Plasma Enhanced Chemical Vapor Deposition Nanocrystalline Tungsten Carbide Thin Film and Its Electro-catalytic Activity

Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.

Effect of Reaction Temperature and Pressure on the Metathesis Reaction between Ethene and 2-Butene to Propene on the WO_3/Al_2O_3-HY Catalyst

Effect of reaction temperature and pressure on the metathesis reaction between ethene and 2-butene to propene was studied on the WO3/γ-Al2O3-HY catalyst. The activity is found to increase with elevated temperature and reaches a plateau at 150-240 ℃. After that, the activity undergoes a remarkable decrement at too high temperature. The effect of temperature is elucidated by the oxidation state of tungsten species. The evaluation results also indicate that the stability is dependent on this reaction parameter. Medium pressure （0.5-0.8 MPa） is favorable for stability, while atmospheric pressure or too high pressure （〉1.0 MPa） deteriorates the stability. For explanation, UV Vis, FT-IR, O2-TPO, and TG techniques are used to characterize the spent catalysts.

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,c-Al_(2)O_(3) 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/c-Al_(2)O_(3) catalyst.The WP/c-Al_(2)O_(3) 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/c-Al_(2)O_(3) catalyst.The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/c-Al_(2)O_(3) catalyst.In general,a support or promoter in the WP/c-Al_(2)O_(3) catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.

A Kinetic Approach to Photomineralization of Methane in Air by Membranes Based on TiO2/WO3

Photomineralization of methane in air(10.0-1,000 ppm(mass/volume)of C)at 100%relative humidity(dioxygen as oxygen donor),was systematically studied at 318±3 K,in an annular laboratory-scale reactor,by photocatalytic membranes immobilising titanium dioxide and tungsten trioxide as co-photocatalysts.Kinetics of both substrate disappearance,to yield intermediates,and total organic carbon(TOC)disappearance,to yield carbon dioxide,were followed.A kinetic model was employed,from which,by a set of differential equations,four final optimised parameters,k1 and K1,k2 and K2,were calculated,able to fit the whole kinetic profile adequately.Modelling of quantum yields,as a function of substrate concentration and irradiance,as well as of concentration of photocatalysts,was carried out very satisfactorily.Kinetics of hydroxyl radicals reacting between themselves,leading to hydrogen peroxide,other than with substrate or intermediates leading to mineralization,were considered,paralleled by second competition kinetics involving superoxide radical anion.When using appropriate blends of the two photocatalysts,limiting quantum yieldsF∞values increase considerably and approach the maximum allowable value for the investigated molecule,in a much wider range of irradiances than that shown by the single catalysts mainly at low irradiances.This may be interpreted by strong competition kinetics of superoxide radicals generated by the catalyst defects,in the corresponding range of high irradiances.By this way,operation at high irradiance values is possible,without losing any efficiency for the mineralization process.

Nanostructure and Formation Mechanism of Pt-WO_3/C Nanocatalyst by Ethylene Glycol Method

Pt-WO3 nanoparticles uniformly dispersed on Vulcan XC-72R carbon black were prepared by an ethylene glycol method.The morphology,composition,nanostructure,electrochemical characteristics and electrocatalytic activity were characterized,and the formation mechanism was investigated.The average particle size was 2.3 nm,the same as that of Pt/C catalyst.The W/Pt atomic ratio was 1/20,much lower than the design of 1/3.The deposition of WO3·xH2O nanoparticles on Vulcan XC-72R carbon black was found to be very difficult by TEM.From XPS and XRD,the Pt nanoparticles were formed in the colloidal solution of Na2WO4,the EG insoluble Na2WO4 resulted in the decreased relative crystallinity and increased crystalline lattice constant compared with those of Pt/C catalyst and,subsequently,the higher specific electrocatalytic activity as determined by CV.The Pt-mass and Pt-electrochemically-active-specific-surface-area based anodic peak current densities for ethanol oxidation were 422.2 mA·mg-1Pt and 0.43 mA·cm-2Pt,1.2 and 1.1 times higher than those of Pt/C catalyst,respectively.