Adiabatic burning velocity of H2–O2 mixtures diluted with CO2/N2/Ar

Global warming due to CO₂ emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO₂, N₂, and Ar) on the laminar burning velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar burning velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO₂, N₂, and Ar as diluents. Measured burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar burning velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H₂/O₂/CO₂ flames with 65% CO₂ dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H₂/O₂/CO₂ cellular flame structure and cell count from computed flame matched well with the experimental cellular flame.     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Effects of MoS2 addition on the hydrogen storage properties of 2LiBH4–MgH2 systems

A 2LiBH₄–MgH₂–MoS₂ composite was prepared by solid-state ball milling, and the effects of MoS₂ as an additive on the hydrogen storage properties of 2LiBH₄–MgH₂ system together with the corresponding mechanism were investigated. As shown in the TG–DSC and MS results, with the addition of 20 wt.% of MoS₂, the onset dehydrogenation temperature is reduced to 206 °C, which is 113 °C lower than that of the pristine 2LiBH₄–MgH₂ system. Meanwhile, the total dehydrogenation amount can be increased from 9.26 wt.% to 10.47 wt.%, and no gas impurities such as B₂H₆ and H₂S are released. Furthermore, MoS₂ improves the dehydrogenation kinetics, and lowers the activation energy (E_a) 34.49 kJ mol⁻¹ of the dehydrogenation reaction between Mg and LiBH₄ to a value lower than that of the pristine 2LiBH₄–MgH₂ sample. According to the XRD test, Li₂S and MoB₂ are formed by the reaction between LiBH₄ and MoS₂, which act as catalysts and are responsible for the improved hydrogen storage properties of the 2LiBH₄–MgH₂ system.     

Effect of N2/CO2 dilution on laminar burning velocity of H2–air mixtures at high temperatures

The laminar burning velocities of H₂–air mixtures diluted with N₂ or CO₂ gas at high temperatures were obtained from planar flames observed in externally heated diverging channels. Experiments were conducted for an equivalence ratio range of 0.8–1.3 and temperature range of 350–600 K with various dilution rates. In addition, computational predictions for burning velocities and their comparison with experimental results and detailed flame structures have been presented. Sensitivity analysis was carried out to identify important reactions and their contribution to the laminar burning velocity. The computational predictions are in reasonably good agreement with the present experimental data (especially for N₂ dilution case). The burning velocity maxima was observed for slightly rich mixtures and this maxima was found to shift to higher equivalence ratios (Ф) with a decrease in the dilution. The effect of CO₂ dilution was more profound than N₂ dilution in reducing the burning velocity of mixtures at higher temperatures.     

First-principles GGA + U calculation investigating the hydriding and diffusion properties of hydrogen in PuH2+x, 0 ≤x≤ 1

The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (H_i) in “perfect” PuH_2+x (0 $\le x\le$ 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra H_i atom interacts much further with surrounding host atoms in PuH₃ than in other Pu hydride matrixes. The minimum migration paths of a H_i atom in PuH_2+x are characterized by the image nudged elastic band (CINEB) method. The H_i atom diffuses in PuH₂, PuH_2.25, and PuH₅ matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable I_H-site plays a dominant role for the H_i migration into the O-site in PuH_2.75. The diffusion path of the H_i atom in PuH₃ is I_Pu $\to$ I_H0160 $\to$ I_PU path with the lowest migration energy of 0.72 eV, which concludes the H_i has relatively higher mobility in PuH₃. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH₂, PuH₃, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors.     

Effect of RuO2–CoS2 anode nanostructured on performance of H2S electrolytic splitting system

An innovative, nanostructured composite, anode electrocatalyst, material has been developed for the electrolytic splitting of (100%) H₂S feed content gas operating at 135 kPa and 150 °C. A new class of anode electrocatalyst with general composition, RuO₂–CoS₂ has shown great stability and desired properties at typical operating conditions. This configuration showed stable electrochemical operation over the period of 24 h and also exhibited a maximum current density of (0.019 A/cm²). The kinetic behaviors of various anode-based electrocatalysts demonstrated that, exchange current density, which is a direct measure of the electrochemical reaction, increased with RuO₂–CoS₂-based anodes. Moreover, high levels of feed utilization were possible using these materials. Electrochemical performance, current density, and sulfur tolerance were enhanced compared to the other tested anode configurations. The structural, microstructural and surface behavior of RuO₂–CoS₂ anode electrocatalyst was investigated in detail.     

CO2 reforming of CH4 by combination of cold plasma jet and Ni/γ-Al2O3 catalyst

CO₂ reforming of CH₄ to synthesis gas was investigated by cold plasma jet (CPJ) only and combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst at atmospheric pressure. The higher selectivity of H₂ and CO, and higher energy efficiency was obtained by this novel process. The optimum experimental conditions are: CH₄ = 3.33 Nl/min, CO₂ = 5.00 Nl/min, N₂ = 8.33 Nl/min, and the input power at 770 W. The results showed that, for the plasma only, the conversions of CH₄ and CO₂ were 46% and 34%, the selectivities of CO and H₂ were 85% and 78%, the energy efficiency was 2.9 mmol/kJ, respectively; for the combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst, the conversions of CH₄ and CO₂ were increased by 14% and 6%, the yield of H₂ and CO increased by 18% and 11%, the energy efficiency reached at 3.7 mmol/kJ, respectively. And the catalyst hasn't accessorial heating. The CPJ method has the advantage of simple processing and is easy to be industrialized.     

顺应新潮流 把握新趋势简

Mean wind force coefficients of nacelles are investigated by a wind tunnel test and are compared with those in current codes, such as the Germanischer Lloyd Guideline 2010 (GL2010) and Eurocode, in order to clarify the effects of the ground, presence of a hub, turbulence in the incident flow and nacelle length on these coefficients. Formulas for the mean wind force coefficients are proposed as a function of yaw angles. It is found that mean wind force coefficients of wind turbine nacelles specified in GL2010 are underestimated in comparison with those obtained by wind tunnel tests. Pressure measurements of a nacelle are also conducted. Notably, the mean pressure coefficients for design load case 6.2 (DLC6.2) are significantly larger than those for design load case 6.1 (DLC6.1) in IEC61400‐1. Maximum and minimum mean pressure coefficients are proposed for the DLC6.1 and DLC6.2 by the wind tunnel test, which are similar to those in Eurocode and are larger than those proposed in GL2010. Copyright © 2012 John Wiley & Sons, Ltd.     

Reversible hydrogenation/dehydrogenation performances of the Na2LiAlH6–Mg(NH2)2 system

Complex hydrides and Metal–N–H-based materials have attracted considerable attention due to their high hydrogen content. In this paper, a novel amide–hydride combined system was prepared by ball milling a mixture of Na₂LiAlH₆–Mg(NH₂)₂ in a molar ratio of 1:1.5. The hydrogen storage performances of the Na₂LiAlH₆–1.5Mg(NH₂)₂ system were systematically investigated by a series of dehydrogenation/hydrogenation evaluation and structural analyses. It was found that a total of ∼5.08 wt% of hydrogen, equivalent to 8.65 moles of H atoms, was desorbed from the Na₂LiAlH₆–1.5Mg(NH₂)₂ combined system. In-depth investigations revealed that the variable milling treatments resulted in the different dehydrogenation reaction pathways due to the combination of Al and N caused by the energetic milling. Hydrogen uptake experiment indicated that only ∼4 moles of H atoms could be reversibly stored in the Na₂LiAlH₆–1.5Mg(NH₂)₂ system perhaps due to the formation of AlN and Mg₃N₂ after dehydrogenation.     

O2/CO2和O2/N2氛围下煤粉富氧燃烧数值模拟

在目前煤炭依然作为能源主体的背景下，控制燃煤污染物排放有着重要意义。基于CFD数值模拟，建立伴流燃烧器模型，控制燃料、氧化剂入口流量恒定，设计了O₂/CO₂、O₂/N₂氧化剂氛围中O₂浓度在21%～40%内的多种工况，对煤粉燃烧特性及燃烧产生的污染物进行了研究。分析了不同工况下煤粉燃烧的温度分布、燃烧速率、碳烟、NO_x的生成情况。结果显示，在O₂/CO₂、O₂/N₂两种氧化剂氛围中，随着O₂浓度的上升，煤粉燃烧温度升高、燃烧速率增大，碳烟生成量均增加，同等O2浓度条件下，O₂/CO₂氛围的煤粉燃烧温度和燃烧速率均高于O₂/N₂氛围，碳烟生成量小于O₂/N₂氛围，且O₂/CO₂...     

Improved hydrogen storage performance of MgH2–NaAlH4 composite by addition of TiF3

In a previous paper, it was demonstrated that a MgH₂–NaAlH₄ composite system had improved dehydrogenation performance compared with as-milled pure NaAlH₄ and pure MgH₂ alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH₂–NaAlH₄ composite in the presence of TiF₃. 10 wt.% TiF₃ was added to the MgH₂–NaAlH₄ mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH₂–NaAlH₄ composite milled with 10 wt.% TiF₃ had lower dehydrogenation temperatures, by 100, 73, 30, and 25 °C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH₂–NaAlH₄ composite. Kinetic desorption results show that the MgH₂–NaAlH₄–TiF₃ composite released about 2.4 wt.% hydrogen within 10 min at 300 °C, while the neat MgH₂–NaAlH₄ sample only released less than 1.0 wt.% hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, E_A, for the decomposition of MgH₂, NaMgH₃, and NaH in the MgH₂–NaAlH₄–TiF₃ composite was reduced to 71, 104, and 124 kJ/mol, respectively, compared with 148, 142, and 138 kJ/mol in the neat MgH₂–NaAlH₄ composite. The high catalytic activity of TiF₃ is associated with in situ formation of a microcrystalline intermetallic Ti–Al phase from TiF₃ and NaAlH₄ during ball milling or the dehydrogenation process. Once formed, the Ti–Al phase acts as a real catalyst in the MgH₂–NaAlH₄–TiF₃ composite system.     

Rh promoted and ZrO2/Al2O3 supported Ni/Co based catalysts: High activity for CO2 reforming,steam–CO2 reforming and oxy–CO2 reforming of CH4

Ni (2.5 wt%) and Co (2.5 wt%) supported over ZrO₂/Al₂O₃ were prepared by following a hydrolytic co-precipitation method. The synthesized catalysts were further promoted by Rh incorporation (0.01–1.00 wt%) and tested for their catalytic performance for dry CO₂ reforming, combined steam–CO₂ reforming and oxy–CO₂ reforming of methane for production of syngas. The catalysts were characterized by using N₂ physical adsorption, XRD, H₂–TPR, SEM, CO₂–TPD, NH₃–TPD, TEM and TGA. The results revealed that ZrO₂ phase was in crystalline form in the catalysts along with amorphous Al oxides. Ni and Co were confirmed to be in their respective spinel phases that were reducible to metallic form at 800 °C under H₂. Ni and Co were well dispersed with their nano-crystalline nature. The catalyst with 0.2% loading of Rh showed superior performance in the studied reactions for reforming of methane. This catalyst also showed good coke resistance ability for dry CO₂ reforming reaction with 3.8 wt% of carbon formation during the reaction as compared to 11.6 wt% carbon formation over the catalyst without Rh. The catalyst performance was stable throughout the reaction time for CH₄ conversions, irrespective of carbon formation with slight decline (～1%) in CO₂ conversion. For dry CO₂ reforming reaction, this catalyst showed good conversion for both CH₄ and CO₂ (67.6% and 71.8% respectively) with a H₂/CO ratio of 0.84, while for the Oxy-CO₂ reforming reaction, the activity was superior with CH₄ and CO₂ conversions (73.7% and 83.8% respectively) and H₂/CO ratio of 1.05.     

Combination of CO2 reforming and partial oxidation of methane to produce syngas over Ni/SiO2 and Ni–Al2O3/SiO2 catalysts with different precursors

Ni/SiO₂ and Ni–Al₂O₃/SiO₂ catalysts were prepared by incipient wetness impregnation using citrate and nitrate precursors and tested with a reaction of combination of CO₂ reforming and partial oxidation of methane to produce syngas (H₂/CO). The catalytic activity of Ni/SiO₂ and Ni–Al₂O₃/SiO₂ greatly depended on interaction between NiO and support. NiO strongly interacted with support formed small nickel particles (about 4 nm for NiSC which is abbreviation of Ni/SiO₂ prepared with Nickel citrate precursor) after reduction. The small nickel particles over NiSC catalysts exhibited a good catalytic performance.     

Raman spectroscopic observation of dehydrogenation in ball-milled LiNH2–LiBH4–MgH2 nanoparticles

In situ Raman spectroscopy was used to monitor the dehydrogenation of ball-milled mixtures of LiNH₂–LiBH₄–MgH₂ nanoparticles. The as-milled powders were found to contain a mixture of Li₄BN₃H₁₀ and Mg(NH₂)₂, with no evidence of residual LiNH₂ or LiBH₄. It was observed that the dehydrogenation of both of Li₄BN₃H₁₀ and Mg(NH₂)₂ begins at 353 K. The Mg(NH₂)₂ was completely consumed by 415 K, while Li₄BN₃H₁₀ persisted and continued to release hydrogen up to 453 K. At higher temperatures Li₄BN₃H₁₀ melts and reacts with MgH₂ to form Li₂Mg(NH)₂ and hydrogen gas. Cycling studies of the ball-milled mixture at 423 K and 8 MPa (80 bar) found that during rehydrogenation of Li₄BN₃H₁₀ Raman spectral modes reappear, indicating partial reversal of the Li₄BN₃H₁₀ to Li₂Mg(NH)₂ transformation.