Takaaki Hanaoka

Effect of transition metals on oxygenates formation from syngas over Co/SiO2

Effects of precursors and modification on Co/SiO2 catalyst for carbon monoxide hydrogenation were studied at elevated pressures. Although Co/SiO2 derived from cobalt (II) acetate (Co(A)/SiO2) was quite inactive, it exhibited dramatically high activity especially for the formation of ethanol by modification with some transition metals such as iridium, ruthenium, rhodium, rhenium, osmium and platinum. At the same time, ethanol productivities of other Co/SiO2 catalysts derived from cobalt(II) nitrate (Co(N)/SiO2) or chloride (Co(Cl)/SiO2) were not so much improved by modification with rhenium as to Co(A)/SiO2. Chloride compounds were especially unfavorable as precursors of the component elements for the formation of oxygenated compounds. The catalytic activities and product distributions of Co(A)-Sr/SiO2 catalysts modified with these noble metals were very similar to each other. An ethanol selectivity of more than 20% was obtained using these catalysts. On the other hand, iridium and ruthenium did not have any important effect as modifiers of Co/SiO2 catalyst derived from Co2(CO)8 (Co(CO)/SiO2) which itself had an activity similar to that of modified Co(A)/SiO2 catalysts. Using X-ray diffraction, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure to characterize the catalyst, it is concluded that highly dispersed cobalt metal is the main active site on the Co(A)/SiO2 catalyst and that transition metals promote the reduction of Co2+ cation to a metallic state by a hydrogen spill-over mechanism.

Synthesis of new microporous layered organic–inorganic hybrid nanocomposites by alkoxysilylation of a crystalline layered silicate, ilerite

We have developed microporous organic–inorganic hybrid nanocomposites by alkoxysilylation of 4,4′-biphenyl-bridged alkoxysilane compounds, which contain triethoxysilyl, methyldiethoxysilyl, and dimethylethoxysilyl groups at each end of the 4,4′-biphenylene unit ((CH3)n(C2H5O)3−n-Si-C12H8-Si-(OC2H5)3−n(CH3)n, n = 0, 1, or 2, abbreviated as BESB(0), BESB(2), or BESB(4), respectively, where the number in parentheses indicates the number of methyl groups in these molecules), in the interlayer of a crystalline layered silicate, ilerite. XRD, 29Si solid-state NMR and fluorescence spectroscopy revealed the immobilization and bridging formation of the BESB molecules between the silicate layers by condensation, not only with H-ilerite, but also with the BESB molecules. The interlayer structures exhibited different molecular arrangements. BESB(0) and BESB(4) molecules are present as a monolayer arrangement in which BESB(0) molecules form the oligomeric species caused by close stacking like a dimer. BESB(2) molecules form mainly bilayer-like aggregates in the interlayer. The structural differences are caused by the different reactivities of the BESB molecules, which control their polymerization in the interlayer. The resultant BESB(0)- and BESB(2)-ilerite had high microporosity with BET surface areas (508 and 578 m2 g−1 for BESB(0)- and BESB(2)-ilerite, respectively). The micropores showed higher toluene adsorptivity than several other porous silica materials due to the successful surface modification. Consequently, this approach provides a new method for constructing novel microporous nanocomposites, the key to improved selectivity and activity in separation and catalytic applications.

Amperometric l-lactate biosensor based on screen-printed carbon electrode containing cobalt phthalocyanine, coated with lactate oxidase-mesoporous silica conjugate layer

A novel amperometric biosensor for the measurement of L-lactate has been developed. The device comprises a screen-printed carbon electrode containing cobalt phthalocyanine (CoPC-SPCE), coated with lactate oxidase (LOD) that is immobilized in mesoporous silica (FSM8.0) using a polymer matrix of denatured polyvinyl alcohol; a Nafion layer on the electrode surface acts as a barrier to interferents. The sampling unit attached to the SPCE requires only a small sample volume of 100 μL for each measurement. The measurement of l-lactate is based on the signal produced by hydrogen peroxide, the product of the enzymatic reaction. The behavior of the biosensor, LOD-FSM8.0/Naf/CoPC-SPCE, was examined in terms of pH, applied potential, sensitivity and operational range, selectivity, and storage stability. The sensor showed an optimum response at a pH of 7.4 and an applied potential of +450 mV. The determination range and the response time for L-lactate were 18.3 μM to 1.5 mM and approximately 90s, respectively. In addition, the sensor exhibited high selectivity for L-lactate and was quite stable in storage, showing no noticeable change in its initial response after being stored for over 9 months. These results indicate that our method provides a simple, cost-effective, high-performance biosensor for l-lactate.

Alcohol synthesis from syngas over cobalt catalysts prepared from Co2(CO)8

Carbon monoxide hydrogenation catalyzed by silica-supported cobalt catalysts prepared from dicobalt octacarbonyl [Co2(CO)8] yields alcohols with greater than 20% selectivity accompanied by 80% hydrocarbons. Modification by alkaline earth metal oxides enhanced the formation of alcohols in the order: Mg ⪡ Ca < Sr ⩽ Ba. A maximum selectivity as high as 60% for oxygenated compounds was observed at a Ba:Co mole ratio of 1.5 – 2.2. Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies of these catalysts show that Co2(CO)2 supported on SiO2 changes to Co4(CO)12in vacuo, and then to highly dispersed cobalt metal when heated in a stream of hydrogen at 673 K. High-pressure in situ FT-IR studies show that the formation of alcohols may be related to the presence of bridged-CO species on the surface of the catalysts.

Synthesis of C2-oxygenates from syngas over cobalt catalysts promoted by ruthenium and alkaline earths

Abstract Silica-supported cobalt catalysts doubly modified with ruthenium and alkaline earths were active for the synthesis of C 2 -oxygenates (C 2 O) from syngas. Triruthenium dodecacarbonyl was more effective than ruthenium trichloride as a ruthenium precursor. Ruthenium increased the catalytic activity by promoting the reduction of cobalt. Alkaline earths improved the selectivity of C 2 O by controlling the oxidation states of the cobalt catalysts. The chain-growth probabilities of hydrocarbons, oxygenates and total products in the Schultz-Flory equation on a Co Ru Sr/ SiO 2 catalyst were 0.48–0.49.

Oxygenates from syngas over highly dispersed cobalt catalysts

Highly dispersed cobalt metal catalyst has been prepared by the deposition of Co2(CO)8 on silicagel in an oxygen-free condition and has been characterized with EXAFS. This catalyst exhibited high activity for the formation of C2+ oxygenates from syngas without any modification. The formation of hydrocarbons was strongly suppressed and the selectivity of oxygenates, especially C2-oxygenates, was enhanced by the modification with alkali or alkaline earth cations. From the modification effects on CO hydrogenation and by the studies of in situ FT-IR, these basic cations were considered to reduce the hydrogenating ability of the catalyst by controlling the electronic state of the active cobalt site. Noble metals such as iridium and ruthenium have little effect on the catalyst of CO hydrogenation. Similar cobalt catalysts were prepared from C02(CO)8 on other oxide supports and some oxides showed a similar effect on the basic additives. The effect of the cations and the reaction mechanism for the formation of oxygenates were discussed.

Transparent cubic Fd3m mesoporous silica monoliths with highly controllable pore architectures

Ordered cubic Fd3m mesoporous silica monoliths (HOM-11) were fabricated by using lyotropic and microemulsion phases of block copolymers (EOm–POn–EOm) as templates. Aromatic and aliphatic hydrocarbon molecules were used in the formation of true microemulsion liquid crystal phases, in the expansion of pore sizes, and in the changes in the phase geometrical shape. Large cylinder-like pores in the range of 6–11 nm with uniform constrictions and bimodal mesopore sizes can be easily produced (within minutes) by adopting this simple and reproducible strategy. The degree of solubilization of the hydrocarbons crucially influenced the generation of the more open-pore systems with cylindrical cubic Fd3m channels. Our results also show that enlargement of pore sizes of cubic Fd3m monoliths was achieved with the use of a high concentration of copolymers in the composition phase domains, a high degree of swelling and a large size of PO–EO blocks (core–corona) of the copolymer templates. In addition, this synthetic approach is also efficient in designing cubic Fd3m silica monoliths with large-sized glass, thick-walled frameworks up to 30 nm thick and high mesopore/micropore volumes. Although XRD patterns show well-defined Bragg diffraction peaks indicative of highly ordered cubic Fd3m structures, TEM micrographs reveal that worm-like mesopore channels in large domains were observed with samples synthesized from copolymers with small EO–PO block ratios. This finding indicates that the molecular nature (i.e. the flexibility of the corona- and core-blocks) of the copolymer templates not only led to disordered pore channels but also reduced the ability to design more mesostructured phases.

Enhancement in thermal stability and resistance to denaturants of lipase encapsulated in mesoporous silica with alkyltrimethylammonium (CTAB)

We assembled a highly durable conjugate with both a high-density accumulation and a regular array of lipase, by encapsulating it in mesoporous silica (FSM) with alkyltrimethylammonium (CTAB) chains on the surface. The activity for hydrolyzing esters of the lipase immobilized in mesoporous silica was linearly related to the concentration of lipase, whereas that of non-immobilized lipase showed saturation due to self-aggregation at a high concentration. The lipase conjugate also had increased resistance to heating when stayed in the silica coupling with CTAB. In addition, encapsulating the enzyme with FSM coupled CTAB caused the lipase to remain stable even in the presence of urea and trypsin, suggesting that the encapsulation prevented dissociation and denaturing. This conjugate had much higher activity and much higher stability for hydrolyzing esters when compared to the native lipase. These results show that FSM provides suitable support for the immobilization and dispersion of proteins in mesopores with disintegration of the aggregates.

Niobic acid as a solid acid catalyst for ring-opening reactions of phenyloxirane

Abstract Catalyst performance of niobic acid were examined in titled reactions. Isomerization and hydrolysis of phenyloxirane occurred under mild conditions in high activities and selectivities. The surface hydrophilicity of niobic acid was much more suitable for the hydrolysis than that of other solid acid catalysts such as SiO2Al2O3, H-ZSM5 and H-silicalite, because of the affinity for both water and organic substrate. The active site on niobic acid could be assigned for each reaction.

Preparation of Copper Nitride (Cu3N) Nanoparticles in Long-Chain Alcohols at 130–200 °C and Nitridation Mechanism

In our laboratory, we are studying copper nitride (Cu3N) nanoparticles as a novel conductive ink that is stable to oxidation and can be metallized at low temperature. In this study, Cu3N nanoparticles prepared via the reaction of copper(II) acetate monohydrate with ammonia gas in long-chain alcohol solvents were characterized by X-ray diffraction analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. In addition, we used thermogravimetry-differential thermal analysis to compare the thermal decomposition properties of the prepared Cu3N particles and commercially available Cu3N particles. The decomposition temperature of the prepared particles was more than 170 °C lower than that of the commercial particles. We also examined the influences of the reaction temperature and the alkyl chain length of the alcohol solvent on the product distribution of the reaction and the morphology of the particles. Our results indicated that increasing the solvent hydrophobicity and eliminating water from the reaction system by increasing the temperature affected the product distribution. On the basis of an observation of chromatic change of the reaction solvent and an analysis of the byproducts in the alcohol solvent after the reaction, we propose a mechanism for the formation of Cu3N.