Hydrogenation of n-octanoic acid over the MoPt alloy of Mo-Pt/SiO2 catalyst under solvent-free conditions.

SiO2-Supported bimetallic Mo and Pt worked as an effective heterogeneous catalyst for hydrogenation of n-octanoic acid at a low temperature of 373 K in the absence of solvent, providing 78% yield of hydrogenated products (62% yield of 1-octanol and 32% yield of octyl octanoate). Based on the catalyst characterization, MoPt alloy (Mo/Pt = 1) was formed by high-temperature reduction and was proposed to be the active site for the reaction.

Porous nanographene formation on γ-alumina nanoparticles via transition-metal-free methane activation.

γ-Al2O3 nanoparticles promote pyrolytic carbon deposition of CH4 at temperatures higher than 800 °C to give single-walled nanoporous graphene (NPG) materials without the need for transition metals as reaction centers. To accelerate the development of efficient reactions for NPG synthesis, we have investigated early-stage CH4 activation for NPG formation on γ-Al2O3 nanoparticles via reaction kinetics and surface analysis. The formation of NPG was promoted at oxygen vacancies on (100) surfaces of γ-Al2O3 nanoparticles following surface activation by CH4. The kinetic analysis was well corroborated by a computational study using density functional theory. Surface defects generated as a result of surface activation by CH4 make it kinetically feasible to obtain single-layered NPG, demonstrating the importance of precise control of oxygen vacancies for carbon growth.

Deoxydehydration of Biomass-Derived Polyols Over Silver-Modified Ceria-Supported Rhenium Catalyst with Molecular Hydrogen.

Olefin production from polyols via deoxydehydration (DODH) was carried out over Ag-modified CeO2 -supported heterogeneous Re catalysts with H2 as a reducing agent. Both high DODH activity and low hydrogenation ability for C=C bonds were observed in the reaction of erythritol, giving a 1,3-butadiene yield of up to 90 % under "solvent-free" conditions. This catalyst is applicable to other substrates such as methyl glycosides (methyl α-fucopyranoside: 91 % yield of DODH product; methyl ß-ribofuranoside: 88 % yield), which were difficult to be converted to the DODH products over the DODH catalysts reported previously. ReOx -Ag/CeO2 was reused 3 times without a decrease of activity or selectivity after calcination as regeneration. Although the transmission electron microscopy energy-dispersive X-ray spectroscopy and X-ray absorption fine structure analyses showed that Re species were highly dispersed and Ag was present as metal particles with various sizes from well-dispersed species (<1 nm) to around 5 nm particles, the catalysts prepared from size-controlled Ag nanoparticles showed similar performance, indicating that the catalytic performance is insensitive to the Ag particle size.

CeO2-Catalyzed Synthesis of 2-Imidazolidinone from Ethylenediamine Carbamate.

CeO2 acted as an effective and reusable heterogeneous catalyst for the direct synthesis of 2-imidazolidinone from ethylenediamine carbamate (EDA-CA) without further addition of CO2 in the reaction system. 2-Propanol was the best solvent among the solvents tested from the viewpoint of selectivity to 2-imidazolidinone, and the use of an adequate amount of 2-propanol provided high conversion and selectivity for the reaction. This positive effect of 2-propanol on the catalytic reaction can be explained by the solubility of EDA-CA in 2-propanol under the reaction conditions and no formation of solvent-derived byproducts. This catalytic system using the combination of the CeO2 catalyst and the 2-propanol solvent provided 2-imidazolidinone in up to 83% yield on the EDA-CA basis at 413 K under Ar. The reaction conducted under Ar showed a higher reaction rate than that with pressured CO2, which clearly demonstrated the advantage of the catalytic system operated at low CO2 pressure or even without CO2.

Adsorption of Keggin-Type Polyoxometalates on Rh Metal Particles under Reductive Conditions.

The adsorption of POMs on Rh/SiO2 in water solvent under strongly reductive conditions was investigated. Aqueous solutions of α-Keggin type silicotungstate and silicovanadotungstates were mixed with Rh/SiO2 at 393-473 K under 1 MPa of H2. Monovanadium-substituted silicotungstate, α-SiVW11O405- (SiVW11), was more readily adsorbed than nonsubstituted silicotungstate, α-SiW12O404- (SiW12). After adsorption at 433 K, SiVW11 was desorbed from Rh/SiO2 by oxidation with Br2 water without change of the Keggin structure, as evidenced by 51V NMR. Trivanadium-substituted silicotungstate, α-1,2,3-SiV3W9O407-, was not stable, and the desorbed species from Rh/SiO2 by oxidation with Br2 did not maintain the Keggin structure. The very high temperature for adsorption (473 K) also led to the decomposition of the Keggin structure of SiVW11. An increase in the concentration of SiVW11 in the liquid phase gave a saturation of the amount of desorbable SiVW11, up to five SiVW11 anions per one Rh particle with a 3 nm size. The elemental analysis and W L3-edge extended X-ray absorption fine structure of Rh/SiO2 after the adsorption of SiVW11 showed that a part of SiVW11 was decomposed and irreversibly adsorbed as metallic W species incorporated into the surface of Rh metal particles. The amount of decomposed SiVW11 was almost the same as that of SiVW11 adsorbed as the original Keggin structure. The desorbable SiVW11 was probably bonded on the W atom incorporated on the Rh metal particles as the two-electron-reduced form (α-SiVIIIW11O407-).

Selective Hydrogenolysis of Erythritol over Ir-ReOx /Rutile-TiO2 Catalyst.

Partial hydrogenolysis of erythritol, which can be produced at large scale by fermentation, to 1,4-butanediol (1,4-BuD) is investigated with Ir-ReOx /SiO2 and Ir-ReOx /rutile-TiO2 catalysts. In addition to the higher conversion rate over Ir-ReOx /TiO2 than over Ir-ReOx /SiO2 , which has been also reported for glycerol hydrogenolysis, Ir-ReOx /TiO2 showed higher selectivity to 1,4-BuD than Ir-ReOx /SiO2 , especially at low conversion levels, leading to high 1,4-BuD productivity of 20 mmol1,4-BuD gIr -1 h-1 at 373 K (36 % conversion, 33 % selectivity). The productivity based on the noble metal amount is higher than those reported previously, although the maximum yield of 1,4-BuD (23 %) is not higher than the highest reported values. The reactions of various triols, diols and mono-ols are tested and the selectivity and the reaction rates are compared between catalysts and between substrates. The Ir-ReOx /TiO2 catalyst showed about twofold higher activity than Ir-ReOx /SiO2 in hydrogenolysis of the C-OH bond at the 2- or 3-positions in 1,2- and 1,3-diols, respectively, whereas the hydrogenolysis of C-OH at the 1-position is less promoted by the TiO2 support. Lowering the loading amount of Ir on TiO2 (from 4 wt % to 2 or 1 wt %) decreases the Ir-based activity and 1,4-BuD selectivity. Similarly, increasing the loading amount on SiO2 from 4 wt % to 20 wt % increases the Ir-based activity and 1,4-BuD selectivity, although they remain lower than those for TiO2 -supported catalyst with 4 wt % Ir. High metal loadings on the support seem to be important.

One-pot imine synthesis from methylarenes and anilines under air over heterogeneous Cu oxide-modified CeO2 catalyst.

Cu oxide-modified CeO2 (CuOx-CeO2) with 2 wt% Cu loading amount was the most effective and reusable heterogeneous catalyst for selective one-pot imine synthesis from methylarenes and anilines via direct oxidation of the sp3 C-H bond in the methylarenes with atmospheric air (0.1 MPa) as an oxidant.

Erythritol: Another C4 Platform Chemical in Biomass Refinery.

The potential of erythritol as a platform chemical in biomass refinery is discussed in terms of erythritol production and utilization. Regarding erythritol production, fermentation of sugar or starch has been already commercialized. The shift of the carbon source from glucose to inexpensive inedible waste glycerol is being investigated, which will decrease the price of erythritol. The carbon-based yield of erythritol from glycerol is comparable to or even higher than that from glucose. The metabolic pathway of erythritol biosynthesis has become clarified: erythrose-4-phosphate, which is one of the intermediates in the pentose phosphate pathway, is dephosphorylated and reduced to erythritol. The information about the metabolic pathway may give insights to improve the productivity by bleeding. Regarding erythritol utilization, chemical conversions of erythritol, especially deoxygenation, have been investigated in these days. Erythritol is easily dehydrated to 1,4-anhydroerythritol, which can be also used as the substrate for production of useful C4 chemicals. C-O hydrogenolysis and deoxydehydration using heterogeneous catalysts are effective reactions for erythritol/1,4-anhydroerythritol conversion.

Biobased Cycloolefin Polymers: Carvone-Derived Cyclic Conjugated Diene with Reactive exo-Methylene Group for Regioselective and Stereospecific Living Cationic Polymerization.

Carvone, a naturally abundant chiral cyclic α,ß-unsaturated carbonyl compound, was chemically transformed into cyclic exo-methylene conjugated dienes. The exo-methylene group had high reactivity in cationic polymerization and was efficiently polymerized in a controlled manner via regioselective 1,4-conjugated additions using initiating systems effective for living cationic polymerization of vinyl ethers. The obtained polymers with 1,3-cyclohexenyl units and tetra-substituted olefins in the main chain showed high glass transition temperatures over 110 °C. The chiral monomer underwent stereospecific polymerization to result in polymers with low solubility and weak packing of the rigid main chain in the lamellar layers. The racemic mixture resulted in soluble amorphous polymers, which were subsequently hydrogenated into cycloolefin polymers with enhanced thermal properties.

A nickel-iridium alloy as an efficient heterogeneous catalyst for hydrogenation of olefins.

Nickel and iridium supported on SiO2 (Ni-Ir/SiO2) acted as an effective and reusable heterogeneous catalyst for hydrogenation of olefins, and it showed higher activity and selectivity than the monometallic counterparts. The Ni-Ir/SiO2 catalyst has small Ni-Ir alloy and monometallic Ni particles, and the high catalytic performance can be attributed to the isolated Ni atom in the Ni-Ir alloys.

Preparation of Highly Active Monometallic Rhenium Catalysts for Selective Synthesis of 1,4-Butanediol from 1,4-Anhydroerythritol.

1,4-Butanediol can be produced from 1,4-anhydroerythritol through the co-catalysis of monometallic mixed catalysts (ReOx /CeO2 +ReOx /C) in the one-pot reduction with H2 . The highest yield of 1,4-butanediol was over 80 %, which is similar to the value obtained over ReOx -Au/CeO2 +ReOx /C catalysts. Mixed catalysts of CeO2 +ReOx /C showed almost the same performance, giving 89 % yield of 1,4-butanediol. The reactivity trends of possible intermediates suggest that the reaction mechanism over ReOx /CeO2 +ReOx /C is similar to that over ReOx -Au/CeO2 +ReOx /C: deoxydehydration (DODH) of 1,4-anhydroerythritol to 2,5-dihydrofuran over ReOx species on the CeO2 support with the promotion of H2 activation by ReOx /C, isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran catalyzed by ReOx on the C support, hydration of 2,3-dihydrofuran catalyzed by C, and hydrogenation to 1,4-butanediol catalyzed by ReOx /C. The reaction order of conversion of 1,4-anhydroerythritol with respect to H2 pressure is almost zero and this indicates that the rate-determining step is the formation of 2,5-dihydrofuran from the coordinated substrate with reduced Re in the DODH step. The activity of ReOx /CeO2 +ReOx /C is higher than that of ReOx -Au/CeO2 +ReOx /C, which is probably related to the reducibility of ReOx /C and the mobility of the Re species between the supports. High-valent Re species such as Re7+ on the CeO2 and C supports are mobile in the solvent; however, low-valent Re species, including metallic Re species, have much lower mobility. Metallic Re and cationic low-valent Re species with high reducibility and low mobility can be present on the carbon support as a trigger for H2 activation and promoter of the reduction of Re species on CeO2 . The presence of noble metals such as Au can enhance the reducibility through the activation of H2 molecules on the noble metal and the formation of spilt-over hydrogen over noble metal/CeO2 , as indicated by H2 temperature-programmed reduction. The higher reducibility of ReOx -Au/CeO2 lowers the DODH activity of ReOx -Au/CeO2 +ReOx /C in comparison with ReOx /CeO2 +ReOx /C by restricting the movement of Re species from C to CeO2 .

CO2 Conversion with Alcohols and Amines into Carbonates, Ureas, and Carbamates over CeO2 Catalyst in the Presence and Absence of 2-Cyanopyridine.

Recent progress on the CeO2 catalyzed synthesis of organic carbonates, ureas, and carbamates from CO2 +alcohols, CO2 +amines, and CO2 +alcohols+amines, respectively, is reviewed. The reactions of CO2 with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H2 O is essential in order to get the target product in high yield. One of the effective method of the H2 O removal from the related reaction systems is the combination with the hydration of 2-cyanopyridine to 2-picolinamide, which is also catalyzed by CeO2 .

Ring-opening polymerization of trimethylene carbonate to poly(trimethylene carbonate) diol over a heterogeneous high-temperature calcined CeO2 catalyst.

CeO2 calcined at 1273 K showed higher activity per surface area than other metal oxides in the ring-opening polymerization of trimethylene carbonate under neat conditions without any additives, providing metal-free and additive-free poly(trimethylene carbonate) diols with no ether bonds with high selectivity. It was demonstrated that CeO2 was a robust and reusable heterogeneous catalyst.

Selective hydrogenation of amides to alcohols in water solvent over a heterogeneous CeO2-supported Ru catalyst.

CeO2-supported Ru (Ru/CeO2) worked as an effective and reusable heterogeneous catalyst for the selective dissociation of the C-N bond in amides, particularly primary amides, with H2 in water solvent at low reaction temperature of 333 K, and high yields of the corresponding alcohols were obtained from primary amides.

Transformation of Sugars into Chiral Polyols over a Heterogeneous Catalyst.

Transformation of sugars, while maintaining the intrinsic stereochemical structure, is desirable. However, such a transformation requires multistep synthesis with protection and deprotection of the OH groups. Herein, a new method for selective transformation of sugar derivatives into chiral building blocks and a diol synthon, with retention of the intrinsic configuration (stereo- and regioselectively), is demonstrated. The method is based on the selective recognition of cis-vicinal OH groups in sugars and leads to the one-pot removal of the cis-vicinal OH groups, without protection of OH groups (except the OH group of the hemiacetal group), over a heterogeneous CeO2 -supported ReOx and Pd (ReOx -Pd/CeO2 ) catalyst by using H2 as a reducing agent.

Formation of a New, Strongly Basic Nitrogen Anion by Metal Oxide Modification.

Development of new hybrid materials having unique and unprecedented catalytic properties is a challenge for chemists, and heterogeneous-homogeneous hybrid catalysts have attracted much attention because of the preferable and exceptional properties that are highly expected to result from combination of the components. Base catalysts are widely used in organic synthesis as key materials, and a new class of base catalysts has made a large impact from academic and industrial viewpoints. Here, a principle for creating a new strong base by hybridization of homogeneous and heterogeneous components is presented. It is based on the modification of organic compounds with metal oxides by using the acid-base property of metal oxides. Based on kinetic and DFT studies, combination of CeO2 and 2-cyanopyridine drastically enhanced the basicity of 2-cyanopyridine by a factor of about 109 (∼9 by pKa (in CH3CN)), and the pKa was estimated to be ∼21, which locates it in the superbase category. 2-Cyanopyridine and CeO2 formed a unique adsorption complex via two interaction modes: (i) coordinative interaction between the Ce atom of CeO2 and the N atom of the pyridine ring in 2-cyanopyridine, and (ii) covalent interaction between the surface O atom of CeO2 and the C atom of the CN group in 2-cyanopyridine by addition of the lattice oxygen of CeO2 to the CN group of 2-cyanopyridine. These interactions established a new, strongly basic site of N- over the CeO2 surface.

Selective hydrogenation of nitroarenes to aminoarenes using a MoOx-modified Ru/SiO2 catalyst under mild conditions.

Modification of Ru/SiO2 with metal oxides (MoOx, WOx, and ReOx) improved the activity and selectivity in the hydrogenation of 3-nitrostyrene to 3-aminostyrene under mild conditions such as 0.3 MPa H2, 303 K, and no solvent. Ru-MoOx/SiO2(Mo/Ru = 1/2) catalyst was applicable to various substituted nitroarenes, providing the corresponding substituted aminoarenes in high yields (85-99%).

Regioselectivity and Reaction Mechanism of Ru-Catalyzed Hydrogenolysis of Squalane and Model Alkanes.

The dependence of the C-C hydrogenolysis activity on reaction parameters and the structure of the substrate alkanes was investigated for Ru/CeO2 catalyst with very small (dispersion: H/Ru=0.89) Ru particles. The substrate concentration and reaction temperature did not have a significant effect on the selectivity pattern, except that methane production was promoted at high temperatures. However, the hydrogen pressure had a marked effect on the selectivity pattern. Ctertiary -C bond dissociation, terminal Csecondary -Cprimary bond dissociation, and fragmentation to form excess methane had negative reaction order with respect to hydrogen partial pressure, whereas Csecondary -Csecondary bond dissociation had an approximately zero reaction order. Therefore, a high hydrogen pressure is essential for the regioselective hydrogenolysis of Csecondary -Csecondary bonds in squalane. Ru/SiO2 catalyst with larger Ru particles showed similar changes in the product distribution during the change in hydrogen pressure. The reaction mechanism for each type of C-C bond dissociation is proposed based on reactivity trends and DFT calculations. The proposed intermediate species for the internal Csecondary -Csecondary dissociation, terminal Csecondary -Cprimary dissociation, and Ctertiary -C dissociation is alkyls, alkylidynes, and alkenes, respectively.

Synthesis of 2-Butanol by Selective Hydrogenolysis of 1,4-Anhydroerythritol over Molybdenum Oxide-Modified Rhodium-Supported Silica.

Rh-MoOx /SiO2 (Mo/Rh=0.13) is an effective catalyst for the hydrogenolysis of 1,4-anhydroerythritol (1,4-AHERY) and provides 2-BuOH in high yield of 51 %. This is the first report of the production of 2-BuOH from 1,4-AHERY by hydrogenolysis. 1,4-AHERY was more suitable as a starting material than erythritol because the 2-BuOH yield from erythritol was low (34 %). Based on the kinetics and comparison of reactivities of the related compounds using Rh-MoOx /SiO2 and Rh/SiO2 catalysts, the modification of Rh/SiO2 with MoOx leads to the high activity and high selectivity to 2-BuOH because of the generation of reactive hydride species and the strong adsorption of 1,4-AHERY on MoOx species. The reaction proceeds by main two routes, (I) the combination of single C-O hydrogenolysis with the desorption of intermediates, a usual route in hydrogenolysis, and (II) multiple C-O hydrogenolysis without the desorption of intermediates from the active site, and the reaction mechanism for Route (II) is proposed.

Direct Copolymerization of CO2 and Diols.

Direct polymerization of CO2 and diols is promising as a simple and environmental-benign method in place of conventional processes using high-cost and/or hazardous reagents such as phosgene, carbon monoxide and epoxides, however, there are no reports on the direct method due to the inertness of CO2 and severe equilibrium limitation of the reaction. Herein, we firstly substantiate the direct copolymerization of CO2 and diols using CeO2 catalyst and 2-cyanopyridine promotor, providing the alternating cooligomers in high diol-based yield (up to 99%) and selectivity (up to >99%). This catalyst system is applicable to various diols including linear C4-C10 α,ω-diols to provide high yields of the corresponding cooligomers, which cannot be obtained by well-known methods such as copolymerization of CO2 and cyclic ethers and ring-opening polymerization of cyclic carbonates. This process provides us a facile synthesis method for versatile polycarbonates from various diols and CO2 owing to simplicity of diols modification.