Tuning the Selectivity of Catalytic Nitrile Hydrogenation with Phase-Controlled Co Nanoparticles Prepared by Hydrosilane-Assisted Method.

Cobalt (Co) is a promising candidate to replace noble metals in the hydrogenation process, which is widely employed in the chemical industry. Although the catalytic performance for this reaction has been considered to be significantly dependent on the Co crystal phase, no satisfactory systematic studies have been conducted, because it is difficult to synthesize metal nanoparticles that have different crystalline structures with similar sizes. Here we report a new method for the synthesis of cobalt nanoparticles using hydrosilane as a reducing agent (hydrosilane-assisted method). This new method uses 1,3-butanediol and propylene glycol to successfully prepare fcc and hcp cobalt nanoparticles, respectively. These two types of Co nanoparticles have similar sizes and surface areas. The hcp Co nanoparticles exhibit higher catalytic performance than fcc nanoparticles for the hydrogenation of benzonitrile under mild conditions. The present hcp Co catalyst is also effective for highly selective benzyl amine production from benzonitrile without ammonia addition, whereas many catalytic systems require ammonia addition for selective benzyl amine production. Mechanistic studies revealed that the fast formation of the primary amine and the prevention of condensation and secondary amine hydrogenation promote selective benzonitrile hydrogenation for benzylamine over hcp Co nanoparticles.

Low-Temperature Ammonia Synthesis on Iron Catalyst with an Electron Donor.

Haber-Bosch process produces ammonia to provide food for over 5 billion people; however, it is currently required to be produced without the use of fossil fuels to reduce global CO2 emissions by 3% or more. It is indispensable to devise heterogeneous catalysts for the synthesis of ammonia below 100-150 °C to minimize the energy consumption of the process. In this paper, we report metallic iron particles with an electron-donating material as a catalyst for ammonia synthesis. Metallic iron particles combined with a mixture of BaO and BaH2 species in an appropriate manner could catalyze ammonia synthesis even at 100 °C. The iron catalyst revealed that iron can exhibit a high turnover frequency (∼12 s-1), which is over an order of magnitude higher than those of other transition metals used in highly active catalysts for ammonia synthesis. This can be attributed to the intrinsic nature of iron to desorb adsorbed hydrogen atoms as hydrogen molecules at low temperatures.

Synthesis and Aerobic Oxidation Catalysis of Mesoporous Todorokite-Type Manganese Oxide Nanoparticles by Crystallization of Precursors.

The pursuit of a high surface area while maintaining high catalytic performance remains a challenge due to a trade-off relationship between these two features in some cases. In this study, mesoporous todorokite-type manganese oxide (OMS-1) nanoparticles with high specific surface areas were synthesized in one step by a new synthesis approach involving crystallization (i.e., solid-state transformation) of a precursor produced by a redox reaction between MnO4- and Mn2+ reagents. The use of a low-crystallinity precursor with small particles is essential to achieve this solid-state transformation into OMS-1 nanoparticles. The specific surface area reached up to ca. 250 m2 g-1, which is much larger than those (13-185 m2 g-1) for Mg-OMS-1 synthesized by previously reported methods including multistep synthesis or dissolution/precipitation processes. Despite ultrasmall nanoparticles, a linear correlation between the catalytic reaction rates of OMS-1 and the surface areas was observed without a trade-off relationship between particle size and catalytic performance. These OMS-1 nanoparticles exhibited the highest catalytic activity among the Mn-based catalysts tested for the oxidation of benzyl alcohol and thioanisole with molecular oxygen (O2) as the sole oxidant, including highly active ß-MnO2 nanoparticles. The present OMS-1 nanomaterial could also act as a recyclable heterogeneous catalyst for the aerobic oxidation of various aromatic alcohols and sulfides under mild reaction conditions. The mechanistic studies showed that alcohol oxidation proceeds with oxygen species caused by the solid, and the high surface area of OMS-1 significantly contributes to an enhancement of the catalytic activity for aerobic oxidation.

N-Rich, Polyphenolic Porous Organic Polymer and Its In Vitro Anticancer Activity on Colorectal Cancer.

N-rich organic materials bearing polyphenolic moieties in their building networks and nanoscale porosities are very demanding in the context of designing efficient biomaterials or drug carriers for the cancer treatment. Here, we report the synthesis of a new triazine-based secondary-amine- and imine-linked polyphenolic porous organic polymer material TrzTFPPOP and explored its potential for in vitro anticancer activity on the human colorectal carcinoma (HCT 116) cell line. This functionalized (-OH, -NH-, -C=N-) organic material displayed an exceptionally high BET surface area of 2140 m2 g-1 along with hierarchical porosity (micropores and mesopores), and it induced apoptotic changes leading to high efficiency in colon cancer cell destruction via p53-regulated DNA damage pathway. The IC30, IC50, and IC70 values obtained from the MTT assay are 1.24, 3.25, and 5.25 µg/mL, respectively.

Effect of MnO2 Crystal Structure on Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid.

Aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) as a bioplastics monomer is efficiently promoted by a simple system based on a nonprecious-metal catalyst of MnO2 and NaHCO3. Kinetic studies indicate that the oxidation of 5-formyl-2-furancarboxylic acid (FFCA) to FDCA is the slowest step for the aerobic oxidation of HMF to FDCA over activated MnO2. We demonstrate through combined computational and experimental studies that HMF oxidation to FDCA is largely dependent on the MnO2 crystal structure. Density functional theory (DFT) calculations reveal that vacancy formation energies at the planar oxygen sites in α- and γ-MnO2 are higher than those at the bent oxygen sites. ß- and λ-MnO2 consist of only planar and bent oxygen sites, respectively, with lower vacancy formation energies. Consequently, ß- and λ-MnO2 are likely to be good candidates as oxidation catalysts. On the other hand, experimental studies reveal that the reaction rates per surface area for the slowest step (FFCA oxidation to FDCA) decrease in the order of ß-MnO2 > λ-MnO2 > γ-MnO2 ≈ α-MnO2 > δ-MnO2 > ε-MnO2; the catalytic activity of ß-MnO2 exceeds that of the previously reported activated MnO2 by three times. The order is in good agreement not only with the DFT calculation results, but also with the reduction rates per surface area determined by the H2-temperature-programmed reduction measurements for MnO2 catalysts. The successful synthesis of high-surface-area ß-MnO2 significantly improves the catalytic activity for the aerobic oxidation of HMF to FDCA.

Intramolecular Electron Transfer and Oxygen Transfer of Phosphomolybdate Molecular Wires.

Phosphomolybdates with different P species exhibiting a 1D molecular structure are synthesized. The materials are constructed by a {[MoVI6O21]6-}n molecular tube as a shell with trapping a redox-active species P in the center. The building units ([(HPIIIO3)MoVI6O18]2- or [(PV2O7)MoVI12O36]4-) form at room temperature, which further polymerize linearly along the c-axis. Interestingly, the material shows an unusual heat-triggered intramolecular redox property, which undergoes an electron-transfer-oxygen-transfer procedure from [{(HPIIIO3)MoVI6O18]2-}n to {[(PV2O7)MoVI12O36]4-}n/2. The crystal structure of the material is stable during the oxidation reaction, while the central P is oxidized and the local structure changes.

Redox-Active Zeolitic Transition Metal Oxides Based on ε-Keggin Units for Selective Oxidation.

The design and development of zeolitic transition metal oxides for selective oxidation are interesting due to the combination of the redox properties and microporosities. Redox-active zeolitic transition metal oxides based on ε-Keggin iron molybdates were synthesized. O2 can be activated by the materials via an electron-transfer-based process, and the materials can be oxidized even at room temperature. The materials are oxidized and reduced reversibly while the crystal structures are maintained. V is uniformly incorporated in the materials without changing the basic structures, and the redox properties of the materials are tuned by V. The materials are used as robust catalysts for ethyl lactate oxidation to form ethyl pyruvate using O2 as an oxidant.

Large Oblate Hemispheroidal Ruthenium Particles Supported on Calcium Amide as Efficient Catalysts for Ammonia Decomposition.

Ammonia decomposition is an important technology for extracting hydrogen from ammonia toward the realization of a hydrogen economy. Herein, it is reported that large oblate hemispheroidal Ru particles on Ca(NH2 )2 function as efficient catalysts for ammonia decomposition. The turnover frequency of Ru/Ca(NH2 )2 increased by two orders of magnitude when the Ru particle size was increased from 1.5 to 8.4 nm. More than 90 % ammonia decomposition was achieved over Ru/Ca(NH2 )2 with large oblate hemispheroidal Ru particles at 360 °C, which is comparable to that of alkali-promoted Ru catalysts with small Ru particle sizes. XAFS analyses revealed that Ru particles are immobilized on Ca(NH2 )2 by Ru-N bonds formed at the metal/support interface, which lead to oblate hemispheroidal Ru particles. Such a strong metal-support interaction in Ru/Ca(NH2 )2 is also substantiated by DFT calculations. The high activity of Ru/Ca(NH2 )2 with large Ru particles primarily originates from the shape and appropriate size of the Ru particles with a high density of active sites rather than the electron-donating ability of Ca(NH2 )2 .

Self-organized Ruthenium-Barium Core-Shell Nanoparticles on a Mesoporous Calcium Amide Matrix for Efficient Low-Temperature Ammonia Synthesis.

A low-temperature ammonia synthesis process is required for on-site synthesis. Barium-doped calcium amide (Ba-Ca(NH2 )2 ) enhances the efficacy of ammonia synthesis mediated by Ru and Co by 2 orders of magnitude more than that of a conventional Ru catalyst at temperatures below 300 °C. Furthermore, the presented catalysts are superior to the wüstite-based Fe catalyst, which is known as a highly active industrial catalyst at low temperatures and pressures. Nanosized Ru-Ba core-shell structures are self-organized on the Ba-Ca(NH2 )2 support during H2 pretreatment, and the support material is simultaneously converted into a mesoporous structure with a high surface area (>100 m2 g-1 ). These self-organized nanostructures account for the high catalytic performance in low-temperature ammonia synthesis.

Electronic Effect of Ruthenium Nanoparticles on Efficient Reductive Amination of Carbonyl Compounds.

Highly selective synthesis of primary amines over heterogeneous catalysts is still a challenge for the chemical industry. Ruthenium nanoparticles supported on Nb2O5 act as a highly selective and reusable heterogeneous catalyst for the low-temperature reductive amination of various carbonyl compounds that contain reduction-sensitive functional groups such as heterocycles and halogens with NH3 and H2 and prevent the formation of secondary amines and undesired hydrogenated byproducts. The selective catalysis of these materials is likely attributable to the weak electron-donating capability of Ru particles on the Nb2O5 surface. The combination of this catalyst and homogeneous Ru systems was used to synthesize 2,5-bis(aminomethyl)furan, a monomer for aramid production, from 5-(hydroxymethyl)furfural without a complex mixture of imine byproducts.

Ultrathin Anionic Tungstophosphite Molecular Wire with Tunable Hydrophilicity and Catalytic Activity for Selective Epoxidation in Organic Media.

The extended 1D tungstophosphite molecular wire is obtained by connection of polyoxometalates. Self-assembly of a triangular PIII O3 unit with tungstate produces a hexagonal [HPIII W6 O21 ]2- building block, which then connects linearly to form the molecular wire. The surface property of the molecular wire is tuned to hydrophobic using organoammonium cations, and the surface-modified material disperses easily in organic media. The multifunctional material, which possesses nanostructure, hydrophobicity, and redox properties simultaneously, is suitable for olefin epoxidation in organic solvent.

The Assembly of an All-Inorganic Porous Soft Framework from Metal Oxide Molecular Nanowires.

An all-inorganic soft framework is rare but interesting for both fundamental research and practical applications. Here, an all-inorganic soft framework based on a transition metal oxide is reported. The periodic connection of a one-dimensional anionic tungstoselenate molecular wire building block with a CoII ion is used to construct the crystalline material. The crystal structure of the material was determined by high-angle annular dark-field scanning transmission electron microscopy combined with several characterization techniques. The soft framework of the material enables water adsorption/desorption with a change in its structure, leading to a high level of water adsorption. The framework of the material is flexible, and the structure of the molecular wire building block is stable during the water adsorption/desorption process.

Structural Characterization of 2D Zirconomolybdate by Atomic Scale HAADF-STEM and XANES and Its Highly Stable Electrochemical Properties as a Li Battery Cathode.

The structural determination of nanomaterials and their application in energy storage and transfer are of great importance. Herein, a layered zirconomolybdate with a two-dimensional structure was synthesized. Atomic resolution electron microscopy was utilized for direct visualization of the structure that was further confirmed by powder X-ray diffraction and X-ray absorption near-edge structure analyses. The structure of the molecular sheet was stable at a high temperature in an oxidative atmosphere. The electrochemical performance of the material was evaluated with a Li battery composed of the calcined material as a cathode. Li ions were reversibly inserted and extracted between the layers without collapse of the structure of the material. The electrochemical properties of the material were derived from the reversible redox activity of the Mo ions and Zr ions in the material as well as the flexibility of the molecular layer of the material.

Photoassist-phosphorylated TiO2 as a catalyst for direct formation of 5-(hydroxymethyl)furfural from glucose.

Photo-assisted phosphorylation of an anatase TiO2 catalyst was examined to improve its catalytic performance for the direct production of 5-(hydroxymethyl)furfural (HMF), a versatile chemical platform, from glucose. In phosphorylation based on simple esterification between phosphoric acid and surface OH groups on anatase TiO2 with water-tolerant Lewis acid sites, the density of phosphates immobilized on TiO2 is limited to 2 phosphates nm-2, which limits selective HMF production. Phosphorylation of the TiO2 surface under fluorescent light irradiation increases the surface phosphate density to 50%, which is higher than the conventional limit, thus preventing the adsorption of hydrophilic glucose molecules on TiO2 and resulting in a more selective HMF production over photoassist-phosphorylated TiO2.

Acidic Ultrafine Tungsten Oxide Molecular Wires for Cellulosic Biomass Conversion.

The application of nanocatalysis based on metal oxides for biomass conversion is of considerable interest in fundamental research and practical applications. New acidic transition-metal oxide molecular wires were synthesized for the conversion of cellulosic biomass. The ultrafine molecular wires were constructed by repeating (NH4 )2 [XW6 O21 ] (X=Te or Se) along the length, exhibiting diameters of only 1.2 nm. The nanowires dispersed in water and were observed using high-angle annular dark-field scanning transmission electron microscopy. Acid sites were created by calcination without collapse of the molecular wire structure. The acidic molecular wire exhibited high activity and stability and promoted the hydrolysis of the glycosidic bond. Various biomasses including cellulose were able to be converted to hexoses as main products.

Mechanism Switching of Ammonia Synthesis Over Ru-Loaded Electride Catalyst at Metal-Insulator Transition.

The substitution of electrons for O(2-) anions in the crystallographic cages of [Ca24Al28O64](4+)(O(2-))2 was investigated to clarify the correlation between the electronic properties and catalytic activity for ammonia synthesis in Ru-loaded [Ca24Al28O64](4+)(O(2-))2-x(e(-))2x (0 ≤ x ≤ 2). This catalyst has low catalytic performance with an electron concentration (Ne) lower than 1 × 10(21) cm(-3) and a high apparent activation energy (Ea) for ammonia synthesis comparable to that for conventional Ru-based catalysts with a basic promoter such as alkali or alkaline earth compounds. Replacement of more than half of the cage O(2-) anions with electrons (Ne ≈ 1 × 10(21) cm(-3)) significantly changes the reaction mechanism to yield a catalytic activity that is an order higher and with half the Ea. The metal-insulator transition of [Ca24Al28O64](4+)(O(2-))2-x(e(-))2x also occurs at Ne ≈ 1 × 10(21) cm(-3) and is triggered by structural relaxation of the crystallographic cage induced by the replacement of O(2-) anions with electrons. These observations indicate that the metal-insulator transition point is a boundary in the catalysis between Ru-loaded [Ca24Al28O64](4+)(O(2-))2 and [Ca24Al28O64](4+)(e(-))4. It is thus demonstrated that whole electronic properties of the support material dominate catalysis for ammonia synthesis.

Recent progress in the development of solid catalysts for biomass conversion into high value-added chemicals.

In recent decades, the substitution of non-renewable fossil resources by renewable biomass as a sustainable feedstock has been extensively investigated for the manufacture of high value-added products such as biofuels, commodity chemicals, and new bio-based materials such as bioplastics. Numerous solid catalyst systems for the effective conversion of biomass feedstocks into value-added chemicals and fuels have been developed. Solid catalysts are classified into four main groups with respect to their structures and substrate activation properties: (a) micro- and mesoporous materials, (b) metal oxides, (c) supported metal catalysts, and (d) sulfonated polymers. This review article focuses on the activation of substrates and/or reagents on the basis of groups (a)-(d), and the corresponding reaction mechanisms. In addition, recent progress in chemocatalytic processes for the production of five industrially important products (5-hydroxymethylfurfural, lactic acid, glyceraldehyde, 1,3-dihydroxyacetone, and furan-2,5-dicarboxylic acid) as bio-based plastic monomers and their intermediates is comprehensively summarized.

Slow reactant-water exchange and high catalytic performance of water-tolerant Lewis acids.

(31)P nuclear magnetic resonance (NMR) spectroscopic measurement with trimethylphosphine oxide (TMPO) was applied to evaluate the Lewis acid catalysis of various metal triflates in water. The original (31)P NMR chemical shift and line width of TMPO is changed by the direct interaction of TMPO molecules with the Lewis acid sites of metal triflates. [Sc(OTf)3] and [In(OTf)3] had larger changes in (31)P chemical shift and line width by formation of the Lewis acid-TMPO complex than other metal triflates. It originates from the strong interaction between the Lewis acid and TMPO, which results in higher stability of [Sc(OTf)3TMPO] and [In(OTf)3TMPO] complexes than other metal triflate-TMPO complexes. The catalytic activities of [Sc(OTf)3] and [In(OTf)3] for Lewis acid-catalyzed reactions with carbonyl compounds in water were far superior to the other metal triflates, which indicates that the high stability of metal triflate-carbonyl compound complexes cause high catalytic performance for these reactions. Density functional theory (DFT) calculation suggests that low LUMO levels of [Sc(OTf)3] and [In(OTf)3] would be responsible for the formation of stable coordination intermediate with nucleophilic reactant in water.

La1-xSrxFeO3-δ Perovskite Oxide Nanoparticles for Low-Temperature Aerobic Oxidation of Isobutane to tert-Butyl Alcohol.

The development of reusable solid catalysts based on naturally abundant metal elements for the liquid-phase selective oxidation of light alkanes under mild conditions to obtain desired oxygenated products, such as alcohols and carbonyl compounds, remains a challenge. In this study, various perovskite oxide nanoparticles were synthesized by a sol-gel method using aspartic acid, and the effects of A- and B-site metal cations on the liquid-phase oxidation of isobutane to tert-butyl alcohol with molecular oxygen as the sole oxidant were investigated. Iron-based perovskite oxides containing Fe4+ such as BaFeO3-δ, SrFeO3-δ, and La1-xSrxFeO3-δ exhibited catalytic performance superior to those of other Fe3+- and Fe2+-based iron oxides and Mn-, Ni-, and Co-based perovskite oxides. The partial substitution of Sr for La in LaFeO3 significantly enhanced the catalytic performance and durability. In particular, the La0.8Sr0.2FeO3-δ catalyst could be recovered by simple filtration and reused several times without an obvious loss of its high catalytic performance, whereas the recovered BaFeO3-δ and SrFeO3-δ catalysts were almost inactive. La0.8Sr0.2FeO3-δ promoted the selective oxidation of isobutane even under mild conditions (60 °C), and the catalytic activity was comparable to that of homogeneous systems, including halogenated metalloporphyrin complexes. On the basis of mechanistic studies, including the effect of Sr substitution in La1-xSrxFeO3-δ on surface redox reactions, the present oxidation proceeds via a radical-mediated oxidation mechanism, and the surface-mixed Fe3+/Fe4+ valence states of La1-xSrxFeO3-δ nanoparticles likely play an important role in promoting C-H activation of isobutane as well as decomposition of tert-butyl hydroperoxide.