Kyoto University · Materials Science
Professor Masato Machida's research lab specializes in the development and fundamental investigation of advanced functional oxides for sustainable energy and environmental applications. The lab focuses on rare-earth-based materials, particularly lanthanide oxides, oxysulfates, and tantalates, with an emphasis on their redox properties, oxygen storage capacity, and photocatalytic activity. Key research directions include designing efficient catalysts for diesel soot oxidation and low-temperature NOx removal, as well as exploring novel photocatalysts for solar-driven water splitting using UV light. The lab integrates materials synthesis, spectroscopic characterization (e.g., in situ FT-IR, XPS), and theoretical calculations to understand structure-activity relationships at the electronic level.
Figures are computed from collected data and may differ slightly.
The present work has demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles. Four typical fluorite-type oxides, CeO2, ZrO2, Pr6O11, and a CeO2−ZrO2 solid solution have been studied as model catalysts for soot oxidation in conjunction with the redox property and the reactivity of solid oxygen species. It was found that the redox property measured in terms of oxyg
Interactions of nitrogen oxides (NOx) with (n)MnOx−(1 − n)CeO2 binary oxides were studied to use them for sorptive NOx removal at low temperatures (≃150 °C). The formation of MnOx−CeO2 solid solutions with the fluorite-type structure at n ≃ 0.5 was found to be quite effective in accelerating NOx sorption from flowing mixtures of 0.08% NO, 2% O2, and He balance (W/F = 0.24 g·s/cm3). The cumulative NOx uptake was increased by decreasing the reaction temperature and/or by increasing O2 concentratio
The first example of an active layered tantalate photocatalyst containing partly filled lanthanide 4f shell is reported. A single phase of layered perovskite tantalates, RbLnTa2O7, could be obtained with Ln = La, Pr, Nd, and Sm; the ionic radii of these trivalent cations are required to be larger than 0.126 nm for constructing a perovskite slab. Under UV irradiation from a high-pressure Hg lamp, these layered tantalates demonstrated the photocatalytic activity for water splitting into stoichiome
Photocatalytic activity of lanthanide tantalates, LnTaO4 (Ln = La, Ce, Pr, Nd, and Sm), for water splitting was studied in connection to the effect of Ln 4f levels on the electronic structure. Valence band XPS, UV−vis, and first-principle electronic calculations suggested that the position of Ln 4f levels becomes lowered monotonically across the series of Ln. The empty La 4f level is supposed to be higher than the conduction band edge, whereas the filled 4f levels of the Nd and Sm compounds lie
The present work has demonstrated the large-capacity oxygen storage of various isomorphous lanthanide oxysulfates, Ln2O2SO4 (Ln = La, Pr, Nd and Sm), which utilize the nonmetallic element (S) as a redox site instead of metallic cations. The reduction by H2 or hydrocarbons and subsequent reoxidation by O2 between Ln2O2SO4(S6+) and Ln2O2S(S2-) achieved an oxygen storage of 2 (mol of O2)·mol-1, which is 8 times larger than that of the conventional CeO2−ZrO2 material. Although the reversible redox c
Layered lanthanide tantalates and their ion-exchanged phases (MLnTa2O7, M = Cs, Rb, Na, and H; Ln = La, Pr, Nd, and Sm) were prepared to evaluate their photocatalytic activity for water splitting under UV irradiation. The optical band gap energy was dependent on the lanthanide, Ln, but negligibly affected by the monovalent interlayer cations, M. By contrast, the photocatalytic activity was strongly affected by not only Ln but also M; the highest activity was attained by a series of M = Rb with a
The Dion-Jacobson series of triple-layered perovskite tantalates (MCa2Ta3O10, M = Cs, Na, H, and C6H13NH3) were synthesized to evaluate their photocatalytic activity for overall water splitting to evolve H2/O2 under UV irradiation. The photocatalytic activity was susceptible to the hydration of interlayer space. The hydrous Na phase exhibited much higher activity (H2: 308 micromol.h(-1)) compared to the anhydrous Cs phase (24 micromol.h(-1)) and the hydrous H phase (22 micromol.h(-1)) in the pre
Abstract Barium hexaaluminate, BaO·6Al2O3, exhibited excellent heat resistance in maintaining a large surface area. Preparation from hydrolysis of metal alkoxides was a superior process in deriving the large surface area of BaO·6Al2O3, to that from mixtures of BaCO3⁄γ-Al2O3. Direct formation of BaO·6Al2O3 phase at low temperature plays the key role in retaining the fine particle size. The amount of water added for hydrolysis and the aging period of hydrolyzed precursors strongly influenced the s
Surfactant-assisted synthesis of the oxysulfate Pr2O2SO4 with a large oxygen-storage capacity was studied with the aim of increasing the rate of redox cycles at lower temperatures. From an aqueous solution of nitrate, Pr-based surfactant mesophases templated by dodecyl sulfate anion (DS = C12H25OSO3−) were synthesized using ammonia or urea as precipitants. The precipitated mesophases, Pr-DS-NH3 and Pr-DS-N2H4CO, exhibited ordered layered structures with interlayer spacings of 2.63 and 3.68 nm, r
Under UV irradiation, RbNdTa2O7, the first example of an active photocatalyst containing partially occupied 4f levels, demonstrated efficient evolution of stoichiometric H2/O2 mixtures from pure water even in the absence of loaded metal catalysts.
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