Junya Ohyama

Selective hydrogenation of 2-hydroxymethyl-5-furfural to 2,5-bis(hydroxymethyl)furan over gold sub-nano clusters

We report a gold sub-nano cluster supported on Al2O3 catalyzed hydrogenation of 2-hydroxymethyl-5-furfural without furan ring hydrogenation and its opening reaction, which resulted in excellent conversion to 2,5-bis(hydroxymethyl)furan (>96% yield), Fig. 1(a).

Size Specifically High Activity of Ru Nanoparticles for Hydrogen Oxidation Reaction in Alkaline Electrolyte

The hydrogen oxidation reaction (HOR) in alkaline electrolyte was conducted on carbon-supported Ru nanoparticles (Ru/C) of which size was controlled in the range from approximately 2 to 7 nm. The HOR activity of Ru/C normalized by the metal surface area showed volcano shaped dependence on the particle size with a maximum activity at approximately 3 nm. The HOR activity of approximately 3 nm Ru/C was higher than commercially available Pt nanoparticles (ca. 2 nm) supported on carbon. The structural analysis of Ru/C using Cs-corrected scanning transmission electron microscopy with atomic resolution revealed the unique structural change of Ru/C different from Pt/C: Ru nanoparticle structure changed from amorphous-like structure below 3 nm to metal nanocrystallite with roughened surface at approximately 3 nm and then to that with well-defined facets above 3 nm, although Pt/C kept well-defined facets even at approximately 2 nm. It is proposed that the generation of unique structure observed on approximately 3 nm Ru nanoparticles, that is, long bridged coordinatively unsaturated Ru metal surface atoms on its nanocrystallite, is a key to achieve high HOR activity.

Investigation of the Formation Process of Photodeposited Rh Nanoparticles on TiO2 by In Situ Time-Resolved Energy-Dispersive XAFS Analysis

The photodeposition process of Rh metal nanoparticles on a TiO(2) photocatalyst from RhCl(3) aqueous solution in the presence of methanol as a sacrificial oxidant, which consists of the direct reduction of Rh(3+) ions to Rh metal and the formation of Rh nanoparticles, was uncovered by in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis in a liquid-solid suspension state. The fractions of Rh metal particles and Rh(3+) precursor were estimated by the least-squares fitting of each X-ray absorption near-edge structure (XANES) spectrum by a linear combination of authentic spectra corresponding to Rh(0) and Rh(3+). The fraction of Rh metal linearly increased with photoirradiation time and saturated after 90 min of photoirradiation. The coordination number (Rh-Rh pair) was evaluated by the curve fitting of the Rh-Rh scattering at 2.45 A in the Fourier transforms (FT) of extended XAFS (EXAFS) spectra. The coordination number linearly increased with photoirradiation time and attained a constant value of 10 after 90 min of photoirradiation. This value is lower than that for the Rh foil (12). These suggest the formation of fine Rh metal nanoparticles on TiO(2). In addition, the diminution rate of Rh(3+) as determined by ICP analysis was in good agreement with the increased rates for the fraction of Rh metal particles estimated by XANES spectra and the coordination number (Rh-Rh pair) evaluated by FT-EXAFS spectra. This result strongly supports the fact that electrons generated by charge separation reduce the Rh(3+) precursor to an Rh metal particle at a moment in time and at a constant rate. The Rh particles do not grow in incremental steps, but Rh particles with a uniform size appear one after another on the surface.

The effect of heterogeneous acid–base catalysis on conversion of 5-hydroxymethylfurfural into a cyclopentanone derivative

The effect of heterogeneous acid–base catalysis on conversion of 5-hydroxymethylfurfural (HMF) to 3-hydroxymethylcyclopentanone (HCPN) was investigated. It was demonstrated that acidic metal oxides, in particular Ta2O5, significantly enhanced the yield of HCPN due to their moderate Lewis acidity.

Promotion of low-temperature oxidation of CO over Pd supported on titania-coated ceria

The design of a metal oxide support for Pd was investigated to promote the oxidation of CO at lower temperatures. Through a screening study using pure metal oxides, Pd/CeO2 showed the highest activity above 100 °C, while homemade TiO2 was more effective below 100 °C as a support for Pd. Applying the advantages of CeO2 and TiO2, we proposed a TiO2–CeO2 support having a monolayer amount of surface TiO2 supported on CeO2. The Pd/TiO2–CeO2 catalyst showed higher activity than both Pd/TiO2 and Pd/CeO2, which was not achieved by using the CeO2–TiO2 mixed-oxide. The light-off temperature over Pd/TiO2–CeO2 was 100 °C lower than Pd/Al2O3. The effect of surface TiO2 was attributed to the promotion of the reduction–oxidation cycle of supported Pd.

Enhanced activity for methane combustion over a Pd/Co/Al2O3 catalyst prepared by a galvanic deposition method

A Pd/Co/Al2O3 catalyst prepared by a galvanic deposition method exhibited notable catalytic activity for methane combustion, due to the higher reducibility of PdO nanoparticles on CoOx.

In situ observation of the dynamic behavior of Cu–Al–Ox catalysts for water gas shift reaction during daily start-up and shut-down (DSS)-like operation

To compare the catalytic performances against daily start-up and shut-down (DSS) operations between co-precipitated (CP) and impregnated (IMP) Cu–Al–Ox catalysts for the water gas shift (WGS) reaction, in situ X-ray adsorption fine structure (XAFS) measurements, temperature-programmed reduction (TPR) profiles, X-ray diffraction (XRD) patterns and high resolution transition electron microscopy with an energy dispersive X-ray spectroscopy (TEM-EDS) analysis were performed. In situ XAFS studies clearly indicated that the Cu species were frequently oxidized and reduced during DSS operations with steam treatment (DSS-like operation). Based on in situ XAFS and H2-TPR profiles, the highly active and stable CP-catalyst possessed more susceptible Cu particles to oxidation/reduction (described as redoxable) than the IMP-catalyst even after the DSS-like operations. Interestingly, the XRD and TEM-EDS analysis showed small Cu particles which were covered with a card-house structure of the in situ formed boehmite in the case of the CP-catalyst after the DSS-like operations. According to these results, we concluded that the superior durability of the CP-catalyst against frequent redox changes was attributed to the nanoscale coordination with the in situ formed boehmite structure which preserves the small-redoxable Cu particles.

Statistical distribution of single atoms and clusters of supported Au catalyst analyzed by global high-resolution HAADF-STEM observation with morphological image-processing operation.

We have developed a quantitative particle size analytical method at the single atomic level employing electron microscopy and image processing for the investigation of supported metal catalysts. In the present study, a supported gold (Au) catalyst containing sub-nano clusters and individual atoms was globally observed by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) using spherical aberration (Cs)-corrected TEM. To fully extract structural information of the Au clusters and individual atoms from the HAADF-STEM images, a morphological image-processing operation was applied. The resulting mean particle size was in good agreement with particle sizes estimated from average information provided by X-ray absorption fine structure analysis. It is demonstrated that the present HAADF-STEM image analysis gives a quantitative particle size distribution measurement of supported Au clusters and individual atoms.

NiFe2O4 as an active component of a platinum group metal-free automotive three-way catalyst

To develop a platinum group metal (PGM)-free automotive three-way catalyst (TWC), we investigated the structure–activity relationship for Fe–Ni oxide catalysts and found NiFe2O4 with a spinel structure is an active component of the three-way catalytic reaction (NO–C3H6–CO–O2). The NiFe2O4 catalyst exhibited a light-off temperature below 300 °C for NO reduction, which was more than 50 °C lower than previously reported PGM-free TWCs at a high space velocity (GHSV = 140 000 h−1).

Dynamic Behavior of Rh Species in Rh/Al2O3 Model Catalyst during Three-Way Catalytic Reaction: An Operando X-ray Absorption Spectroscopy Study

The dynamic behavior of Rh species in 1 wt% Rh/Al2O3 catalyst during the three-way catalytic reaction was examined using a micro gas chromatograph, a NOx meter, a quadrupole mass spectrometer, and time-resolved quick X-ray absorption spectroscopy (XAS) measurements at a public beamline for XAS, BL01B1 at SPring-8, operando. The combined data suggest different surface rearrangement behavior, random reduction processes, and autocatalytic oxidation processes of Rh species when the gas is switched from a reductive to an oxidative atmosphere and vice versa. This study demonstrates an implementation of a powerful operando XAS system for heterogeneous catalytic reactions and its importance for understanding the dynamic behavior of active metal species of catalysts.