The reactivity of delithiated Li(Ni1/3Co1/3Mn1/3)O2, Li(Ni0.8Co0.15Al0.05)O2 or LiCoO2 with non-aqueous electrolyte

The high temperature reactions of 1 M LiPF₆ EC:DEC and LiCoO₂, Li(Ni_1/3Co_1/3Mn_1/3)O₂ (NCM) or Li(Ni_0.8Co_0.15Al_0.05)O₂ (NCA) charged to 4.2 V and 4.4 V, respectively, were studied by accelerating rate calorimetry (ARC). The results indicate that NCM shows better thermal stability than both LiCoO₂ and NCA. The state-of-the-art NCA sample shows better safety properties than LiCoO₂. The reactivity of the samples depends on the electrolyte:active material ratio used during ARC testing. Electrode materials charged to 4.4 V are more reactive than the electrode materials charged to 4.2 V. These results should be useful for Li-ion battery researchers interested in maximizing the safety of high energy density cells and also as a benchmark for other researchers using ARC.     

非负载Ni(Co)-Mo-Al_2O_3纳米催化剂的制备及其生物油模型化合物加氢脱氧性能研究

采用热沉淀法制备了纳米级(粒径在15~30nm)非负载Ni(Co)-Mo-Al2O3催化剂,并用BET、XRD、SEM、TEM等技术对催化剂进行了表征;并以乙酸为探针分子,在连续流动固定床反应器上评价了催化剂的加氢脱氧活性,考察了Ni、Co活性组分、焙烧温度对催化剂的晶态结构及催化性能的影响.结果表明:在考察的反应条件下,Ni、Co活性组分加入后,使Mo-Al2O3催化剂的活性明显提高;而且Ni-Mo-Al2O3催化剂的加氢脱氧活性明显高于Co-Mo-Al2O3催化剂的活性;焙烧温度由500℃升高到550℃时,催化剂的比表面积增大,晶化度提高,催化剂的活性提高.     

Epitaxial growth of single-crystalline Al(2)O(3) films on Cr(2)O(3)(0001)

Thin, crystallographically oriented single-crystalline Al2O3 films can be grown epitaxially on Cr2O3(0001) by codeposition of Al vapor and O2 at a substrate temperature of 825 K. The properties and growth of these films were monitored by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), low-energy ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Two routes of preparation were investigated: (i) stepwise growth by alternating deposition of Al at room temperature and subsequent exposure to O2 at elevated temperatures; (ii) codeposition of Al and O2 at T > 800 K. The first route was consistently found to result in the growth of a complex interfacial oxide followed by the growth of polycrystalline Al2O3. The second mode of preparation provided homogeneous and ordered, probably (0001)-oriented, films of Al2O3 that maintained a LEED pattern up to a thickness around 10 A. The surface sensitive Cr MVV Auger transition at 34 eV was completely attenuated once the Al2O3 layer had reached a thickness of 6 A, pointing to film homogeneity at an early stage. This was confirmed by the absence of a significant Cr signal in LEIS spectra.     

Ni-Al类水滑石的制备及其Ni/Al2O3加氢脱硫研究

采用共沉淀方法合成了不同Ni/Al比的镍铝类水滑石,将其作为催化剂前驱体,制备了Ni/Al2O3加氢脱硫催化剂.通过X射线衍射法(XRD),程序升温还原(H2-TPR),热重分析(TG),傅里叶变换红外光谱(FT-IR)等技术对催化剂进行了表征.利用10 mL固定床装置在不同温度,压力,体积空速和氢油比条件下对Ni/Al2O3催化剂的加氢脱硫活性进行了评价.结果表明,XRD图和FT-IR图中均出现了Ni-Al类水滑石的特征峰,TG图呈现出两个明显阶段的失重,在Ni-Al2O3-HT的XRD图中最强的衍射角对应单质金属Ni粒子的(111)晶面.脱硫结果显示Ni-Al类水滑石作为前驱体在适当的条件下,FCC汽油的硫含量降至10 ppm以下.类水滑石作为前驱体的Ni/Al2O3加氢脱硫活性很好,说明类水滑石作为前驱体在加氢脱硫领域有好的应用前景.     

Growth and electronic structure of Sm on thin Al2O3/Ni3Al(111) films

The growth and electronic structure of vapor-deposited Sm on a well-ordered Al(2)O(3)/Ni(3)Al(111) ultrathin film under ultrahigh vacuum conditions at room temperature have been studied comprehensively using synchrotron radiation photoemission spectroscopy, X-ray photoelectron spectroscopy, work function measurements, scanning tunneling microscopy, and low-energy electron diffraction. Our results indicate that at room temperature Sm grows in a layer-by-layer fashion up to at least 1 ML, followed by three-dimensional growth. The interaction of Sm with Al(2)O(3) thin films leads to an initial oxidation of Sm, accompanied by a parallel reduction of the Al(2)O(3) substrate. Both the oxidation states of Sm(2+) and Sm(3+) are found at low coverage (<1 ML). The concentration of Sm(2+) saturates below 0.4 ML, while that of Sm(3+) keeps increasing until the metallic state of Sm appears at high coverages.     

Coating of Al2O3 on layered Li(Mn1/3Ni1/3Co1/3)O2 using CO2 as green precipitant and their improved electrochemical performance for lithium ion batteries

Li(Mn_1/3Ni_1/3Co_1/3)O₂ cathode materials were fabricated by a hydroxide precursor method. Al₂O₃ was coated on the surface of the Li(Mn_1/3Ni_1/3Co_1/3)O₂ through a simple and effective one-step electrostatic self-assembly method. In the coating process, a NHCO₃-H₂CO₃ buffer was formed spontaneously when CO₂ was introduced into the NaAlO₂ solution. Compared with bare Li(Mn_1/3M_1/3Co_1/3)O₂, the surface-modified samples exhibited better cycling performance, rate capability and rate capability retention. The Al₂O₃-coated Li(Mn_1/3Ni_1/3Co_1/3)O₂ electrodes delivered a discharge capacity of about 115 mAh·g^?1 at 2 A·g^?1, but only 84 mAh·g^?1 for the bare one. The capacity retention of the Al₂O₃-coated Li(Mn_1/3Ni_1/3Co_1/3)O₂ was 90.7% after 50 cycles, about 30% higher than that of the pristine one.     

Temperature-dependent structuring of Au-Pt bimetallic nanoclusters on a thin film of Al2O3/NiAl(100)

Au-Pt bimetallic nanoclusters on a thin film of Al(2)O(3)/NiAl(100) undergo significant structural evolution on variation of the temperature. Au and Pt deposited sequentially from the vapor onto thin-film Al(2)O(3)/NiAl(100) at 300 K form preferentially bimetallic nanoclusters (diameter ≦ 6.0 nm and height ≦ 0.8 nm) with both Au and Pt coexisting at the cluster surface, despite the order of metal deposition. These bimetallic clusters are structurally ordered, have a fcc phase and grow with their facets either (111) or (001) parallel to the θ-Al(2)O(3)(100) surface. Upon annealing the clusters to 400-500 K, the Au atoms inside the clusters migrate toward the surface, resulting in formation of a structure with a Pt core and an Au shell. Annealing the sample to 500-650 K reorients the bimetallic clusters--all clusters have their (001) facets parallel to the oxide surface--and induces oxidation of Pt. Such annealed bimetallic clusters become encapsulated with the aluminium-oxide materials and a few Au remain on the surface.     

Ni/Al2O3和Fe/Al2O3催化剂催化乙醇水蒸气重整制氢的对比研究

甲醇、乙醇等低碳醇催化重整制氢是燃料电池氢源的重要技术之一.乙醇和甲醇相比,更容易存储,低毒且可以从生物质经发酵获得[1,2].乙醇可以通过裂解、部分氧化、水蒸气重整和氧化重整等途径制氢[3~6].已有的文献表明,Pt、Ru、Rh、Pd等贵金属可有效地催化乙醇重整反应,载体多选用     

Growth of Co clusters on thin films Al2O3NiAl(100)

We present a scanning tunnel microscopy study of Co clusters grown through vapor deposition on Al(2)O(3) thin films over NiAl(100) at different coverages and temperatures. Formation of Co clusters was observed at 90, 300, 450, and 570 K. At the three lower temperatures, we find narrow cluster size distributions and the mean sizes (with a diameter of 2.6 nm and a height of 0.7 nm) do not change significantly with the coverage and temperature, until the clusters start to coalesce. Even on 3-4-nm-wide crystalline Al(2)O(3) strips where the deposited Co atoms are confined, the same features sustain. Only at 570 K the normal growth mode where the cluster size increases with the deposition coverage is observed, although the data are less conclusive. A simple modeling of kinetic surface processes on a strip confirms the normal growth mode, but fails to show a favored size unless additional energetic constraints are applied on the cluster sizes. Increasing Co coverages to cluster coalescence, a larger preferable size (mean diameter of 3.5 nm and height of 1.4 nm) appears for growth at 450 K. These two sizes are corroborated by morphology evolution of high Co coverages deposited at 300 K and annealed to 750 K, in which the coalescence is eliminated and the two preferable geometries appear and coexist.     

DNA as a template for synthesis of fluorescent gold nanoclusters

Water-soluble blue-emitting gold nanoclusters have been synthesized using dsDNA as a template without any additional reducing agent. The features of the formed nanoclusters have been revealed by fluorescence and electronic absorption spectroscopy as well as transmission electron microscopy. The prepared gold nanoclusters have been highly stable at physiological pH without any further modification.     

Fischer-Tropsch synthesis on anchored Co/Nb2O5/Al2O3 catalysts: the nature of the surface and the effect on chain growth

A series of Co/x%Nb2O5/Al2O3 catalysts were prepared by anchoring niobia on an Al2O3 support at different niobia concentrations. Characterization of the structure and nature of surface active sites was attempted in order to correlate the CO hydrogenation activity of these systems with those of the Co/Al2O3 and Co/Nb2O5 catalysts. The effect of the reduction temperature on the CO hydrogenation activity and selectivity was studied, showing that interaction of cobalt and niobia surface species favored the selectivity for hydrocarbon chain growth. However, this effect is less pronounced on the niobia-promoted Co/Al2O3 compared to Co/Nb2O5 catalysts. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS) results on Co/x%Nb2O5/Al2O3 showed prevailing amounts of Co2+ and Co3+ after calcination and reduction at 573 K, while, after reduction at 773 K, besides metallic cobalt, the Co2+ species still remains in contact with alumina, even for higher niobia loading. It seems that during this process formation and destruction of new interfaces involving Co0-NbOx sites takes place. Results suggest that Co0, Co0-Co2+, and Co0-NbOx are the active sites at the surface. The relative abundance of Co2+ species affects greatly the performance of the catalysts. DRIFTS and selectivity results suggest that these sites might be responsible for the reaction chain growth and therefore for the drastic change in the selectivity of CH4 and C5+ hydrocarbons mainly on the Co/Nb2O5 catalyst. DRIFTS results on Co/Nb2O5/Al2O3 showed the formation of -C=C- and -CH3- besides CHxO species. With increasing reduction temperature, the -C=C- species disappear while -CH3- fragments increased markedly, suggesting the formation of increasing amounts of hydrocarbons with higher chain length.     

Adsorption of Cs(I), Sr(II) and Co(II) on Al2O3

The sorption of Cs(I), Sr(II) and Co(II) from aqueous solutions on alumina under various experimental conditions has been studied by batch techniques. Freundlich, Langmuir and Dubnin-Raduskevich equations have been used to interpret the sorption data. The values of various thermodynamic parameters have been determined. The sorption of Cs(I) and Sr(II) on alumina is exothermic in nature while that of Co(II) is an endothermic process. The H ^o values for Cs(I), Sr(II) and Co(II) were–23.29 KJ/mol at 298K,–35.3 KJ/mol at 293 K and 13.49 KJ/mol at 293 K, respectively. Negative values of G ^o show the spontaneity of the sorption processes; G ^o values of Cs(I) and Sr(II) becomes less negative at higher temperatures while the G ^o values of Co(II) become more negative with increasing temperature. At higher temperatures, less amounts of Cs(I) and Sr(II) and greater amounts of Co(II) are sorbed on alumina. The values of the mean free energies of sorption,E, for Sr(II) and Co(II) at various temperatures were within the range of 7–10 KJ/mol which show that these metals are sorbed on alumina predominantly by an ion-exchange process.     

Vibrational spectra of MII3Pb(P2O7)2 (MII = Ni,Co)

Raman and IR spectra of polycrystalline Ni₃Pb(P₂O₇)₂ and Co₃Pb(P₂O₇)₂ have been recorded and analyzed. The internal modes are assigned in terms of PO₃ and POP vibrations. The results point to a bent POP bridge configuration in Co₃Pb(P₂O₇)₂ as in Ni₃Pb(P₂O₇)₂. In the cobalt compound, the P₂O⁴⁻₇ ions are distorted. Non-coincidence of the majority of the Raman and IR bands confirms a centrosymmetric structure for Ni₃Pb(P₂O₇)₂, and Co₃Pb(P₂O₇)₂. The POP bridge angle is slightly higher in the cobalt compound than in the nickel compound.     

Local electronic structure of layered Li(x)Ni0.5Mn0.5O2 and Li(x)Ni(1/3)Mn(1/3)Co(1/3)O2

Samples of Li(x)Ni0.5Mn0.5O2 and Li(x)Ni(1/3)Mn(1/3)Co(1/3)O2 were prepared as active materials in electrochemical half-cells and were cycled electrochemically to obtain different values of Li concentration, x. Absorption edges of Ni, Mn, Co, and O in these materials of differing x were measured by electron energy loss spectrometry (EELS) in a transmission electron microscope to determine the changes in local electronic structure caused by delithiation. The work was supported by electronic structure calculations with the VASP pseudopotential package, the full-potential linear augmented plane wave code WIEN2K, and atomic multiplet calculations that took account of the electronic effects from local octahedral symmetry. A valence change from Ni2+ to Ni4+ with delithiation would have caused a 3 eV shift in energy of the intense white line at the Ni L3 edge, but the measured shift was less than 1.2 eV. The intensities of the "white lines" at the Ni L-edges did not change enough to account for a substantial change of Ni valence. No changes were detectable at the Mn and Co L-edges after delithiation either. Both EELS and the computational efforts showed that most of the charge compensation for Li+ takes place at hybridized O 2p states, not at Ni atoms.     

Temperature-dependent growth shapes of Ni nanoclusters on NiAl(110)

Scanning tunneling microscopy studies reveal that two-dimensional nanoscale Ni islands formed by deposition of Ni on NiAl(110) between 200-400 K exhibit far-from-equilibrium growth shapes which change systematically with temperature. Island structure reflects the two types of adsorption sites available for Ni adatoms, and island shapes are controlled by the details of adatom diffusion along island edges accounting for numerous local configurations. The temperature dependence of the island shapes is captured and elucidated by kinetic Monte Carlo simulation of a realistic atomistic-level multisite lattice-gas model incorporating precise diffusion barriers. These barriers are obtained by utilizing density functional theory to probe energetics not just at adsorption sites but also at transition states for diffusion. This success demonstrates a capability for predictive atomistic-level modeling of nanocluster formation and shape selection in systems that have a high level of energetic and kinetic complexity.     

EXAFS characterization of Ti/Al2O3 supports and Co/Ti/Al2O3 catalysts

The structure of Ti/Al₂O₃ supports (0–14 wt% Ti) and Co/Ti/Al₂O₃ catalysts (3 wt% Co) was examined by EXAFS. The results indicated that the Ti was present primarily as a highly dispersed surface phase. The Ti EXAFS results indicated that the Ti species were octahedrally coordinated. Evidence of Ti—Ti interactions was found for all loadings (2–14 wt% Ti) suggesting that the Ti surface species are present as small clusters of TiO₂.The Co EXAFS results showed evidence for several structurally different Co surface phases as a function of Ti loading. Evidence of a Co species interacting with the Ti surface phase was observed for the 3% Co/2% Ti-3%Co/6%Ti catalysts. At the highest loadings studied, 3%Co/8%Ti and 3%Co/14%Ti, evidence was found for a CoTiO₃-like phase.     

Ni/Al2O3 catalysts for CO methanation: Effect of Al2O3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al₂O₃ supports calcined at different temperatures and the catalytic performance of Ni/Al₂O₃ catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al₂O₃ catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al₂O₃ supports were adjusted by calcining the commercial γ-Al₂O₃ at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g^?1·h^?1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al₂O₃ supports due to the rapid decrease of the specific surface area and acidity of Al₂O₃ supports. Interestingly, Ni catalysts supported on Al₂O₃ calcined at 1200 °C (Ni/Al₂O₃-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al₂O₃-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al₂O₃ methanation catalyst for SNG production.     

Island morphology statistics and growth mechanism for oxidation of the Al(111) surface with thermal O2 and NO

Scanning tunneling microscopy (STM) was employed to study the mechanism for the oxidation of Al(111) with thermal O2 and NO in the 20%-40% monolayer coverage regime. Experiments show that the islands formed upon exposure to thermal O2 and NO have dramatically different shapes, which are ultimately dictated by the dynamics of the gas surface interaction. The circumference-to-area ratio and other island morphology statistics are used to quantify the average difference in the two island types. Ultrahigh-vacuum STM was employed to make the following observations: (1) Oxygen islands on the Al(111) surface, formed upon exposure to thermal oxygen, are elongated and noncompact. (2) Mixed O/N islands on the Al(111) surface, formed upon exposure to thermal nitric oxide (NO), are round and compact. (3) STM movies acquired during thermal O2 exposure indicate that a complex mechanism involving chemisorption initiated rearrangement of preexisting oxygen islands leads to the asymmetric and elongated island shapes. The overall mechanism for the oxidation of the Al(111) surface can be summarized in three regimes. Low coverage is dominated by widely isolated small oxygen features (<3 O atoms) where normal dissociative chemisorption and oxygen abstraction mechanisms are present. At 20%-40% monolayer coverage, additional oxygen chemisorption induces rearrangement of preexisting islands to form free-energy minimum island shapes. At greater than approximately 40% monolayer coverage, the apparent surface oxygen coverage asymptotes corresponding to the conversion of the 2D islands to 3D Al2O3 surface crystallites. The rearrangement of oxygen islands on the surface to form the observed islands indicates that there is a short-range oxygen-oxygen attractive potential and a long-range oxygen-oxygen repulsive potential.