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A noble metal-free apatite-type La10Si5CoO27−δcatalyst with high thermal durability for toluene combustion has been prepared via coprecipitation followed by calcination at 1000 °C. It completely oxidized toluene at 310 °C, which was comparable to that of 0.1 wt % Pt/Al2O3calcined at 1000 °C (290 °C). Furthermore, La10Si5CoO27−δexhibited high catalytic activity even after calcination at 1400 °C via a solid-state reaction route, and the complete oxidation of toluene was realized at 330 °C, lower than that of 0.1 wt % Pt/Al2O3calcined at 1400 °C (380 °C).An apatite-type La10Si5CoO27−δcatalyst with high thermal durability was prepared. After calcination at 1000 °C, this catalyst completely oxidized toluene at 310 °C, comparable to that of Pt/Al2O3calcined at 1000 °C (290 °C). For La10Si5CoO27−δcalcined at 1400 °C, complete toluene combustion was realized at 330 °C, lower than that of Pt/Al2O3calcined at 1400 °C (380 °C).

Toluene is one of the volatile organic compounds that are harmful to the environment and human health. One promising approach for eliminating toluene is catalytic combustion. Although precious metal-based catalysts are known to show high activity for toluene combustion, the high price of precious metals has restricted their widespread applications. In this study, precious metal-free catalysts of Co3O4/ZrSn1−xFexO4−δwere synthesized for toluene combustion. Here, scrutinyite-type ZrSnO4was focused as a promoter, which can supply active oxygen species from inside the lattice toward the Co3O4activator. In addition, Fe2+/3+ions were introduced into the ZrSnO4lattice to enhance the oxygen supply ability considering the improvement of redox properties and the formation of oxygen vacancies for a smooth oxide ion migration. The oxygen supply from the ZrSn1−xFexO4−δlattice facilitated toluene oxidation on Co3O4, and the highest catalytic activity was obtained for the 19 wt.% Co3O4/ZrSn0.93Fe0.07O4−δ(Co3O4/ZSF0.07) catalyst, wherein the complete combustion was realized at a temperature as low as 250 °C. The toluene combustion reaction over Co3O4/ZSF0.07 was considered to proceed along a typical route of the rapid transformation of toluene into the intermediates (benzyl alcohol, benzaldehyde, benzoate, and maleic anhydride) and, finally, to the formation of carbon dioxide and water.Graphical AbstractThe precious metal-free catalysts of Co3O4/ZrSn1−xFexO4−δwere synthesized for toluene combustion. The active oxygen supply from the scrutinyite-type ZrSn1−xFexO4−δsolids promoted toluene oxidation on the Co3O4activator. The highest catalytic activity was obtained for the Co3O4/ZrSn0.93Fe0.07O4−δcatalyst, wherein complete combustion was realized at a temperature as low as 250 °C.

Novel environmentally friendly blue pigments, Na4Cu1−xMgx(PO4)2(0 ≤ x≤ 0.25), were synthesized. By doping Mg2+with lower electronegativity into Cu2+sites, the crystal lattice was distorted, which strongly affects the charge transfer from O2−to Cu2+and the d–dtransition of Cu2+. In the series of Na4Cu1−xMgx(PO4)2, the Na4Cu0.85Mg0.15(PO4)2solid showed a vivid blue hue with a blueness value (−b*) of 38.2 in the CIE L*a*b*system.Novel environmentally friendly blue pigments, Na4Cu1−xMgx(PO4)2were synthesized by a conventional solid-state reaction method. As a result of doping of Mg2+with lower electronegativity into Cu2+sites, the Na4Cu0.85Mg0.15(PO4)2solid with the highest reflectance in blue region (around 460 nm) showed the most vivid blue hue with a blueness value (−b*) of 38.2 in the CIE L*a*b*system.

Mixed-anion compounds, in which multiple anions such as O2−, N3−, and H−are contained in the same compound, have recently attracted attention. Because mixed-anion compounds have a unique crystal structure with multiple anions coordinated to cations, materials with fundamentally new and innovative functions are expected to be developed for various chemistry and physics applications, including catalysts, batteries, and superconductors. In this Account, recent progress in the development of new mixed-anion compounds by the MEXT mixed-anion project is described, with emphasis on results related to the development of materials used as photocatalysts/photoelectrodes, phosphors, secondary battery components, conductors, and thermoelectric materials.Mixed-anion compounds containing more than one anionic species in the same phase can exhibit emergent properties and/or functions that are unattainable with their single-anion counterparts. This Account describes recent progress in the development of new mixed-anion compounds for various applications related to energy, with emphasis on our interdisciplinary collaboration in a national project on mixed-anion materials.

(Yb1-xCox)2O3-dcatalysts with cubic (C-type) rare-earth sesquioxide structure were synthesized by a co-precipitation method. The introduction of Co2+/3+ions into the Yb2O3lattice resulted in an improved catalytic activity for N2O decomposition, due to the enhanced redox properties and increased amount of active sites. Among the prepared catalysts, (Yb0.90Co0.10)2O3-dexhibited the highest activity for the decomposition of N2O, which was completely converted to N2and O2at 500 °C. Moreover, (Yb0.90Co0.10)2O3-dalso showed high durability in the presence of H2O, O2, or CO2.For N2O decomposition, Yb2O3-Co3O4catalysts with C-type structure were synthesized by introducing Co2+/3+to increase the active sites and the redox property. Among them, (Yb0.90Co0.10)2O3-dexhibited the highest catalytic activity, and N2O was completely decomposed into N2and O2at 500 °C.

Novel catalytic combustion-type CO gas sensors were successfully devised by applying precious metal-free catalysts composed of the p- or n-type semiconducting Ln2CuO4-loaded CeO2-ZrO2-ZnO (Ln2CuO4/CZZn; Ln = La, Nd, and Sm). Complete CO oxidation using the p-type semiconducting La2CuO4/CZZn catalyst occurred at 350 °C, while the n-type semiconducting Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts completely oxidized CO gas at 220 °C and 200 °C, respectively. All the fabricated sensors exhibited quantitative detection of CO gas over 250 °C. The La2CuO4/CZZn catalyst has the smallest heat capacity, which dramatically increases the Pt coil temperature compared with the other catalysts, resulting in the highest sensor signal. However, the sensor applying Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts exhibited faster response time to CO gas than the sensor employing La2CuO4/CZZn catalyst due to their superior CO oxidation activity.The sensor employing p-type semiconductor catalyst of La2CuO4/CeO2-ZrO2-ZnO exhibited the high sensor signal due to the smallest heat capacity value compared with the n-type semiconductor catalysts of Ln2CuO4/CeO2-ZrO2-ZnO (Ln = Nd, Sm). However, the sensor incorporating n-type semiconductor catalysts presented rapid response against CO gas because the CO oxidation activity of the catalysts with n-type semiconductor was higher than that of the p-type semiconductor catalyst.

This study focuses on the development and characterization of precious-metal-free Co3O4/ZrSn1−xFexO4−δcatalysts for the purpose of direct N2O decomposition. The oxygen supply from ZrSn1−xFexO4−δfacilitated N2O decomposition. Among the prepared catalysts, the 19 wt.% Co3O4/ZrSn0.93Fe0.07O4−δcatalyst exhibited the highest catalytic activity. Furthermore, N2O was completely decomposed at a relatively low temperature of 500∘C.

(Yb1-xPrx)2O3+dcatalysts with C-type cubic structure were synthesized by a co-precipitation method. By introducing the Pr ion into Yb2O3, the enhancement in the catalytic N2O decomposition activity was recognized through the improvement of the redox behavior due to the synergistic effects of Yb2+/3+and Pr3+/4+ions without any noble metal contribution. Among the samples prepared, (Yb0.85Pr0.15)2O3+dexhibited the highest N2O decomposition activity, and can completely decompose N2O at 600 °C.(Yb1-xPrx)2O3+dcatalysts with C-type cubic structure were synthesized by a co-precipitation method. By introducing the Pr ion into Yb2O3, the enhancement in the catalytic N2O decomposition activity was recognized through the improvement of the redox behavior due to the synergistic effects of Yb2+/3+and Pr3+/4+ions without any noble metal contribution. Among the samples prepared, (Yb0.85Pr0.15)2O3+dexhibited the highest N2O decomposition activity, and is possible to completely decompose N2O at 600 °C.

Pt/CeO2-ZrO2-Bi2O3/SBA-16 catalysts were prepared to realize complete oxidation of formaldehyde at room temperature. Due to the high oxygen release and storage abilities of the CeO2-ZrO2-Bi2O3promoter, formaldehyde was effectively decomposed even with a low amount of the Pt activator. For the Pt(0.7 wt%)/Ce0.68Zr0.17Bi0.15O2-d(16 wt%)/SBA-16 catalyst, complete decomposition of formaldehyde was achieved at temperatures as low as 20 °C, and this catalytic activity is higher than the Pt(0.7 wt%)/Ce0.80Zr0.20O2(16 wt%)/SBA-16 case (98% of formaldehyde conversion at 80 °C).We developed the Pt/CeO2-ZrO2-Bi2O3/SBA-16 catalysts to realize complete oxidation of formaldehyde at room temperature. Due to the high oxygen release and storage abilities of the CeO2-ZrO2-Bi2O3promoter, the Pt(0.7 wt%)/CeO2-ZrO2-Bi2O3/SBA-16 catalyst exhibited higher catalytic activity than the Pt(0.7 wt%)/CeO2-ZrO2/SBA-16 catalyst, and formaldehyde was completely decomposed at 20 °C even with a low amount of the Pt activator.

We investigated the relationship between the conductivities of CeO2-ZrO2-MOx(M = Bi, Ca, Sn, Ni, Fe) solid solutions and the catalytic abilities of catalysts composed of PdO on CeO2-ZrO2-MOx/γ-Al2O3supports. The oxide-ionic conductivities of the CeO2-ZrO2-MOxpromoters increased with increasing oxygen vacancy concentrations and the electronic conductivities of these promoters were significantly enhanced by doping with Sn4+/2+, Ni3+/2+and Fe3+/2+, all of which readily undergo valency changes. Studies of the oxygen release characteristics of CeO2-ZrO2-MOx/γ-Al2O3samples found that the reduction temperatures obtained from hydrogen temperature programmed reduction data were primarily determined by the electronic conductivity of the promoter rather than by the oxide-ionic conductivity. However, the oxygen storage capacity of each CeO2-ZrO2-MOx/γ-Al2O3sample was related to both the oxide-ionic and electronic conductivities. The catalytic methane oxidation activities of these materials were evidently affected by both the reduction temperature and the oxygen storage capacity. As a result, the activities of the PdO/CeO2-ZrO2-MOx/γ-Al2O3catalysts were clearly dependent on the oxide-ionic and electronic conductivities of the CeO2-ZrO2-MOxpromoters.We demonstrated that the oxide-ionic and electronic conductivities of CZM (M = Bi, Ca, Sn, Ni, Fe) clearly affected the enhancement of oxygen release and storage abilities which induced the facilitation of the oxidation of methane by supplying active oxygen to the activator over the PdO/CZM/Al2O3catalysts.

Novel PdO/La10Si6–xCoxO27−δ/γ-Al2O3catalysts with applications to methane combustion were developed. These materials were based on the use of La10Si6–xCoxO27−δas a promoter because this compound has an oxide-ion conducting apatite-type structure that allows the smooth migration of active oxygen to the PdO activator. Co3+/2+ions were also introduced into the original La10Si6O27lattice to enhance its redox properties. Temperature-programmed reduction measurements revealed that the oxygen supply was facilitated by introducing Co3+/2+, where the reduction was observed at 290 °C for La10Si6–xCoxO27−δ(x= 1.0), whereas no reduction was observed below 460 °C for La10Si6O27. Among the samples synthesized in this work, PdO/La10Si6–xCoxO27−δ/γ-Al2O3(x= 1.0) exhibited the highest catalytic activity, allowing the complete oxidation of methane at 310 °C, a temperature 80 °C lower than the 390 °C required when employing PdO/La10Si6O27/γ-Al2O3.

Divalent calcium ion conducting solid electrolyte with three-dimensional NASICON-type structure, (CaxHf1-x)4/(4-2x)Nb(PO4)3, was successfully developed by introducing Ca2+cations into HfNb(PO4)3as mother solid. The existence of three kinds of high valence cation, Hf4+, Nb5+, and P5+, in the structure successfully realized the effective reduction of electrostatic interaction functioned to Ca2+in the structure. The (Ca0.05Hf0.95)4/3.9Nb(PO4)3solid showed considerably higher Ca2+cation conductivity and lower activation energy than those of previously reported NASICON-type Ca0.5Zr2(PO4)3solid.Divalent calcium ion conducting solid electrolyte with three-dimensional NASICON-type structure, (CaxHf1-x)4/(4-2x)Nb(PO4)3, was successfully developed. The existence of three kinds of high valence Hf4+, Nb5+, and P5+cations in the structure realized the effective reduction of electrostatic interaction function to Ca2+. The (Ca0.05Hf0.95)4/3.9Nb(PO4)3solid showed higher Ca2+cation conductivity and lower activation energy than those of NASICON-type Ca0.5Zr2(PO4)3solid.

Novel catalysts of Rh/ZrSnO4were synthesized, and their catalytic activities for the direct decomposition of nitrous oxide (N2O) were investigated. ZrSnO4with an α-PbO2-type structure was used as a promoter, since the oxygen supply from its lattice was expected to facilitate N2O decomposition. Among the prepared catalysts, 1.0 wt.% Rh/ZrSnO4exhibited the highest catalytic activity: N2O was completely decomposed at 450∘C. This activity was higher than those for 1.0 wt.% Rh/ZrO2and 1.0 wt.% Rh/SnO2, indicating that the ZrSnO4solid promoted N2O decomposition. In addition, the 1.0 wt.% Rh/ZrSnO4catalyst featured high durability in the presence of O2, CO2, and H2O vapors.

Photocatalytic activity has been demonstrated for ZrSnO4by controlling the bandgap and the bottom of the conduction band of ZrO2and SnO2. A single-phase with the metastable ZrSnO4solid was successfully obtained, and ZrSnO4exhibited photocatalytic activity for hydrogen and oxygen production from water under UV irradiation.ZrSnO4was prepared as a novel photocatalyst for water splitting. ZrSnO4supported with Pt generated hydrogen gas from the aqueous methanol solution under the UV light irradiation, and the photocatalytic activity of ZrSnO4was higher than those of ZrO2and SnO2.

Novel Pt/ZrSn1−xSrxO4−δ/SBA-16 (SBA-16: Santa Barbara Amorphous No. 16) catalysts were developed for liquid-phase phenol oxidation. As the promoter to accelerate phenol oxidation on Pt, a ZrSnO4solid with an α-PbO2-type structure was chosen because its interstitial open spaces are expected to facilitate phenol adsorption. Additionally, the redox reaction of Sn4+/2+provides oxygen release and storage abilities, and the introduction of low-valent Sr2+ions into the ZrSnO4lattice improves oxide ion migration via the generation of oxygen vacancies in the lattice structure. Among the samples prepared, the 9.0 wt.% Pt/8.1 wt.% Zr1.11Sn0.85Sr0.04O4−δ/SBA-16 catalyst showed the highest activity, resulting in a phenol removal percentage of up to 99.7% after 6 h of reaction at 80∘C under atmospheric pressure.

Partial oxidation of cyclohexane into cyclohexanone and cyclohexanol (KA-oil) is an industrially significant reaction for producing precursors for the synthesis of ɛ-caprolactam and adipic acid, which are the building blocks of nylon. However, to date, the cyclohexane conversion ratio has usually been limited to less than 6% to prevent further oxidation of the cyclohexanol and cyclohexanone targets. In this study, we report that Pt/CeO2-ZrO2-SnO2/SiO2, in which CeO2-ZrO2-SnO2provide reactive oxygen molecules from inside the bulk, can act as efficient catalysts. Optimization of the catalyst composition and reaction conditions provided a cyclohexane conversion ratio of 24.1% and a total selectivity for cyclohexanol and cyclohexanone of 83.4% at 130 °C in 0.5 MPa (4.9 atm) air for 7 h over a 5wt%Pt/16wt%Ce0.68Zr0.17Sn0.15O2.0/SiO2catalyst. This catalyst has significant advantages over conventional catalysts because the reaction proceeds at a lower pressure, and there is no need for toxic radical initiators or free-radical scavengers.

1 wt % Pt/11 wt % (Co1−xCux)3O4−δ/16 wt % Ce0.62Zr0.20Sn0.18O2.0/γ-Al2O3catalysts were prepared to realize complete combustion of toluene at lower temperatures than that of a 1 wt % Pt/11 wt % Co3O4/16 wt % Ce0.62Zr0.20Sn0.18O2.0/γ-Al2O3catalyst previously reported by our group without increasing the amount of platinum. Addition of copper into the Co3O4lattice was effective to facilitate oxygen release and storage, and thereby, the toluene oxidation activity was enhanced. The highest activity for the combustion of toluene was observed using a 1 wt % Pt/13 wt % (Co0.97Cu0.03)3O4−δ/16 wt % Ce0.62Zr0.20Sn0.18O2.0/γ-Al2O3catalyst, and despite a smaller platinum loading in the present catalyst, toluene was completely oxidized to carbon dioxide and water vapor at the lower temperature of 140 °C compared to that (160 °C) using 1 wt % Pt/11 wt % Co3O4/16 wt % Ce0.62Zr0.20Sn0.18O2.0/γ-Al2O3.

A Pt/CeO2-ZrO2-Bi2O3/SBA-16 (Santa Barbara Amorphous No. 16) catalyst was prepared by hydrothermal and wet impregnation methods for catalytic purification of 1,4-dioxane in water. SBA-16 has a number of mesopores and the average size of the pores is 9.4 nm. In the present catalyst, platinum and CeO2-ZrO2-Bi2O3were successfully dispersed in the pores of the SBA-16 support, and the temperature dependence of the liquid phase oxidation of 1,4-dioxane was examined. The oxidation reaction proceeded effectively in the air atmosphere in the temperature range of 40–80 °C.

Novel environmentally friendly inorganic red pigments based on calcium bismuth oxide, Ca3(Bi1−xREx)8O15(0 ⩽ x⩽ 0.09; RE = Sc3+, Er3+, Y3+, Ho3+and Dy3+), were successfully synthesized and the color properties were characterized. The color of these pigments depended on the composition and the synthesis condition, and the most vivid red color was obtained for the Ca3(Bi0.93Y0.07)8O15sample calcined thrice at 800 °C for 2 h. The L* and a* values corresponding to brightness and red chromaticity for this pigment were 45.6 and +30.6, respectively, which were greater than those of a commercially available Fe2O3pigment (L* = 38.4, a* = +29.5). Since the present pigment is composed of nontoxic and safe elements, it should be an attractive alternative to the conventional Fe2O3pigment.

A CeO2–ZrO2–Bi2O3(CZB) solid solution supported on a mesoporous silica support, SBA-16 (Santa Barbara Amorphous No. 16; SBA), was synthesized using hydrothermal and impregnation methods and was used as a catalyst for the liquid-phase oxidation of bisphenol-A (BPA). CZB was successfully inserted into the mesoporous structure of SBA. For CZB/SBA, the removal percentage of BPA reached 82% even with the relatively moderate reaction conditions of 80 °C for 3 h under atmospheric pressure.A CeO2–ZrO2–Bi2O3(CZB) solid solution supported on a mesoporous silica support, SBA-16 (Santa Barbara Amorphous No. 16; SBA), was synthesized using hydrothermal and impregnation methods and used as a catalyst for the liquid-phase oxidation of bisphenol-A (BPA). CZB was successfully inserted into the mesoporous structure of SBA. For CZB/SBA, the removal percentage of BPA reached 82% even with the relatively moderate reaction conditions of 80 °C for 3 h under atmospheric pressure.

Red-emitting Ca3[?]xEuxZr1[?]yAlySi2O9+(x[?]y)/2 (0.05 [?] x [?] 0.25, 0 [?] y [?] 0.07) phosphors were synthesized in a single phase form by the conventional solid-state reaction method and their photoluminescence properties were characterized. The charge-transfer efficiency from O2[?] to Eu3+ was controlled by the Al3+ doping into the Zr4+ site in the host Ca3ZrSi2O9 lattice, which resulted in the successful enhancement of the luminescent emission intensity of these phosphors. The highest emission intensity was obtained for Ca2.88Eu0.12Zr0.95Al0.05Si2O9.035, where the relative emission intensity of this phosphor was 94% compared with that of a commercial Y1.94Eu0.06O3 phosphor.

A novel La1−xCaxCoO3−x/2/CeO2–ZrO2–ZnO catalyst was synthesized at 1400 °C to realize refractory and noble metal-free materials. On this catalyst, the temperature differential between complete toluene oxidation and catalyst calcination was over 1000 °C, elucidating that this novel catalyst can be used stably over a significantly wide temperature range.

Highly water durable ammonia gas sensor was fabricated by the combination of Al3+ ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte and NH4+-b-gallate (NH4+-Ga11O17) auxiliary sensing electrode, and its NH3 gas sensing performance was investigated in humid atmospheres. The present sensor showed an advanced sensing performance of continuous, quantitative and reproducible response which obeys the theoretical Nernst relationship even in a highly humidified condition containing 4.2 vol% H2O at 230 {degree sign}C.

Novel environmentally friendly Ce0.36Si0.31-zBi0.33AlzO2-(0.33+z)/2yellow pigments were synthesized to enhance the thermal stability of a Ce0.36Si0.31Bi0.33O1.835pigment, which was previously reported by our group. The thermal stability depends on the Al3+content in the pigments, and the most significant effect was achieved for the Ce0.35Si0.24Bi0.32Al0.09O1.795sample in which the Al3+content was 9 mol %. The conventional Ce0.36Si0.31Bi0.33O1.835pigment was stable up to 1023 K, while the Ce0.35Si0.24Bi0.32Al0.09O1.795pigment maintained its cubic fluorite structure even after calcination at 1173 K. Furthermore, optical absorbance in the wavelength region between 435 and 480 nm was the most significant for the Ce0.35Si0.24Bi0.32Al0.09O1.795pigment calcined at 1123 K, and the yellow hue corresponding to the b*value in the L*a*b*coordination system (b*= +75.1) was higher than those of the previous Ce0.36Si0.31Bi0.33O1.835pigment calcined at 1023 K (b*= +72.7) and at 1123 K (b*= +70.7) as well as that of the commercial praseodymium yellow (b*= +70.3). Therefore, the Al3+addition was effective for improving not only the thermal stability, but also the optical properties of the Ce0.36Si0.31Bi0.33O1.835pigment.

C-type cubic Y2O3, (Y0.70Tb0.30)2O3+δ, and (Y0.99−xTbxBa0.01)2O2.99+δ(x= 0, 0.10, 0.20, 0.30, and 0.40) were prepared to investigate their catalytic performance for NO decomposition. In the direct NO decomposition process, NO is adsorbed on basic sites of the catalyst surface to form adsorbed nitrosyl, and the number of basic sites affects the NO decomposition activity. In particular, the negative effect of CO2presence on the catalytic activity is related to the number of the surface basic sites. Furthermore, it was evidenced from temperature programmed desorption (TPD) of NO and IR measurements that adsorbed nitrosyl reacts with gas-phase NO and decomposes to N2. The effects of Ba2+and Tb3+/4+introduction on the activity of the catalyst are discussed based on this NO reaction mechanism. It is concluded that the principal effects of Ba2+doping are an increase in the number of basic sites and the generation of oxide anion vacancies in the lattice. In addition, we demonstrate that Tb3+/4+ions in the lattice facilitate O2desorption and act as NO adsorption sites, so that the catalytic activity is significantly enhanced by Tb3+/4+introduction, despite the small number of basic sites on the catalyst surface.

Solid electrolyte type ammonia (NH3) gas sensors were fabricated using Al3+ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3solid electrolyte with an aluminum thin film as a reference electrode. A rare-earth ammonium sulfate double salt of R2(SO4)3·(NH4)2SO4(R = rare earth) or a lanthanum oxysulfate La2O2SO4-based solid solution was selected as the auxiliary sensing electrode on the basis of thermal stability or water durability. Both sensors with R2(SO4)3·(NH4)2SO4or La2O2SO4–NH4H2PO4auxiliary sensing electrodes exhibited a quantitative and theoretical NH3sensing performance at 230–300 or 170–190 °C, respectively; therefore, sensors based on the (Al0.2Zr0.8)20/19Nb(PO4)3solid electrolyte are expected to be promising candidates as NH3detectors that can operate in a wide temperature range of 170–300 °C by changing the auxiliary sensing electrode component.

Catalytic combustion of volatile organic compounds (VOCs) such as ethylene, toluene, and acetaldehyde over novel Pt/CeO2–ZrO2–SnO2/?-Al2O3catalysts prepared by a coprecipitation method was investigated. The introduction of a small amount of SnO2within the CeO2–ZrO2lattice as a promoter was considerably effective to enhance the oxygen release and storage abilities of the catalysts, so that complete oxidation of VOCs was markedly activated. This improvement of the reducibility of the catalyst can be ascribed to the simultaneous reduction of Ce4+and Sn4+in the CeO2–ZrO2–SnO2solid solutions. By the optimization of the composition and the Pt amount, complete oxidation of ethylene, toluene, and acetaldehyde was realized at temperatures as low as 55, 110, and 140 °C over a Pt(10 wt %)/Ce0.68Zr0.17Sn0.15O2.0(16 wt %)/?-Al2O3catalyst, respectively.

Red-emitting (Gd1[?]x[?]yLaxEuy)2O(WO4)2 (0 [?] x [?] 0.05, 0.30 [?] y [?] 0.50) phosphors were synthesized by the conventional solid state reaction method. Single phase gadolinium oxytungstate phosphors with high crystallinity and monoclinic structure were obtained, exhibiting excellent luminescence efficiency under excitation at wavelengths of 394 and 464 nm. The luminescence emission intensities of these phosphors were successfully enhanced by La3+ doping into the host Gd2O(WO4)2 lattice. The highest emission intensity was obtained for (Gd0.56La0.04Eu0.40)2O(WO4)2, of which the emission intensities were 18.9 and 37.0 times higher than those of a commercial (Y0.98Eu0.02)2O2S phosphor under excitation at 394 and 464 nm, respectively.

A novel tetravalent tin (Sn4+) ion conducting solid electrolyte of the NASICON-type, Sn(Nb1[?]xWx)5/(5+x)(PO4)3, was developed. Although Sn4+ has been considered to be an inappropriate ion species for conduction in solids, due to the valence change between +2 and +4 and its high electronegativity, pure Sn4+ ionic conduction in a solid was successfully realized by introducing the higher valency W6+ ion into NASICON-type SnNb(PO4)3 solids. Among the samples prepared, the highest Sn4+ ion conductivity was obtained for the Sn(Nb0.65W0.35)5/5.35(PO4)3 solid.

Excellent oxidation catalysts, which can completely oxidize volatile organic compounds (VOCs) and methane at moderate temperatures, have been prepared. A new concept based on the design of solid electrolytes has been applied to the preparation of the catalysts. By the synergetic effect of precious metals and rare earth oxides, complete oxidation of VOCs and methane into CO2and steam at moderate temperatures has been realized for the present catalysts.

Catalytic activities for direct NO decomposition were investigated on C-type cubic Y2O3–ZrO2and Y2O3–ZrO2–BaO prepared by coprecipitation. Introduction of excess oxide anions in the Y2O3lattice was achieved by partial substitution of the Y3+sites with Zr4+, and high NO decomposition activity was obtained for the (Y0.97Zr0.03)2O3.03catalyst. In addition, the catalytic activity was further enhanced by partial substitution of the Y3+sites in the Y2O3–ZrO2solid solution with Ba2+, and the (Y0.89Zr0.07Ba0.04)2O3.03catalyst exhibited the highest NO decomposition activity among the samples prepared; NO conversion to N2reached 90% at 1173 K in the absence of O2(NO/He atmosphere), and a relatively high conversion ratio was observed even in the presence of O2, H2O, or CO2, compared with the activities of conventional direct NO decomposition catalysts. These results indicate that the C-type cubic Y2O3–ZrO2–BaO catalyst is a new potential candidate for direct NO decomposition.

Trivalent cation conduction has been successfully demonstrated by two strategies. One is crystal structure selection, and the other is the selection of the constituent ions in solids. Since the trivalent cations possess certain ionic volume, a suitable mobile ion pathway should appear in the structure. One candidate structure we selected is a two-dimensional layered structure and the other is a three-dimensional network crystal structure. The selection of the constituent ions in solids is performed by considering the electrostatic interaction between cations and anions in the structure.

phosphor powders of submicrometer particle size were synthesized using an original flux method with a eutectic mixture. The crystal field around the ions was controlled by doping ions into the lattice, which resulted in a superior emission intensity compared to that of our previously developed phosphor, of which the relative emission intensity was 111% that of a commercially available phosphor. The highest emission intensity was successfully obtained by optimizing the composition of the phosphor while maintaining a submicron particle size. The relative green emission reached a maximum intensity for the composition, which was 131% that of . By increasing the crystallinity of the phosphor as well as the crystal field around , the fluorescence quantum yield of the terbium emission for this phosphor became 75%, which is significantly higher than that of (55%).

Tetravalent hafnium ion conducting solid electrolytes with a NASICON-type structure, HfNbP3−xVxO12and Hf1−y/4NbP3−yWyO12, were developed by partially replacing the P5+site in a HfNb(PO4)3solid with larger V5+or W6+ions. Although the Hf4+ion conductivity monotonically increased with increasing V content in the HfNbP3−xVxO12solids, the electronic conduction appeared to be due to the valence change of V5+. In contrast, the Hf1−y/4NbP3−yWyO12series maintained a high ionic transference number, above 0.995 for single-phase NASICON-type samples (y≤ 0.15). The optimum lattice volume for Hf4+conduction was determined to be 1.482 nm3, which was obtained for samples with x= 0.1 or y= 0.05. The Hf395/400NbP2.95W0.05O12solid, which contains the higher valence W6+ion rather than the V5+ion, showed the highest conductivity of 2.8 × 10−4S cm−1at 600 °C, approximately 2.5 times that of HfNb(PO4)3.

A new solid electrolyte type ammonia gas sensor was fabricated by combining the trivalent aluminum cation conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte and the praseodymium ammonium sulfate Pr2(SO4)3*(NH4)2SO4 auxiliary sensing electrode. Since the present sensor showed such a superior sensing performance of quantitative, continuous, and reproducible response with obeying the theoretical Nernst relationship, it is expected to be a practical NH3 gas sensor.

A new solid electrolyte type sulfur dioxide (SO2) gas sensor was developed by the combination of trivalent Al3+ ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid and divalent O2- ion conducting yttria stabilized zirconia (YSZ) with 0.8Gd2O2SO4-0.2NaAl(SO4)2 as an auxiliary sensing electrode. Since the present sensor exhibited such a superior sensing performance of continuous and rapid response obeying the theoretical Nernst relationship, it is greatly expected to be a practical SO2 gas sensing device.

Trivalent rare earth ion conductors of the (R0.05Zr0.95)80/79Nb(PO4)3(R: rare earths) series with NASICON-type structures were successfully prepared and the optimum size of ion-conducting pathways for rare earth ions in (R0.05Zr0.95)80/79Nb(PO4)3solids was investigated. The most suitable ion-conducting pathway for rare earth ion conduction in this series was realized for R=Dy and the highest conductivity of 3.2×10-4S cm-1at 600 °C was obtained for (Dy0.05Zr0.95)80/79Nb(PO4)3solids. Since R3+ion conduction was strongly dependent on the ratio of conducting R3+ion size to crystal lattice size (VR3+/Vlattice; we denote this ratio as Aratio in this article), it was clear that the Aratio is a key factor to optimize R3+ion conduction in NASICON-type structures.

A Ce0.64Zr0.16Bi0.20O1.90solid solution supported on La-stabilized -alumina was prepared by an impregnation method using citrate aqueous solutions. The low-temperature redox activity was demonstrated by the Ce0.64Zr0.16Bi0.20O1.90/Al2O3catalyst, which is effective at low temperatures below 100 °C even after calcination at 1000 °C. Furthermore, the redox activity of the catalyst was promoted by the addition of silver, which is an oxygen permeable component. Partial dissolution of silver ions into the Ce0.64Zr0.16Bi0.20O1.90lattice and the surface deposition of metallic silver were observed for the Ag/Ce0.64Zr0.16Bi0.20O1.90/Al2O3catalyst. By detailed characterization of Ag-supported catalysts using X-ray photoelectron spectroscopy, the reason for the promotion of the redox activity was attributed to both the increase in the defect oxygen species in the near-surface region and the oxygen withdrawal behavior from silver to Ce0.64Zr0.16Bi0.20O1.90/Al2O3.

Abstract.: The ionic conduction of mono-, di-, and trivalent ions in solids is popular in solid state science and the next target ion species to migrate in solids are tetravalent ions. Here, a tetravalent cation conductor which shows high conductivity, comparable to the conductivity range of the representative divalent oxide anion conductors, was artificially designed by strictly selecting the constituent elements and the structure. The tetravalent ion conducting solid electrolyte proposed here shows considerable high ion conductivity and promising applications, such as in rechargeable batteries and chemical sensors for global environmental monitoring, are greatly expected.

A method based on a hydrothermal process was applied to obtain not only ultrafine but also well-dispersed CeO₂ nanoparticles by the application of citric acid as a protective agent against particle growth. The well-defined crystallites have a narrow size distribution, and the mean size and BET specific surface area are 3.1 nm and 211 m2 g−1, respectively. A mixture of the condensation product of boric acid and 2,2'-iminodiethanol (diethanolamine) and cerium oxide nanoparticles has been found to yield turbostratic boron nitride (tBN) coatings on the cerium oxide surface after heating the mixture in a flow of ammonia. Formation of a tBN layer was identified using high-resolution electron microscopy and infrared and X-ray photoelectron spectroscopies. The surface tBN layer was found to be a few nanometres thick with a surface coverage of 51.2%. However, coating of cerium oxide with such a tBN layer is suitable both for whitening the colour whilst maintaining good ultraviolet absorption properties and for restraining the high oxidation activity of cerium oxide.

Solid solutions in the trivalent cationic conducting system (Lu1−xMx)2(WO4)3 (M = Er, Ho, Sm) that crystallize in the Sc2(WO4)3 type structure were prepared and their conducting behaviors were characterized electrochemically. The partial replacement of the Lu³⁺ cation site in (Lu1−xMx)2(WO4)3 by larger M³⁺ cations caused a crystal lattice expansion. Due to the opened ion-migration pathways, the solid solutions generally exhibited an increased cationic conductivity relative to pure Lu2(WO4)3. The ion conductivity can be optimized by substituting the appropriate amount of M³⁺ into (Lu1−xMx)2(WO4)3 in order to adjust the expansion of the migration pathways for the Lu³⁺ cations. Furthermore, a relationship between the average ionic radius of the trivalent cations involved and the ionic conductivity was characterized which makes it possible to predict the composition of the optimum ion-conducting compound in each solid solution system with the Sc2(WO4)3 type structure.

The divalent Mg²⁺ ion conducting solid electrolyte was synthesized with a composite form by intentionally changing the starting material mixing ratio to the nonstoichiometric region. By such a preparation technique, spontaneous and microscopic dispersion of the secondary Zr₂O(PO₄)₂ phase was successfully realized and the Mg²⁺ ion conductivity was considerably enhanced by dispersing the secondary phase, showing the highest conductivity among the Mg²⁺ ionic conducting solid electrolytes reported. The Mg²⁺ migration in the composite solid was clearly demonstrated by dc electrolysis and the Mg²⁺ ion transference number was precisely determined to be unity by a modified Tubandt method. The development of pure Mg²⁺ ion conducting phosphate based solid electrolytes with high stability and considerably high ionic conductivity contributes greatly to opening a new door for the application of advanced materials such as rechargeable batteries and other specific sensor elements.

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