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Naturally occurring fungi have been used in the traditional production of dried bonito, Katsuobushi, in Japan. In this study, we analyzed the fungal population present during Katsuobushi production. Amplicon sequence analysis of ITS1 indicated that Aspergillus spp. are predominant throughout the production process. In addition, culture-dependent analyzes identified three species Aspergillus chevalieri, Aspergillus montevidensis, and Aspergillus sydowii, based on sequencing of benA, caM, and rpb2 genes. A. chevalieri isolates were classified into teleomorphic and anamorphic strains based on morphological analysis. A. chevarieri was the dominant species throughout the production process, whereas A. montevidensis increased and A. sydowii decreased in abundance during Katsuobushi production. Our study will enhance the understanding of fungal species involved in traditional Katsuobushi production.

Isotropic pitch-based carbon fiber has been utilized for various applications such as thermal insulation materials for high-temperature furnace and additives for slide member, but the structure of the carbon fiber is still under debate. This is because the precursor pitch contains various aromatic compounds in addition to the complicated oxidation and carbonization reaction during production process of carbon fiber. In this work, oxidation processes of model compounds of pitch such as pyrene (sp2C H with zigzag-like edges), triphenylene (sp2C H with armchair edges), fluorene (pentagon with sp3CH2), and 9-methylanthracene (hexagon with sp3CH3) were analyzed using mass spectrometry, elemental analysis, infrared (IR), Raman, and X-ray photoelectron spectroscopy (XPS) in addition to calculation such as molecular dynamic simulation with a reactive force field (ReaxFF) and simulation of IR, Raman, and XPS spectra (Gaussian09). Combination of calculations and experiments revealed that oxidation proceeded in the order of zigzag-like edges > sp3CH3 > sp2CH2 > armchair edges, and the quinone formed by oxidation worked as a precursor for a crosslinking reaction. It is expected that the results of this work, which revealed the origin of the crosslinking, could lead to improve properties as well as to estimate the detailed structures of isotropic pitch-based carbon fiber.

Edges of carbon materials have been known to work as active sites for various applications such as catalysts, adsorbent, and electrodes, but selecting precursors for carbon materials with controlled edges in the absence of metallic substrate is challenging. This work developed a method to select the superior precursors instantaneously using molecular dynamic simulation. This simulation predicted that hydrogen in precursors gasified and the hydrogen attacked the active sites in precursors upon carbonization, causing the decrement of active sites. Thus, it is essential to reduce the concentration of hydrogen in precursors and it is also necessary to introduce reactive functional groups near the active site to protect the active sites. We indeed synthesized the selected precursors such as diethynyl anthracene, diethynyl chrysene, divinyl naphthyridine, and divinyl phenanthroline and proved that edges in those precursors were maintained even after carbonization at 773 K using diffuse reflectance infrared Fourier transform and X-ray photoelectron spectroscopy with the aid of spectra simulated by density functional theory calculation. Especially, ca. 100% of edge structures of zigzag edges and armchair edges in diethynyl anthracene and diethynyl chrysene was maintained even after carbonization at 773 K.

Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) to produce 3-buten-2-ol (3B2OL) was investigated over several monoclinic ZrO 2 (m-ZrO 2 ) catalysts modified with alkaline earth metal oxides (MOs), such as SrO, BaO, and MgO, to compare with the previously reported CaO/m-ZrO 2 . It was found that these modifiers enhanced the 3B2OL formation to the same level as CaO did by loading an appropriate MO content. Among all the tested catalysts, the BaO/m-ZrO 2 calcined at 800 °C with a low BaO content (molar ratio of BaO/ZrO 2 = 0.0452) shows the highest 2,3-BDO conversion (72.4%) and 3B2OL selectivity (74.4%) in the initial stage of 5 h at 350 °C. In order to characterize those catalysts, their catalytic activities, crystal structures, and basic properties were studied in detail. In X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiment, it was elucidated that highly dispersed M-O-Zr (M = Ca, Sr, and Ba) hetero-linkages were formed on the surface by loading these MOs onto m-ZrO 2 with an appropriate content and then calcining at 800 °C. It can be concluded that the M-O-Zr hetero-linkages generate the proper base-acid balance for the efficient formation of 3B2OL from 2,3-BDO.

Nitrogen-doped carbon materials such as graphene and activated carbon have been studied as solid base catalysts. However, active sites of carbon catalysts have long been ambiguous because of the presence of various functional groups. This work clarified the dependence of positions of nitrogen atoms in aromatic hydrocarbons on catalytic activities of well-known Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate to produce ethyl cyanocinnamate (ECC) as one of the examples for catalytic reactions. Catalytic activities of 30 kinds of aromatic hydrocarbons composed of one, two, and three aromatic rings with zero, one, two, and three nitrogen atoms were compared. Phenazine with zigzag edges and pyridinium ion with quaternary nitrogen showed low catalytic activities. On the other hand, 1,10-phenanthroline with armchair edges showed a high ECC selectivity of 99.3% and a high ECC yield of 59.0%. Among various aromatic hydrocarbons carbonized on silica, 1,10-phenanthroline carbonized at 923 K exhibited the highest ECC selectivity of 89.5% and the highest ECC yield of 10.2% because of the highest percentage of 1,10-phenanthroline-like N after carbonization. We believe that this work can serve as a perfect example to examine the performance of carbon catalysts at a molecular level in the future.

Selective doping of nitrogen into carbon materials in the absence of catalysts is a key for various applications of carbon materials. It is well known that most nitrogen-containing raw materials generate unnecessary functional groups during carbonization. Many researchers have noticed the significance of the selective nitrogen doping, whereas only a few works have reported the selective doping. In addition, those few works used catalysts to synthesize nitrogen-doped carbon materials, but the presence of catalysts limits the applications of nitrogen-doped carbon materials. This study found an unusual aromatic compound, imidazo[1,2-a]pyridine (IP), which maintained 88 % of the functional groups of as-received IP even after carbonization at 673 K in the absence of catalysts, and the functional groups were further maintained up to 773 K. The percentage of remaining functional groups was revealed using our state-of-the-art techniques of simulated X-ray photoelectron spectroscopy and Raman spectroscopy combined with transition state calculation using density functional theory. The low carbonization temperature as well as selective doping of nitrogen was achieved because of the low activation energy of dehydrogenation reaction among IP molecules compared to the high activation energy of radical formation for scission of C–N bonding.