Influences of reaction conditions on methane decomposition over non-supported Ni catalyst

Effects of reaction temperature and methane gas hourly space velocity (GHSV) on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni.The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 gC/gNi and 2667 molH2/molNi at 500 -C and 45000 mL/(gcat h).Scanning electron microscope (SEM),X-ray powder diffraction (XRD) and temperature-programmed oxi- dation (TPO) have been carried out to characterize the used catalysts.The deposited carbon was carbon nanofibers,among which graphitic carbon formation increased with the reaction time of methane decomposition.Ni particle size was not the decisive factor during the carbon growing stage.     

模板法制备的掺镧氧化镍多孔空心微球及电化学电容性能

采用模板法在水热条件下合成了掺La的NiO多孔空心球。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)、透射电子显微镜(TEM)和X射线能谱(EDS)对其结构和形貌进行了表征。采用循环伏安、恒流充放电技术对其电化学性能进行了测试,研究结果表明,La掺杂对NiO空心球的粒径、壳层厚度和电化学性能均有显著影响,当La掺杂量为1.30mol%时,掺杂后NiO的单电极比电容达到205 F.g-1,比未掺杂的提高了50%,并且表现出良好的循环稳定性和可逆性。     

NiO增强Pt/C催化剂催化氧化甲醇活性的研究

本文基于NiO作为Pt催化甲醇助催化剂的思路,通过Pt纳米颗粒担载在NiO修饰的碳材料载体上制备了Pt/NiO-C催化剂,系统地研究了不同的NiO/C热处理温度对Pt粒径的影响,并重点探讨了Pt对NiO的质量比对催化氧化甲醇的影响。X射线衍射分析结果显示NiO和Pt均为立方晶系,且NiO的加入有利于主催化剂Pt形成较小的粒径,且经400℃热处理NiO修饰的C材料作为载体有利于Pt的有效分散。所获得的Pt/NiO-C催化剂的电化学活性在甲醇酸性溶液中通过循环伏安法(CV)和计时电流法(CA)进行性能测试。CV测试结果显示以Pt/NiO重量比为4∶1的催化剂其电氧化甲醇活性最大,其峰值氧化电流密度达806 mA/mgPt,是Pt/C催化剂的1.64倍。CA测试结果显示Pt/NiO-C比Pt/C具有更好的抗CO中毒性能和稳定性。     

Interpretation of the Ni K-edge EXAFS in nanocrystalline nickel oxide using molecular dynamics simulations

Analysis of atomic structure at the nanoscale is a challenging task, complicated by relaxation phenomena and thermal disorder. In this work, the x-ray absorption spectroscopy at the Ni K-edge was used to address this problem in nanocrystalline NiO (nano-NiO) at 300 K. The analysis of the first two coordination shells using conventional two-shell single-scattering approximation allowed us to determine the expansion of the average lattice but contraction of the Ni―O bonds in the first coordination shell in nano-NiO in comparison with the bulk nickel oxide. The EXAFS signal generated within the first six coordination shells (up to ~ 6.5 Å) was successfully interpreted using classical molecular dynamics and ab initio multiple-scattering EXAFS theory. We found that simple rigid-ion force-field model is able to describe the structure relaxation and dynamics in both bulk and nano-NiO. Such approach requires less parameters than conventional EXAFS analysis and allows accounting explicitly for thermal effects and many-atom distribution functions. Finally, we showed that the EXAFS signal is rather sensitive to small variations of the force-field model and, thus, the agreement between the experimental and calculated EXAFS signals can be used for the force-field model optimization.     

Structural and magnetic properties of Fe doped NiO

Mott-Hubbard anti-ferromagnetic insulator, NiO shows p-type semiconducting behaviour due to vacancy at Ni²⁺ site in its bunsenite structure. We report the modification of structural and magnetic order in NiO on Fe doping. NiO samples at different Fe concentrations in the range 0 to 5 at.% have been prepared by chemical co-precipitation and post thermal decomposition method. Both structural and magnetic characterization reveal that with increasing Fe doping concentration, NiO evolves as a magnetically inhomogeneous state out of the parent homogeneous antiferromagnetic state. In addition, structural inhomogeneity was also observed with Fe precipitating to γ-Fe₂O₃ phase, the signature of which could be clearly seen for Fe content beyond 2 at.%. At lower Fe content however, some amount of Fe occupies lattice and interstitial sites in the NiO matrix and drive the latter to acquire ferromagnetic ordering, which was evident from a clear hysteresis loop at 300 K.      

Synthesis of NiFe2O4 Nanowires with NiO Nanosheet as Precursor via a Topochemical Solid State Method

Large scale NiFe₂O₄ nanowires were synthesized with NiO nanosheets as precursor by means of the topochemical solid state method. The morphologies and magnetic properties of NiFe₂O₄ annealed at different temperatures were studied. An appropriate annealing temperature was requested to transfer NiO nanosheets and Fe^- ions into NiFe₂O₄ nanowires. In the beginning stage of synthesizing process, the shape of NiO nanosheets remained unchanged at low temperatures. And then, NiO nanosheets split into nanowires from 400℃ to 600℃. At last they transformed into nanoparticles from 700℃ to 1000℃. Thus, the optimized annealing temperature was selected as 600℃ because the NiFe₂O₄ obtained at 600℃(N600) exhibited a maximum aspect ratio of 50 with a diameter of 20 nm and a length of 1 μm. Furthermore, N600 also displayed the largest magnetization value of 26.86 A·m²/kg and the lowest coercivity(H_c) of 8914 A/m.     

Multiple Interfaces Structure Derived from Metal–Organic Frameworks for Excellent Electromagnetic Wave Absorption

Hierarchical yolk–shell nanostructure (NiO/Ni/GN@Air@NiO/Ni/GN) derived from Ni‐based metal–organic frameworks (Ni‐MOFs) is synthesized by solvothermal reactions. After successive carbonization and oxidation treatments, hierarchical NiO/Ni nanocrystals covered with a graphene shell are obtained with the yolk–shell nanostructure intact. The NiO/Ni/GN@Air@NiO/Ni/GN composites are characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the NiO/Ni/GN@Air@NiO/Ni/GN composites exhibit superior electromagnetic wave absorption properties. A minimum reflection loss (RL_min) of ?34.5 dB is obtained at 17.2 GHz with the thin thickness of 1.7 mm. In addition, the best microwave absorption properties are achieved with a 2.0 mm absorber layer (RL_min = ?22.5 dB, bandwidth of 6.0 GHz). The outstanding absorption ability may arise from the unique yolk–shell structure and nanoporous carbon, which can tune the dielectric of the NiO/Ni/GN@Air@NiO/Ni/GN composites to acquire good impedance matching. Moreover, the interspaces can induce interfacial polarization and multiple reflections.     

NiO的高压结构和等温状态方程研究

 运用金刚石对顶砧（Diamond Anvil Cell,DAC）技术,以液氩作为传压介质,在最高压力为67 GPa的压力范围内对NiO进行了原位的同步辐射X射线衍射研究。在整个实验过程中,并未发现第一类结构相变,也没有发现T.Sasaki等预测的在60 GPa左右轴比c/a随压力的变化率而突然增大的现象,且此压力范围内NiO的结构畸变程度随压力的变化趋势相比以前的研究结果要平缓一些。用三阶的Brich-Murnaghan方程对实验数据进行拟合,得到的体弹模量及其对压力的一阶导数分别为B₀=195(4) GPa和B₀′=5.3(2)。     

Interactions of NiO particles with polycyclic aromatic hydrocarbons and acetylene generated from the pyrolysis of a model fuel

Experiments have been conducted to study the effects of NiO, a prevalent form of nickel in combustion-generated ash particles, on polycyclic aromatic hydrocarbons (PAH) and other hydrocarbons in a fuel product mixture. The fuel product mixture is generated from the gas-phase pyrolysis, in N₂, of the model fuel catechol in a quartz tube reactor at 1100 K and 5 s, a condition that ensures full conversion of the catechol and produces a mixture—of PAH, hydrocarbon gases, and oxygen-containing species—that is representative of the products of practical liquid and solid fuels in pyrolysis and fuel-rich combustion environments. Once formed, the product mixture is passed, at the same temperature, through a bed of ultrafine NiO particles held in place by quartz wool, in the contact zone of the reactor. The products exiting the reactor are quenched, collected, and analyzed by non-dispersive infrared analyzers, gas chromatography, and high-pressure liquid chromatography with diode-array ultraviolet–visible absorbance detection. The results from the experiments at 1100 K show that—compared to the case of no inorganics in the contact zone—when NiO is present: PAH yields are reduced 86% (from 10.8% to 1.48% fed carbon); all of the highly mutagenic 5- and 6-ring PAH are eliminated; and all of the acetylene, the highest-yield hydrocarbon product when NiO is absent, and other hydrocarbons with carbon–carbon triple bonds are eliminated from the gas phase. Most of the surface-bound carbon is released as CO. Similar experiments at 1275 K show that—except for the release of the surface-bound carbon as CO—the selective surface effects of NiO bring about similar results at higher temperature: 89% reduction in PAH yield, elimination of mutagenic 5- and 6-ring PAH, removal of acetylene and acetylenic species, as well as a decrease in the production of solid carbon (not formed at 1100 K).