野崎 安衣

Pt is an excellent and widely used hydrogen evolution reaction (HER) catalyst. However, it is a rare and expensive metal, and alternative catalysts are being sought to facilitate the hydrogen economy. As tungsten carbide (WC) has a Pt-like occupied density of states, it is expected to exhibit catalytic activity. However, unlike Pt, excellent catalytic activity has not yet been observed for mono WC. One of the intrinsic differences between WC and Pt is in their magnetic properties; WC is non-magnetic, whereas Pt exhibits high magnetic susceptibility. In this study, the WC lattice was doped with ferromagnetic Co nanocrystals to introduce an ordered-spin atomic configuration. The catalytic activity of the Co-doped WC was ~30% higher than that of Pt nanoparticles for the HER during the hydrolysis of ammonia borane (NH3BH3), which is currently attracting attention as a hydrogen fuel source. Measurements of the magnetisation, enthalpy of adsorption, and activation energy indicated that the synergistic effect of the WC matrix promoting hydrolytic cleavage of NH3BH3and the ferromagnetic Co crystals interacting with the nucleus spin of the protons was responsible for the enhanced catalytic activity. This study presents a new catalyst design strategy based on the concept of an internal magnetic field. The WC-Co material presented here is expected to have a wide range of applications as an HER catalyst.

In recent years, chemical hydrogen storage systems utilizing compounds with a high hydrogen capacity have attracted significant attention. In the present study, Ru-Fe supported on porous CeO2 was prepared for application in hydrogen generation systems using ammonia borane. The catalytic activity of the material for partial oxidation was elucidated. Specifically, the oxidation pathway was evaluated by thermodynamic calculations using the Ru-Fe-O ternary phase diagram. It was determined that the Ru-Fe alloy exhibited enhanced catalytic activity compared to pure Ru particles. In the alloy, the Ru component was self-organized, forming nailed particles in the oxidation films during preferential oxidation of Fe. The exposed nailed Ru particles prevented self-aggregation and coarsening, which was proposed as one of the reasons for the excellent catalytic activity. Moreover, it was speculated that in the exposed Ru-Fe alloy matrices, the density of states in the vicinity of the Fermi level was high due to the charge transfer from Fe to Ru. This meant that the number of molecular levels contributing to the catalytic reaction increased. It was concluded that a synergistic effect of the intrinsic charge state of the Ru-Fe alloy and the self-organized Ru assembly in the oxidation film resulted in remarkable catalytic activity.

Amorphous alloys are advantageous to obtain excellent catalytic activity from a disordered atomic arrangement and more dangling bonds. The compositional range of the Ni-B amorphous alloy was thermodynamically predicted. The function of the Gibbs energy of mixing. Delta(mix) G(Ni-B)(liquid), and the activities of the Ni and B components, a(Niin amor.), and, a(Bin amor), of the liquid phase was extrapolated to room temperature. The negative Delta(mix) G(Ni-B)(liquid) was found from X-Ni = 0.45 to 0.92, indicating the existence of the liquid phase as metastable state, i.e. formation of amorphous alloy. The small a(Niin amor.), and, a(Bin amor) that is, the strong attractive interaction between the Ni and B components suggested the liquid phase structure was stable. The Ni-B amorphous alloys were prepared from aqueous solution using reducing agent consistent well with the thermodynamic prediction. The preparation method from aqueous solution was useful to prevent from thermal migration of the atoms toward the equilibrium state. The quasi equilibrium oxygen pressures, po(2)(Ni-in amor), and, po(2)(B-in amor), of Ni and B components in the amorphous alloys were evaluated froma(Niin amor.), and, a(Bin amor.).Po-2(B-in amor) was found to be smaller than po(2)(Ni-in amor), revealing that B components in amorphous alloy were preferentially oxidized and inhibited Ni oxidation. Not only a characteristic disordered atomic arrangement but also chemical alloying effect of B results in the excellent catalytic activity of the Ni-B alloy.

The electrodeposition of Fe-Al alloy in AlCl3-NaCl-KCl-FeCl2 quaternary molten salts was investigated by potentiostatic electrolysis to prepare Fe-Al alloy film with a thermoelectric conversion function. In the AlCl3-NaCl-KCl-FeCl2 molten salts with an AlCl3/FeCl2 mole ratio of 200 (FeCl2: 32.6 mmol l(-1)), the electrodeposited Al formed a solid solution with Fe in the potential range from 0.5 to 0.2 V vs Al(III)/Al and formed the intermetallic compound of Fe3Al at the potential of 0.1 V. Fe-Al alloys containing 0.8-34.5 mol% Al were obtained by controlling the AlCl3/FeCl2 mole ratio (FeCl2 concentration) in AlCl3-NaCl-KCl-FeCl2 molten salts and the applied potential in the potential range from 0.2 to -0.1 V vs Al(III)/Al. The Fe-Al alloy films prepared in the present study exhibited the p- or n-type thermoelectric conversion, depending on their composition.

The standard Gibbs energies of formation, Delta(f)G(o), of CrB4, CrB2, Cr3B4, Cr5B3, and CrBO3 existing along the oxidation path of Cr-B binary alloy were determined using the electromotive forces of galvanic cell composed of the ZrO2-Y2O3 solid electrolyte. The electromotive force showed plateaus and decreases in the process that CrB4-CrB2 two-phase alloy used for the cell materials were oxidized via two- and three-phase regions along its oxidation path. From the plateaus of electromotive forces corresponding to the cell materials in the three-phase regions, the values of Delta(f)G(o)(CrB4), Delta(f)G(o)(CrB2), Delta(f)G(o)(Cr3B4), Delta(f)G(o)(Cr5B3), and Delta(f)G(o)(CrBO3) in the temperature range from 1273 to 1346 K were determined as follows:Delta(f)G(o)(CrB4)/J (mol of compd.)(-1) = 167500 - 261.2 T +/- 7200Delta(f)G(o)(CrB2)/J (mol of compd.)(-1) = -21020 - 79.22 T +/- 2100Delta(f)G(o)(Cr3B4)/J (mol of compd.)(-1) = -173400 - 95.47 T +/- 2500Delta(f)G(o)(Cr5B3)/compd.)(-1) = -318900 + 20.64 T +/- 5800Delta(f)G(o)(CrBO3)/J (mol of compd.)(-1) = -958800 + 59.24 T +/- 4100The Delta(f)G(o) values determined in the present study satisfied the phase equilibria in the Cr-B binary system. Using the determined Delta(f)G(o) values, the composition-oxygen partial pressure diagram of the Cr-B-O system was constructed under the conditions at 1300 K and a total pressure of 1 bar (100 kPa). It is useful to understand the oxidation property of the Cr-B binary alloys.

Amorphous alloys are still attracting great attention in the field of catalysis despite the fact that they have been investigated since the 1950s. One of the reasons why amorphous alloys have been in the spotlight until now, are their physical and chemical properties, which would make them suitable materials to be used as catalysts at industrial scale. This review deals with the recent research on applications of amorphous alloys for catalysis. These investigations were addressed to elucidate the relationship between the structural changes (morphology, surface-exposed metal sites, etc.) and the catalytic activity for representative reactions such as hydrogenations, oxidations and hydrogen production from hydrogen carrier molecules. Furthermore, the impact of the combination of an amorphous alloy with another kind of material (MOF and CeO2) and the introduction of a third metal was also discussed.

The relationship between preparation method and the catalytic activity as well as reusability for Pd-CeO2 catalyst was investigated. Pddispersed CeO2 prepared from dealloying in NaOH aqueous solution of a Pd-Ce-Al ternary amorphous alloy as a precursor. The dealloying proceeded by active dissolution of Al and Ce to form sodium aluminate ion, Na[Al(OH4)](aq), and CeO2 particles, respectively. At the same time, Pd acting as cathode resulted in directly to be metallic nailed-particles exposing partly from the matrices of the CeO2 particles. Its catalytic activity and reusability as a function of its surface area of exposed-Pd as well as sample surface area were investigated, compared with those of Pd-supported CeO2 which was prepared by conventional liquid phase reduction. Pd-dispersed CeO2 was higher in exposed Pd surface area than Pd-supported CeO2 despite its lower sample surface area. It is likely that the nailed Pd on the CeO2 prevents themselves from aggregation during sample preparation and reusability study. As a result, in the oxidation reaction of methyl benzyl alcohol, Pd-dispersed CeO2 showed higher catalytic activity and reusability than Pd-supported CeO2. The oxidation reaction of methyl benzyl alcohol is a measure of the oxidative decomposition reaction of harmful substances. Pd-dispersed CeO2 is expected to be widely used for the oxidative decomposition reaction of harmful substances.

The standard Gibbs energies of formation, Delta(f)G degrees, of intermediate compounds of Cr3B4, CrB2, and CrB4 in the boron-rich side of the Cr-B binary system were determined by measuring electromotive forces of the galvanic cells using ZrO2-Y2O3 solid electrolyte. The phase equilibria for the Cr-B binary system were clarified to construct the cells using the solid electrolyte. The measured electromotive forces of the cells were evaluated as linear temperature functions under the conditions that the transport numbers of oxide ion in solid electrolyte were regarded as 1.0. The Delta(f)G degrees functions determined from the electromotive forces via the Nernst equation were as follows:Delta(f)G degrees(Cr3B4)/J (mol of compd)(-1) = -264540 - 26.697 T +/- 970 (1256-1322 K),Delta(f)G degrees(CrB2)/J (mol of compd)(-1) = -84572 - 32.442 T +/- 790 (1253-1350 K),Delta(f)G degrees(CrB4)/J (mol of compd)(-1) = -105120 - 57.921 T +/- 2200 (1280-1352 K).The present Delta(f)G degrees values satisfied the phase equilibria in the Cr-B binary system. Using the Delta(f)G degrees values determined in the present study, the composition-oxygen partial pressure diagram of the Cr B-O ternary system was constructed under the conditions of 1300 K and a total pressure of 1 bar (100 kPa). It is useful to understand the oxidation path of the boron-rich side of Cr-B binary alloys.

© 2019 The Japan Institute of Metals and Materials Nanoporous CeO2 was prepared implementing the dealloying method on precursors consisting of CeAl alloys characterized by different atomic arrangements. In fact, the atomic arrangement of the precursor alloy strongly influence the surface area of CeO2 in the final product. Nanoporous CeO2 with quite high surface area were formed when an amorphous CeAl alloy was used as the precursor. The catalytic performance of the catalyst that Ni was supported on CeO2 prepared from amorphous alloy were evaluated based on the reaction whereby molecular hydrogen is released from ammonia borane. A high level of catalytic activity was observed due to that fine Ni particles were dispersed on CeO2 prepared from amorphous alloy with quite high surface area.

© 2019 Iron and Steel Institute of Japan. All rights reserved. Synopsis : Skeletal Ni catalysts were prepared by the combined process of thermal treatment, mechanical milling, and dealloying using Ni40Ti60 amorphous alloy as a starting material. The influence of processing sequence on the catalytic activity of the prepared catalyst was investigated. The skeletal Ni catalyst prepared via i) thermal treatment at around the crystallization temperature (ca. 743 K), ii) mechanical milling, iii) dealloying by immersion in 1.0 mol/L HF aqueous solution showed the highest catalytic activity in the dehydrogenation reaction from ammonia borane compared with other skeletal Ni analogues prepared via different processing sequences. Thermal treatment around the crystallization temperature caused atomic rearrangement, which lead to a formation of electron-deficient Ni species on the surface of skeletal Ni alloy after dealloying treatment. SEM morphological observation and surface-area measurement indicated that thermal treatment decreased mechanical strength of the Ni-Ti alloy and that mechanical milling allowed the formation of finer Ni-Ti particles, which facilitated the formation of high-surface-area skeletal Ni after dealloying treatment. We found that processing sequence on Ni-Ti amorphous alloy made drastic impacts on surface area and electronic state of the resulting skeletal Ni, which consequently affected the catalytic performance in the dehydrogenation reaction.

© 2019 The Japan Institute of Metals and Materials. CeO2 supports were prepared via a dealloying method from amorphous alloy. The activities of Ru/CeO2 catalysts were examined in the hydrogen generation reaction from ammonia borane. To investigate the effects of atomic arrangement of CeO2 precursor on the activities of Ru/ CeO2 catalysts, CeO2 supports were prepared from amorphous alloys and crystalline alloys. The use of amorphous alloys as the precursor of CeO2 created fine porous structures, resulting in high catalytic activities of Ru/CeO2 catalysts.

©2018 The Japan Institute of Metals and Materials. The thermodynamic properties for Nd 2 (MoO 4 ) 3 were investigated. Nd 2 (MoO 4 ) 3 is one of the end member of the yellow phases which are known as hygroscopic harmful phases in the nuclear fuel waste glasses. The standard molar entropy, T0 S m , at 298.15 K of Nd 2 (MoO 4 ) 3 was determined by measuring its isobaric heat capacities, C p; m, from 2 K via the fitting functions including the Debye-Einstein formula and electronic- as well as magnetic terms. The Neel temperature, T N , estimated by extrapolating the magnetic-term in the fitting function. Its standard Gibbs energy of formation, f G m , was determined by combining T0 S m datum with the standard enthalpy of formation, f H m , which were estimated from ones for Ce 2 (MoO 4 ) 3 and Sm 2 (MoO 4 ) 3 . The unknown standard Gibbs energy of solution, sol G m , at 298.15 K of Nd 2 (MoO 4 ) 3 was predicted from the reference data for MoO 421 (aq) and Nd 3+ (aq). The obtained thermodynamic values are as follows: T0 S m (Nd 2 (MoO 4 ) 3 (cr), 298.15 K)/(J K 11 mol 11 ) = 439.29 « 4.39 f G m (Nd 2 (MoO 4 ) 3 (cr), 298.15 K)/(kJ mol 11 ) = 1 4072.13 « 6.14 sol G m (Nd 2 (MoO 4 ) 3 , 298.15 K)/(kJ (mol of MoO 421 (aq)) 11 ) = 73.12 « 2.33 T N /K = 1.55 « 0.16 The data obtained in the present work are expected to be useful for geochemical simulations of the diffusion of radioactive elements through underground water. [doi:10.2320/matertrans.M2018305]

© 2018 Elsevier Ltd The standard molar entropyΔ0TSm°, at 298.15 K of MgMoO4(cr) of the end-members of the yellow phases formed in the nuclear fuel waste glasses was determined by measuring Cp,m° at the temperature of 2 K and above using the most recent Debye-Einstein formula. The Δ0TSm° data obtained in our previous study for SrMoO4(cr) and BaMoO4(cr) were re-evaluated using this most recent formula. The standard Gibbs free energies of formation, ΔfGm°, of MgMoO4, SrMoO4(cr) and BaMoO4(cr) were determined by combining the Δ0TSm° data with the reference data for the standard enthalpy of formation,ΔfHm°. The ΔfGm° of MoO42−(aq) was updated from the thermodynamic cycle based on the data obtained in the present work. The unknown standard Gibbs free energy of solution, ΔslnGm°, and the solubility product, Ks, at 298.15 K for MgMoO4 were predicted. The thermodynamic values were obtained as follows: Δ0TSm°(MgMoO4(cr), 298.15 K)/(J K−1 mol−1) = 119.11 ± 1.19; Δ0TSm°(SrMoO4(cr), 298.15 K)/(J K−1 mol−1) = 136.44 ± 1.36; Δ0TSm°(BaMoO4(cr), 298.15 K)/(J K−1 mol−1) = 152.61 ± 1.53; ΔfGm°(MgMoO4(cr), 298.15 K)/(kJ mol−1) = −1295.73 ± 0.91; ΔfGm°(SrMoO4(cr), 298.15 K)/(kJ mol−1) = −1441.32 ± 1.36; ΔfGm°(BaMoO4(cr), 298.15 K)/(kJ mol−1) = −1443.29 ± 1.33; ΔfGm°(MoO42−(aq), 298.15 K)/(kJ mol−1) = −836.63 ± 0.97. ΔslnGm°(MgMoO4(aq),298.15 K)/(kJ (mol of MoO42−(aq))−1) = 3.72 ± 1.88. Ks(MgMoO4(aq), 298.15) = 2.23×10−1 ± 4.46×10−2 The thermodynamic data obtained in this work are expected to be useful for nuclear fuel waste safety management.

© 2018 American Chemical Society. Au-CeO2 catalysts are prepared from amorphous Ce-Al alloys by the dealloying method, and their catalytic performances are examined in the oxidation of benzyl alcohol to benzaldehyde using O2 as an oxidant. The catalytic activity of the Au-CeO2 catalysts is improved using an amorphous alloy as a precursor, and further improved activity is attained by directly alloying Au with Ce-Al rather than by depositing Au on preformed CeO2. Consequently, Au-CeO2 prepared directly from an amorphous Au-Ce-Al alloy exhibits the highest activity among the prepared samples, despite its low surface area. Detailed characterization by means of XPS analysis indicates that most of the Au species in Au-CeO2 prepared from the amorphous Au-Ce-Al alloy exist in a +1 oxidation state (Au+). The presence of Au+ facilitates the migration of oxygen atoms through the lattice, which likely contributes to the high catalytic activity of the Au-CeO2 catalyst.

© 2018, Springer-Verlag GmbH Austria, part of Springer Nature. Abstract: The thermodynamic properties for Sm2(MoO4)3were investigated. Sm2(MoO4)3is the one of the yellow phase-related substances. Yellow phases are known as hygroscopic harmful phases in the nuclear fuel glasses. The standard molar entropy, Δ0TSm∘, at 298.15 K of Sm2(MoO4)3was determined by measuring its isobaric heat capacities, Cp,m∘, from 2 K via the fitting functions including the Debye–Einstein formula and electronic as well as magnetic terms. The Néel temperature, TN, was estimated by extrapolating the magnetic term in the fitting function. Its standard Gibbs energy of formation, ΔfGm∘, was determined by combining the obtained Δ0TSm∘ datum with the reference datum of the standard enthalpy of formation,ΔfHm∘, where Δ0TSm∘ at 298.15 K of the elemental molybdenum as the standard state was re-evaluated by re-reviewing the literature. The unknown standard Gibbs energy of solution, ΔslnGm∘, and the solubility product, Ks, at 298.15 K for Sm2(MoO4)3were predicted on the basis of the data obtained in this study and the reference datum of MoO42−(aq) and Sm3+(aq). The thermodynamic values determined in the present study are as follows:TN/K=1.30±0.30,Δ0TSm∘(Mo(cr),298.15K)/(JK-1mol-1)=28.573±0.086.These data are expected to be useful for geo-chemical simulation of diffusion of radioactive elements through underground water. Graphical abstract: [Figure not available: see fulltext.].

The thermodynamic properties for CaMoO4(cr), MoO3(cr) and MoO42 (aq) were investigated. CaMoO4(cr) is the one of the host crystals of the yellow phases which are known as hygroscopic harmful phases in the nuclear fuel glasses. MoO3(cr) is the main component of the host crystals. MoO42 (aq) is the aqueous ion present in underground water after dissolution of the yellow phases. The standard molar entropies, Delta S-T(0)m degrees, at 298.15 K for CaMoO4(cr) and MoO3(cr) were determined by measuring their isobaric heat capacities, C degrees(p,m), from 2 K. Their standard Gibbs energies of formation, Delta(f)G(m)degrees, were determined by combining the Delta(T)(0) S-m degrees data with the reference data of the standard enthalpies of formation, Delta H-f(m)degrees. The standard electrochemical potential, E degrees, of MoO42 (aq) was determined from the thermodynamic cycle on the basis of thermodynamic properties obtained for CaMoO4(cr) and MoO3(cr). The unknown standard Gibbs energies of solution, Delta(sln)G(m)degrees, at 298.15 K for the actinide molybdates ThMo2O8(cr) and UMoO6(cr) were predicted from the presently obtained thermodynamic data for CaMoO4(cr), MoO3(cr) and MoO42 (aq). The obtained thermodynamic values are as follows: Delta(T)(0) S-m degrees (CaMoO4(cr), 298.15 K)/(J K (1) mol (1)) = 122.23 +/- 1.22. Delta(T)(0) S-m degrees(MoO3(cr), 298.15 K)/(J K (1) mol (1)) = 75.43 +/- 0.75. Delta(T)(0) S-m degrees (MoO42 (aq), 298.15 K)/(J K (1) mol (1)) = 32.25 +/- 4.41. Delta(f)G(m)degrees (CaMoO4(cr), 298.15 K)/(kJ mol (1)) = -1437.78 +/- 1.11. Delta(f)G(m)degrees (MoO3(cr), 298.15 K)/(kJ mol (1)) = -667.20 +/- 0.63. Delta(f)G(m)degrees(MoO42 (aq), 298.15 K)/(kJ mol (1)) = -836.61 +/- 1.02. E degrees (MoO42 (aq), 298.15 K)/V = 4.34 +/- 0.01. Delta(sln)G(m)degrees (ThMo2O8(cr), 298.15 K)/(kJ mol (1)) = 184.84 +/- 42.48. Delta(sln)G(m)degrees (UMoO6(cr), 298.15 K)/(kJ mol (1)) = 68.33 +/- 34.47. The present obtained data are expected to be useful for geo-chemical simulation of diffusion of radioactive elements through underground water. (C) 2017 Elsevier Ltd.

The isobaric heat capacities, C degrees(p,m), for Ag2MoO4 at 2-300 K were measured by the relaxation method. Ag2MoO4 is harmful phase formed in nuclear fuel waste glasses. The third law entropy, S degrees(m), determined via the Debye-Einstein function was: S degrees(m)(Ag2MoO4(cr), 298.15 K)/J K-1 mol(-1) = 219.87 +/- 2.20. The phase stability of Ag2MoO4 was discussed on the basis of its standard Gibbs energy of formation, Delta fG degrees(m), which was derived by combining S degrees(m) determined in this study with the reference datum of the standard enthalpy of formation, Delta fH degrees(m). Ag2MoO4 was found to exhibit greater phase stability in nuclear fuel waste glasses than transition metal molybdates such as NiMoO4 and ZrMo2O8.

Highly efficient carbon-supported Ru catalysts towards the H-2 production from the ammonia borane (AB: NH3BH3) hydrolysis reaction have been developed by using tri(2,2'-bipyridyl) ruthenium (II) chloride hexahydrate as metal precursor. Different temperatures were used to decompose the metal precursor, which afford the preparation of various nanoparticles sizes, ranging from 3.8 to 13.5 nm. The catalytic results revealed that both geometric and electronic features of the metal nanoparticles are crucial to attain optimum catalytic activity towards the H2 production from the hydrolysis of AB. The optimum catalyst under the experimental condition used was that prepared at 800 degrees C, which efficiently boosts the hydrolysis of AB, achieving an average TOF number of 670 mol H-2/mol metal min, which is among the highest values ever reported for a monometallic Ru catalyst in this reaction up to date. (C) 2016 Elsevier B.V. All rights reserved.

An alternative approach to fabricate thin layers of metal organic frameworks (MOFs) on metal substrates without any needs of specific apparatuses was developed. Cu substrates were immersed into acid solution containing 1,3,5-benzenetricarboxylic acid (H3BTC) organic linker for the MOFs synthesis, where in-situ dissolved Cu2+ ions were assembled to form [Cu-3(BTC)(2)] (HKUST-1; BTC: 1,3,5-benzenetricarboxylate) crystals on the Cu substrates. The optimization of the choice of acids, solvents and preparation conditions were carried out to fabricate densely packed MOFs thin layers on Cu substrates. Use of a low-polarity solvent, benzyl alcohol (epsilon = 13), afforded a best balance between a dissolution rate of Cu and a coordination rate of the ligands, which led to the formation of a homogeneous thin layer composed of densely deposited small HKUST-1 crystals with a thickness of up to ca. 5 mu m on the Cu substrates. The thus synthesized MOFs thin layers exhibited a gas-adsorption property for H-2 and CO2 with an excellent mechanical stability, making this method a promising approach to functionalize metal substrates.

Layers of metal organic framework (MOF) crystals on skeletal Cu were prepared. The use of DMF as a solvent led to the deposition of densely packed MOF crystals on skeletal Cu and to high catalytic activity in the gas-phase hydrogenation reaction of ethylene.

A screening of carbon-supported PdAg nanoparticles (NPs) (PdAg/C) in H-2 production from formic acid (FA) dehydrogenation was carried out by using uniform similar to 3-5 nm PdAg alloy NPs with a wide compositional range in terms of PVP/metal and Pd/Ag ratios. The evaluation of the catalytic performance combined with the detailed characterization indicated the beneficial effect of the Ag incorporation and also revealed that the best performance achieved by PdlAg2/C (PVP/metal = 1) can be ascribed to its optimum composition and electronic features.

The size effect in the hydrogen production from formic acid decomposition has been investigated using a series of carbonsupported Pd NPs with different particle sizes ranging from 2.7 to 5.5 nm. A volcano type relationship between catalytic activity and NPs size was obtained. This result suggests that there is an optimum relative proportion of low-and high-coordination surface atoms within a regular arrangement of the Pd NPs, which was achieved at 3.9 nm in diameter under the present experimental conditions. By performing calculations on the pal-ladium crystallites, decomposition of formic acid is considered as a structure-sensitive reaction, and high-coordination sites principally act as catalytically active species in this size range. Kinetic isotope effect using HCOOD and DCOOH was well corresponded to the catalytic tendency. A k(H)/k(D) value obtained with Pd/C with optimal size was smallest among investigated, indicating the positive promoting effect in the rate-determining C-H bond dissociation step from the Pd-formate intermediate.

Skeletal (nanoporous) gold catalysts were prepared from Au-Zr amorphous alloys by immersion in HF solution to extract Zr moieties. The catalytic performance of the skeletal Au catalyst for the oxidation of benzyl alcohol to benzaldehyde was examined using O-2 as an oxidant. The amount of benzaldehyde formed over skeletal Au treated with HF solution for 1 h was the highest among the prepared samples, despite the tow surface area. Detailed characterization indicated that residual ZrO2 species on the skeletal Au promoted the oxidation reaction. The oxygen storage capacity (OSC) of skeletal Au was measured for the quantitative estimation of active sites and showed a positive correlation with the catalytic activity of skeletal Au, verifying the presence of Au-ZrO2 interfaces. Skeletal Au was also prepared from a Au-Zr crystalline alloy and its catalytic activity was compared with that of the one prepared from the amorphous alloy. The atomic arrangement of the Au-Zr amorphous alloy had a strong effect on the catalytic activity due to the surface structure (coordination number and morphology) of skeletal Au. The unsaturated Au atoms created in the skeletal Au catalysts contributed to the reduction of activation energy for oxidation of benzyl alcohol.

The skeletal Pd catalysts were prepared from Pd-Zr alloys which possess amorphous or crystalline state. The hydrogenation of 1-octene to octane over skeletal Pd catalysts proceeded efficiently while Pd-Zr alloy was inactive. The skeletal Pd prepared from amorphous alloy showed higher catalytic activities despite the smaller surface area compared to that prepared from the corresponding crystalline alloy. These catalytic activities were attributed to the number of surface-exposed Pd of skeletal Pd which was strongly affected by the atomic arrangement of the precursor. Moreover, we investigated the effect of Ni addition to the P-Zr alloy as the third metal. Skeletal Pd with 16 at% Ni showed an excellent selectivity while keeping as high catalytic activity as skeletal Pd. (C) 2015 Elsevier B.V. All rights reserved.

Skeletal Ni catalysts were prepared from Ni-Zr alloys, which possess different chemical composition and atomic arrangements, by a combination of thermal treatment and treatment with aqueous HF. Hydrogen generation from ammonia borane over the skeletal Ni catalysts proceeded efficiently, whereas the amorphous Ni-Zr alloy was inactive. Skeletal Ni prepared from amorphous Ni30Zr70 alloy had a higher catalytic activity than that prepared from amorphous Ni40Zr60 and Ni50Zr50 alloys. The atomic arrangement of the Ni-Zr alloy also strongly affected the surface structure and catalytic activities. Thermal treatment of the amorphous Ni-Zr alloys at a temperature slightly lower than the crystallization temperature led to an increase of the number of surface-exposed Ni atoms and an enhancement of the catalytic activities for hydrogen generation from ammonia borane. The skeletal Ni catalysts also showed excellent durability and recyclability.

Skeletal Ni catalysts were prepared from an amorphous Ni40Zr60 alloy (a-NiZr) by the selective extraction of Zr moieties by the HF treatment, followed by heating at various temperatures under vacuum, oxygen and hydrogen atmosphere. The HF treatment selectively extracted Zr moieties from a-NiZr, which resulted in the formation of high-surface-area and skeletal Ni metals. The oxygen treatment at 423 K and following hydrogen treatment at 473 K enhanced the catalytic activities of the skeletal Ni catalyst in the hydrogenation reaction of 1-octene with molecular H-2. The temperatures and atmosphere of the pretreatment strongly affected to the catalytic performances of the skeletal Ni catalysts. (C) 2015 Elsevier B.V. All rights reserved.

The catalytic performances of skeletal Cu prepared from Cu-Ti amorphous alloy heated at various temperatures were tested for the hydrogen generation from ammonia borane. The catalytic activity per surface area decreased with increasing heating temperatures of Cu-Ti amorphous alloy. The thermal treatment of Cu-Ti amorphous alloy leads to the high surface area of skeletal Cu. A skeletal Cu catalyst prepared from heated Cu-Ti amorphous alloy at 300 degrees C which is a moderate temperature somewhat lower than crystallization temperature, exhibited a higher catalytic activity in this reaction.

Skeletal Ni catalysts were prepared from an amorphous Ni40Zr60 alloy (a-NiZr) by heating at various temperatures under vacuum, followed by the selective extraction of Zr moieties by an HF treatment. Each sample was characterized by various spectroscopic methods, and the catalytic performance was tested in the hydrogenation of 1-octene. The differences in preparation temperatures of a-NiZr strongly affected the catalytic performance of the obtained catalysts, whereby those prepared from heated a-NiZr in the pre-crystallization state exhibited higher catalytic activity. Especially, moderate thermal treatment of a-NiZr at a temperature slightly lower than that for its crystallization, that is, similar to 573 K, resulted in a significant enhancement of the catalytic activity. Such prepared skeletal Ni catalyst can also be used efficiently for hydrogen generation from aqueous hydrazine.

Skeletal Cu was prepared from Cu-Ti amorphous alloy (amor-CuTi) via heating at various temperatures followed by HF treatment for extraction of Ti moieties. Thermal treatment at somewhat lower crystallization temperature of amor-CuTi followed by HF treatment leads to higher catalytic activity in the hydrogenation reaction of p-nitrophenol to p-aminophenol.