valence PEDCSZ-Fe(II-III) showed both magnetic and paramagnetic splitting. The magnetic splitting is so broad such that it was fitted with three magnetic sextets and one quadrupole doublet. The relative intensity of the magnetic phase was the highest for the PEDCSZ-Fe(II-III) with 1:1 ratio. The magnetic phase could be attributed to an iron oxide phase (Fe₃O₄ or FeOOH phase) in a fine powder form as it is clear from the Mössbauer parameters. The XRD patterns of the PEDCSZ-Fe(II-III) with 1:1 ratio contained additional diffraction peaks similar to those observed for Fe₃O₄ in a fine particle form.     

半导体型Mo－Fe二元氧化物催化剂的研制

通过共沉淀法和进一步焙烧制得Ｍｏ－Ｆｅ二元氧化物。经ＸＲＤ定性分析表明，它们是由含量不同的Ｆｅ２（ＭｏＯ４）３和ＭｏＯ３所组成。利用固定床反应器研究了Ｍｏ－Ｆｅ氧化物／载体催化剂对甲醇氧化制甲醛的催化性能。对二元Ｍｏ－Ｆｅ氧化物进行了气体敏感性能测试，发现对甲醇具有较高的灵敏度，对氧气的灵敏度较低。其中，具有较高活性的催化剂对被测气体的灵敏度也较高     

A vibrational study of the activation sequence of C–H and C–C bonds of isobutene and 1-butene on Mo(110) and (4 × 4)-C/Mo(110) surfaces

The thermal decomposition pathways of isobutene and 1-butene on both Mo(110) and 4 × 4-C/Mo(110) surfaces have been studied using high-resolution electron energy loss spectroscopy (HREELS) in order to highlight the substantially different activities of these two surfaces towards the cleavage of C–H and C–C bonds. On clean Mo(110), the CH₂ group of isobutene decomposes upon heating to 150 K, producing either a /-bonded isobutenylidene [(CH₃)₂CCH] species or a 1,1-di-/-bonded isobutenyl [(CH₃)₂CC] species. Upon further heating, extensive C–H bond scission occurs to form hydrocarbon fragments which do not contain CH₃ or CH₂ groups, but appear to have largely intact carbon skeletons. By contrast, isobutene is molecularly adsorbed on the carbide-modified surface at 150 K. Further heating produces isobutylidyne [(CH₃)₂HCC] by 300 K, which subsequently decomposes via C–C bond scission to generate surface methyl groups. The different activation sequence of the C–H and C–C bonds of isobutene on clean and carbide-modified Mo(110) surfaces is also qualitatively confirmed by comparative studies of 1-butene on the two surfaces.     

High-temperature compressive properties and tribological behaviour of Mo2NiB2–Ni cermets

The present work investigated the high-temperature compressive strength and tribological behaviours of Mo₂NiB₂–Ni cermets from 25 to 900 °C. Mo₂NiB₂–Ni cermets with four different Ni additions were first fabricated successfully and then tested. The results show that cermets with Ni/B 1.1 have the best compressive strength of 531.8 MPa at 900 °C and superior strength retention at high temperature. With the best high-temperature compressive strength, Mo₂NiB₂–Ni cermets with Ni/B 1.1 are used as pins with Si₃N₄ disks in a tribological test. The wear rate of Mo₂NiB₂–Ni cermets gradually increases as the temperature increases from 25 to 900 °C, while the friction coefficient shows the opposite trend. Within the entire testing temperature range, the friction coefficient decreases, and the minimum friction coefficient is obtained at 900 °C. The decline of the friction coefficient is attributed to the self-lubricating oxidation tribolayer covering the worn surface. Moreover, the dominant wear mechanism changes from abrasive wear to oxidation wear as the temperature exceeds 600 °C.     

Analysis of Fe(Ⅵ) characteristics and its application to water treatment

Ferrate（Fe(Ⅵ)）is a new type of water treatment chemicals. From the point of view of structural chemistry,electrochemistry,thermal decomposition characteristics and stability,the physical and chemical characteristics of Fe(Ⅵ) were analyzed,and the preparation of ferrate was described. Its application to water treatment was summarized,such as pre-oxidation by ferrate,and the specific applications were outlined. The results showed that 1.0 mg / L ferrate pre-oxidation could significantly improve the effect on coagulation,Water after sedimentation and filtration turbidity removal rate reached 98.58% and 99.9% respectively. Water colority,UV₂₅₄ and other organic composite indicator were significantly decreased. At the same time,manganese and iron were also significantly reduced. In addition,ferrate pre-oxidation could effectively remove bacteria and E.coli. Finally,according to the practical situation,the paper offers advice on engineering application of ferrate.     

Effect of Mo addition mode on the microstructure and mechanical properties of TiC–high Mn steel cermets

In TiC- and Ti(C,N)-based cermets, the wettability of the ceramic phase with the metallic binder is commonly increased through supplementation with Mo in the form of pure Mo powder or Mo₂C. Herein, TiC–high Mn steel cermets were fabricated by conventional powder metallurgy techniques using Fe–Mo pre-alloyed powders as binders to guarantee uniform Mo distribution, and the cermet preparation process was optimized and investigated in detail. The microstructures of the thus obtained cermets were observed by scanning electron microscopy and compared to those of a Mo-free cermet and a cermet prepared using pure Mo powder. The grain size of Fe–Mo powder cermets exceeded that of the Mo-free cermet but was much smaller and more homogeneous than that of the Mo powder cermet. For Fe–Mo powder cermets, angular and tetragonal TiC particles were observed at Mo contents of <1.2 wt%, while round shapes became dominant at higher Mo contents. The hardness of Fe–Mo powder cermets increased with increasing Mo content, as did transverse rupture strength, which was maximal (2264 MPa) at a Mo content of 2.4 wt%, while impact toughness was maximal (11.2 J/cm²) at a Mo content of 1.2 wt%. The above values exceeded those reported for similar conventional cermets, and the use of Fe–Mo pre-alloyed powder as a metallic binder was therefore concluded to be an attractive strategy of increasing the strength and toughness of TiC–high Mn steel cermets.