The multi-structure of oxidized-reduced tungsten carbide surface(s)

The XPS of bulk tungsten carbide, partially oxidized WC surfaces at 373 and 573 K as well as tungsten trioxide have been reported. Bulk WC has been prepared from WO₃ as a starting material in a mixture of CH₄ (20%) and H₂ (80%) at 1150 K for 4 h, while partially oxidized WC surfaces were prepared by oxygen chemisorption on a clean WC surface at 200 K, then the temperatures were raised to 373 and 573 K respectively. The XPS of a freshly prepared WC reveals the presence of a small amount of WO₃ on the surface and a slightly higher concentration in the bulk. The oxygen-exposed fresh WC surfaces and surfaces treated at temperatures higher than 373 K show the presence of WO₃ in a considerable quantity depending on the length and the treatment temperature. Ar⁺ bombardment of this partially oxidized surface reduces WO₃ to WO₂ and W(0), while WC is partially reduced to W(0). Isomerization reactions of alkanes on oxygen-exposed WC surface occurs in reality on a composite surface structure containing WC, WO₃, WO₂ and elemental W(0).     

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, γ-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al₂O₃ catalyst. The WP/γ-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al₂O₃ catalyst. In general, a support or promoter in the WP/γ-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh₃)(NO₃) (1) and a phosphine-stabilized gold cluster [Aug(PPh₃)₈](NO₃)₃ (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe₂O₃, TiO₂, and SiO₂ were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h₂/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe₂O₃ and TiO₂ were much more efficient supports than SiO₂ for the gold particles which were characterized by XRD and EXAFS.     

Preparation,characterization, and catalytic behavior of MoRh2O6 supported on SiO2

Rh double-oxide compound (MoRh₂O₆) supported on SiO₂ was prepared by air calcination treatment of a molybdenum oxide-promoted Rh/SiO₂ catalyst at 700 °C, and the chemisorptive and catalytic properties of the compound, as well as the changes in those behaviors by H₂ reduction, have been studied.The MoRh₂O₆/SiO₂ catalyst exhibited almost no ability of H₂ and CO chemisorption, but a high activity for CO oxidation reaction. After H₂ treatment at 200 °C, X-ray diffraction showed that the MoRh₂O₆ compound was reduced to a MoRh alloy, and this catalyst now exhibited a significant activity for the hydrogenolysis of cyclohexane. A drastic decrease in the activity was, however, observed after H₂ treatment at 500 °C.     

Surface characterization and properties of functionalized nonwoven

Nonwoven materials have been increasingly used in many industries. The surface properties of nonwoven materials are of importance in these applications. In this study, functional nonwoven materials were prepared by sputtering deposition of copper (Cu), zinc oxide (ZnO), and polytetrafluoroethylene (PTFE) on the surface of polypropylene (PP) fibers. Atomic Force Microscopy (AFM) and Environmental Scanning Electron Microscopy (ESEM) were employed to study the surface morphology and chemical compositions. The observations by AFM revealed the formation of functional nanostructures on the fibre surfaces and the ESEM examination confirmed the formation of functional compositions on the fiber surface. The metallic coating of Cu significantly improved the surface conductivity of the material. The transmittance analysis indicated that the ZnO coating obviously increased the ultra‐violet absorption of the material. The surface hydrophobicity of the nonwoven material was enhanced by the sputter coating of PTFE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

负载钛体系催化合成聚1-丁烯的结构与性能

对负载钛体系催化合成的聚1－丁烯（PBt)进行了结构表征和性能的测试。DSC测试表明，PBt有两个熔融峰，分别为43.5℃和112．4℃，玻璃化温度为－23．4℃；热－机械分析表明PBt的软化点为80℃，粘流温度为165℃；脆性温度为－21℃；PBt的物理交联点间平均相对分子质量为2400；应力－应变曲线呈典型的弹性体特征；PBt具有优良的耐酸碱性、良好的绝缘性和介电性，其介电损耗正切值介于极性和非极性材料之间；永久形变在90％－150％之间     

Colloidal Co nanoparticles supported on SiO2: Synthesis, characterization and catalytic properties for steam reforming of ethanol

Colloidal Co nanoparticles with sizes in the 3–8 nm range were obtained by thermal decomposition of Co₂(CO)₈ in the presence of ligands and impregnated on SiO₂ to prepare SiO₂-supported Co nanocatalysts. The catalysts showed activity for the steam reforming of ethanol with higher values for smaller Co particles. H₂ adsorption results and Fourier transform infrared spectroscopy of adsorbed CO suggested that the fraction of accessible Co sites also depended on the synthesis conditions. Precipitation of the Co nanoparticles with methanol instead of ethanol before impregnation had a positive effect on the density of accessible Co sites to catalysis; similar result was verified by increasing the thermal treatment temperature under H₂ flow before the reaction. Based on the distribution of products with temperature of reaction, a mechanism for steam reforming of ethanol on SiO₂-supported Co nanocatalysts is suggested.     

Catalytic properties of Rh, Ni, Pd and Ce supported on Al-pillared montmorillonites in dry reforming of methane

A natural Maghnia clay was pillared by Al₁₃ and impregnated by 3–10 wt.% Me (Me = Rh, Ni, Pd, Ce) to be used as catalysts in the reforming of methane with carbon dioxide to synthesis gas. The structural and textural properties of materials calcined at 450 °C were determined by several techniques (XRD, FT-IR, ²⁷Al magic angle spinning (MAS) NMR, X-ray photoelectron spectroscopy (XPS), BET, thermogravimetric analysis (TGA)–DSC, H₂-temperature programmed reduction (TPR) and NH₃-TPR). Although impurities are present in the Al-pillared layered clay (PILC) support, most properties are close to those of pure Al-pillared Na-montmorillonite. Impregnation and calcination leads to the plugging of most micropores by clusters or microparticles of oxides. The NMR resonances of Al_VI and Al_IV specie are not modified after impregnation, and Al_VI/Al_IV ratio only varies on loading when compared to Al-PILC. Catalytic experiments show that the most active catalyst is 3% Rh/Al-PILC on which 88 mol.% of methane is converted at 650 °C with a minimum amount of carbon deposit. The conversions decrease along the 3% Rh ≈ 10% Ni > 3% Pd > 3% Ni > 3% Ce series. The H₂/CO ratio amounts to 1.1 with Rh and to 0.85 with Pd which are metallic at the temperature of reaction, but it has a lower value with Ni and Ce due to the RWGS reaction known to proceed in the presence of oxides.     

A comparative study of the partial oxidation of methane to formaldehyde on bulk and silica supported MoO3 and V2O5 catalysts

The mechanism of the partial oxidation of methane to formaldehyde with O₂ has been investigated on bulk and differently loaded silica supported (4–7 wt%) MoO₃ and (5–50 wt%) V₂O₅ catalysts at 600–650°C in a pulse reactor connected to a quadrupole mass spectrometer. The reaction rate and product distribution in the presence and in the absence of gas-phase O₂ have been evaluated. On bare SiO₂, low and medium loaded silica supported MoO₃ and V₂O₅ catalysts the reaction proceeds via a concerted mechanism involving the activation of gas-phase oxygen on the reduced sites of the catalyst surface as proved by the direct correlation between catalytic activity and density of reduced sites evaluated in steady-state conditions, while on highly loaded catalysts as well as on bulk MoO₃ and V₂O₅ the reaction rate drops dramatically and the reaction pathway via redox mechanism becomes predominant. The results indicate that the surface mechanism is essentially more effective than the redox mechanism enabling also a higher selectivity to HCHO.     

Syntheses and adsorption properties for Hg2+ of chelating resin of crosslinked polystyrene‐supported 2,5‐dimercapto‐1,3,4‐thiodiazole

A novel chelating resin with functional group containing S and N atoms was prepared using chloromethylated polystyrene and 2,5‐dimercapto‐1,3,4‐thiodiazole (also called bismuththiol I, BMT) as materials. Its structure was characterized by infrared spectra and elementary analysis. The results showed that the content of the functional group was 2.07 mmol BMT g^?1 resin, 47% of which were in the form of monosubstitution (PS‐BMT‐1) and 53% in the form of double substitution (PS‐BMT‐2). The adsorption for mercury ion was investigated. The adsorption dynamics showed that the adsorption was controlled by liquid film diffusion. Increasing the temperature was beneficial to adsorption. The Langmuir model was much better than the Freundlich model to describe the isothermal process. The adsorption activation energy (E_a), ΔG, ΔH, and ΔS values calculated were 18.56 kJ·mol^?1, ‐5.99 kJ·mol^?1, 16.38 kJ·mol^?1, and 37.36, J·mol^?1·K^?1, respectively. The chelating resin could be easily regenerated by 2% thiourea in 0.1 mol·L^?1 HCl with higher effectiveness. Five adsorption–desorption cycles demonstrated that this resin was suitable for repeated use without considerable change in adsorption capacity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1646–1652, 2004     

Mechanism of sulfur poisoning on supported noble metal catalyst — The adsorption and transformation of sulfur on palladium catalysts with different supports

A series of supported palladium catalysts (Pd/Al₂O₃, Pd/MgO and Pd/TiO₂) were prepared by the impregnating method and treated with H₂S, H₂ +O₂ or O₂, among which H₂S is used as a poison and H₂ +O₂ or O₂ are as purging atmospheres. The S^2– species in the supports was introduced by means of mechanically mixing Na₂S with the supports or catalysts. X-ray photoelectron spectroscopy (XPS) was employed to determine the changes in the chemical states of oxygen, palladium and sulfur in the catalysts before and after the treatment, while infrared (IR) spectroscopy was used to measure the SO^2– ₄ group produced in the catalysts and supports. The results show that on MgO and TiO₂ carriers whose acidities are weak, there exist two kinds of oxygen species, one is the lattice oxygen, the other one is the active species of oxygen. The latter can oxidize the S^2– into SO^2– ₄ even at room temperature in air. Because of the weak acidities and smaller specific surface area of MgO and TiO₂, the S^2– is liable to adsorb on the catalysts and to transform into SO^2– ₄. But for the case of Al₂O₃ support its acidity is rather strong, and its surface oxygen species under the experimental conditions is not so active as that in MgO and TiO₂ carries. The poison H₂S on the Al₂O₃ support only experiences a process of physical adsorption-desorption. In Pd/Al₂O₃ catalyst, the negatively charged sulfur ions are not so easily adsorbed and transformed as those in Pd/MgO and Pd/TiO₂. It is also implied that the properties of the carriers are related to the ability of self-regeneration of the corresponding catalysts. Pd/Al₂O₃ catalyst is more able to self-regenerate than Pd/MgO and Pd/TiO₂ catalyst.     

Effect of CO2 and melt decarbonation on the dimerization of methane in molten Li2CO3-Na2CO3-K2CO3 supported by LiAlO2 or Li2TiO3 at 750–850°C

The oxidative dimerization of methane was investigated at 750–850°C in Li₂CO₃-Na₂CO₃-K₂CO₃ immobilized within LiAlO₂ or Li₂TiO₃ supports. Catalytic performance was enhanced with moderate melt decarbonation (i.e. with molten phase/LiAlO₂ at 850°C: CH₄ conversion of 25% and C₂ yield of 12.5%), then dramatically fell with the precipitation of sodium and lithium oxide. The effect of the partial pressure of CO₂ was analyzed. As in the case of binary carbonate eutectics, catalytic activity of the ternary melt was correlated with the presence of peroxide species. This activity was more important when using LiA1O₂ support.     

Preparation, characterization and catalytic properties of Co–Nb2O5–SiO2 catalysts

Co–Nb₂O₅–SiO₂ catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl₅ and SiCl₄ as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl₄. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min⁻¹) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb₂O₅) were obtained. The characterization of the catalysts was performed using various techniques: N₂ adsorption and desorption curves at 77 K, NH₃- and H₂-chemisorption, TPO, XPS, XRD, and solid state ¹H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support.     

On the development of metallic particles and their initial catalytic properties in the CO + H2 reaction over Co/Al2O3 catalyst

Formation of Co^o phases with different surface structure over 10 wt% Co/Al₂O₃ and their catalytic properties were induced by pretreatments in H₂ at 570 K for 1 h or 20 h. Electronic behaviour of the Co^o phase, which consists of small (after 1 h reduction) or large bulk-like particles (after 20 h reduction), did not change during the CO hydrogenation after 5 h on stream as was determined by XPS. On the basis of the measured C₂₊ hydrocarbon selectivities the CO molecules are suggested to dissociate on small Co particles to a larger extent than on large cobalt particles. The slight decrease in the catalytic activity with increasing time on stream obtained for the long-term reduced sample is explained by the change in the surface Co^o content detected by XPS. The increase in the catalytic activity along with the change in olefin selectivity, measured for the sample reduced for 1 h, is interpreted by the change of a reaction path involving the Co^o-support interface during the initial period of the reaction.