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The stability of a zirconium (Zr)-substituted face-centered cubic (FCC) yttrium (Y) hydride (Y1-xZrx hydride) phase was investigated experimentally and theoretically. Two possible sites for hydrogen atoms exist in the FCC structure, namely, T- and O-sites, where hydrogen is present at the center of the tetrahedron and the octahedron composed of Y and/or Zr metals. The P-C isotherms revealed that the hydrogen content per metal (H/M) with 33% Zr-substituted YH3-δ was 2.2-2.3, which was lower than the expected value calculated from the starting composition of YH3-33% ZrH2 (Y0.67Zr0.33H2.67, H/M = 2.67). Hydrogen at the O-site in Y1-xZrx hydride mainly reacted during hydrogen desorption/absorption. On the basis of theoretical analyses, the hydrogen atoms do not occupy the center of the octahedron, when at least two of the six vertices of the octahedron were composed of Zr. The O-sites, where more than two Zr atoms coordinate, nonlinearly increased with the Zr content, and when the Zr content was >50%, almost no hydrogen atoms occupy the O-sites. The theoretical discussion supported the experimental results, and the Zr substitution was confirmed to reduce the occupancy of H at the O-site in the FCC YH3 significantly.

A σ-π extended aryldisilane, comprising a thienopyrazine group as an acceptor fragment and phenothiazine groups as the donor moiety, has been prepared through the introduction of two Si-Si bridges (compound 1). X-ray diffraction analysis determined the crystal structure of 1, and experimental and theoretical approaches investigated its optical properties. Solvatochromic studies revealed the dual emission of 1 in all solvents tested. Compound 1 also exhibited fluorescence in the solid state upon excitation with a hand-held UV lamp, as well as mechanochromic luminescent properties. The packing mode in the crystal structure, variation of phenothiazine conformation, morphological changes between crystalline and amorphous phases are the major factors showing reversible fluorescence under external stimuli. A theoretical conformer study found that 1 exists in distinct conformational groups differing in Gibbs free energy by less than 3 kcal mol-1 . The conformer in the crystalline state of 1 can promote the complete separation of the HOMO and LUMO between the phenothiazine donor and the thienopyrazine acceptor, linked by the disilane linker. HOMO-LUMO energy transition in the crystalline state is forbidden due to the lack of frontier orbital overlap. Crystalline state emission showed LUMO → HOMO-1 transition (locally excited (LE) state). In the amorphous state, the partial presence of quasi-axial conformers allows intramolecular charge-transfer type emission via energy transfer from dominant quasi-equatorial conformers. The strategy proposed in this work provides important guidance for developing stimuli-responsive materials with controlled excited states.

In this paper, selective formation of noncentrosymmetric (Cc; α-crystal) and centrosymmetric (P21/c; β-crystal) 1,1,2,2-tetramethyl-1-(4-(N,N-dimethylamino)phenyl)-2-(2′-cyanophenyl)disilane (1) wa...

Metal hydrides may play a paramount role in a future hydrogen economy. While most applications are based on nanostructured and confined materials, studies considering the structural response of these materials to hydrogen concentrate on bulk material. Here, using in situ in- and out-of-plane X-ray diffraction and reflectometry, we study the fcc ↔ fct transition in Hf thin films, an optical hydrogen-sensing material. We show that the confinement of Hf affects this transition: compared to bulk Hf, the transition is pushed to a higher hydrogen-to-metal ratio, the tetragonality of the fct phase is reduced, and phase coexistence is suppressed. These nanoconfinement effects ensure the hysteresis-free response of hafnium to hydrogen, enabling its remarkable performance as a hydrogen-sensing material. In a wider perspective, the results highlight the profound influences of the nanostructuring and nanoconfinement of metal hydrides on their structural response to hydrogen with a significant impact on their applicability in future devices.

Hexagonal boron nitride (h-BN) was ball-milled at various rotation speeds (150–600 rpm) using a planetary ball-mill. Ball-milling disrupted the layered structure of the h-BN, resulting in significant increases of surface area. Ball-milling at 400 rpm gave the highest surface area of 412 m2 g−1 while higher rotation speeds decreased the surface areas due to agglomeration. Moreover, ball-milling resulted in the emergence of amino- and hydroxyl groups on the surface which were observed by Fourier transform infrared spectroscopy, and partial oxidation of the surface boron by the formation of B–OH groups was confirmed by X-ray photoelectron spectroscopy. The appearance of trigonal B–O and tetrahedral B–O was observed by boron-11 magic-angle spinning nuclear magnetic resonance spectroscopy. The number of base sites was increased with the increase of rotation speeds of milling, corresponding to the formation of amino groups. The ball-milled h-BN showed catalytic activity for the nitroaldol reaction between nitromethane and benzaldehyde in which the h-BN milled at 400 rpm exhibited the highest reaction rate and turnover frequency. In addition, the ball-milled h-BN could convert glucose with the formation of fructose at 40 °C whereas pristine h-BN showed no activity. The base sites were mainly responsible for the catalytic activity.

Hydrogenation of nonequilibrium alloys may form nanometer-sized metal hydride clusters, depending on the alloy compositions and hydrogenation conditions. Here in the Ti-rich compositions of the immiscible Mg-Ti system MgH2 clusters are embedded in a Ti-H matrix. Our previous works have indicated that the interface energy between the two metal hydrides reduces the stability of MgH2. The aim of our study is to obtain the structural information on the nanometer-sized clusters. Indeed, MgD2 clusters embedded in a face-centered-cubic (FCC) Ti-D matrix is found in Mg0.25Ti0.75D1.65 by means of 2H magic angle spinning nuclear magnetic resonance (MAS NMR). The atomic pair distribution function (PDF) analysis of neutron total scattering data suggests that the MgD2 clusters have an orthorhombic structure, which is different from a rutile-type body-centered-tetragonal (BCT) structure of α-MgD2 observed in the Mg-rich compositions. Our results suggest that we can tune the thermodynamics of hydrogen absorption and des...

Direct depolymerization of crystalline cellulose into water-soluble sugars by solvent-free ball milling was examined in the presence of a strongly acidic layered metal oxide, HNbMoO6 , resulting in full conversion with 72 % yield of water-soluble sugars. Measurements by 13 C cross-polarization magic angle spinning NMR spectroscopy and X-ray diffraction revealed that amorphization of cellulose occurred rapidly within 10 min. Scanning electron microscopy equipped with an energy dispersive X-ray indicated that the substrate and the catalyst were well mixed during milling. The time course of the product distribution showed that most of the resultant water-soluble sugars were produced not by successive degradation of oligosaccharides but by direct depolymerization of cellulose chains. The products included glucose, mannose, and cello-oligomers, as well as anhydrosugars. Addition of small amounts of polar solvents increased the sugar yield, whereas further addition of water decreased the selectivity to anhydrosugars. Calculations of the mechanical energy required for the ball-milling process showed that 0.02 % was utilized for the chemical transformation under the conditions examined in this study.

Inorganic solid acid salts with hydrogen bond networks frequently show very long spin-lattice relaxation times even for 1H because the hydrogen bonds suppress motions. In the present work, the 1H spin-lattice relaxation in Cs2(HSO4)(H2PO4) containing a small amount of ammonium ions were studied in detail by use of the effect of magic angle spinning (MAS) on the relaxation. The 1H spin-lattice relaxation times of the acid protons decrease with increase in the content of ammonium ions. Reorientation of the NH4 group fluctuates the dipole-dipole interaction and relaxes the ammonium protons as well as the acid protons. The 1H relaxation times of the acid protons are a little bit longer than those of the ammonium protons at the MAS rate of 8 kHz. The spinning at 50 kHz makes the relaxation times of the acid protons longer and those of the ammonium protons shorter. Spin diffusion between the acid and the ammonium protons averages partially the 1H relaxation of the acid and the ammonium protons at the MAS rate of 8 kHz. The spin diffusion is suppressed completely at the MAS rate of 50 kHz. Spin diffusion between the acid protons is not suppressed at the MAS rate of 50 kHz. The acid protons always show the same relaxation times. The intrinsic relaxation times not affected by spin diffusion are evaluated quantitatively for both the acid and the ammonium protons. Those values are independent of the ammonium content. Contribution of the spin diffusion between the acid and the ammonium protons to the relaxation is estimated quantitatively. Using those parameters, the effect of ammonium ions on the 1H spin-lattice relaxation can be predicted. The 1H spin-lattice relaxation is a sensitive tool to study the distribution of ammonium ions in solids.

Inorganic solid acid salt Cs 2 (HSO 4 )(H 2 PO 4 ) showed high proton conductivity in the superprotonic phase, and the phase was retained on cooling even at room temperature for a long period. In the present work, we attempt partial replacement of Cs ions by ammonium ions. Incorporation of ammonium ions up to 2.3% of the total cations is succeeded. Successful incorporation of ammonium ions is confirmed by the crystal structure measured by X-ray powder diffraction, the phase transition measured by thermal analyses and phosphorus environments measured by 31 P magic-angle-spinning (MAS) NMR. Furthermore, we present 1 H and 133 Cs MAS NMR spectra and the result of 1 H{ 31 P} rotational-echo double resonance (REDOR) experiments. The 1 H and 133 Cs MAS NMR spectra show that incorporation of ammonium ions leads to increase of disordered structures.

This work explores the use of hexagonal boron nitride (h-BN), a graphite-like compound, as a novel catalyst with base and acid functionalities. For use as a solid catalyst, the layered structure of h-BN was disrupted by ball-milling, exposing boron and nitrogen edge sites as well as increasing the surface area from 3 to ca. 400 m 2 g −1 . Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and proton magic-angle spinning nuclear magnetic resonance spectroscopy ( 1 H MAS NMR) indicated simultaneous and adjacent formation of amino and hydroxyl groups by milling, which function as Bronsted base and acid sites, respectively. Analysis using color indicator reagents and pyrrole-adsorbed 1 H MAS NMR results revealed that the ball-milled h-BN had basic sites of strength +9.3 > H − ≥ +7.2, comparable to those of KY zeolite. Measurements of 31 P MAS NMR of adsorbed trimethylphosphine oxide indicated that the ball-milled h-BN had weak acid sites, comparable to those in HY zeolite. Despite its weak basicity, the ball-milled h-BN showed high activity and selectivity toward β-nitroalkenes for the nitroaldol reaction (Henry reaction) and the Knoevenagel condensation, whereas nontreated h-BN did not show activity. The nitroaldol reaction was considered to proceed in two steps: the abstraction of a proton from nitromethane by the amino group and the formation of an imine followed by a nucleophilic attack of the deprotonated nitromethane. Kinetic isotope effect experiments using D -substituted nitromethane revealed that the first step was the rate-determining step. Several nitroaldol reactions using a variety of monosubstituted benzaldehydes indicated that electron-donating groups enhanced the activity, suggesting that the formation of adjacent base and acid sites is responsible for it. This study shows the high catalytic activity of BN, a solid catalyst with moderate basicity and weak acidity.

Mechanisms of the 1 H spin-lattice relaxation in NH 4 H 2 PO 4 were studied in detail by use of the effect of magic angle spinning on the relaxation. The acid and the ammonium protons have different relaxation times at the spinning rates higher than 10 kHz due to suppression of spin diffusion between the two kinds of protons. The intrinsic relaxation times not affected by the spin diffusion and the spin-diffusion assisted relaxation times were evaluated separately, taking into consideration temperature dependence. Both mechanisms contribute to the 1 H relaxation of the acid protons comparatively. The spin-diffusion assisted relaxation mechanism was suppressed to the level lower than the experimental errors at the spinning rate of 30 kHz.

Both symmetrical and unsymmetrical cyclophanes containing disilane units, tetrasila[2.2]cyclophanes 1–9, were synthesized. The syn and anti conformations and the kinetics of inversion between two anti-isomers were investigated by X-ray diffraction and variable-temperature NMR analysis, respectively. The flipping motion of two aromatic rings was affected by the bulkiness of the aromatic moiety (1 vs 6), the phase (solid vs solution), and the inclusion by host molecules (1 vs 1⊂[Ag2L]2+). The photophysical, electrochemical, and structural properties of the compounds were thoroughly investigated. Unsymmetrical tetrasila[2.2]cyclophanes 5–8 displayed blue–green emission arising from intramolecular charge transfer. Compound 6 emitted a brilliant green light in the solid state under 365 nm irradiation and showed a higher fluorescence quantum yield in the solid state (Φ = 0.49) than in solution (Φ = 0.05). We also obtained planar chiral tetrasila[2.2]cyclophane 9, which showed interesting chiroptical properties,...

The inorganic solid acid salt Cs2(HSO4)(H2PO4) showed high proton conductivity in the superprotonic phase above 370 K, and the phase was retained on cooling even at room temperature for a long period. These characteristic properties should correlate to the hydrogen bond network connecting the SO4 and PO4 groups. In the present work, the structures of the hydrogen bond network were studied by solid-state NMR. We present 31P, 1H, and 133Cs magic-angle-spinning (MAS) NMR spectra, 31P static NMR spectra to derive chemical shift anisotropy, a 31P{1H} dipolar dephasing experiment, and 1H{31P} rotational-echo double resonance (REDOR) experiments. The 31P NMR spectra indicate that all the P sites are crystallographically equivalent, and the negative value of the chemical shift anisotropy suggests that four hydrogen bonds are formed around the PO4 tetrahedron. The 31P{1H} dipolar dephasing experiment strongly supports that the number of hydrogen bonds around the PO4 tetrahedron is four. The 1H and 133Cs MAS NMR sp...

The interfacing carbon materials can improve the visible light absorption of titanium dioxide (TiO2). Here TiO2 was anchored on carbon spheres (CSs) obtained by the hydrothermal polymerization of sucrose to bathochromically expand its light-response region. Nano-TiO2 is condensed on the CS surface upon hydrothermal treatment to generate a core–shell structure (TiO2@CS). Because of interface formation between the two materials, TiO2@CS achieved an enhanced visible light absorption compared to pure TiO2. In addition, it degraded organic pollutants, such as methyl orange, bisphenol A, and Oseltamivir, more efficiently than pure TiO2 and the well-known graphene–P25 TiO2 nanocomposite under visible light irradiation. This promoted visible light photoactivity was evidenced by the enhanced photocurrent responses and structure-dependent changes of electron spin resonance spectra that disclosed the critical role of an interfacial structure containing a doping level formed by tuning electrons from CS to TiO2. Therefore, the facile hydrothermal formation of TiO2@CS reveals new avenues for cost-effective ultraviolet-free photocatalysts exhibiting high efficiency.

Hydrogen storage is a key technology for the advancement of hydrogen and fuel cell power technologies in stationary and portable applications. MgH2, an example of a high-capacity hydrogen storage material, has two major material challenges for practical applications: slow hydrogen desorption kinetics and high hydrogen desorption temperature. Numerous studies have reported enhancements in kinetics but only a few in thermodynamics. Here, we present a simple but effective way to improve upon both the kinetic and thermodynamic aspects of desorption by utilizing the immiscibility of Mn, a non-hydrogen absorbing metal, with Mg. Mg0.25Mn0.75, prepared through ball milling MgH2 and Mn powders, is a nanocomposite where the nanometer-sized MgH2 domains are randomly embedded in a Mn matrix. This sample readily and reversibly absorbs and desorbs deuterium even at a temperature of 200 °C without the addition of any catalysts. This is nearly 180 °C lower than the typical operating temperature of conventional bulk Mg. Furthermore, at a given temperature, its deuterium desorption pressure is clearly elevated compared to that of pure Mg, indicating the destabilization of MgD2. The average crystallite size of MgD2 in deuterated Mg0.25Mn0.75 determined from X-ray diffraction data is around 9 nm. Nuclear magnetic resonance spectroscopy studies show that MgD2 domains are heavily strained and some of the D atoms are coordinated by a few Mn atoms, suggesting that a large number of lattice defects, including the partial substitution of Mg with Mn, are introduced during ball milling. Furthermore, the Mn matrix firmly locks nanosized MgD2, preventing the agglomeration of MgD2 below 250 °C. Our study suggests that a synergistic effect created by nanosizing, large lattice distortions, and robust interfaces between MgD2 and the Mn matrix can effectively and concurrently improve the kinetics and thermodynamics of MgD2 in Mg0.25Mn0.75. Our work demonstrates the possibility of utilizing the immiscibility of metals with Mg to synthesize a robust nanostructure that can alter the kinetics and stability of MgH2.

High hydrogen density and low material costs make Mg as one of the most promising candidates for solid-state hydrogen storage. However, the practical applications of Mg are restricted by high reaction temperature and slow kinetics of hydrogen absorption/desorption. Here we present the improvements of both thermodynamics and kinetics of the hydride/deuteride of Mg (MgH2/MgD2) by utilizing the immiscible Mg–Cr system. Nanometer-sized MgD2 domains with the average crystallite size of ~10 nm embedded in a Cr matrix are formed in deuterated Mg0.25Cr0.75. X-ray diffraction and nuclear magnetic resonance spectroscopy studies show that the MgD2 domains are heavily distorted, which leads to the thermodynamic destabilization lowering the reaction temperature. Mg0.25Cr0.75 can reversibly absorb and desorb hydrogen/deuterium at a low temperature of 473 K. The enthalpy ΔH for deuterium desorption of Mg0.25Cr0.75−D is 72.1 kJ mol−1−D2, which is lower than ~74 kJ mol−1−D2 for bulk MgD2. The apparent activation energy for hydrogen desorption of Mg0.25Cr0.75−H is decreased to 75 kJ mol−1 from ~160 kJ mol−1 for bulk Mg, in which the dehydrogenation of nanometer-sized MgH2 is controlled by one-dimensional diffusion of hydrogen. Our work demonstrates that MgH2 nanostructured by an immiscible matrix is a useful strategy to alter the thermodynamic and kinetic properties.

We elucidate the effect of Fe addition on the phase transformation and the diffusion of hydrogen in the V–H system. V forms monohydride (β) and dihydride (γ) phases by hydrogenation. The γ phase of VH2 has a face centered cubic (FCC) structure but V1−xFex (0.03 ≤ x ≤ 0.10) forms the FCC hydride phase though the hydrogen content is less than half of VH2, resulting in decreasing the hydrogen storage capacity. On the other hand, for the β phase proton nuclear magnetic resonance (1H NMR) demonstrates that addition of Fe increases the density of states at the Fermi energy N(EF) and the activation energy for hydrogen diffusion EH. This indicates that Fe has the effects of stabilizing the hydride phase and of suppressing the diffusion of hydrogen in the V–H system.

Porous boron nitride (BN) was synthesized using a pyrolysis method in conjunction with varying NH3 flow rates, followed by washing as a post-treatment. The performance of this material as a solid base catalyst was assessed. It was found that the post-treatment rather than the synthesis conditions significantly improved the activity of the BN during the nitroaldol reaction. The BN catalyst obtained after washing gave a ten times higher product yield. Both an increase in the surface areas of the material and the emergence of micropores after washing were observed. 11B solid-state nuclear magnetic resonance spectroscopy demonstrated that boron oxide species were present in the BN after synthesis but were removed by the washing process. B K-edge X-ray absorption fine structure analyses indicated the formation of oxygen-substituted trigonal boron sites on the BN surface. Fourier transform infrared spectroscopy showed that amino groups on the samples functioned as moderately strong basic sites.

We elucidate the effect of dissolved oxygen on the phase transformation and the diffusion of hydrogen in the V–H system. V forms monohydride (β) and dihydride (γ) phases by hydrogenation but a small amount of dissolved oxygen (O/V ≈ 0.01) leads to formation of another β phase expanded along the c -axis in a body centered tetragonal structure (BCT) rather than the γ phase. This change in the phase transformation is due to trapping hydrogen atoms by oxygen atoms, resulting in the shift of site occupation of hydrogen from octahedral ( O ) sites to tetrahedral ( T ) sites. Proton nuclear magnetic resonance ( 1 H NMR) demonstrates that the activation energy for hydrogen diffusion is increased by the trapping effect. Oxygen dissolved in V suppresses not only the formation of the γ phase but also the diffusion of hydrogen.

Through various in situ analyses, we have revealed the structural changes that occur during the reversible melting-solidification process of layered alkylsiloxanes (CnLSiloxanes) with carbon numbers (n) of 18 and 16. In situ high-resolution solid-state (13)C nuclear magnetic resonance (NMR) analysis at controlled temperatures indicates drastic conformational changes of the long alkyl chains during the melting-solidification process. A (13)C NMR signal at 33 ppm, which shows the highest intensity at room temperature (RT), is assigned to an inner methylene group with an all-trans conformation. As the temperature increases, the 33-ppm signal intensity decreases while the signal intensity at 30.5 ppm simultaneously increases. The 30.5 ppm signal is assigned to an inner methylene group with a trans-gauche conformation. Subsequently, upon cooling, the signal at 33 ppm recovers, even after CnLSiloxanes have melted. In situ X-ray diffraction measurements at controlled temperatures reveal that the ordered arrangement of the long alkyl chains becomes disordered with elevating temperatures and reordered upon cooling to RT. In situ high-resolution solid-state (29)Si NMR analysis shows that the melting-solidification process progresses without any structural change in siloxane sheets of the CnLSiloxanes. Thus, the in situ analyses show that disordering of the long alkyl chains causes the CnLSiloxanes to melt. Because the majority of long alkyl chains are packed again in the ordered arrangement with the all-trans conformation upon cooling, the CnLSiloxanes are reversibly solidified and the CnLSiloxane structure is recovered.

Niobium-doped titanate nanotubes (Nb–TiNTs) with various Nb contents were prepared by hydrothermal treatment of Nb-doped TiO2 with an aqueous NaOH solution and subsequent proton exchange. Nb–TiNTs effectively catalyzed the Friedel–Crafts alkylation of toluene with benzyl chloride or benzyl alcohol and the activity increased with the Nb content, reaching a maximum at 5%. Furthermore, Nb–TiNTs exhibited much higher catalytic activity than other Nb-containing solid acid catalysts such as Nb2O5·nH2O, Nb–Ti mixed oxides and Nb–Ti nanosheet materials. Fourier transform-infrared (FT-IR) spectroscopy measurements revealed that Nb–TiNTs possess both Lewis and Bronsted acid sites, and the amounts of these acid sites are comparable to those of non-doped TiNTs. The high catalytic performance of Nb–TiNTs is attributable to their higher Bronsted acid strength and to the enhanced accessibility of reactant molecules to acid sites.

The diffusion and site occupation of hydrogen in the monohydride phase (β phase) of the V 1− x Al x –H ( x ⩽ 0.1) system was studied by means of proton nuclear magnetic resonance ( 1 H NMR). Hydrogen atoms which occupied the octahedral ( O z ) sites along the c -axis in a body-centered tetragonal structure shifted to the tetrahedral ( T ) sites with the Al content. V 0.90 Al 0.10 H 0.68 had a body-centered cubic structure and the component observed in the temperature dependence of 1 H spin-lattice relaxation time was due to the contribution of hydrogen on the T sites. The addition of Al reduced the site radius of the O z sites and resulted in reducing the activation energy for hydrogen diffusion, E H , for the O z sites. Moreover, the diffusion of hydrogen was enhanced by a shift of site occupation from the O z sites to the T sites, which had lower E H than the O z sites. The addition of larger substitutional Al atoms than V enhanced the diffusion of hydrogen in the β phase of V–H.

Acid properties of ZSM-5 type zeolite are studied by solid-state NMR using trimethylphosphine oxide (TMPO) as a probe molecule. TMPO is introduced from the gas phase at 373 K. The amounts of the loaded TMPO are quantified by the signal intensities of 1 H MAS NMR spectra, which are compared with the numbers of Bronsted acid sites estimated by the Si/A ratio of the framework derived from 29 Si MAS NMR spectra and the content of fourfold-coordinated Al from 27 Al MAS NMR spectra. The use of 373 K for loading the probe molecules increases the loading level of TMPO, and thus almost all the acid sites are probed. The 31 P chemical shifts in the range between 90 and 60 ppm are attributed to TMPO adsorbed on Bronsted acid sites, whereas the signals between 60 and 40 ppm are ascribed to TMPO adsorbed on other sites than Bronsted acid sites. The 13 C chemical shift of methyl groups in the adsorbed TMPO depends mainly on the confined space as well as on the acid strength.

The adsorption state of trimethylphosphine oxide (TMPO) on siliceous MFI-type zeolite, silicalite, has been studied by solid-state NMR. TMPO was loaded by vapor as well as the solvent methods, and ...

Aqueous-phase transformation of C3- and C6-sugars toward valuable intermediates such as lactic acid and 5-hydroxymethylfurfural (HMF) using boehmite, an abundant, inexpensive and simple aluminium oxide hydroxide γ-AlO(OH) was demonstrated. Pyridine-adsorbed Fourier transform infrared (FTIR) spectroscopy and trimethylphosphine oxide-adsorbed 31P magic angle spinning (MAS) nuclear magic resonance (NMR) revealed that boehmite had no Bronsted acid sites and a small amount of weak Lewis acid sites. The amount of Lewis acid sites and the initial reaction rate for lactic acid synthesis from dihydroxyacetone increased with increase of calcination temperature of boehmite whereas the selectivity for lactic acid remained unchanged and turnover frequency decreased. Boehmite afforded lactic acid selectively from aqueous C3-sugars solution with the yields of 32% and 42% from dihydroxyacetone and glyceraldehyde, respectively, which were higher than those of hydrotalcite, titanium oxide, tin oxide and tungsten oxide. Moreover, boehmite gave both lactic acid and HMF simultaneously from aqueous glucose solution as well as fructose. The total yields of lactic acid and HMF from aqueous glucose solution reached 40%. Boehmite was found to catalyse a variety of reactions including isomerization, retro-aldol condensation, dehydration and hydration in water.

We have successfully prepared H2Ti12O25 by soft chemical synthetic technique using Na2Ti6O13 as a starting compound for the first time. In this synthetic route, we first prepared Li2Ti6O13 by Na+/Li+ ion-exchange reaction. Then, H2Ti6O13 was prepared by Li+/H+ ion-exchange reaction using HCl solution, and H2Ti12O25 was synthesized by heating the obtained H2Ti6O13 at 260 °C. The XRD pattern and 1H-MAS NMR spectrum of the H2Ti12O25 sample thus obtained were well consistent with those for the H2Ti12O25 sample prepared from Na2Ti3O7 as a starting compound. The H2Ti12O25 sample prepared from Na2Ti6O13 exhibited superior cycling performance with the initial discharge capacity of 229 mAh g−1 in the voltage range between 1.0 and 3.0 V with a fixed current density of 10 mA g−1 at 25 °C, which was higher than that (213 mAh g−1) for the H2Ti12O25 sample from Na2Ti3O7. The improvement of the discharge capacity may be explained by the smaller particle size for the present H2Ti12O25 sample. Accordingly, the initial coulombic efficiency for the H2Ti12O25 sample was improved from 86% to 92%. These facts suggest that H2Ti12O25 is one of the promising high-voltage oxide negative electrodes in advanced lithium ion batteries.

Nanostructured titanate materials with different morphologies, including layered materials, nanosheets, and nanotubes, were examined as solid acid catalysts to elucidate the relationship between the structure and the catalytic properties. The titanate nanotube consists of a scroll-like layered structure derived from lamellar titanate nanosheets that exhibits excellent catalytic performance for the Friedel–Crafts alkylation of toluene with benzyl chloride near room temperature, exceeding the activities of layered titanates (H2Ti3O7, H0.7Ti1.825□0.175O4·H2O) and nanosheets that have similar crystal structures to that of the titanate nanotubes. Fourier transform infrared (FT-IR) spectroscopy and 31P magic angle spinning nuclear magnetic resonance (31P MAS NMR) spectroscopy using basic probe molecules have revealed that these titanate materials possess both Bronsted and Lewis acid sites, and the Bronsted acid strength of the titanate nanotubes is higher than that of the titanate nanosheets. The strong Bronste...

SO₃H-bearing amorphous carbon prepared from polyvinyl chloride (PVC) is studied as a heterogeneous Bronsted acid catalyst. Sulfonation of partially carbonized PVC produces amorphous carbon consisting of small SO₃H-bearing carbon sheets linked by sp³ -based aliphatic hydrocarbons. This carbon material exhibits much higher catalytic performance in the hydrolysis of cellobiose than conventional heterogeneous Bronsted acid catalysts with SO₃H groups, including SO₃H-bearing amorphous carbon derived from cellulose. This can be attributed to a high density of SO₃H groups and the fast diffusion of reactants and products enabled by a flexible carbon network.

The diffusion of hydrogen in the monohydride phase (β phase) of the V1−xCrx–H (x ≤ 0.1) system was studied by means of 1H nuclear magnetic resonance (NMR). Hydrogen atoms in the hydrides occupied the octahedral (O) sites in a body centered tetragonal (BCT) structure. The BCT lattice was contracted by addition of Cr because Cr has a smaller atomic radius than V. The activation energy for hydrogen diffusion, EH, and the Korringa constant, T1eT, were estimated from the temperature and frequency dependence of 1H spin–lattice relaxation times, T1. The value of EH increased with increase in the Cr content. The contraction of the BCT lattice by addition of Cr suppressed the diffusion of hydrogen which occupied the interstitial sites. Addition of Cr also increased the T1eT, which was accompanied by reducing in the stability of the monohydride phase of the V–H system.

Ion dynamics in alkali borohydrides, LiBH4, NaBH4, and KBH4, was studied by solid-state NMR. NMR spectra and spin–lattice relaxation times, T1, of 1H and 11B were measured and analyzed. The T1 results of 1H and 11B indicated that two types of motions take place in the low-temperature (LT) phase of LiBH4. The second moments of 1H and 11B NMR spectra suggested that the sum of the two types of motions resembles isotropic reorientation of the BH4 unit. The T1 minimum values of 1H and 11B supported that the C3 rotation takes place at first. The second type of motion might be either C3 rotation or C2 rotation. The second moments of NMR spectra and the T1 minimum values of 1H and 11B supported that the BH4 unit reorients isotropically in NaBH4 and KBH4.

(E,E,E)-1,6-di(4-formylphenyl)-1,3,5-hexatriene (1) undergoes [2 + 2] photocycloaddition in the solid state, while the unsubstituted parent, (E,E,E)-1,6-diphenyl-1,3,5-hexatriene (DPH), is photochemically inert as we reported previously. Although the steering effect of the formyl group for the photoreaction is very clear, the crystal structure of 1 had been unknown. In this study, single crystals of 1 suitable for X-ray diffraction (XRD) analysis were prepared and the crystal structure was investigated. The molecules in crystal are linked through intermolecular CH⋯O-type hydrogen bonds involving formyl groups to form a 3D structure of π-stacked crystal packing arrangement with intermolecular distance of 3.926 A (=b), less than the Schmidt’s criteria of 4.2 A for the [2 + 2] photoreaction. The existence of CH⋯O hydrogen bonds is evidenced by FT-IR, 1H and 13C NMR spectroscopic measurements. For the IR peak assignments, ab initio and DFT calculations were performed. The solid-state 1H and 13C NMR spectra were measured using the CRAMPS and CP/MAS techniques, respectively. Owing to the small CH⋯O angular dependence of the interaction energy (directionality), the CH⋯O hydrogen bonds are formed in a multiple manner. Thus, although being rather weak, these hydrogen bonds play a decisive role in constructing the [2 + 2] photoreactive crystal structure, without any other stronger intermolecular interactions coexisting.

We have modified the surface of TiO2 nanoparticles by propylphosphonic acid (PPA) and decylphosphonic acid (DPA), and have characterized the surface layer of titania (=titanium dioxide) nanoparticl...

We have studied the state of adsorbed dichloromethane molecules not removed by evacuation in several H-type zeolites, ZSM5, mordenite, β, and Y, by means of solid-state NMR. The amount of undesorbe...

The correlation between catalytic performance and structure of a cellulose-derived and carbon-based solid acid (CCSA), an amorphous carbon bearing SO(3)H, COOH, and phenolic OH groups, was investigated. Sulfonation of partially carbonized cellulose under a N(2) atmosphere resulted in the formation of a CCSA, which was amorphous carbon consisting of small polycyclic aromatic carbon sheets with a high density of SO(3)H groups (ca. 2 mmol g(-1)). CCSAs were prepared from carbon precursors, which were obtained at temperatures ≤723 K, and exhibited a high catalytic performance for the esterification of acetic acid with ethanol and for the hydrolysis of cellobiose, although the surface areas were small (

Acidic properties of H-type mordenite have been studied by solid-state NMR. The framework Si/Al ratios are determined by 29 Si MAS NMR spectra, and the contents of framework Al and Bronsted acid sites are determined. 27 Al MAS NMR spectra show a presence of extra-framework Al as well as "invisible" Al. The 1 H MAS NMR spectra consist of hydrogen-bonded Si-OH, Bronsted acid site, tightly adsorbed water, Al-OH and isolated Si-OH, the amounts of which are evaluated. The average 1 H chemical shifts ofBronsted acid sites without proton exchange are roughly estimated, which are in the following order; HM10 < HM15 < HM20. The acid strength of Bronsted acid sites increases with increase in the Si/Al ratio. Trimethylphosphine oxide (TMPO) is adsorbed as a probe molecule from the gas phase to avoid the effect of solvents. A part of the acid sites are sampled by TMPO molecules. The average 31 P chemical shift of chemisorbed TMPO increases with increase in the Si/Al ratio, demonstrating again that the acid strength increases with increase in the Si/Al ratio.

A SO 3 H-bearing mesoporous carbon material was investigated as a new type of heterogeneous catalyst. Carbonization of resorcinol–formaldehyde resin at 773 K, followed by sulfonation results in amorphous carbon consisting of graphene with high densities of SO 3 H (0.9 mmol g −1 ) and phenolic OH (2.0 mmol g −1 ) groups. The mesoporous carbon that has a large surface area (433 m 2 g −1 ) due to uniform mesopores (ca. 10 nm) exhibits remarkable catalytic performance for the selective dimerization of α-methylstyrene (AMS); the selectivity for unsaturated AMS dimers exceeds 99%. This catalysis is attributed to not only the large surface area based on large mesoporosity, but also to preventing intramolecular Friedel–Crafts alkylation.

The diffusion and site occupation of hydrogen in the monohydride phase of V1−xMox–H (0 ≤ x ≤ 0.1) were studied by means of 1H nuclear magnetic resonance (NMR). Hydrogen atoms in VH0.68 occupied the octahedral (O) sites in a body centered tetragonal (BCT) structure. The addition of Mo to V reduced the activation energy for hydrogen diffusion, EH, for the O sites. In V0.9Mo0.1H0.68 hydrogen atoms occupied both the O and tetrahedral (T) sites, which was demonstrated by two components observed in the temperature dependence of the 1H spin-lattice relaxation time. The value of EH for the T sites was lower than that for the O sites. Hydrogen atoms in V0.9Mo0.1H0.68 diffused faster than those in VH0.68.

SO 3 H-bearing amorphous carbon, prepared by partial carbonization of cellulose followed by sulfonation in fuming H 2 SO 4 , was applied as a solid catalyst for the acid-catalyzed hydrolysis of β-1,4 glucan, including cellobiose and crystalline cellulose. Structural analyses revealed that the resulting carbon material consists of graphene sheets with 1.5 mmol g −1 of SO 3 H groups, 0.4 mmol g −1 of COOH, and 5.6 mmol g −1 of phenolic OH groups. The carbon catalyst showed high catalytic activity for the hydrolysis of β-1,4 glycosidic bonds in both cellobiose and crystalline cellulose. Pure crystalline cellulose was not hydrolyzed by conventional strong solid Bronsted acid catalysts such as niobic acid, Nafion ® NR-50, and Amberlyst-15, whereas the carbon catalyst efficiently hydrolyzes cellulose into water-soluble saccharides. The catalytic performance of the carbon catalyst is due to the large adsorption capacity for hydrophilic reactants and the adsorption ability of β-1,4 glucan, which is not adsorbed to other solid acids.

Layered and nanosheet aggregates of HTaMoO 6 were examined as solid acid catalysts. The HTaMoO 6 aggregated nanosheets were formed by soft chemical processing of layered HTaMoO 6 using tetra ( n -butylammonium) hydroxide. The catalytic activity and acid properties of the HTaMoO 6 compounds were compared with those of layered HNbMoO 6 and a range of conventional solid acids. The catalytic activity of HTaMoO 6 for Friedel–Crafts alkylation with benzyl alcohol, hydrolysis of disaccharides, and esterification of acetic acid and lactic acid increased after exfoliation and aggregation, consistent with the acid strengths determined by NH 3 temperature-programmed desorption and 31 P magic-angle spinning nuclear magnetic resonance spectroscopy measurements. HTaMoO 6 nanosheets possess additional strong acid sites on the oxide formed by exposure of a single layer, along with strong acid sites within the interlayer of the layered aggregate structure, resulting in higher acid catalytic activity than that of the original layered oxide.

Solid acid catalysts offer the opportunity to reduce environmental impact owing to such advantages as ease of product separation and recyclability of the catalyst, which contribute considerably to green chemistry. Nanosheets, crystalline two-dimensional metal oxide sheets prepared from cation-exchangeable layered metal oxides through exfoliation and aggregation, are a novel class of potential solid acid catalysts for replacing liquid acids, such as sulfuric acid. This article reviews the acid strength and acid catalysis of several types of nanosheets, which are strongly dependent on novel strong Bronsted acid sites attributed to bridged OH groups formed only on nanosheets. An efficient acid catalysis of layered protonated niobium molybdate in Friedel–Crafts alkylation, esterification and hydrolysis, owing to its unique intercalation availability, is also discussed.

The formula expressing the proton transverse magnetization decay for elastomers is reconsidered. It is improved by incorporating the relaxation contribution. The spin–spin relaxation times T2 are estimated from spin–lattice relaxation times in the laboratory frame T1 and spin–lattice relaxation times in the rotating frame T1ρ measured at the low static magnetic field. The improved formula together with distributed residual dipolar couplings is applied to several samples of elastomers, and residual dipolar couplings are estimated. A good correlation between a swelling ratio and the residual dipolar coupling is obtained.

Cesium hydrogen sulfate CsHSO 4 was introduced in a nanospace of mesoporous silica FSM-16, and we have investigated proton dynamics of CsHSO 4 confined in the mesopores by means of 1 H solid-state NMR. X-ray powder diffraction patterns demonstrate accommodation of CsHSO 4 in the mesopores and suggest that confined CsHSO 4 is amorphous. Thermal analyses indicate that the confinement suppresses the transition from phases II to I and the melting. The motional narrowing in the 1 H static NMR spectra takes place in the temperature range lower than that for bulk CsHSO 4 , and the spectral line shape indicates that the proton motional rate has a distribution. The proton mean residence times are estimated from the spectrum simulation assuming the distribution of the motional rate. The obtained central values are smaller by one order of magnitude than those for bulk CsHSO 4 although the central values of the activation energies are comparable.

Protonated, layered transition-metal oxides H1−xNb1−xMo1+xO6 with various Nb and Mo ratios were examined as solid acid catalysts. The effects of transition-metal composition on layered crystal stru...

Proton diffusion in [(NH 4 ) 1 − x Rb x ] 3 H(SO 4 ) 2 (0 x 1 H spin-lattice relaxation times, T 1 . The relaxation times were measured at 200.13 MHz in the range of 296–490 K and at 19.65 MHz in the range of 300–470 K. In the high-temperature phase (phase I), translational diffusion of the acidic protons relaxes both the acidic protons and the ammonium protons. Spin diffusion averages the relaxation rate of the two kinds of protons, whereas proton exchange between them are slow. The spin-lattice relaxation times in phase I were analyzed theoretically, and parameters of proton diffusion were obtained. The mean residence time of the acidic protons increases with increase in x for [(NH 4 ) 1 − x Rb x ] 3 H(SO 4 ) 2 (0 ≤ x ≤ 0.54). Rb 3 H(SO 4 ) 2 does not obey this trend. The results of NMR well explain the macroscopic proton conductivity.

Nanosheet aggregates prepared from protonated layered tungstates HMWO6 (M = Nb, Ta) are examined as potential solid acid catalysts. The nanosheet aggregates are formed by soft chemical processing of the layered compound with tetra(n-butylammonium) hydroxide, and the catalytic activity and acid strength of the aggregates are compared with those for HTiNbO5, HNb3O8, and a range of conventional solid acids. The catalytic activity for the Friedel−Crafts alkylation of anisole in the presence of benzyl alcohol increases in the order HTiNbO5 < HNb3O8 < HMWO6 (M = Nb, Ta), consistent with the acid strengths determined by desorption measurements and nuclear magnetic resonance spectroscopy. Nuclear magnetic resonance spectroscopy indicates that the acid catalytic activity of the nanosheet aggregates is attributable to strong Bronsted acid sites, presumably M(OH)M′ (M = Ti, Nb, Ta; M′ = Nb, W).

The acid properties and catalytic activity of layered HNbMoO 6 for liquid-phase Friedel–Crafts alkylation are examined. 31 P MAS NMR spectroscopy using trimethylphosphine oxide as a probe molecule reveals that HNbMoO 6 possesses strong acid sites in the interlayer region. Layered HNbMoO 6 is demonstrated to display remarkable catalytic performance for this reaction, substantially exceeding the activities of niobic acid, niobium–molybdenum mixed oxide, ion-exchange resins, and zeolites. It is determined that benzyl alcohol is intercalated into the HNbMoO 6 interlayer during alkylation to form a monolayer configuration, allowing the strong interlayer acid sites to participate in the reaction.

The reaction mechanism of the hydrolysis of cellulose by a carbon-based solid acid, amorphous carbon containing graphene sheets bearing SO(3)H, COOH, and phenolic OH groups, has been investigated in detail through the hydrolysis of water-soluble beta-1,4-glucan. Whereas a range of solid strong Brønsted acid catalysts (inorganic oxides with acidic OH groups, SO(3)H-bearing resins, and the carbon-based solid acid) can hydrolyze the beta-1,4-glycosidic bonds in cellobiose (the shortest water-soluble beta-1,4-glucan), the tested solid acids except for the carbon material, consisting of conventional solid acids, cannot function as effective catalysts for the hydrolysis of cellohexaose (a long-chain water-soluble beta-1,4-glucan). However, the carbon material exhibits remarkable catalytic performance for the hydrolysis of cellohexaose: the turnover frequency (TOF) of SO(3)H groups in the carbon material exceeds ca. 20 times those of the conventional solid acids, reaching that of sulfuric acid, which is the most active catalyst. Experimental results revealed that inorganic oxides with acidic OH groups are not acidic enough to decompose the hydrogen and beta-1,4-glycosidic bonds in cellohexaose molecules aggregated by strong hydrogen bonds as well as cellulose and that the SO(3)H groups of the resins that do not adsorb beta-1,4-glucan are unable to attack the hydrogen and beta-1,4-glycosidic bonds in cellohexaose molecules effectively. In contrast, the carbon material is capable of adsorbing beta-1,4-glucan by phenolic OH or COOH groups in the carbon material, and SO(3)H groups bonded to the carbon therefore function as effective active sites for both decomposing the hydrogen bonds and hydrolyzing the beta-1,4-glycosidic bonds in the adsorbed long-chain water-soluble beta-1,4-glucan aggregate. These results suggest that the synergetic combination of high densities of the functional groups bonded to amorphous carbon causes the efficient hydrolysis of beta-1,4-glucan, including cellulose, on the carbon material.