佐藤 智司

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C = O, pyran-like ether, and lactone-like groups.

Interactions of metal cations such as Li+, Na+, K+, Mg+, Ca2+, Sr+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+ with ammonia-treated graphene sheets (G) and thermal stability of metal cations coordinated with oxygen- and nitrogen-containing functional groups on G were investigated by rinsing G coordinated with metal cations (G-Metal) in 2-propanol using sonication and by heating G-Metal at 773 K, respectively. Monovalent alkali metal cations, divalent alkaline-earth metal cations, divalent transition metal cations such as Mn2+, and the other metal cation such as Zn2+ were removed by rinsing because of either no interaction or weak interactions between metal cations and G including various thermally stable nitrogen- and oxygen-containing functional groups. Trivalent transition metal cations such as Cr3+ and Fe3+ were agglomerated by heat treatment at 773 K, whereas divalent transition metal cations such as Co2+, Ni2+, and Cu2+ remained without severe agglomeration. Phenanthroline-like groups on edges of graphene showed the strongest interaction with Ni2+ among all of investigated nitrogen- and oxygen-containing functional groups as results of density functional theory calculation. The thermal stability of N-Ni bonding was confirmed as above 873 K as results of heat treatment of a standard compound (Ni phthalocyanine) in a glass ampoule. (C) 2014 Elsevier Ltd. All rights reserved.

X-ray photoelectron spectroscopy (XPS) is among the most powerful methods to determine the surface chemical properties of carbon materials. Because heat-treated graphite oxide includes various defects, analyses of the structure by XPS help us understand the structures of various carbon materials. Thus, XPS spectra of graphene-related materials containing various functional groups and other defects on edges and in the basal plane were simulated and full width at half maximums (FWHMs) and peak shifts were obtained by density functional theory calculation. Shifts of whole C1s spectra were influenced by the electron-withdrawing functional groups such as C=O-containing functional groups. FWHMs of the main peak of C1s spectra were influenced by mainly electron-withdrawing functional groups in addition to defects such as vacancy, pentagons, and heptagons. Analyses using only XPS provide us limited information, even though the peak tops and FHWMs of simulated XPS spectra are used for assignment. Combination use of peak shifts and FWHMs of XPS spectra, infrared spectroscopy, and density functional theory calculation provided more reliable assignments of defects including oxygen-containing functional groups of carbon materials than commonly used methods using only peak shifts of XPS spectra.

Dimerization of 1,3-butadiene was investigated in a closed batch system under high-pressure conditions. 4-Vinylcyclohexene was mainly produced without using any solvents or catalysts at temperatures of 150-215 degrees C. The conversion of 1,3-butadiene was significantly dependent on the temperature and pressure. 1,3-Butadiene was converted to 4-vinylcyclohexene at selectivity higher than 90 mol % with by-products of 1,5-cyclooctadiene and 1,2-divinylcyclobutane. Large charges of reactant are efficient in achieving high conversions of 1,3-butadiene. Use of solvents, which dilute the reactant and absorb the reaction heat, is not favorable in the present dimerization of 1,3-butadiene under pressured conditions.

Vapor-phase synthesis of 3,4-2H-dihydropyran (DHP) from tetrahydrofurfuryl alcohol (THFA) was investigated over acidic catalysts modified with transition metals. Catalytic activity of alumina was seriously deactivated in the reaction of THFA in nitrogen at 300 degrees C although the initial activity was high. Tetragonal ZrO2 showed the catalytic activity to produce DHP at 350 degrees C. Alumina modified with Cu exhibits stable catalytic activity with high selectivity to DHP under hydrogen flow conditions, and the optimum activity was obtained at CuO contents of 5-10 wt.%: the selectivity to DHP was as high as 85%. Prior to the reaction, CuO was reduced to metallic Cu, which probably works as a product remover together with hydrogen to prevent coke formation. The reaction pathway from THFA to DHP was discussed: it is speculated that THFA is initially rearranged into 2-hydroxytetrahydropyran, which rapidly dehydrated to DHP. (C) 2012 Elsevier B.V. All rights reserved.

Solvent-free Diels-Alder reactions were carried out by heating a mixture of a volatile diene, such as 1,3-butadiene, isoprene, or 2,3-dimethyl-1,3-butadiene, and a dienophile, such as methyl vinyl ketone, methyl acrylate, or maleic anhydride, in a closed batch reactor. High yields of Diels-Alder products were obtained without using solvents and catalysts within a short reaction time in most of the reactions. In particular, several reactions of dienophiles with 1,3-butadiene, which is known as a diene with low reactivity because of its gaseous form, also proceeded with high yields of Diels-Alder products in the closed batch reactor under conditions pressured by the reactant vapor. Solvent-free reactions provided high yields compared to reactions in solvent since the reaction heat directly resulted in increasing the reaction temperature and pressure. Energy in the exothermic reaction was used effectively in the closed batch system under solvent-free conditions.

Vapor-phase dehydration of 1,4- and 1,5-alkanediols was investigated over three scandium ytterbium mixed oxides, Sc 2-xYb xO 3 (x = 0.5, 1.0, and 1.5), to produce the corresponding unsaturated alcohols. In the dehydration of 1,5-pentanediol, Sc 0.5Yb 1.5O 3 was more active than simple rare earth oxides such as Sc 2O 3, Lu 2O 3, Yb 2O 3, and Tm 2O 3. The selectivity to 4-penten-1-ol surpassed 80 mol% over the Sc 2-xYb xO 3 catalysts. The highest formation rate of 4-penten-1-ol was obtained at x = 1.5 and affected by lattice parameter of cubic bixbyite Sc 2-xYb xO 3. In the dehydration of 1,4-butanediol, however, Tm 2O 3 was the most active among the catalysts. © 2012 Elsevier B.V.

Silica-supported silver exhibited high catalytic activity in the dehydration of glycerol: glycerol was dehydrated into hydroxyacetone with the selectivity higher than 86% at 91% conversion over Ag/SiO2 in H-2 flow at 240 degrees C. Silver metal provides an active site and showed stable catalytic activity for the glycerol dehydration in H-2 atmosphere, while the dehydration activity decreased in N-2 atmosphere. The hydrogenation of hydroxyacetone into 1,2-propanediol and the decomposition to ethylene glycol did not proceed over silver.

In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene from pinacolone over modified alumina catalysts, it was found that alumina modified with transition metals such as Co stabilized the conversion of pinacolone and produced 2,3-dimethyl-1,3-butadiene selectively under hydrogen flow conditions, whereas the catalytic activity of pure alumina was seriously deteriorated irrespective of its high initial activity.

Er2O3 nanorods were successfully prepared with hydrothermal treatment without using organic additives such as surfactant, fatty acid, or alcohol. Er2O3 nanorods were obtained under high temperature and/or long reaction times. Er2O3 nanorods mainly exposed {440} and {400} facets on the surface. Er2O3 nanorods showed excellent catalytic activity compared to commercial Er2O3 nanoparticles in the dehydration of 1,4-butanediol to produce 3-buten-1-ol.

Vapor-phase catalytic dehydration of 1,5-pentanediol was investigated over rare earth oxides (REOs) at 325-450°C. The conversion of 1,5-pentanediol over REOs calcined at 700 and 800°C was higher than that calcined at 500°C. Sc 2O 3, Yb 2O 3, and Lu 2O 3 with cubic bixbyite structure showed the selectivity to 4-penten-1-ol with higher than 74 mol%, while REOs with hexagonal and monoclinic structures showed the selectivity with less than 50 mol%. Especially, Yb 2O 3 and Lu 2O 3 calcined at 1000°C showed high formation rate of 4-penten-1-ol per specific surface area over 1 mmol h -1 m -2 at 400°C. In the Yb 2O 3 catalyst calcined at 800°C, the conversion of 1,5-pentanediol was increased up to 74.4 mol% with increasing contact time, together with stable selectivity to 4-penten-1-ol of 71.8 mol%. In comparing the reactivity of alkanediols to form the corresponding unsaturated alcohols over Yb 2O 3, we found the reactivity of alkanediols into the corresponding unsaturated alcohols was the following order: 1,4-butanediol &gt 1,3-diols ≫ 1,5-pentanediol ≫ 1,6-hexanediol. © 2012 Elsevier B.V. All rights reserved.

Exfoliated graphene ligands were prepared by heating exfoliated graphene sheets in ammonia gas at 1023 K. The functional groups of the functionalized exfoliated graphene ligands were mainly pyridine on the edges of the vacancy defects. Copper cations were coordinated with the ligands. Even after being heated at 773 K, coordinated copper did not show severe agglomeration. On the other hand, copper supported on exfoliated graphene sheets prepared by the conventional method agglomerated and ca. 20 nm of copper oxide was formed. This difference clearly shows that exfoliated graphene ligands stabilized copper cations. (C) 2011 Elsevier Ltd. All rights reserved.

A series of rare earth oxides were investigated as catalysts in the ketonization of acetic acid. High selectivity to acetone over 99% was obtained by reacting acetic acid over rare earth oxides such as La2O3, CeO2, Pr6O11, and Nd2O3. Especially, Pr6O11 showed the highest yield of 80% at 350 degrees C among the 14 rare earth oxides. The bulk structure of CeO2 was stable during the ketonization, while the surface acetate species were observed over CeO2 after ketonization. In contrast, the other active rare earth oxides such as La2O3, Pr6O11, and Nd2O3 were mainly basic oxides due to the formation of bulk oxyacetate such as MO(AcO), where M is La, Pr, and Nd and AcO indicates CH3COO group, in the initial period of the reaction. In any case, the catalytic ketonization proceeds over the surface of the oxyacetates and CeO2. Catalytic cycle of the ketonization is composed of two steps: the decomposition of surface M2O(AcO)(4) to produce MO(AcO), acetone, and carbon dioxide and the regeneration of surface M2O(AcO)(4) by reacting MO(AcO) and acetic acid to produce water. (C) 2011 Elsevier B.V. All rights reserved.

Vapor-phase catalytic reactions of several terminal diols were investigated over several rare earth oxides, such as Sc(2)O(3), Y(2)O(3), CeO(2), Yb(2)O(3), and Lu(2)O(3). Sc(2)O(3) showed selective catalytic activity in the dehydration of terminal diols with long carbon chain, such as 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-dodecanediol, to produce the corresponding unsaturated alcohols. In the dehydration of 1,6-hexanediol, 5-hexen-1-ol was produced with selectivity over 60 mol%, together with by-products such as epsilon-caprolactone and oxacycloheptane. In the dehydration of 1,10-decanediol, 9-decen-1-ol was produced with selectivity higher than 70 mol%. In addition to Sc(2)O(3), heavy rare earth oxides such as Lu(2)O(3) as well as monoclinic ZrO(2) showed moderate selectivity in the dehydration of the terminal diols. (C) 2010 Elsevier B. V. All rights reserved.

Silica gel samples with macropores were prepared from solutions of silicate and poly(vinyl alcohol) (PVA), where macropores were formed by fixing a transitional structure of phase separation. Among the silica sources tested, tetraethoxysilane (TEOS), colloidal silica and water glass, only the system with water glass shows phase separation and forms macroporous silica gel. In the system with TEOS, ethanol formed during hydrolysis of TEOS becomes good solution and stabilizes the system not to induce phase separation. In the system with colloidal silica, dense structure of silica is probably not suitable for controlling phase separation and gelation. In the system with water glass, driving force of phase separation is considered to be a repulsive interaction between solvent molecules and PVA interacting with silica surface and the solution separates into a phase rich in solvent and that rich in silica and PVA. One of the features in the water glassPVA system is insensitivity of macropore size against compositional change in the solution, i.e. macroporous morphology in the resultant silica gel hardly changes by changing the composition ratio in the solution. This would be an advantage in the preparation of well-defined macroporous silica from water glass, whose composition varies among the product lot number, because reproducibility in macroporous morphology is ensured regardless of the lot number of the water glass. © 2004 Elsevier B.V.

Ni/TiO2 with bimodal pore structure was prepared from nickel nitrate and titanium alkoxide by a sol-gel process under acidic conditions in the presence of formamide. The Ni/TiO2 has continuous macropores which are formed by fixing the transitional structure of phase separation. Although the addition of nickel nitrate in the sol-gel reaction of titanium alkoxide steeply decreases the phase separation tendency, the macropore size can be controlled by changing the composition of preparation. The Ni/TiO2 prepared by sol-gel has higher dispersion of Ni compared with that prepared by impregnation, and shows catalytic activity for the selective hydrogenation of crotonaldehyde: selectivity in the hydrogenation of C=C bond is much higher than that of C=O bond over sol-gel-derived Ni/TiO2. (C) 2010 Elsevier B.V. All rights reserved.

Dehydration of 1,4-butanediol (14BDO) was investigated over indium oxide. Over the indium oxide prepared by precipitation, both conversion of 14BDO and selectivity to unsaturated alcohol, 3-buten-1-ol (3B1ol), increase with the increase in calcination temperature of indium oxide irrespective of the decrease in the specific surface area. The maximum values of 79.6% conversion and 79.0% selectivity to 3B1ol are obtained over indium oxide calcined at 900 °C. The values are much higher than the activities of commercial indium oxide. The activities of indium oxide depend on the shape of particles. Indium oxides prepared by the precipitation are composed of particles with diameter of 10-70 nm. The size and shape of particles change by calcination: spherical shape at low temperature of < 800 °C varies to angular one at > 800 °C with a slight growth of particle size. The change in the shape of the particles means that indium oxide crystallites calcined at > 800 °C mainly expose 2 2 2 facets. The dehydration reaction of 14BDO to 3B1ol is preferentially promoted over 2 2 2 surface of bixbyite structure. © 2010 Elsevier B.V. All rights reserved.

Vapor-phase catalytic dehydration of 1,3-butanediol was investigated over rare earth oxides (REOs) calcined at different temperatures. In the dehydration of 1,3-butanediol over REOs such as Dy(2)O(3), Ho(2)O(3), Er(2)O(3), Tm(2)O(3), Yb(2)O(3), Lu(2)O(3), and Y(2)O(3), 3-buten-2-ol and 2-buten-1-ol were preferentially produced. REOs exhibited different catalytic activities in the dehydration of 1,3-butanediol depending on their crystal structures. CeO(2) showed the highest formation rate with the highest selectivity to the unsaturated alcohols among the REOs. Cubic REOs also selectively produced the unsaturated alcohols: cubic Er(2)O(3), Yb(2)O(3), and Lu(2)O(3) showed high formation rate of the unsaturated alcohols. Since the formation rates of the unsaturated alcohols over Er(2)O(3) and CeO(2) were suppressed in CO(2) and NH(3) carrier gas flows more than in H(2) flow, it is probable that the acid-base sites play a major role of the formation of the unsaturated alcohols. (C) 2010 Elsevier B.V. All rights reserved.

Phase separation in an acidic aqueous solution with sodium silicate and sodium dodecyl sulfate (SDS) was investigated. The solution separated into silica-rich and SDS-rich phases during condensation of silica components. During the phase separation, the transition structure was fixed by gelation, resulting in mutually continuous morphology. The addition of a small amount of water-miscible organic solvents, such as methanol, ethanol, 1-propanol, and 1-butanol, into the reacting solution greatly decreases both viscosity and phase separation tendency of the solution. In the system with high concentration of strong acid. SDS molecules form wormlike micelles, which not only increase viscosity of the solution hut also play an important role in the phase separation in the solution because the to of wormlike micelles increases apparent molecular weight of SDS and decreases mixing entropy. The decrease in the viscosity by the addition of organic solvents suggests that wormlike in become small in the presence of organic solvent molecules. Consequently, the addition of appropriate amount of organic solvent is effective for controlling phase separation tendency and size of the resulted macropores in the system with SDS through the change in the structure of the micelles. (C) 2010 The Ceramic Society of Japan All rights reserved

The catalytic Beckmann rearrangement of cyclododecanone oxime (CDOX) was investigated in silane-nitrile-solvent systems. We have found that chlorosilanes, such as trimethylchlorosilane and tetrachlorosilane, are effective catalysts to produce ω- laurolactam (LRL) at 100 °C. Tetrachlorosilane is the most active catalyst, and hydrocarbon solvents such as cyclohexane, hexane, and decane are suitable for the system. Nitriles such as acetonitrile and benzonitrile would play an important role as a remover of silane species from the produced LRL-silane salt. © 2010 The Chemical Society of Japan.

水ガラスから調製した二元細孔シリカゲルを構造規定在としてのテトラプロピルアンモニウムイオン共存下で水蒸気処理を行うことにより、マクロ孔構造を維持したゼオライト成形体を合成した。生成した試料は、相分離の過渡構造を凍結して得られたマクロ孔、ゼオライト結晶子間隙に相当するメゾ孔、ゼオライト格子内のミクロ孔が階層的に配列した三元細孔構造を有していることが確認された。シリカゲルの水蒸気処理の際の結晶化挙動は、構造規定材濃度や水蒸気処理温度などの処理条件の他に、シリカゲルのメゾ孔サイズやマクロ孔のサイズにも依存して変化することがわかった。マクロ孔構造を維持したまま結晶化するのに最適な条件を決定した。また、得られたゼオライトの固体触媒としての物性評価を行った。

Magic-angle spinning pulsed field gradient nuclear magnetic resonance (MAS PFG NMR) was applied for selective self-diffusion measurements of acetone -n-alkane (C(6) up to C(9)) mixtures in nanoporous silica gel. Two specimens of silica gel with mean pore sizes of about 4 and 10 nm are considered. In the smaller pores, the n-alkane diffusivities are by about one and the acetone diffusivities by about two orders of magnitude smaller than in the larger pores. In addition, the acetone diffusivities in the narrow-pore specimen exhibit a pronounced oscillation with increasing chain length of the solvent n-alkanes: the diffusivities of acetone dissolved in odd-carbon number n-alkanes exceed those of acetone dissolved in even-carbon number n-alkanes by about 50%! These findings reproduce the tendencies observed in previous macroscopic release studies (Phys. Chem. Chem. Phys. 2003, 5, 2476) and suggest the formation of acetone -n-alkane complex-like assemblages in the narrow-pore silica gel.

Bimodal porous silica gel with both macropores and mesopores was prepared from water glass (WG) in the presence of low-molecular-weight surfactant, sodium dodecyl sulfate (SDS), by inducing phase separation during sol-gel reaction. The macroporous morphology was controlled by changing starting composition and gelation temperature: the change in the concentration of SDS was effective to control connectivity of macropores and silica gel skeleton in micrometer size, and the gelation temperature significantly affected macropore size. From the change in morphology with the concentration of SDS, it is considered that a homogeneous reacting solution separated into a phase of SDS and that of polymerized silica in contrast to other silica-surfactant systems, where phase separation proceeds between solvent and surfactant associated with silica gel surface. It is also suggested that SDS forms associated complex or micelle in aqueous acidic solution, and the formation of such structure plays an important role in the phase stability. We also controlled mesopore structures in the macroporous silica gel by aging as-geled samples under basic conditions.

Monolithic polycrystalline zeolites with through-macropores were prepared by steam treatment of bimodal porous silica gel monolith in the presence of tetrapropylammonium hydroxide, where the bimodal porous silica gel was prepared by inducing phase separation during sol-gel process. The silica skeleton with mesopores was transformed into polycrystalline zeolites maintaining continuous macropore morphology and monolithic shape. In the zeolites, there are three different pores arranged hierarchically: through-macropores originally existed in the precursor silica gel, small macropores at interstitial of zeolite crystallites, and micropores in zeolite framework.