||Shohei Nakamura, Atsushi Takagaki, Motonori Watanabe, Kanta Yamada, Masaaki Yoshida, Tatsumi Ishihara, Porous Boron Nitride as a Weak Solid Base Catalyst, CHEMCATCHEM, 10.1002/cctc.202001435, 12, 23, 6033-6039, 2020.12, Porous boron nitride was synthesized by pyrolysis from boric acid and urea mixed in varying molar ratios. The boron nitride prepared had high surface areas ranging from 376 to 647 m(2) g(-1)with both microporous and mesoporous structures. The sample prepared with a urea-to-boric acid molar ratio of 5 exhibited the highest pore volume with the highest surface area of mesopores. Boron-K edge X-ray absorption fine structure spectroscopy revealed that the surface structure consisted of BN(3)sites along with BN2O, BNO2, and BO(3)sites. Fourier transform infrared (FTIR) spectroscopy indicated the formation of amino and hydroxyl groups on the surface. Analysis using color indicator reagents and deuterated chloroform-adsorbed FTIR results indicated that the porous boron nitride had very weak base sites of strength +7.2>H->=+6.3. Porous boron nitride exhibited a high activity for the nitroaldol reaction with a high selectivity for nitroalkene (>97 %). A good correlation was observed between the catalytic activity of the boron nitride catalysts and their porous structures..
||Shoichiro Namba, Atsushi Takagaki, Keiko Jimura, Shigenobu Hayashi, Ryuji Kikuchi, S. Ted Oyama, Effects of ball-milling treatment on physicochemical properties and solid base activity of hexagonal boron nitrides, CATALYSIS SCIENCE & TECHNOLOGY, 10.1039/c8cy00940f, 9, 2, 302-309, 2019.01, 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 m(2) 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 degrees C whereas pristine h-BN showed no activity. The base sites were mainly responsible for the catalytic activity..
||Shogo Furusato, Atsushi Takagaki, Shigenobu Hayashi, Akio Miyazato, Ryuji Kikuchi, S. Ted Oyama, Mechanochemical Decomposition of Crystalline Cellulose in the Presence of Protonated Layered Niobium Molybdate Solid Acid Catalyst, CHEMSUSCHEM, 10.1002/cssc.201702305, 11, 5, 888-896, 2018.03, 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 C-13 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..
||Shusaku Torii, Keiko Jimura, Shigenobu Hayashi, Ryuji Kikuchi, Atsushi Takagaki, Utilization of hexagonal boron nitride as a solid acid-base bifunctional catalyst, JOURNAL OF CATALYSIS, 10.1016/j.jcat.2017.09.013, 355, 176-184, 2017.11, 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 (H-1 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 H-1 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 P-31 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 beta-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 nitro methane 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. (C) 2017 Elsevier Inc. All rights reserved..
||Atsushi Takagaki, Kinetic Analysis of Aqueous-phase Cyclodehydration of 1,4-Butanediol and Erythritol over a Layered Niobium Molybdate Solid Acid, Catalysis Science and Technology, 10.1039/C5CY01126D, 6, 791-799, Year 2016, 2015.08.