Kiyotaka Nakajima

Niobic acid, Nb(2)O(5)·nH(2)O, has been studied as a heterogeneous Lewis acid catalyst. NbO(4) tetrahedra, Lewis acid sites, on Nb(2)O(5)·nH(2)O surface immediately form NbO(4)-H(2)O adducts in the presence of water. However, a part of the adducts can still function as effective Lewis acid sites, catalyzing the allylation of benzaldehyde with tetraallyl tin and the conversion of glucose into 5-(hydroxymethyl)furfural in water.

Homogeneous Brønsted acid catalysts such as H2SO4 and HCl are used for the production of industrially important chemicals. However, their use requires significant energy costs for separation, reuse, and treatment of salt wastes. Alternatively, heterogeneous Brønsted acid catalysts are promising candidates that can decrease the environmental impact associated with chemical production. In this review, we highlight amorphous carbon bearing SO3H groups as an insoluble Brønsted acid available for var

The utilization of 5-(hydroxymethyl)furfural (HMF) for the large-scale production of essential chemicals has been largely limited by the formation of solid humin as a byproduct, which prevents the operation of stepwise batch-type and continuous flow-type processes. The reaction of HMF with 1,3-propanediol produces an HMF acetal derivative that exhibits excellent thermal stability. Aerobic oxidation of the HMF acetal with a CeO₂ -supported Au catalyst and Na₂ CO₃

Ethenylene groups within the silicate framework of hybrid mesoporous ethenylene-silica (HME) are successfully modified via a two-step chemical modification process (see Figure) to produce a sulfonic acid-functionalized hybrid mesoporous solid acid catalyst. The material exhibits high activity for various acid-catalyzed reactions and can be used repeatedly without deactivation. The Diels–Alder modification described can be extended to the creation of other functional materials.

Sulfonic acid group (SO3H)-bearing amorphous carbon/mesoporous silica composites were studied for use as solid acid catalysts. Sugar-derived amorphous carbon with SO3H cannot catalyze hydrophobic acid-catalyzed reactions, such as the dimerization of α-methylstyrene, because of the small surface area. However, SO3H-bearing sugar-derived amorphous carbon supported on mesoporous silica exhibits remarkable catalytic performance for the dimerization of α-methylstyrene. Under optimal conditions, the s

This paper reviews amorphous carbon bearing sulfonic acid groups as an efficient solid acid catalyst for the production of various chemicals. The material is produced by the sulfonation of incompletely carbonized organic carbon to yield an insoluble, stable, and inexpensive catalyst with acid catalytic activity comparable to that of sulfuric acid (H 2 SO 4 ). The carbon material can also be readily separated from liquid products by decantation or filtration, and can be repeatedly reused without

New logic circuits are designed which employ as information bits the flux-quantum vortices occurring in Josephson junctions of extended dimensions. It is shown that Josephson lines can be interconnected in certain direct ways so that complete logic capability can be achieved with networks of Josephson lines alone.

Anatase TiO2 prepared by a simple sol–gel reaction of Ti(i-pro)4 was studied as an early transition metal oxide with Lewis acid sites workable in water. Fourier transform infrared (FT-IR) measurements revealed that TiO2 has a significantly higher density of effective Lewis acid sites in water than niobic acid (Nb2O5·nH2O), a heterogeneous water-tolerant Lewis acid, because most Lewis acid sites on TiO2 can maintain Lewis acidity even in the presence of water, which is in contrast to those on Nb2

A combination of ethanol solvent and hydrotalcite (HT) with a Mg/Al ratio of 3:1 was effective for the isomerization of glucose to fructose in up to 56% yield with a high selectivity of 80%. The ethanol solvent shifts the isomerization equilibrium between glucose and fructose, which allows the fructose yield to exceed the upper limit of enzymatic isomerization conducted in water at modest temperatures (i.e., 50%). The HT catalyst maintained such high catalytic performance in repeated use at leas

Hydrothermal treatment of NH4[NbO(C2O4)2(H2O)2]·nH2O in water at 448 K for 3 days produced crystalline Nb2O5 with a deformed orthorhombic structure and a high surface area (208 m2 g–1). Fourier-transform infrared spectroscopy measurements of pyridine adsorption revealed that the Nb2O5 catalyst has both high densities of Brønsted and Lewis acid sites that can work in the presence of water. One feature of the Nb2O5 catalyst is its high density of water-compatible Lewis acid sites (0.21 mmol g–1),

Mesoporous Nb2O5·nH2O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250−350 m2 g−1 and pore volumes of 0.2−0.4 mL g−1, which are larger than that of bulk Nb2O5·nH2O. Fourier transform-

Aerobic oxidation of biomass-derived furfural to furoic acid was studied with an N-heterocyclic carbene as a homogeneous catalyst. Carbene species generated in situ on 1,3-bis(2,4,6-trimethylphenyl) imidazolium chloride with a strong organic base (1,8-diazabicyclo[5.4.0]undec-7-ene) was highly active and selective for the formation of furoic acid in dimethyl sulfoxide at 40 °C. This reaction initiates the formation of a Breslow intermediate between an N-heterocyclic carbene and a furfural molecu

A discussion is presented of one of the simplest models of Josephson computer systems (phase mode system), in which quantized vortices of magnetic flux (fluxoids) are employed as information bits and in which all logic functions are achieved by interactions between fluxoids. In a phase mode system, device operation depends on the existence of many stable states differing from each other by integer multiples of 2 pi in the phase plane. As an example, the authors propose a simple model of a comple

A unique strategy for the formation of furan-2,5-dicarboxylic acid (FDCA)-derived esters with methanol and ethylene glycol in concentrated solutions was reported using a six-membered ring acetal of (5-hydroxymethyl)furfural (HMF) with 1,3-propanediol in order to improve the economics for the production of polyethylene 2,5-furandicarboxylate (PEF), a biobased polyester. Aerobic oxidative esterification with methanol and ethylene glycol in the presence of a CeO 2 -supported Au catalyst gave 80-95%