Search

The production of high-value-added chemicals and their raw materials by partial oxidation of methane (POM) is advantageous. The screening of 31 simple oxide catalysts for direct POM showed that ZrO2had the highest syngas yield (CO and H2) and was thus a promising catalyst. Kinetic analysis indicated that POM over the ZrO2catalyst proceeded in a Langmuir–Hinshelwood mechanism and that CH4activation was the rate-limiting step. Density functional theory calculations showed that CH4was activated on coordinatively unsaturated Zr4+cations formed by the dehydration of the hydroxyl groups on the ZrO2surface. In situdiffuse reflectance infrared Fourier transform spectroscopy revealed that CH4was converted into CO and H2through CH4-oxygenated intermediates, such as methoxy and formate species. The CH4-oxygenated intermediates on the ZrO2catalyst were closely related to the catalytic performance of the oxide catalysts in POM. A comprehensive investigation of the POM reaction over ZrO2-based catalysts was then conducted. ZrO2modification with tungsten oxide (WOx) or lanthanum oxide (LaOx) was examined to determine their ability to improve the catalytic properties of ZrO2for POM. ZrO2modification with WOxand LaOxenhanced its acidity and basicity, respectively. CO selectivity was increased by modifying ZrO2with a small amount of WOx. Moreover, modification with LaOxincreased CH4conversion and H2yield at low temperatures.

Metal nanoparticles (MNPs) supported on oxides are used in various catalytic reactions, such as petrochemical processes and exhaust gas purification. Metal–support interactions (MSIs) between MNPs and oxides affect the morphology and thermal stability of the MNPs, which are known to be related to the catalytic activity of the MNPs. However, the effect of MSIs is still a matter of debate. We conducted density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) to investigate the geometric structure and migration behavior of Pd clusters on various Al2O3surfaces. The MSIs of the Pd clusters with different Al2O3surfaces resulted in different morphologies of the clusters. The shape of Pd clusters on α-Al2O3(0001) were deformed to oblate and on γ-Al2O3(110) to prolate. On the other hand, the shape of Pd clusters on γ-Al2O3(100) did not change from that in a vacuum. The migration rate of Pd clusters was also affected by the MSI, which was higher on γ-Al2O3(110) than on α-Al2O3(0001) and γ-Al2O3(100). To evaluate the interactions between Pd clusters and Al2O3surfaces, we calculated the interaction energies for Pd clusters with various sizes on Al2O3surfaces. The interaction energy of Pd/Al2O3systems depended on the coordination number (CN, number of bonds per Pd atom) of Pd–Al and Pd–O. Despite the smaller atomic density of Al and O of the γ-Al2O3(110) surface than that of α-Al2O3(0001) and γ-Al2O3(100) surfaces, the number of bonds formed between Pd clusters and γ-Al2O3(110) was greater than that of α-Al2O3(0001) and γ-Al2O3(100). According to AIMD simulations and perpendicular displacements of Al and O atoms bound to the Pd cluster on the Al2O3surface from the bare Al2O3surface, coordinatively unsaturated Al3+sites on γ-Al2O3(110) were more flexible than those on α-Al2O3(0001) and γ-Al2O3(100). The flexibility of γ-Al2O3(110) facilitated the formation of bonds with the Pd cluster, resulting in stronger MSIs. When the coordinatively unsaturated Al3+sites were hydrated, the MSIs were found to be weakened.

Iron-containing zeolites possess active sites capable of catalyzing the low-temperature partial oxidation of methane using hydrogen peroxide as an environmentally benign oxidant. However, only a trace number of active sites have been found in zeolites so far. The high turnover frequency was limited to low loading samples, resulting in an upper limit of ∼50 mmol gcat−1h−1yield of C1 oxygenates. In this study, we synthesized a ZSM-5 catalyst containing a high concentration of single Fe sites with a high turnover frequency, and achieved a conversion of methane to C1 oxygenates of ∼200 mmol gcat−1h−1yield. It was important to use ZSM-5 as a carrier, which can be synthesized by hydrothermal treatment of aluminosilicate gel containing only tetra-propyl ammonium cations as the structure-directing agent (SDA). This ZSM-5 carrier has a large fraction of local environments possessing the nearest framework AlO4tetrahedra required for the fixation of Fe cations in the mononuclear state while suppressing the co-generation of oligomeric Fe sites, making it possible to design a reaction field for the highly efficient partial oxidation of methane. The findings in the present study clearly showed that the fraction of single Fe cations and the Al distribution in the zeolite matrix are powerful activity descriptors for this class of materials. Furthermore, Al-distribution modification based on previously-established protocols, i.e., rational choice of an SDA used in the zeolite synthesis, is a meaningful way to tune not only the fabrication efficiency of single Fe cations but also the catalytic performance of Fe/ZSM-5 catalysts.

We found a positive correlation between C=C selective hydrogenation activity of cinnamaldehyde (CAL) and the fraction of the Pd step site on Pd nanoparticles. Owing to a high fraction of step sites, Pd/θ-Al2O3catalysts with Pd particle size of 5–10 nm were highly active for the C=C selective hydrogenation of CAL.Pd/θ-Al2O3with weaker metal-support interaction (MSI) showed a volcano-shaped size dependence of the C=C selective hydrogenation activity; however, Pd/γ-Al2O3with stronger MSI showed a constant and low catalytic activity against particle size. The turnover frequency for C=C selective hydrogenation of CAL is found to correlate positively to the relatively abundant Pd step sites.

In the present study, the redispersion behavior of Ag particles on ZSM-5 in the presence of coke was observed using in situX-ray absorption fine structure (XAFS) spectroscopy. The dynamics of Ag particle redispersion into the ZSM-5 pores were evaluated by linear combination fitting (LCF) of the X-ray absorption near edge structure (XANES) spectra. In addition, the behavior of coke combustion in Ag-ZSM-5 was observed by thermogravimetric analysis (TGA). The rate constant of Ag particle redispersion was smaller than that of coke combustion at ≥500 °C, but it was three times larger than that of coke combustion at <500 °C. According to 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), the Ag+ions in the ZSM-5 pores improved the hydrothermal stability of Ag-ZSM-5. Therefore, a two-step regeneration process, in which the Ag particle redispersion proceeded first at low temperature (<500 °C) followed by a complete combustion of the coke at high temperature (≥500 °C) to prolong the catalyst lifetime, was used.

Pd/Al2O3catalysts were prepared using various Al2O3supports with different structural features such as crystalline phase and crystallinity related to Al3+coordination, revealing a significant insight into the methane (CH4) combustion activity of Pd nanoparticles with the fraction of penta-coordinated Al3+sites in the Al2O3supports.

Carbon monoxide (CO) molecules are attracting attention as capping agents that control the structure of metal nanoparticles. In this study, we aimed to control the shape and surface structure of Pd particles by reducing the supported Pd precursor with CO. The reduction of Pd nanoparticles with CO promoted the exposure of step sites and generated spherical and concave-tetrahedral Pd particles on carbon and SiO2supports. On the other hand, conventional H2-reduced Pd particles show a flattened shape. The preferential exposure of the step sites by the adsorbed CO molecules was supported by the density functional theory-calculated surface energy and the Wulff construction. Morphology- and surface-controlled Pd nanoparticles were used to study the surface structure and morphology effects of Pd nanoparticles on cinnamaldehyde (CAL) hydrogenation. With an increase in the fraction of step sites on Pd nanoparticles, the hydrogenation activity and selectivity of hydrocinnamaldehyde (HCAL) increased. On step sites, the adsorption of the C═C bond of CAL proceeded preferentially, and HCAL was efficiently and selectively generated.

Anion exchange membrane fuel cells (AEMFCs) are being developed for practical use. However, it is necessary to improve the hydrogen oxidation reaction (HOR) under alkaline conditions to enhance the performance of AEMFCs. In this study, carbon-supported Ru–Ir alloy nanoparticle catalysts (Ru–Ir/C) were developed because they offer higher HOR activity compared with the Pt-based catalysts. The mechanism of HOR enhancement on Ru–Ir/C was studied to reveal the effect of the surface composition of Ru/Ir on the HOR activity. The results showed that the HOR activity is related to the surface pair probability of Ru–Ir, Ru–Ru, and Ir–Ir but not to the hydrogen binding energy (HBE). In addition, the Ru–Ir pair site was found to be highly active, which can promote the HOR through a bifunctional mechanism that involves Ru–Ir pairs providing reactive OH–and H species, respectively.

To develop highly active soot combustion catalysts for gasoline direct injection exhausts under low oxygen concentration conditions, CeO2supported-metal catalysts (M/CeO2, M = Mn, Fe, Co, Ni, Cu, Rh, Pd, and Ag) were examined. Among the catalysts tested, Cu/CeO2and Rh/CeO2displayed the highest soot combustion activity. By comparing the activities of Cu-based catalysts with and without a Cu–CeO2interface, the importance of such an interface for soot combustion was inferred. The oxygen release rate of CeO2-based catalysts, enhanced by metal–CeO2interactions, was indicated as the controlling factor of catalytic activity. The soot oxidation activity and oxygen release rate were also demonstrated to correlate with metal–oxygen bond energy. Based on the redox properties and structural characteristics of CeO2-based catalysts, loading CeO2with Cu or Rh, which have moderate M–O bond energy, was concluded to be optimal both in terms of the dispersion of supported-metal species and reducibility of the CeO2-based catalyst.

A Pd/Co/Al2O3catalyst prepared by a galvanic deposition method exhibited notable catalytic activity for methane combustion, due to the higher reducibility of PdO nanoparticles on CoOx.

Measurements of singlet oxygen (1O2) quenching rates (kQ(S)) and the relative singlet oxygen absorption capacity (SOAC) values were performed for seven rice bran extracts 1–7, which contained different concentrations of antioxidants (AOs) (such as α-, β-, γ-, and δ-tocopherols and -tocotrienols, three carotenoids (lutein, β-carotene, and zeaxanthin), and γ-oryzanol), in ethanol at 35 °C using UV–vis spectrophotometry. The concentrations of four tocopherols and four tocotrienols, three carotenoids, and γ-oryzanol contained in the extracts were determined using HPLC-MS/MS, UV-HPLC, and UV–vis absorption spectroscopy, respectively. Furthermore, comparisons of kQ(S) (Obsd.) values observed for the above extracts 1–7 with the sum of the product {[AO-i]} of the values obtained for each AO-iand the concentration ([AO-i]) of AO-icontained in extracts 1–7 were performed. From the results, it has been ascertained that the SOAC method is applicable to general food extracts to evaluate their 1O2-quenching activity.

A dominant gene Bph9of rice (Oryza sativaL.) confers resistance against a serious insect pest, brown planthopper (BPH; Nilaparvata lugensStål). To map the Bph9locus, a susceptible japonicabreeding line ‘Norin-PL9’ was crossed as a seed parent with an indicacultivar ‘Pokkali’, which is a Bph9-carrier. Due to high sterility in the F1and F2progenies, genotypes for BPH response of F2individuals were estimated indirectly by the phenotypes of F3:4families in BPH bioassay. Segregation of BPH resistance in 62 F2individuals did not deviate from the single dominant gene ratio. Seven RFLP and two RAPD markers were selected in the bulked segregant analysis, all of which showed normal segregation in the mapping population. Bph9was mapped on the long arm of rice chromosome 12.