Zhaobin Wei

Carbon nanotubes as support for cathode catalyst of a direct methanol fuel cell

Colloid Interface Sci 1990;138:590–2.[4] Suzuki T, Kaneko K. Structural change of activated carbon [6] Suzuki T, Kasuh T, Kaneko K. The structural change offibers with desorption by in situ X-ray diffraction. Carbon graphitization-controlled microporous carbon upon adsorp-1988;26:743–5. tion of H O and N . Chem Phys Lett 1992;191:569–73.

Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed

Ammonia synthesis over Ru/C catalysts with different carbon supports promoted by barium and potassium compounds

Ammonia synthesis over ruthenium catalysts supported on different carbon materials using Ba or K compounds as promoters has been investigated. Ba(NO3)(2), KOH, and KNO3 are used as the promoter or promoter precursor, and activated carbon (AC), activated carbon fiber (ACF). and carbon molecular sieve (CMS) are used as the support. The activity measurement for ammonia synthesis was carried out in a flow micro-reactor under mild conditions: 350-450 degreesC and 3.0 MPa. Results show that KOH promoter was more effective than KNO3. and that Ba(NO3)(2) was the most effective promoter among the three. The roles of promoters can be divided into the electronic modification of ruthenium, the neutralization of surface functional groups on the carbon support and the ruthenium precursor. The catalyst with AC as the support gave the highest ammonia concentration in the effluent among the supports used, while the catalyst with ACF as the support showed the highest turnover-frequency (TOF) value. It seems that the larger particles of Ru on the carbon supports are more active for ammonia synthesis in terms of TOF value

Hydrodesulfurization activity of NiMo/TiO2-Al2O3 catalysts

The hydrodesulfurization activities and other physico-chemical properties of NiMo/TiO2Al2O3 catalysts were studied and compared with those of a commercial NiMo/Al2O3 catalyst. The TiO2Al2O3 mixed oxides carrier was prepared by impregnating Al2O3 with an ethanol solution of TiCl4 or an isoproponol solution of Ti(C4H9O)4. The active component MoO3 and the promoter NiO were supported by impregnation of a mixed solution of Ni(NO3)2·6H2O and (NH4)6Mo7O24·4H2O. BET measurements showed no large decrease of surface area or pore volume for the carrier and catalyst-containing TiO2. LRS data demonstrated that TiO2 on Al2O3 was present as the anatase phase, and only the vibration band of MoO at 960 cm−1 appeared over NiMo/TiO2Al2O3 when TiO2 loading was less than 20 wt %. TPS results reveal that the presence of TiO2 can facilitate sulfidation of MoO species. Catalytic activity measurements showed that NiMo/TiO2Al2O3 catalysts without presulfiding exhibited very high HDS activity for a model reactant containing 100 ppm thiophene or industrial naphtha. The capability of sulphur removal over the non-pretreated NiMo/TiO2Al2O3 catalyst is even better than over a sulfided commercial hydrotreating NiMo/Al2O3 catalyst.

Catalytic Decomposition of Hydrazine over Supported Molybdenum Nitride Catalysts in a Monopropellant Thruster

The catalytic decomposition of hydrazine over a series of MoNx/γ-Al2O3 catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO3 on γ-Al2O3, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/γ-Al2O3 catalyst. The MoNx/γ-Al2O3 catalyst with a loading of about 23 wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoNx/γ-Al2O3 catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.

The synthesis of nanostructured W2C on ultrahigh surface area carbon materials via carbothermal hydrogen reduction

Nanostructured tungsten carbides were synthesized, for the first time, with a size distribution of 5–12 nm on ultrahigh surface area carbon material, by carbothermal hydrogen reduction (CHR) at 850°C and metal Ni promoted CHR at 650°C.

Investigation of the sulfidation of Mo/TiO2-Al2O3 catalysts by TPS and LRS

A series of Mo/Al2O3 and Mo/TiO2-Al2O3 catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO2 on the sulfidability of molybdena was studied in detail. It is found that Mo/Al2O3 catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H2 to produce H2S. At 530–550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS2. When the surface of Al2O3 was covered by a monolayer of TiO2, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H2S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80–100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO2 loading. The function of TiO2 is explained by the weakened interaction between MoO3 and Al2O3 due to the coverage of the Al2O3 surface by TiO2.

Synthesis and hydrodesulfurization (HDS) and hydrogenation (HYD) activity of dimolybdenum nitride

Abstract Various kinds of surface area γ-Mo 2 N were synthesized by a topotactic reaction between MoO 3 and NH 3 under relatively mild conditions. It was found that the space velocity of NH 3 and the particle size of MoO 3 were very important for the synthesis of high surface area γ-Mo 2 N in a large batch. The percent of micropore volume in the range of 20–30 A gradually increased with increase of surface area. XRD results indicated that the intensities of diffraction peaks of high surface area γ-Mo 2 N was different from those of low surface area. The measurements of catalytic activities for thiophene hydrodesulfuriztion and cyclohexene hydrogenation showed that high surface area γ-Mo 2 N exhibited much higher activity than those of medium and low surface area γ-Mo 2 N. Meanwhile, a hydrodesulfurizing mechanism of thiophene is proposed.

Direct gas-phase epoxidation of propylene to propylene oxide using air as oxidant on supported gold catalyst

Abstract Gold catalysts supported on SiO 2 , TiO 2 , TiO 2 -SiO 2 , and ZrO 2 -SiO 2 supports were prepared by impregnating each support with a basic solution of tetrachloroauric acid. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize their structure and surface composition. The results indicated that the size of gold particles could be controlled to below 10 nm by this method of preparation. Washing gold catalysts with water could markedly enhance the dispersion of metallic gold particles on the surface, but it could not completely remove the chloride ions left on the surface. The catalytic performance of direct vapor-phase epoxidation of propylene using air as an oxidant over these catalysts was evaluated at atmospheric pressure. The selectivity to propylene oxide (PO) was found to vary with reaction time on the stream. At the reaction conditions of atmosphere pressure, temperature 325° C, feed gas ratio V (C 3 H 6 )/ V (O 2 )= ½, and GHSV = 6000 h −1 , 17.9% PO selectivity with 0.9% propylene conversion were obtained at initial 10 min for Au/SiO 2 catalyst. After reacting 60 min only 8.9% PO selectivity were detected, but the propylene conversion rises to 1.4% and the main product is transferred to acrolein (72% selectivity). Washing Au/TiO 2 -SiO 2 and Au/ZrO 2 -SiO 2 samples with magnesium citrate solution could markedly enhance the activity and PO selectivity because smaller gold particles were obtained.

Selective hydrogenation of ethyne on γ-Mo2N

Abstract The hydrogenation of ethyne on a γ-Mo 2 N catalyst has been investigated at 50–210°C. With reaction time increasing, the selectivity of ethene in the products rose up gradually at 150°C. A conversion of ca. 85% ethyne and selectivity of ca. 85% for ethene were obtained at 130°C after the reaction became steady. Selectivity remained almost unchanged with the varying of reaction temperature and space velocity. These results can be explained by Bond’s model, and firmly held adspecies (FHA) and/or coke species from ethyne may be responsible for the high selectivity of ethene.