Atsushi Takagaki

Green chemistry: Biodiesel made with sugar catalyst

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for ‘biodiesel’ production.

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.

Nanosheets as highly active solid acid catalysts for green chemical syntheses

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.

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.

Highly Active Mesoporous Nb–W Oxide Solid-Acid Catalyst†

The synthesis of mesoporous transition-metal oxides has been extensively studied because of their wide range of potential applications. Examples of such compounds include mesoporous TiO2, [2, 3] ZrO2, [2, 4] Nb2O5, [2,3b, 5] Ta2O5, [2, 6] (Nb,Ta)2O5, [2, 7] SnO2, [2, 8] and WO3, [2] which are used as a variety of heterogeneous catalysts, such as solid-acid catalysts, 5d, 6f,g] photocatalysts, 6b,h] oxidation catalysts, and catalyst supports. Solid-acid catalysts, which are reusable and readily separable from reaction products, have been widely investigated as direct replacements for liquid acids to reduce the impact on the environment and to decrease costs. The use of mesoporous transition-metal oxides is an interesting approach to developing a solid-acid catalyst with enhanced activity. The mesopores in the oxide allows the reactants access additional active acid sites in the pores, resulting in improved rates of acid catalysis. Sulfated mesoporous niobium and tantalum oxides have been reported to exhibit remarkable activity in acid-catalyzed Friedel–Crafts alkylation and isomerization. 6f,g] However, the use of the recycled catalyst remains difficult, a result of the leaching of sulfate species, as reported for mesoporous silica and organosilicas bearing sulfonic acid groups. Herein, mesoporous Nb– W mixed oxides are examined as solid-acid catalysts, these give very high catalytic performance in Friedel–Crafts alkylation, hydrolysis, and esterification, which originates from the mesoporous structure and different acid properties formed by specific Nb and W concentrations. Mesoporous Nb–W mixed oxides were prepared from NbCl5 and WCl6 in the presence of a poly block copolymer surfactant Pluronic P-123 as a structure-directing agent. (Additional details are provided in the Supporting Information) Peaks attributable to mesopores were observed from NbxW(10 x) oxides with x values from 2 to 10 in the small-angle powder X-ray diffraction (XRD) pattern (see Figure S1 in the Supporting Information). Peaks attributed to (110) and (200) of the two-dimensional hexagonal structure were observed from an x = 10 sample (mesoporous Nb oxide), which was consistent with previous studies. Wide-angle powder XRD patterns revealed the presence of crystallized tungsten oxide (WO3) in W-rich samples (x = 0 to 2). The presence of mesopores was also indicated by the N2 sorption isotherms (Figure 1) for the same samples (x = 2 to 10). The surface areas were estimated using the Brunauer–Emmett–Teller (BET) method, and pore volumes were obtained by the Barrett–Joyner–Halenda (BJH) method. Although the surface area decreased gradually from 200 (mesoporous Nb oxide) to 52 m g 1 (non-mesoporous W oxide) with increasing addition of W, up to x = 0, the pore volume decreased up to x = 3. Then, the pore volumes increased in the non-mesoporous W-rich oxides (x = 0 to 2) due to the formation of void spaces between particles (Supporting Information, Figure S2). The pore diameter obtained by the BJH method decreased from 7 (mesoporous Nb oxide) to 4.2 nm (mesoporous Nb3W7 oxide) with increasing W content, and mesopores were not observed in the Nb1W9 oxide (Supporting Information, Figure S3). SEM and TEM images of the porous

Efficient Utilization of Nanospace of Layered Transition Metal Oxide HNbMoO6 as a Strong, Water-Tolerant Solid Acid Catalyst

Layered HNbMoO6 was found to function as a strong solid acid catalyst, exceeding the activity of zeolites and ion-exchange resins for Friedel-Crafts alkylation. HNbMoO6 also exhibited high catalytic activity for esterification of hydrocarboxylic acid and hydration. The catalytic performance of layered HNbMoO6 is attributed to the intercalation of reactants into the interlayer and the development of strong acidity.

Biodiesel made with sugar catalyst.

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for ‘biodiesel’ production.

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.

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