一國 伸之

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

Abstract A highly dispersed carbonate‐intercalated Cu²⁺‐Al³⁺ layered double hydroxide (CuAl LDH) was created on an unreactive α‐Al₂O₃ surface (CuAl LDH@α‐Al₂O₃) via a simple coprecipitation method of Cu²⁺ and Al³⁺ under alkaline conditions in the presence of α‐Al₂O₃. A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl₂O₄ on the surface of α‐Al₂O₃ (CuAlO@α‐Al₂O₃) after calcination at 1073 K in air, as confirmed by powder X‐ray diffraction (XRD) and Cu K‐edge X‐ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in‐situ temperature‐programmed synchrotron XRD (tp‐SXRD). The layered structure of CuAl LDH@α‐Al₂O₃ completely disappeared at 473 K, and CuO or CuAl₂O₄ phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α‐Al₂O₃ catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1‐phenylethanol dehydrogenation. The results suggested that Cu⁰ was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.

Various alkylcarboxylate-intercalated layered yttrium hydroxides (Cn-1H2n-1COO-/Y-layered rare-earth hydroxide (LRH), n = 1-10) were synthesised by a simple anion exchange method using Cl-/Y-LRH as a parent material. The anion exchange from Cl- into CH3COO- proceeded rapidly, as confirmed by the time-resolved synchrotron-radiation X-ray diffraction (t-SXRD) analysis. The interlayer distance of Cn-1H2n-1COO-/Y-LRH could be controlled precisely, and the basal spacings calculated from XRD were linearly proportional to the length of alkyl groups. In water solvent, the basal spacing of the CH3COO-/Y-LRH catalyst based on the (00l) plane increased from 1.00 nm under dry conditions to 1.35 nm, and this lifted-up layered structure was generated immediately. By use of the CH3COO-/Y-LRH catalyst, a wide range of substrates were converted into the corresponding alpha,beta-unsaturated nitriles in water via Knoevenagel condensation. Our synthesised heterogeneous catalyst acted as a Bronsted base for this organic transformation, and it was reusable without any loss of its catalytic activity and selectivity.

Pt<italic>_n</italic> subnanoclusters (<italic>n</italic> = 3–9) on a carbon substrate exhibit 1.6–2.2 times higher activity than the standard Pt/C catalysts. EXAFS experiments and DFT calculations show plausible structures and energetics for reaction intermediates in the processes.

This study aims to investigate the behavior of photoexcited electrons in intentionally distorted Ba-doped NaTaO3 photocatalysts with time-resolved microwave conductivity and steady-state IR absorption induced by UV light. As probed by X-ray absorption fine structure and Raman spectroscopies, doping NaTaO3 with Ba2+ produces structural nonperiodicity and distorts the octahedral sublattice, proposedly resulting in the formation of electron traps. A higher density of shallow electron traps is suggested to be responsible for the longer electron lifetime and larger electron population, because shallowly trapped electrons are less likely to recombine with holes. The half-lifetime of photoexcited electrons is considerably long, even longer than 0.8 ms in the Ba-doped NaTaO3 sample with moderate distortion. The population of photoexcited electrons under Hg-Xe lamp irradiation increases by 32 times in this sample compared to that in undoped NaTaO3, generating H-2/O-2 mixtures with the rates of 385 mu mol h(-1) (H-2) and 180 mu mol h(-1) (O-2) when irradiated with a Hg lamp in the absence of cocatalyst and sacrificial compound. Moderate distortion seems favorable to produce shallow electron traps in comparison to large and small distortions, leading to the highest water splitting rate. The orders of photocatalysts based on their electron lifetime, electron population, and water splitting rate are identical, indicating that the photoexcited electrons worked in the water splitting reactions.

Ni3Sn2/TiO2 alloy catalyst prepared by hydrothermal method was applied for the direct one-pot reductive imination of benzaldehyde with nitrobenzene in the presence of H2 gas as a reducing agent. A desired imine, benzylideneaniline, was produced in an excellent yield of 90% without the formation of any by-products. This is due to the chemoselective molecular recognition of Ni3Sn2 alloy nanoparticles supported on TiO2 for the nitro group over the carbonyl group. By prolonging the reaction time, the desired imine was converted into the corresponding secondary amine, N-phenylbenzylamine, with a remarkably high yield of 80% through the catalytic hydrogenation of the C??N bond. Finally, we demonstrated that it was easy to reuse the catalyst up to five times.

NaTaO3, a semiconductor with a perovskite structure, has long been known as a highly active photocatalyst for overall water splitting when appropriately doped with La cations. A profound understanding of the surface feature and why and how it may control the water splitting activity is critical because redox reactions take place at the surface. One surface feature characteristic of La-doped NaTaO3 is a La-rich layer (shell) capping La-poor bulk (core). In this study, we investigate the role of the shell in core-shell-structured La-doped NaTaO3 through systematic chemical etching with an aqueous HF solution. We find that the La-rich shell plays a role in electron-hole recombination, electron mobility and water splitting activity. The shallow electron traps populating the La-rich shell trap the photoexcited electrons, decreasing their mobility. The shallowly trapped electrons remain reactive and are readily available on the surface to be extracted by the cocatalysts for the reduction reaction evolving H-2. The presently employed chemical etching method also confirms the presence of a La concentration gradient in the core that regulates the steady-state electron population and water splitting activity. Here, we successfully reveal the nanoarchitecture-photoactivity relationship of core-shell-structured La-doped NaTaO3 that thereby allows tuning of the surface features and spatial distribution of dopants to increase the concentration of photoexcited electrons and therefore the water splitting activity. By recognizing the key factors that control the photocatalytic properties of a highly active catalyst, we can then devise proper strategies to design new photocatalyst materials with breakthrough performances.

© 2019 Elsevier B.V. Supported MnOx nanocluster was prepared by PVP-stabilized Mn colloid as a precursor. Obtained catalysts were applied for 1-phenylethanol oxidation to produce acetophenone. Consequently, prepared catalysts were active for the oxidation of 1-phenylethanol using molecular oxygen without any additives such as base reagents. XAFS and TEM measurements revealed that the valence of manganese oxide and cluster size of manganese oxide on prepared catalysts can be controlled. In addition, the chemical state of Mn species varied with the loading amount of Mn.

Understanding the science behind highly active materials is essential for advancement in the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO3) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of the water-splitting activity to the spatial La distribution are discussed. The spatial distribution of La cations placed at the Na site was found to dictate the energy gradient of the conduction band bottom (CBB), resulting in a tunable electron population and hence water-splitting activity. A less homogeneous sample with a sufficiently large CBB gradient exhibited higher water-splitting activity. The mechanism of gradient tuning of the CBB through controlling the spatial dopant distribution is expected to be applicable to a broad range of metal oxide perovskites for artificial photosynthesis.

NaTaO3 doubly doped with La and transition metal cations has been of interest for photocatalytic water splitting under visible light. However, there is not yet convincing evidence to propose a plausible structure for the dopant pair incorporated in the NaTaO3 host. In this study, efforts were made to reveal the local structure of La and Fe cations doped in NaTaO3. For this purpose, we employed X-ray absorption spectroscopy, including extended X-ray absorption fine structure and X-ray absorption near-edge structure. It was revealed that upon double doping, La cations occupied the Na-sites, whereas Fe cations occupied the Ta-sites. A LaFeO3-NaTaO3 solid solution was formed accordingly, together with a trace amount of iron oxide impurities. The solid solution was able to absorb visible light to produce electrons. A volcano-shaped pattern of the electron population with respect to the dopant concentration was present, in which 2 + 2 mol% gave the highest electron population.

Amphoteric YNbO4 was synthesized by the simple coprecipitation using (NH4)(3)[Nb(O-2)(4)] and Y(NO3)(3), and examined as a new solid acid-base bifunctional catalyst for various reactions including aqueous-phase conversion of glucose to lactic acid. After drying the white precipitate at 353 K for 3 h, the resultant oxide is an amorphous YNbO4 with high densities of Lewis acid sites (0.18 mmol g(-1)) and base sites (0.38 mmol g(-1)). Negatively-charged lattice oxygen of amorphous YNbO4 functioned as Lewis base sites that promote a Claisen-Schmidt-type condensation reaction with acetylacetone and benzaldehyde with comparable activity to reference catalysts. Amorphous YNbO4 can also be applicable to the production of lactic acid from glucose in water, which gives relatively high yields (19.6 %) compared with other reference catalysts. Mechanistic studies using glucose-1-d and H-2 nuclear magnetic resonance spectroscopy (NMR) revealed that YNbO4 first converts glucose to two carbohydrates (glyceraldehyde and pyruvaldehyde) through dehydration via the formation of 3-deoxyglucosone and subsequent retro-aldolization, and these intermediates are then converted to lactic acid by both dehydration and isomerization through hydride transfer.

Strontium titanate, SrTiO3, with the perovskite ABO(3)structure is known as one of the most efficient photocatalyst materials for the overall water splitting reaction. Doping with appropriate metal cations at the A site or at the B site substantially increases the quantum yield to split water into H(2)and O-2. The site occupied by the guest dopant in the SrTiO(3)host thus plays a key role in dictating the water splitting activity. However, little is known about the detailed structure of the dopant site in the host lattice. In this study, the local structure of In(3+)cations, which were shown to improve the water splitting activity of SrTiO3, is investigated with X-ray absorption fine structure spectroscopy and density functional theory (DFT) calculations. The In(3+)cations exclusively substitute for Ti(4+)cations at the B site to form InO(6)octahedra. Further optical experiments using UV-Vis diffuse reflectance spectroscopy and DFT calculations of the density of states indicate that the substitution of In(3+)for Ti(4+)does not alter the band structure and bandgap energy (remaining at 3.2 eV). The mechanism underlying the increased water splitting activity is discussed in relation to occupation of the B site by In(3+)cations.

Perovskite-structured tantalates, NaTaO3 in particular, have been at the forefront of solar energy conversion to generate hydrogen fuel via photocatalytic water splitting. However, their application as a photocatalyst remains impractical due to their inability to absorb long-wavelength light. One promising scheme for extending the material response to long-wavelength light is via the charge compensation of doped cations with lanthanum and a transition metal. In this research, NaTaO3 is doubly doped with lanthanum and manganese, a 3d-block transition metal, for visible-light sensitization. Following the double doping, the light absorption is extended to the near-infrared region. The doubly doped samples not only strongly absorb visible light but also produce electrons under visible-light irradiation (420 < ( )lambda < 740 nm). EDX confirms the one-to-one ratio of dopant incorporation, and nanometer-resolution elemental mapping with TEM demonstrating that La and Mn are incorporated at approximately the same location in the particles. EXAFS furthermore reveals that La occupies the Na site, while Mn occupies the Ta site. These findings suggest that La pairs with Mn at the neighboring site to form a LaMnO3-NaTaO3 solid solution.

KTaO3 was doped with Sr cations, and its photocatalytic activity for the overall water splitting was investigated. By doping with Sr, a Sr-rich shell was formed over a Sr-poor core. Extended X-ray absorption fine structure spectroscopy revealed the simultaneous occupation of the K sites and Ta sites by Sr cations. A concentration gradient of Sr cations occupying the Ta sites was suggested to be produced after doping with Sr. The concentration gradient of Sr cations simultaneously induced an energy gradient of the conduction band edge bottom. Hence, photoexcited electrons are separated, which are driven away to the bulk by the energy gradient, from the complementary holes present on the surface. The higher the Sr cation concentration, the higher the energy gradient produced. Thus, the electron-hole separation is improved and the electron population accordingly increases with the increase in the Sr cation concentration. Nevertheless, the increase in the Sr cation concentration led to the decrease in the water splitting activity. The highest water splitting activity was observed for bare KTaO3. The decreased water splitting activity was proposed to be primarily due to the blockage of the electron transfer to the cocatalysts by the Sr-rich shell and the poor O-2 evolution ability of the Sr-rich shell.

Ni3Sn2 alloy catalysts supported on various metal oxides (TiO2, Al2O3, ZrO2, SnO2, and CeO2) were successfully prepared by simple hydrothermal method and then applied to the hydrogenation of 4-nitrostyrene under H-2 3.0 MPa at 423 K. All the supported catalysts hydrogenated the nitro group more preferentially than the olefin group from the initial reaction stages, showing 100% chemoselectivities towards the desired 4-aminostyrene. This may be attributed to sigma-interaction between the oxygen lone pairs in the nitro group and Sn atoms in Ni3Sn2 alloy. By prolonging the reaction times, the 4-aminostyrene yields increased and finally reached the maximum yields. Among the catalysts, Ni3Sn2/TiO2 alloy catalyst showed the highest catalytic activity with remarkably high chemoselectivity towards 4-aminostyrene. The conversion and chemoselectivity were 100% and 79%, respectively, at a reaction time of only 2.5 h. From the physical and chemical characterization of the supported catalysts, it was clear that the catalytic activity was correlated with H-2 uptake. The application of the best catalyst for the hydrogenation of a wide variety of substituted nitroarenes resulted in the chemoselective formation of the corresponding aminoarenes.

Single-size platinum Pt-6 subnanoclusters exhibit superior mass-specific and surface-specific activities for the oxygen reduction reaction. The enhanced activity is attributed to polarized electron distributions based on rigorous structure characterization by X-ray absorption fine structure spectroscopy and density functional theory.

Ni-Sn alloy catalysts were prepared and applied to the hydrogenation of 4-nitrostyrene at 383-423K using H-2 gas as the hydrogen donor. Ni3Sn2 alloy showed a significantly high conversion and selectivity towards 4-aminostyrene (Conv. 100%, Sel. 99%). Various unsaturated nitro compounds were also successfully converted into their corresponding unsaturated amines.

We successfully prepared Pd-containing perovskite strontium titanate (Pd-STO) by a relatively low-temperature hydrothermal method (i.e., 373 K) without posterior calcination. The particle size and porosity of the STO perovskite could be tuned by changing the molar ratio of H2O/NH3 (e.g., 5.0, 12.5 and 25.0) during the preparation of the amorphous titania sources. The mesoporous contained Pd-STO(12.5) showed superior catalytic performance compared to that of the other Pd-STO(x) (x = H2O/NH3) perovskites for alcohol oxidation with molecular oxygen. Both the refluxing of the non-polar solvents and addition of molecular sieves enhanced the reaction yield significantly. The Pd-incorporated perovskite (Pd-STO) showed better recyclability compared with that of the impregnated perovskite (imp-Pd/STO).

Catalytically active and stable catalysts are highly desirable for the acceptorless dehydrogenation (AD) of alcohols. Herein, we developed Cu-Fe catalysts prepared from Cu-Fe layered double hydroxide (LDH) precursors. These Cu-Fe catalysts exhibited outstanding activity and selectivity for the AD of various alcohols under oxidant- and base-free conditions and can be steadily reused for up to 5 consecutive runs with no loss of activity.

Sodium tantalate, NaTaO3, is one of the best semiconductors for photocatalytic water splitting and CO2 reduction. Doping with metal cations is crucial for enhancing the quantum efficiency of the desired reactions. Nevertheless, details related to the doping of the host metal oxide and activation by guest metal cations are not sufficiently known. The most fundamental question concerns the increase in the quantum efficiency via doping with guest cations that are impurities in the host lattice. In this study, the local environment of Sr cations, which are the typically used guest cations in NaTaO3, was characterized by extended X-ray absorption fine structure spectroscopy. The results reveal the presence of two Sr-O shells in the Sr-doped NaTaO3 photocatalysts. The small shell with an unexpectedly short Sr-O bond length of 1.96 Å corresponds to SrO6 octahedra embedded in the corner-shared network of TaO6 octahedra. The other shell with a Sr-O bond length of 2.60 Å corresponds to SrO12 cuboctahedra with Sr cations at positions previously occupied by Na cations. Rietveld analysis of the X-ray diffraction data confirmed the formation of a NaTaO3-Sr(Sr1/3Ta2/3)O3 solid solution to accommodate the two Sr-O shells in NaTaO3 with no requirement for creating oxygen anion vacancies. Mechanisms for increasing the quantum efficiency via doping with Sr cations are discussed in the context of the revealed environment.

A Ni-Y2O3 catalyst containing ruthenium (Ru/Ni-Y2O3) was synthesized and applied to the hydrogenolysis of tetrahydrofurfuryl alcohol (THFA) to produce 1,5-pentanediol (1,5-PeD), which showed superior catalytic performance over that of the Ni-Y2O3 catalyst itself. The optimized ruthenium-containing catalyst, which was prepared by impregnation of 1.0 wt% ruthenium in Ni-Y2O3, showed high catalytic activity for producing 1,5-PeD, giving an 86.5% yield at 93.4% conversion of THFA under 2.0 MPa of H-2 at 423 K after 40 h. The formation of Ru-Ni-0-Y2O3 boundaries was proposed to accelerate the C-O bond scission of the tetrahydrofuran ring to give 1,5-PeD.

The addition of Y2O3 into Ni formed a composite catalyst that selectively produced 1,5-pentanediol rather than 1,2-pentanediol in the hydrogenolysis of furfuryl alcohol at 2.0 MPa H-2 and 423 K. Clearly, 1,5-pentanediol was produced over the Ni-0-Y2O3 boundary. This report highlights the properties of Ni-Y2O3, catalytic performance, and reaction route in the synthesis of 1,5-pentanediol from furfuryl alcohol.

Highly catalytic performance of La2O3 in transfer hydrogenation reactions was achieved following pretreatment involving a sequence of heat treatments under different atmospheric gases. Furfural (FFR) was converted to furfuryl alcohol (FFA) in a very selective manner (98% conversion, with 96% selectivity) using La2O3 that had been calcined under air at 923K and treated under H2 at 673 K. Strongly basic sites and weakly acidic sites were generated after heat pretreatment.

<p>Ni–Fe alloy catalysts prepared by a simple hydrothermal method and subsequent H₂ treatment were shown to be highly selective for the hydrogenation of various unsaturated carbonyls.</p>

Ni-M (M = Y or La)-catalyzed hydrogenolysis of furfural (FFR) to produce 1,5-pentanediol (1,5-PeD) has been developed through the formation of tetrahydrofurfuryl alcohol (THFA) as an intermediate product. Ni(0)-Y2O3 or Ni(0)-La(OH)(3) composite catalysts executed cleavage of the C-O bond of THFA, giving 1,5-PeD with remarkably high selectivity. Consecutive reactions including hydrogenation of the C=O and C=C bonds and subsequent hydrogenolysis of the C-O bond were performed.

<p>Efficient Ni-Fe alloy catalysts prepared by environmentally friendly method exhibited high selectivity in the hydrogenation of furfural (FFald) to give 95% yield of furfuryl alcohol (FFalc) under 1 MPa of H₂ at 423 K using Ni-Fe(2-1) hydrogen treated at 673 K catalyst (denoted as Ni-Fe(2-1)HT-673) within 3 h. No significant loss of catalytic activity after 4 running cycles showed a high stability of the catalysts on furfural hydrogenation.</p>

<p>[Rh(OH)₆]³⁻ intercalated Ni–Zn mixed basic salt (Rh/NiZn) acts as an efficient catalyst for the hydrophenylation of internal alkynes with arylboronic acids under mild conditions.</p>

<p>Efficient hydrogenation of levulinic acid (LA) into γ-valerolactone (GVL) in water using supported Ni–Sn(1.4)/AlOH consisting of Ni₃Sn₂ alloy species was achieved with high selectivity towards GVL and the catalyst could be reused without any significant loss of activity and selectivity.</p>

The formation of polyiodine complexes was investigated in a photocurable poly(vinyl alcohol) modified N-methyl-4(4-formylstyryl)pyridinium methosulfate acetal (PVA-SbQ), which is a photofunctional group that causes photodimerization. PVA-SbQ films with polyiodine complexes were prepared to be photocured, iodinated and soaked in a boric acid solution. The formation of PVA-polyiodine complexes was studied during iodinating and while in the boric acid treatment through UV-vis absorption spectrometry, resonance Raman spectrometry and IR absorption spectrometry. As a result, polyiodines were formed in the photocurable PVA-SbQ films, and the formation of PVA-polyiodine complexes was enhanced by boric acid treatment. It was found that the SbQ-ratio of PVA-SbQ affects the formation of PVA-polyiodine complexes. The photocrosslinking by the dimerization of SbQ groups helps to form the PVA-I-5(-) complex during the boric acid treatment. Based on this effect, we demonstrated a unique recording method by the PVA-polyiodine complex formation. The PVA-SbQ film cured by the irradiation of the liner polarized light showed that dichroism of the PVA-polyiodine complexes formed after iodination. Copyright (c) 2015 John Wiley & Sons, Ltd.