Hidenobu Itoh

Effect of reduction temperature on the transformation of MoO3 to MoOx with a large surface area

Abstract The surface area of MoO 3 was enlarged by H 2 reduction. When the samples reduced at different temperatures were compared at a certain extent of reduction, MoO 3 reduced at 573 and 623 K exhibited much larger surface areas than that at 673 K. MoO 3 reduced at temperature below 623 K had a surface area of 170–180 m 2 g −1 and pores with the diameter of 0.6–3.0 nm when the reduction degree was about 50%. Since the surface area and the porous structure of MoO 3 reduced at 623 K changed little by treatment at 673 K in an N 2 atmosphere, the small surface area of MoO 3 reduced at 673 K cannot be elucidated by thermal stability. XRD studies showed that reduction of MoO 3 at temperature below 623 K proceeded via the formation of hydrogen molybdenum bronze, H x MoO 3 , while the H x MoO 3 phase was not observed at 673 K. We suggest from these results that the enlargement of surface area and the formation of micropores can occur only when reduction of MoO 3 proceeds via the H x MoO 3 phase.

Marked difference in activity of alumina catalysts for selective catalytic reduction of nitrogen monoxide by ethene in excess oxygen

Alumina is well-known as an effective catalyst for the title reaction. The present study revealed that the activity of an alumina catalyst for the reaction largely depended on its type. A critical factor affecting the activity of an alumina was neither the surface area nor pore structure, but the purity; the higher the purity, the higher the activity. Active alumina catalysts showed high activity for both the oxidation of NO to NO2 and the reduction of NO2 by ethene.

Leakage Current Properties of Cation-Substituted BiFeO3Ceramics

Cation-doped BiFeO3 ceramics were fabricated by sintering coprecipitated and calcined powders at 700–900 °C to study the effect of cation doping on the leakage current properties of the sintered samples. Among the dopants examined in this study, Ti4+, Sn4+, or Zr4+ doping was found to effectively reduce the leakage current of the samples. In particular, a marked decrease in the leakage current density was achieved at 10% Ti4+ doping, which also resulted in the structure change from rhombohedral to cubic. The codoping of Ti4+/Zn2+ ions or Ti4+/Ni2+ ions brought about a substantial reduction in the leakage current density of the bulk samples by about four or five orders of magnitude at a small doping amount of 2%. This can be explained by the combined effect of Ti4+ doping, which basically contributes to the decreased number of oxygen vacancies in the sample, and Zn2+ or Ni2+ doping, which might assist the homogeneous substitution of Ti4+ ions for the Fe3+ sites.

Catalytic properties of H2-reduced MoO3 with noble metal for the conversions of heptane and propan-2-ol

Effects of H2 reduction on the catalytic properties of MoO3 with Pt, Pd, Rh, Ir, or Ru for the conversions of heptane and propan-2-ol were studied. The catalytic activity of MoO3 with noble metal for the isomerization of heptane was strongly dependent on the period of H2 reduction at 623 K. This behavior was almost the same as that of MoO3 without noble metal. Among the catalysts tested, Pt/MoO3 was the most active for this reaction. The catalytic activities of MoO3 for dehydration and dehydrogenation of propan-2-ol also increased in proportion with the period of H2 reduction. In the case of MoO3 with noble metal, a higher dehydration activity was obtained by a longer period of H2 reduction, while the dehydrogenation activity was almost independent of the reduction period. Pt/MoO3 exhibited a high dehydration activity compared with the other catalysts, indicating the most acidic property of Pt/MoO3. We conclude from these results that the high isomerization activity of Pt/MoO3 can be attributed to its high acidity as well as to the hydrogenative and dehydrogenative properties of Pt metal.

Dye adsorption behavior of anatase- and rutile-type TiO2 nanoparticles modified by various heat-treatments

TiO2 colloidal particles with a fixed crystalline phase of anatase or rutile were heat-treated under different conditions (air-heating and hydrothermal-heating) to modify their surface characters which essentially affected the adsorption behavior of a Ru-complex dye on the surfaces. Changes in the number of surface OH group (N(OH)), apparent crystallite size, pore structure were evaluated as a function of heat-treatment conditions for various TiO2 nanoparticles. The amount of a Ru-complex dye adsorbed (N(dye)) was correlated to those surface properties of TiO2 samples. N(dye) values tended to increase with increasing crystallinity for only the anatase-type TiO2 particles. However, there was no simple, common relationship between N(dye) and N(OH) for all the TiO2 nanoparticles examined. Considerable difference in N(dye) values obtained in different nanoparticles might be explained on the basis of the surface pore structures of those particles.

Ni Oxyhydroxide Thin Films Prepared by Reactive Sputtering Using O2+ H2O Mixed Gas

In this study, we have examined the preparation of thin films of Ni oxyhydroxide, which are used for batteries, supercapacitors, and electrochromic devices, by reactive sputtering. Transmittance and resistivity were found to decrease with the incorporation of H2O into the sputtering gas. This indicates that the valence state of Ni atoms in the film changes from Ni2+ to Ni3+. Peaks due to Ni–OH and hydrogen bonded OH were observed by Fourier transform IR (FTIR) spectroscopy of the films sputtered in O2 + H2O mixed gas. From the obtained results, it is confirmed that Ni oxyhydroxide films are formed by reactive sputtering in O2 + H2O mixed gas. An electrochromic coloration efficiency of 29 cm2/C was obtained in 1 M KOH aqueous electrolyte solution for the Ni oxyhydroxide films.

Cation Substitution for BaTiO3 Phase in Low-Fired Glass-Ceramics for Tunable Microwave Applications

Cation substitution for the Ba2+ and Ti4+ sites in the BaTiO3 structure was attempted in low-fired glass-ceramics derived from glass powders that have perovskite phase compositions corresponding to (BaTiO3:REAlO3) = 9:1 and 8:2 (RE=La, Nd and Sm) to control the Curie temperature (Tc) of the ferroelectric glass-ceramics. The La3+-substituted (9:1) sample heated at 950°C for 24 h showed a broadened er–temperature relationship with substantial lowering in Tc to ~-55°C. The Ba:La ratio in the perovskite particles was estimated to be in the range of 4:1–6.7:1, whereas very little Al3+ was incorporated into the same particles. It was found that the Tc of the glass-ceramics fabricated in our serial study could be adjusted by A-site cation substitution in BaTiO3. Tailored glass-ceramic samples with room temperature er of 200–300 and Tc of around 0°C had good microwave tunability of 30–40% under dc bias voltage of 10–50 kV/cm. The high tuning sensitivity of the low-fired glass-ceramics was confirmed by comparative examination of the dielectric properties of well-crystallized ceramics and thin films.

Effects of Sputtering Gas Pressure on Electrochromic Properties of Ni Oxyhydroxide Thin Films Prepared by Reactive Sputtering in H2O Atmosphere

Ni oxyhydroxide (NiOOH) thin films were prepared by reactive sputtering in an atmosphere of H2O gas, and the effects of sputtering gas pressure on their electrochromic properties in KOH aqueous electrolyte were studied. The largest optical density change was obtained for the thin films deposited under high sputtering gas pressures of approximately 6.7 Pa because of their low film density and chemical composition close to NiOOH. Stable transmittance change during coloring and bleaching cycles was obtained for the film from the first cycle up to 100 cycles.

Synthesis and Dielectric-Magnetic Properties of Rare-Earth (La, Nd, Sm)-Modified Bi4Ti3O12

Rare-earth (RE = La, Nd, Sm)-substitution into BiT (Bi4-XREXTi3O12) was conducted in a composition range of 0 ≤X ≤3.0. BiT powders, into which fixed amounts of RE cations were incorporated, were directly synthesized by low-temperature calcination of coprecipitated precursors. Complete substitution with RE was achieved for samples up to X = 2.5 at 1100 °C. Dielectric permittivity (er)–temperature curves of the La-2.0, Nd-2.0, and Sm-2.0 ceramics showed er maxima in a frequency-dependent manner. The er maxima were located at around 540–560 °C (at 1 kHz), which corresponded to the transition from the ferroelectric to paraelectric phase. Increasing Nd-substitution from X = 2.0 to 2.5 resulted in a much suppressed er maximum at 200–300 °C, which may be due to substantial reduction in the structural distortion giving rise to ferroelectricity of the BiT-based phase. The appearance and enhancement of magnetization was found for the Nd- and Sm-substituted BiT samples. They revealed specified magnetization–magnetic field curves with a small hysteresis loop, suggesting the presence of a weak canted antiferromagnetic interaction.

Effects of Substrate Cooling during Sputter Deposition of Hydrogen-Containing Ta2O5 Thin Films in H2O Atmosphere on their Ion Conductivity

Hydrogen-containing Ta2O5 (Ta2O5:H) thin films, which are considered to be candidates for proton-conducting solid electrolytes, were prepared by reactive sputtering in H2O atmosphere. The substrate temperature during sputter deposition was changed from -20 to 70 °C because the equilibrium vapor pressure of water depends strongly on temperature. The chemical composition of the films was characterized by Rutherford backscattering (RBS) and hydrogen forward scattering (HFS), and it was found that the H/Ta atomic ratio increased with decreasing substrate temperature, and a maximum ratio of 2.2 was obtained at -20 °C. The ion conductivity measured at room temperature also increased with decreasing substrate temperature and a maximum conductivity of 4 ×10-8 S/cm was obtained at -20 °C. It is considered that the desorption rate of H2O molecules from the growing film surface was decreased by the substrate cooling, which resulted in the increase in the hydrogen content and the improvement of the ion conductivity.