Keitaro Tezuka

The Active Phase of Nickel/Ordered Ce2Zr2OxCatalysts with a Discontinuity (x=7-8) in Methane Steam Reforming

In recent years, there has been a surge in interest in syngas (H2/CO) and H2 production technologies, which utilize a wide variety of hydrocarbon feed stocks, such as gasoline, diesel, LPG, natural gas, methanol, and bio-ethanol. Among fossil fuels, natural gas ( 90 vol% CH4) is the ideal fuel, owing to its ready availability, high energy density, and wide distribution network; CH4 activation and reforming provide attractive ways to produce syngas, which can be transformed to useful larger hydrocarbons. Catalysts based on both noble metals and other metals have been extensively studied for CH4 steam reforming. [1, 2] Noble-metal (Rh, Ru, Ir, Pd, and Pt) catalysts are active and stable; however, because of the limited supply and high cost of noble metals, much attention has been paid to the development of non-noble metal catalysts, among which nickel-based catalysts have attracted particular attention because of their similar mechanistic features to noble-metal catalysts. The strong C H bonds of CH4 (439 kJmol ) and endothermic heat of reforming reactions necessitate high temperatures for practical CH4 conversion, and thus stable catalysts that resist sintering under extreme operating conditions. In CH4 steam reforming, coke formation that deactivates the catalyst is thermodynamically favored at a H2O/CH4 ratio less than 1.4. Thus, industrial CH4 steam reforming is usually carried out at a H2O/CH4 ratio of 1.4 or greater. Although catalytic CH4 steam reforming at low H2O/CH4 ratios have many advantages from operational and energy-consuming viewpoints, conventional nickel-based catalysts suffer from severe carbon deposition under such conditions. Supports and additives (for example, CeO2, ZrO2, CeO2-ZrO2, and La2O3) have been used to confer catalysts with kinetic resistance to carbon deposition and Ni sintering because they enhance redox activity and thermal stability, thereby promoting steam reforming. The efficient CH4 upgrading has long been a challenge in fundamental research. Herein, we report the unique properties and active phase of a new Ni/ordered Ce2Zr2Ox (x = 7–8) catalyst with a regular arrangement of Ce and Zr ions in CH4 steam reforming to produce H2 and CO at H2O/CH4 = 1. The catalytic performance of Ni/Ce2Zr2Ox (x = 7–8) strongly depends on the phase and oxygen content of Ce2Zr2Ox, and it shows a unique discontinuity in catalytic activity at x = 7.5. The 2 wt % Ni/pyrochlore-Ce2Zr2O7 catalyst showed a remarkable performance in CH4 steam reforming at 923 K at H2O/CH4 = 1 (Table 1). Ni/CeO2, Ni/ZrO2, and Ni/CeO2ZrO2 reduced by H2 were much less active and selective than Ni/Ce2Zr2O7, and significant deactivation was observed probably owing to Ni sintering and carbon deposition. On the other hand, the Ni/pyrochlore-Ce2Zr2O7 catalyst was stable, resulting in a remarkably high catalytic performance (for a typical 50 h performance, see the Supporting Information, Figure S4). At 973 K, the Ni/Ce2Zr2O7 catalyst exhibited high CO selectivity of 96–98% and high H2 selectivity of 96– 99% at CH4 and H2O conversions of 92–94% and > 96 %, respectively. Platinum, a typical noble metal active for CH4 steam reforming, was supported on CeO2, ZrO2, or Ce2Zr2O7, but the performance was not significantly enhanced by these types of supports, and the CH4 conversion on these Pt-based catalysts ranged between 29 % and 39 %. For Pt-based catalysts, CH4 steam reforming may be controlled by Pt rather than by the nature of the support. 8] In the presence of 0.8% O2 in the reaction feed, the Ni/ Ce2Zr2O7 catalyst also exhibited high H2 selectivity (97–99%) at a CH4 conversion of 93–94 % for at least 10 h. No significant deactivation was observed. These are great advan[*] Dr. M. Tada, Dr. S. Zhang, N. Ishiguro Institute for Molecular Science 38 Nishigo-naka, Myodaiji, Okazaki, Aichi 444-8585 (Japan) E-mail: mtada@ims.ac.jp

Transparent conductive Cd3TeO6 thin films with perovskite structure

Transparent conductive Cd3TeO6 thin films were deposited by radio-frequency magnetron sputtering using a target composed of CdO and TeO2 powders, and these films’ electrical and optical properties were examined. The electrical resistivity of 1.9×10−2Ωcm and an average transmittance above 85% in the visible region (400–800 nm) were obtained after annealing the film at 500u2009°C. The film’s carrier density and Hall mobility were 8.7×1019cm−3 and 6.8cm2V−1s−1, respectively. The absorption edge of the films was shifted to a lower wavelength by increasing the carrier density. The maximum band gap of these films was found to be 3.69 eV.

Reduction of Dielectric Losses in Pb(Fe1/2Nb1/2)O3-Based Ferroelectric Ceramics

Pseudoternary Pb(Fe1/2Nb1/2)O3–PbZrO3–PbTiO3 (PFN–PZ–PT) ferroelectric ceramics with a pure perovskite phase were fabricated by a conventional solid-state reaction method via a B-site oxide mixing route in the whole composition range. The ceramics obtained exhibit marked frequency-dependent dielectric behavior and a large dielectric loss when the concentration of Pb(Fe1/2Nb1/2)O3 exceeds 40 mol %. The large dielectric loss is thought to correlate with the thermally activated hole conduction induced by the partial reduction of Fe3+ to Fe2+ ions during sintering, which can be greatly decreased by adding a small amount of MnO2 or by cycling under an alternating electric field. The values of the dielectric constant and the frequency-dependent dielectric behavior at temperatures around and below the temperatures of the dielectric maximum (Tm) are reduced accordingly. The decrease in dielectric loss is believed to be related to the ionization of the manganese-substituted donor defects. The effect of manganese doping on the depression of mechanical vibration loss also contributes little to the decrease in total dielectric loss through pinning down the rotation of space-charge polarization induced by the combining of complex manganese-substituted defects (Mn2+) with oxygen vacancies and standing near the grain boundaries.

Improvement of Dielectric Properties in Iron-Containing Ferroelectrics

Iron-containing ferroelectrics tend to exhibit large dielectric loss accompanied by strong frequency dispersion of the dielectric properties, which is considered to correlate with the partial reduction of Fe3+ to Fe2+ ions during sintering. After sintering in an O2 atmosphere, MnO2 and Li2CO3 dopings exhibit superior behavior in decreasing the dielectric loss of the iron-containing dielectrics. The strong frequency dispersion of the dielectric response and the abnormally recurrent increase of the dielectric constant and loss in the paraelectric region are correspondingly suppressed. An electron compensation mechanism is advanced to interpret the reason for the improvement in dielectric properties in the iron-containing dielectrics, in which the generation of donor electrons is based on different ionization paths.

Ferroelectric Phase Transition in CdTiO 3 Single Crystal

Single-crystal X-ray diffraction measurements at low temperature were carried out using the image-plate technique in the vacuum chamber at BL02B1 of SPring-8. The intensity data were collected at 20 K, 70 K, and 150 K, 36 photographs being taken at each temperature. The systematic extinctions observed at 20 K could be summarized as h = 2 n + 1 for ( hk 0) reflections. This observation together with the observations of the ferroelectricity at this temperature uniquely determine the space group as P 2 1 ma though a previous report suggested the space group to be Pn 2 1 a . The structure could be refined with this space group yielding R = 0.056 for 4359 reflections. The structure of CdTiO 3 at 150 K was found to be almost identical to the previously reported one, belonging to the space group Pnma .

Crystal Structures and Properties of Europium Aluminum Oxynitride Eu2AlO3.75N0.1 and Europium Aluminum Oxide EuAl2O4

The reactions among Eu2O3, AlN, and Al2O3 with the ratios Eu:Al = 2:1 and 1:2 at 1200 °C for 10 h yielded Eu2AlO(3.75)N(0.1) and EuAl2O4, respectively. The powder X-ray diffraction pattern of the new oxynitride could be indexed as a monoclinic structure with the space group I2 (No. 5) (a = 3.7113(2) Å, b = 3.6894(2) Å, c = 12.3900(8) Å, and β = 90.6860(5)°). This structure was found to be a novel distorted Ruddlesden-Popper type. For EuAl2O4, isostructural with monoclinic SrAl2O4 (space group P2(1), No. 4), a structural refinement was performed, indicating that the cell parameters were a = 8.44478(11) Å, b = 8.82388(12) Å, c = 5.15643(7) Å, and β = 93.1854(12)°. (151)Eu Mössbauer spectra revealed that the divalent and trivalent Eu ions coexisted in Eu2AlO(3.75)N(0.1), while Eu ions were in the divalent state in EuAl2O4. A photoluminescent mechanism due to 4f(7) ((8)S(7/2)) ↔ 4f(6)5d(1) of europium in EuAl2O4 was proposed on the basis of the calculated band structure, the band gap obtained from UV-vis diffuse reflectance spectra, and the photoluminescence spectra.

Structure and dielectric property of (1 ? x)Pb(Fe1/4 Sc1/4Nb1/2)O3?xPbTiO3 ceramics prepared via a B-site oxide mixing route

Phase pure perovskite (1 − x)Pb(Fe1/4Sc1/4Nb1/2)O3–xPbTiO3 (PFSN–PT) ferroelectric ceramics were prepared by conventional ceramic processing via a B-site oxide mixing route. The PFSN–PT ceramics sintered at 1180 °C for 2 h exhibit rather homogeneous microstructure and improved dielectric properties as compared with those synthesized by the wolframite precursor method accompanied by large relative density except 0.5PFSN–0.5PT and 0.4PFSN–0.6PT. With the increase in the content of PbTiO3 (PT), the crystal structure of PFSN–PT changes from a rhombohedral perovskite structure with some distortion to a tetragonal one accompanied by an increase in tetragonality (defined as the ratio of cell parameter c/a) from 1.0256 of 0.6PFSN–0.4PT to 1.0534 of 0.2PFSN–0.8PT. Furthermore, the ferroelectric phase transition of PFSN–PT changes from a diffused phase transition of relaxor ferroelectrics to a nearly first-order phase transition of normal ferroelectrics with the increase in PT content. The value of the dielectric constant maximum (em) and the temperature of the dielectric maximum (Tm) also increases almost linearly.

Crystallographic, Electronic, and Magnetic Properties of Rock Salt Superstructure Sulfide Lu2CrS4 with Jahn–Teller Distortion

A new chromium(II) sulfide, Lu2CrS4, with a novel structure was prepared by a solid-state reaction. The powder X-ray diffraction pattern could be indexed as a tetragonal system, with a = 7.46373(2) Å, c = 22.6338(2) Å, and space group I4̅2d (No. 122). Rietveld analysis of the pattern provided the crystal structure consisting of CrS6 and LuS6 octahedra sharing edges and apexes and revealed a rock salt superstructure with new cation (vacancy) arrangements. The electrical resistivity indicates semiconducting behavior. The magnetic susceptibility and specific heat measurements showed that the Cr ions are in the high-spin d(4) configuration and that their magnetic moments ordered antiferromagnetically at 55 K. The basic antiferromagnetic structure was determined using powder neutron diffraction data at 10 K. The band structure calculations demonstrate that the densities of states of Cr 3d electrons split into two spin-up eg bands because of Jahn-Teller distortion.

Crystal structures, magnetic properties, and DFT calculation of B-site defected 12L-perovskites Ba2La2MW2O12 (M = Mn, Co, Ni, Zn)

The synthesis, crystal structures and magnetic properties of Ba2La2MW2O12 (Mu2009u2009=u2009u2009Mn, Co, Ni, Zn) were investigated. They crystallize in the 12-layer polytype of the perovskite structure with a regular cation defect in the B-site. The results of neutron diffraction measurements reveal that they adopt a rhombohedral structure with a space group Ru2009u2009-u2009u20093 and have a cation ordering between Ba and La ions in the A-site. In these compounds, the magnetic M ions form the 2D triangular lattice. From the results of magnetic measurements, the ferromagnetic ordering of M2+ ions for Mu2009u2009=u2009u2009Co (T Cu2009u2009=u2009u20091.3u2009K) and Ni (6.2u2009K) and the paramagnetic behavior (Tu2009u2009>u2009u20091.8u2009K) with an antiferromagnetic interaction for Mu2009u2009=u2009u2009Mn are observed. From the DFT calculation, their band structures and magnetic interactions are discussed.

Syntheses of Bi2X3 (X = S, Se, Te) from elements under hydrothermal conditions

Abstract Bismuth chalcogenides (Bi2X3, X = S, Se, Te) were synthesized from the elements under hydrothermal condition. Single phases of Bi2S3 and Bi2Se3 were produced at 240 °C. Bi2Te3 was obtained as an almost single phase with a small amount of Bi2TeO5. From the results of control experiments without water, the hydrothermal condition in the production of Bi2S3 was more effective than that of Bi2Se3. The particles of obtained Bi2S3 were spherical, with a diameter of ∼1 μm. The Bi2Se3 particles were in a plate-like form, with a width of ∼1 μm and a thickness of ∼0.2 μm.