硅表面纳米银团簇的氧助迁移行为

采用原位扫描隧道显微镜研究了Si(111) 7× 7表面蒸镀纳米银团簇的迁移行为以及氧气氛的促进作用 .在覆盖度较低的情况下 ,蒸镀的银原子在Si(111) 7× 7表面形成具有规整三角形结构单元的有序银团簇 ,它们主要占据在Si(111) 7× 7表面有位错的半单胞内 .在氧的存在下 ,形成的结构单元在硅表面发生迁移 ,并逐渐团聚成无明显结构特征的大粒子 .原位观察结果表明 ,在连续扫描过程中 ,团聚后的大粒子在氧覆盖的硅表面也会发生迁移 ,最后稳定在硅表面原子氧吸附位周围 .进一步的观察发现 ,硅表面银团簇的存在对随后氧的吸附状态具有明显的影响 .这些结果为解释纳米银团簇在SiO2

Synthesis of Ni-CeO_2 catalyst for the partial oxidation of methane using RF thermal plasma

Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a precursor containing Ni（～5‐μm diameter） and CeO2（～200‐nm diameter）powders were heated simultaneously using an RF plasma at a power level of ～52 kVA and a powder feeding rate of ～120 g/h. From the X‐ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles（ 50‐nm diameter） on their surfaces. The catalytic performance was evaluated under atmospheric pressure at 500 °C and a CH4：O2 molar ratio of 2：1 with Ar diluent. Although the Ni content was high（～50 mol%）, the experimental results reveal a methane conversion rate of 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on‐stream test at 550 °C for 24 h.However, at 750 °C, the on‐stream test revealed the formation of filament‐like carbons with an increased methane conversion rate over 90%.

Experimental assessment of a plasma-catalyst hybrid reformer for hydrogen production via partial oxidation of dimethyl ether

In this work,hydrogen is produced from partial oxidation reforming of dimethyl ether （DME） by a plasma-catalyst hybrid reformer under atmospheric pressure.The plasma-catalyst hybrid reformer which includes both plasma and catalyst reactors is designed.A spark discharge is used as a non-equilibrium plasma source,and it is used to ionize the mixture of DME and air.The performances of the reformer are characterized experimentally in terms of gas concentrations,hydrogen yield,DME conversion ratio,and specific energy consumption.The effects of discharge frequency,reaction temperature,air-to-DME ratio and space velocity are investigated.The experimental results show that the plasma-catalyst hybrid reformer enhances hydrogen yield when reaction temperature drops below 620 ℃.At 450 ℃,hydrogen yield of hybrid reforming is almost three times that of catalyst reforming.When space velocity is 510 h-1,hydrogen yield is 67.7%,and specific energy consumption is 12.2 k J/L-H2.

Maximum Hydrogen Production by Autothermal Steam Reforming of Bio-oil With NiCuZnAI Catalyst

Autothermal steam reforming （ATR） of bio-oil, which couples the endothermic steam reform- ing reaction with the exothermic partial oxidation, offers many advantages from a technical and economic point of view. Effective production of hydrogen through ATR of bio-oil was performed at lower temperature with NiCuZnAl catalyst. The highest hydrogen yield from bio-oil reached 64.3% with a nearly complete bio-oil conversion at 600℃, the ratio of steam to carbon fed （S/C） of 3 and the oxygen to carbon ratio （O/C） of 0.34. The reaction conditions in ATR including temperature, O/C, S/C and weight hourly space velocity can be used to control both hydrogen yield and products distribution. The comparison between the ATR and common steam reforming of bio-oil was studied. The mechanism of the ATR of bio-oil was also discussed.

Hydrogen production from partial oxidation of dimethyl ether by plasma-catalyst reforming

Hydrogen was produced from partial oxidation reforming of DME （dimethyl ether） by spark discharge plasma at atmospheric pressure. A plasma-catalyst reformer was designed. A series of experiments were carried out to investigate its performance of hydrogen-rich gas production. The effects of reaction temperature, catalyst and flow rate on gas concentrations （volume fraction）, hydrogen yield, DME conversion ratio, specific energy consumption and thermal efficiency were investigated, respectively. The experimental results show that hydrogen concentration and the flow rate of produced H2 are improved when temperature increases from 300 ℃ to 700 ℃. Hydrogen yield, hydrogen concentration and the flow rate of produced H2 are substantially improved in the use of Fe-based catalyst at high temperature. Moreover, hydrogen yield and thermal efficiency are improved and change slightly when flow rate increases. When catalyst is 12 g, and flow rate increases from 35 mL/min to 210 mL/min, hydrogen yield decreases from 66.4% to 57.7%, and thermal efficiency decreases from 35.6% to 30.9%. It is anticipated that the results would serve as a good guideline to the application of hydrogen generation from hydrocarbon fuels by plasma reforming onboard.