Shun Nishimura

Hydrotalcite-supported gold-nanoparticle-catalyzed highly efficient base-free aqueous oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid under atmospheric oxygen pressure

Green synthesis of 2,5-furandicarboxylic acid, one of the most important chemical building blocks from biomass, viaoxidation of 5-hydroxymethylfurfural has been demonstrated using hydrotalcite-supported gold nanoparticle catalyst in water at 368 K under atmospheric oxygen pressure without addition of homogeneous base.

Synthesis of glycerol carbonate from glycerol and dialkyl carbonates using hydrotalcite as a reusable heterogeneous base catalyst

An uncalcined Mg–Al hydrotalcite catalyst involving hydromagnesite with a high surface area acted as a highly active base catalyst for glycerol carbonate synthesis from glycerol and dialkyl carbonates under moderate reaction conditions.

Characterization, synthesis and catalysis of hydrotalcite-related materials for highly efficient materials transformations

This review is intended to introduce recent progress in the characterization, synthesis and catalysis of hydrotalcite (HT) and HT-related materials. NMR, in situ neutron diffraction and TG–DTA techniques have been used to determine the local structure and structural changes of HT. Various synthetic methods of controlling the morphology of HT are introduced together with the crystal formation mechanism. The preparation methods of magnetic HTs are also included. The HT acts as a heterogeneous base catalyst for efficient transformations of organic compounds such as the synthesis of glycerol carbonate, transesterification of oils (biodiesel production) and carbon–carbon bond formations. The HT has also been used as a support for immobilizing various metal species (Ru, Pd, Ag, Au, Pt, Cu, V, Mn etc.), which enables highly selective organic reactions such as dehydrogenation of alcohols and deoxygenation of epoxides. Cooperative actions between basic sites of the HT surface and supported metal species are introduced. It is also shown that the HT can work together with other solid acids and metal catalysts to promote sequential reactions in a one-pot manner, which gives us a very important methodology for environmentally-benign synthesis of value-added chemicals, especially from biomass-derived compounds.

Direct Synthesis of 1,6‐Hexanediol from HMF over a Heterogeneous Pd/ZrP Catalyst using Formic Acid as Hydrogen Source

A new approach is developed for hydrogenolytic ring opening of biobased 5-hydroxymethylfurfural (HMF), dehydration product of hexoses, towards 1,6-hexanediol (HDO) under atmospheric pressure. The highest yield of HDO, 43%, is achieved over reusable Pd/zirconium phosphate (ZrP) catalyst at 413 K in the presence of formic acid as hydrogen source. In comparison with various Brønsted and/or Lewis acidic supports, the specific Brønsted acidity on ZrP support effectively accelerated the cleavage of C-O bond in a furan ring.

Selective Oxidation of Glycerol by Using a Hydrotalcite‐Supported Platinum Catalyst under Atmospheric Oxygen Pressure in Water

A hydrotalcite-supported platinum (Pt/HT) catalyst was found to be a highly active and selective heterogeneous catalyst for glycerol oxidation in pure water under atmospheric oxygen pressure in a high glycerol/metal molar ratio up to 3125. High selectivity toward glyceric acid (78 %) was obtained even at room temperature under air atmosphere. The Pt/HT catalyst selectively oxidized the primary hydroxyl group of 1,2-propandiol to give the corresponding carboxylic acid (lactic acid) as well as glycerol. The activity of the catalyst was greatly influenced by the Mg/Al ratio of hydrotalcite. Glycerol conversion increased with increasing the Mg/Al ratio of hydrotalcite (from trace to 56 %). X-ray absorption fine structure (XAFS) measurements indicated that the catalytic oxidation activity was proportional to the metallic platinum concentration, and more than 35 % of metallic platinum was necessary for this reaction. TEM measurements and titration analysis by using benzoic acid suggested that the solid basicity of hydrotalcite plays important roles in the precise control of platinum size and metal concentration as well as the initial promotion of alcohol oxidation.

The role of negatively charged Au states in aerobic oxidation of alcohols over hydrotalcite supported AuPd nanoclusters

The PVP-protected bimetallic gold–palladium nanoclusters (AuxPdy-PVP NCs) were prepared on the solid base hydrotalcite (HT) with various Au : Pd (x : y) molar ratios. Transmission electron microscopy showed narrow particle size distributions of AuxPdy-PVP NCs with a mean diameter in the range of 2.6–3.0 nm regardless of Pd content. Aerobic oxidations of 1-phenylethanol over the AuxPdy-PVP/HT catalysts showed that their catalytic activities were significantly affected by the Pd content. Correlations between charge transfer between Au and Pd and catalytic activity of the AuxPdy-PVP/HT catalysts were investigated with X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), Michaelis–Menten kinetic studies for alcohol oxidation, and other analytical techniques. The peaks of Au 4f in the XPS spectra were shifted to the lower energy side with increase of Pd content, indicating the electron transfer from Pd to Au atoms according to Paulings electronegativity protocol. The electron densities in the Au 5d orbital in the AuxPdy-PVP/HT catalysts estimated by the Au L3-XANES spectra correlated well with their catalytic activities. Moreover, the kinetic studies also proposed that the electron rich Au 5d states, resulting from the intermetallic electron transfer from Pd atoms, strongly contributed to the rate-determining step in the alcohol oxidation. It was concluded that the electronic negativity of the Au 5d states controlled by the Pd content accelerated the rate-determining step in alcohol oxidation through highly active radical-like intermediates.

Catalytic Transformations of Biomass-derived Materials into Value-added Chemicals

This manuscript reviews recent literatures on synthesis of furfurals (5-hydroxymethylfurfural, furfural, 5-methyl-2-furaldehyde) from various sugars (glucose, fructose, d-galactose, d-arabinose, xylose, l-rhamnose, lactose, cellobiose, sucrose) and furfural conversions into other carbonyl compounds (2,5-diformylfuran, 2,5-furandicarboxylic acid, levulinic acid, succinic acid) using catalytic methodology. Our recent achievements on one-pot synthesis of furfurals using solid acid and base catalysts and selective oxidations of furfurals using heterogeneous catalysts are also included.Graphical Abstract

Production of γ-valerolactone from biomass-derived compounds using formic acid as a hydrogen source over supported metal catalysts in water solvent

γ-Valerolactone (GVL) is a key intermediate for production of fuels and chemicals. In this research, GVL is synthesized from biomass-derived compounds using formic acid (FA) as a hydrogen source over various supported metal catalysts which are prepared by a simple impregnation or co-precipitation method. Under optimum conditions, levulinic acid (LA) is almost converted to GVL by Ru/C, Ru/SBA, Au/ZrC and Au/ZrO2 catalysts with above 90% yield in water solvent. Especially, the Au/ZrO2 showed excellent activity and recyclability; the Au/ZrO2 catalyst can decompose completely FA to CO2 and H2, which gives high yield of GVL (ca. 97%) from hydrogenation of LA, and can retain its activity for at least 5 recycle runs. GVL is also obtained from one-pot dehydration/hydrogenation reaction of fructose in water solvent. In this reaction, FA plays two roles: an acid catalyst for dehydration of fructose to LA, and a hydrogen source for hydrogenation of the obtained LA over supported metal catalysts. The Au/ZrO2 is the best catalyst for dehydration/hydrogenation reaction with overall GVL yield of 48% and can be reused several times.

Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent.

The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs.

Synthesis of levulinic acid from fructose using Amberlyst-15 as a solid acid catalyst

Levulinic acid was obtained from fructose over solid acid catalysts under mild reaction conditions in water. The reaction was carried out at different temperatures and amounts of catalysts to find the best reaction conditions. Among tested heterogeneous catalysts, Amberlyst-15 gave the highest LA yield (52%) with the lowest HMF yield (below 3%) under optimum conditions. Levulinic acid was isolated from the mixture after reaction by rotary vacuum evaporator with 47% isolated yield. The recycling experiments showed that Amberlyst-15 exhibited good activity even after 5 runs, though the LA yield gradually decreased from 52 to 30%.