研究者詳細 - 薩摩　篤

Encapsulated Platinum-Tin Nanoparticles in Silicalite-1 Zeolite for Methylcyclohexane Dehydrogenation

Shi W., Oda A., Yamamoto Y., Harada S., Ohtsu T., Sawabe K., Satsuma A.

ACS Sustainable Chemistry and Engineering 13 巻 ( 9 ) 頁： 3608 - 3621 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Sustainable Chemistry and Engineering

Catalytic dehydrogenation of methylcyclohexane (MCH) is of great importance for hydrogen storage and transportation, but currently used Pt-based nanoparticle catalysts still suffer from insufficient activity, low selectivity, and short-term stability. In this study, we encapsulated Pt-Sn nanoparticles into the silicalite-1 (S-1) matrix and incorporated Sn into the zeolite framework through one-pot hydrothermal synthesis to overcome the above problems. These Pt-Sn bimetallic catalysts were designed for the first time with a high Sn content (2.8-3.9 wt %, Sn/Pt ratio = 6-8) in zeolite mother gel for MCH dehydrogenation. The introduction of Sn significantly improved the activity and durability of Pt@S-1. Especially, the PtSn@S-1 (Sn/Pt ratio = 6) catalyst showed high MCH conversion (>80% for 2 h) and toluene (TOL) selectivity (∼100%) without cofeeding H<inf>2</inf>. Even after a long-term stability test for 33 h under a weight hourly space velocity (WHSV) of 120,000 mL/g/h, no obvious deactivation was observed, and this catalyst retained a superior H<inf>2</inf> evolution rate normalized with a surface Pt content of 1343 mmol<inf>H<inf>2</inf></inf>/g<inf>Pt</inf>/min. The structure-catalytic property relationship of PtSn@S-1 catalysts was systematically studied. Upon Sn introduction, PtO<inf>x</inf> species on Pt@S-1 were transformed into the PtSn alloy. With the further increase of the Sn/Pt ratio from 1 to 6, Sn was gradually incorporated into the zeolite framework, and this PtSn alloy evolved into a core-shell structure with a Pt core and a Sn shell. Despite the reduced proportion of surface Pt, these unique structures enabled the modification of the Pt local structure, promoted TOL desorption, and enhanced the stability of Pt-Sn nanoparticles, therefore achieving high activity, selectivity, and durability for MCH dehydrogenation.

DOI： 10.1021/acssuschemeng.4c09762

Atom-to-nm Scale Engineering of PtCo Alloy Catalysts over Supported Co Nanoparticles for Advanced Toluene Hydrogenation Efficiency in Hydrogen Storage Applications Open Access

Oda A., Ogawa N., Yamamoto Y., Sawabe K., Satsuma A.

ACS Catalysis 15 巻 ( 4 ) 頁： 3191 - 3202 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

Hydrogen storage and transportation are pivotal for a hydrogen- and carbon-neutral society, yet current approaches face considerable limitations in efficiency and cost, which are typically related to catalyst design. Alloying a trace amount of Pt on supported Co nanoparticles has emerged as an innovative catalyst design that leads to a substantial reduction of the amount of precious metal used in the catalytic hydrogenation of toluene (TOL) to methylcyclohexane (MCH), which is an important aspect of hydrogen storage and transportation. However, because of the difficulty in controlling the surface structure of PtCo alloy catalysts, the structure that maximizes the synergistic interaction between the Pt and Co sites has not yet been identified. In this study, we explore the structure-function relationship in TOL hydrogenation over PtCo alloy catalysts by designing three distinct structures: PtCo single-atom alloys, PtCo alloy nanoislands on Co nanoparticles, and PtCo alloy nanoparticles on a support, i.e., monoclinic-phase ZrO<inf>2</inf> (m-ZrO<inf>2</inf>). In the catalyst designs, m-ZrO<inf>2</inf> was employed as a support to control the Co nanoparticle diameter to 5-7 nm, maximizing the fraction of Co plane sites required for efficient TOL fixation/hydrogenation and enhancing the synergy with Pt site-derived functionality. The highest turnover frequency (TOF) had the following magnitude relationship: PtCo single-atom alloy > PtCo alloy nanoislands on Co nanoparticles > PtCo alloy nanoparticles on m-ZrO<inf>2</inf>. Remarkably, the PtCo single-atom alloy enhanced Pt utilization efficiency by up to 51-fold over supported Pt nanoparticle catalysts, resulting in record activity in the literature. Based on the kinetic experiments coupled with in-depth structural analyses using the series of well-defined PtCo alloy catalysts, it was clarified that the high activity is attributed to (1) optimal competitive adsorption of TOL and H<inf>2</inf> created by Pt single atoms-containing Co ensemble sites and (2) large fraction of such sites. Stability tests coupled with microscopy confirmed that PtCo single-atom alloy catalysis remained stable for at least 24 h, indicating that the supported Co nanoparticles also play a crucial role in preventing Pt aggregation. Our findings underscore the importance of optimal atom-to-nm scale design of PtCo alloy catalyst for achieving ultrafast TOL hydrogenation even with extremely low Pt usage, offering an innovative approach for saving precious metal in hydrogen storage and transportation.

DOI： 10.1021/acscatal.4c07206

CO2 Capture and Reduction to CO in the Presence of CO over In-Cs/ZrO2 Dual-Functional Materials

Xie Y., Miyazaki S., Li L., Li K., Wang F., Oda A., Satsuma A., Al Abdulghani A.J., Maeda N., Anzai A., Toyao T., Shimizu K.I.

ACS Catalysis 頁： 12048 - 12062 2025年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

CO<inf>2</inf> exhaust mixed with large amounts of CO from the steel and petroleum industries, as a major source of greenhouse gases, can be a promising renewable carbon resource. However, the reduction of CO<inf>2</inf> under excess CO is thermodynamically limited by the reverse water gas shift (RWGS) reaction. Herein, we report a CO<inf>2</inf> capture and reduction (CCR) system for continuous conversion of CO<inf>2</inf>/CO mixture into high-concentration CO. Screening tests of various dual functional materials (DFMs) show that indium and cesium-coloaded ZrO<inf>2</inf> (In-Cs/ZrO<inf>2</inf>) serves as the best DFM for the selective reduction of CO<inf>2</inf> to CO under cyclic feeds of CO<inf>2</inf>/CO ↔ H<inf>2</inf> at 350 °C. Operando IR and model reaction tests show that the higher CO yield of In-Cs/ZrO<inf>2</inf> compared to the other noble metal (Pt, Pd, Ru, Rh)-based DFMs was due to the lower activity of In-Cs/ZrO<inf>2</inf> in the disproportionation of CO into carbon and CO<inf>2</inf>. Continuous cyclic reactions with an In-Cs/ZrO<inf>2</inf>-based double-reactor under the CO-excess (10% CO<inf>2</inf>/80% CO/10% He ↔ 100% H<inf>2</inf>) conditions at 550 °C for 1000 min (250 cycles) showed a CO yield of 51% (based on the total amount of inlet CO<inf>2</inf>). Operando In K-edge X-ray absorption near-edge structure (XANES) and UV-vis spectroscopy show that In<inf>2</inf>O<inf>3</inf> species are reduced by H<inf>2</inf> to yield reduced In species that are reoxidized by CO<inf>2</inf> to regenerate In<inf>2</inf>O<inf>3</inf>. However, the main CO formation route is not based on the redox mechanism. Operando IR analysis with modulation excitation spectroscopy (MES) showed that Cs species are responsible for CO<inf>2</inf> capture and carbonate formation, while reduced In species are responsible for the H<inf>2</inf> reduction of carbonates to CO via formate intermediates.

DOI： 10.1021/acscatal.5c02675

Reversible Multi-Complexation of CO2 to Alkaline Earth Metal Ion-Pair at 400 ppm and 298 K Open Access

Oda A., Sawabe K., Satsuma A.

Angewandte Chemie International Edition 63 巻 ( 51 ) 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Angewandte Chemie International Edition

The efficient capture of low-pressure CO<inf>2</inf> remains a significant challenge due to the lack of established multi-complexation of CO<inf>2</inf> to active sites in microporous materials. In this study, we introduce a novel concept of reversible multi-complexation of CO<inf>2</inf> to alkaline earth metal (AEM) ion pairs, utilizing a host site in ferrierite-type zeolite (FER). This unique site constrains two AEM ions in proximity, thereby enhancing and isotopically spreading their electrostatic potentials within the zeolite cavity. This electrostatic potential-engineered micropore can trap up to four CO<inf>2</inf> molecules, forming M2+−(CO<inf>2</inf>)<inf>n</inf>−M2+ (n=0–4, M=Ca, Sr, Ba) complexes, where each CO<inf>2</inf> molecule is stabilized by interactions between terminal oxygen (O<inf>t</inf>) in CO<inf>2</inf> and the AEM ions. Notably, the Ba2+ pair site exhibits higher thermodynamic stability for multiple adsorptions due to the optimal binding mode of Ba2+−O<inf>t</inf>−Ba2+. Through high-accuracy energy calculations, we have established the relationship among structure, CO<inf>2</inf> uptake, and operating temperature/pressure, demonstrating that the Ba2+ pair site can capture four CO<inf>2</inf> molecules even at concentrations as low as 400 ppm and at 298 K. Three of the four molecules of CO<inf>2</inf> trapped were removable at room temperature and under vacuum. The findings in the present study provide a new direction for developing efficient CO<inf>2</inf> adsorbents.

DOI： 10.1002/anie.202411969

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol

Oda A., Kimura Y., Ichino K., Yamamoto Y., Kumagai J., Lee G., Sawabe K., Satsuma A.

Journal of the American Chemical Society 146 巻 ( 29 ) 頁： 20122 - 20132 2024年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Chemical Society

Structure-function relationships of supported metal nanoparticle catalysts in the CO-assisted oxidation of ethane to ethanol were investigated. A rutile TiO<inf>2</inf>-supported Pt nanoparticle catalyst exhibited the highest ethanol production rate and selectivity. During the reaction, sequential changes in the geometric/electronic states and the particle size of the Pt nanoparticles were observed. The comparison of the catalytic performances of model catalysts with controlled metal-support interactions revealed that Pt0 nanoparticles of 2-3 nm with a high fraction of the surface Ptδ+ species are highly active for the oxidation of ethane to ethanol. The coadded CO plays a pivotal role not only in tuning the oxidation state of the surface Pt but also in producing H<inf>2</inf>O<inf>2</inf>, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H<inf>2</inf>O<inf>2</inf> to activate ethane, where the C<inf>2</inf>H<inf>5</inf>OOH intermediate is formed through a nonradical mechanism and subsequently converted to C<inf>2</inf>H<inf>5</inf>OH. This reaction occurs even at 50 °C with an apparent activation energy of 32 kJ mol-1. The present study sheds light on the usefulness of surface-engineered Pt nanoparticles for the low-temperature oxidation of ethane to ethanol.

DOI： 10.1021/jacs.4c04381

Pt single atom alloyed sub-1 nm thick Fe overlayer on supported Cu nanoparticles for methylcyclohexane dehydrogenation Open Access

Oda A., Ichihashi K., Yamamoto Y., Ohtsu T., Shi W., Sawabe K., Satsuma A.

Journal of Materials Chemistry A 12 巻 ( 34 ) 頁： 22655 - 22667 2024年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Chemistry A

There is an urgent need for the development of a precious metal-conserving catalyst having high activity, selectivity, and durability for methylcyclohexane (MCH) dehydrogenation, a significant aspect of hydrogen storage and transportation. A Pt-single atom alloyed Fe catalyst with sub-1 nm size is a good candidate for this purpose because of meeting site requirements for enhancement of activity, durability, selectivity, and utilization efficiency of Pt. However, this design is challenging due to the high surface energy of Fe. In this study, to break the limitation of catalyst design, we used a combination of two phenomena spontaneously taking place at the solid surface, i.e., (1) Fe dispersion on Cu, and (2) substitution of metallic Fe atoms with Pt cations. Here, we report a Pt single-atom alloyed sub-1 nm thick Fe overlayer on Cu nanoparticles. The Fe overlayer serves as the host metal to restrict Pt single atoms at the surface and provides an optimal coordination environment for MCH dehydrogenation. Furthermore, the sub-1 nm thick Fe overlayer features low crystallinity and superior decoking properties, which imparts product/coke poisoning resistance to the Pt single atom site, resulting in enhancements of both durability and activity. The H<inf>2</inf>-evolution rate per Pt mass was at least 133 times higher than that of state-of-the-art catalysts: Pt-based intermetallic compounds. This research demonstrates the significance of a single-atom-alloying approach with unique nanostructures specifically formed at the solid surface for the development of more efficient sustainable catalytic transformation processes.

DOI： 10.1039/d4ta03453h

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al2O3 Surfaces: DFT and AIMD Studies Open Access

Murata K., Oda A., Satsuma A., Sawabe K.

Journal of Physical Chemistry C 127 巻 ( 41 ) 頁： 20267 - 20275 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

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 Al<inf>2</inf>O<inf>3</inf> surfaces. The MSIs of the Pd clusters with different Al<inf>2</inf>O<inf>3</inf> surfaces resulted in different morphologies of the clusters. The shape of Pd clusters on α-Al<inf>2</inf>O<inf>3</inf>(0001) were deformed to oblate and on γ-Al<inf>2</inf>O<inf>3</inf>(110) to prolate. On the other hand, the shape of Pd clusters on γ-Al<inf>2</inf>O<inf>3</inf>(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-Al<inf>2</inf>O<inf>3</inf>(110) than on α-Al<inf>2</inf>O<inf>3</inf>(0001) and γ-Al<inf>2</inf>O<inf>3</inf>(100). To evaluate the interactions between Pd clusters and Al<inf>2</inf>O<inf>3</inf> surfaces, we calculated the interaction energies for Pd clusters with various sizes on Al<inf>2</inf>O<inf>3</inf> surfaces. The interaction energy of Pd/Al<inf>2</inf>O<inf>3</inf> systems 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-Al<inf>2</inf>O<inf>3</inf>(110) surface than that of α-Al<inf>2</inf>O<inf>3</inf>(0001) and γ-Al<inf>2</inf>O<inf>3</inf>(100) surfaces, the number of bonds formed between Pd clusters and γ-Al<inf>2</inf>O<inf>3</inf>(110) was greater than that of α-Al<inf>2</inf>O<inf>3</inf>(0001) and γ-Al<inf>2</inf>O<inf>3</inf>(100). According to AIMD simulations and perpendicular displacements of Al and O atoms bound to the Pd cluster on the Al<inf>2</inf>O<inf>3</inf> surface from the bare Al<inf>2</inf>O<inf>3</inf> surface, coordinatively unsaturated Al3+ sites on γ-Al<inf>2</inf>O<inf>3</inf>(110) were more flexible than those on α-Al<inf>2</inf>O<inf>3</inf>(0001) and γ-Al<inf>2</inf>O<inf>3</inf>(100). The flexibility of γ-Al<inf>2</inf>O<inf>3</inf>(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.

DOI： 10.1021/acs.jpcc.3c02483

Self-organized defect-rich RuMOx epitaxial layers (M = Mn, Fe, Co, Ni, Cu) for catalytic applications

Oda A., Ichihashi R., Yamamoto Y., Sawabe K., Satsuma A.

Journal of Materials Chemistry A 11 巻 ( 44 ) 頁： 23854 - 23866 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Chemistry A

Catalysts with epitaxially-grown metal oxide on the substrate have wide catalytic applications. However, manipulations of the surface reactivity remain challenging due to the lack of a simple strategy to engineer the morphology, surface atomic composition, and defect distribution of the epitaxial layer, limiting performance improvement. Here, we report a heterometal dopant-assisted epitaxial growth phenomenon for engineering the surface structure and reactivity of metal-oxide epitaxy. Our method focuses on the regulation of the lattice parameters of the epitaxy by heterometal doping. This approach can reduce the misfit and thereby stabilize the metal-oxide/substrate interface, resulting in epitaxial growth with a high aspect ratio, tunable surface atomic composition, and abundant defects. As a proof of concept, the doping effect of 3d transition metals (M = Mn, Fe, Co, Ni, Cu) on the epitaxial growth mechanism of RuO<inf>x</inf> on a rutile TiO<inf>2</inf> substrate and their catalytic performance were investigated in the present study. It was found that simple co-impregnation of Ru and M nitrate solutions and subsequent calcination under an air atmosphere resulted in a unique set of epitaxial layers consisting of Ru and M oxides with atom thickness (RuMO<inf>x</inf>-ELs). These were grown by Frank-van der Merwe or Stranski-Krastanov growth modes. On the other hand, when only Ru nitrate was used for the catalyst preparation, the RuO<inf>x</inf> epitaxial nanoparticles were grown by the Volmer-Weber growth mode. The heterometal doping plays a pivotal role in tuning the lattice parameters of the epitaxy to reduce the misfit at the interface, driving the self-organization of the novel RuMO<inf>x</inf>-ELs even on a powder substrate without any special procedures. The RuMO<inf>x</inf>-ELs feature a high aspect ratio, and selectively exposed specific facets with abundant Ru-O<inf>latt</inf>/O<inf>vac</inf>-M local structures as the reactive sites. The surface concentration of Ru-O<inf>latt</inf>/O<inf>vac</inf>-M local structures and their reactivity depends on the kind of M; therefore, heterometal dopant-assisted epitaxial growth can be utilized to optimize the surface structure of the epitaxy for the target reaction. Its significance was proven by the fact that we have succeeded in creating the highest activity toward a low-temperature CO oxidation among the Ru-based catalysts reported in the literature.

DOI： 10.1039/d3ta05078e

Breaking the Structure-Activity Relationship in Toluene Hydrogenation Catalysis by Designing Heteroatom Ensembles Based on a Single-Atom Alloying Approach

Oda A., Fujita T., Yamamoto Y., Sawabe K., Satsuma A.

ACS Catalysis 13 巻 ( 15 ) 頁： 10026 - 10040 2023年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

Hydrogenation of toluene (TOL) to methylcyclohexane (MCH) is one of the hydrogen carrier systems desired for social integration. Supported Pt nanoparticle catalysts are effective for this application. However, Pt is rare, expensive, and in short supply, limiting its practical applications. Therefore, the key issue for TOL hydrogenation is how to substantially reduce the amount of Pt required for the catalyst. Because a specific ensemble of Pt atoms, that is dominantly formed on the surface of the Pt nanoparticle, is required for achieving higher catalytic performance, there is a limit to the number of precious Pt that can be conserved by simply reducing the particle size. The structure sensitivity established in the existing heterogeneous catalyst so far makes it difficult to design precious metal-conserving catalysts with both high activity and atomic efficiency. Here, a strategy for breaking the above limitations is reported. Our approach uses the heteroatom ensemble (HAE) on Pt single-atom alloyed 3d transition-metal nanoparticle catalysts (Pt1M SAAs, M = Co, Ni, Cu). The role of the TOL fixation/activation site is assigned to the atomic M sites on HAE, whereas the H<inf>2</inf>-activation site is to the Pt single-atom site on HAE. The atomic-scale division of roles within the HAE improves the efficiency of competitive adsorption of TOL/H<inf>2</inf>, which is important for boosting TOL hydrogenation. To maximize the synergistic effect at the adjacent sites, the atomic composition, geometric configuration, and electronic state of these active sites as well as the density of the HAE were tuned by the chemical composition and particle size of Pt1M SAAs. High activity was observed on the Pt1Co SAA with a particle size of 1.8 nm and Pt/Co molar ratio of 0.002. The Pt mass-specific activity reached 219 mol/g<inf>Pt</inf>/h, which was 23 times higher than that in a conventional Pt nanoparticle-supported catalyst. Using a set of well-defined Pt1M SAAs, high-angle annular dark-field scanning transmission electron microscopy, Pt L<inf>III</inf>-edge X-ray absorption fine structure spectroscopy, coupled with periodic density functional theory and ab initio molecular dynamics simulation, we proved the origin of the structure sensitivity at an atom-to-nanometer scale. The present work sheds light on the significance of regulations of the coordination environment of the Pt single-atom site, atomic composition, and particle size of Pt1M SAA for creating high activity, durability, and Pt-utilization efficiency for catalytic applications relevant to hydrogen carrier systems.

DOI： 10.1021/acscatal.3c02132

Active coordination sites of Co spinel oxides for NO reduction by CO Open Access

Ueda K., Tsuji M., Ohyama J., Satsuma A.

Catalysis Today 411-412 巻 2023年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Today

Cobalt spinel oxides, containing octahedral (O<inf>h</inf>) and tetrahedral (T<inf>d</inf>) sites, exhibit high activity for NO reduction by CO. The active sites of cobalt spinel oxides for NO–CO reaction was identified using various cobalt spinel oxides having different Co<inf>Oh</inf>/Co<inf>Td</inf> ratio. Comparing the Co<inf>Oh</inf>/Co<inf>Td</inf> ratio determined by EXAFS fitting analysis and the rate of NO reduction, it was clarified that octahedral site is responsible for NO reduction by CO. Furthermore, synchrotron-based in-situ XAFS measurements unveiled the contribution of Co<inf>Oh</inf> sites: The cobalt spinel oxides with high Co<inf>Oh</inf> fraction were more easily reduced by CO to form oxygen vacancies than those with low Co<inf>Oh</inf> fraction, and resulted in the higher activity for NO reduction by CO.

DOI： 10.1016/j.cattod.2022.06.031

Enhanced CO oxidation by reversible structural variation of supported Ag nanoparticle catalyst from single to twin by CO treatment Open Access

Tamura T., Ohyama J., Sawabe K., Satsuma A.

Catalysis Today 411-412 巻 2023年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Today

Twinned structure of metal nanoparticles can strongly affect catalysis because of its unique atomic alignment and bond strain in metal nanoparticles. Here, the twin and single crystal structures of supported Ag nanoparticles are controlled reversibly by gas treatment. The single crystal Ag nanoparticles were formed in Ag/Al<inf>2</inf>O<inf>3</inf> by H<inf>2</inf> treatment, and subsequent CO gas treatment changed the Ag particle structure to twin. The change in the Ag particle structure from single to twin caused enhancement of CO oxidation activity. In addition, the catalytic activity was reversibly changed from low to high by applying H<inf>2</inf> and CO gas treatment to Ag/Al<inf>2</inf>O<inf>3</inf>. The kinetic analysis for CO oxidation revealed that the twin Ag nanoparticles have stronger CO adsorption energy than the single crystal ones, which is responsible for the enhanced CO oxidation activity of twin Ag nanoparticles.

DOI： 10.1016/j.cattod.2022.06.029

Tandem Base-Metal Oxide Catalyst for Automotive Three-way Reaction: MnFe2O4 for Preferential Oxidation of Hydrocarbon Open Access

Maruichi K., Sakai R., Ueda K., Oda A., Satsuma A.

Catalysis Surveys from Asia 27 巻 ( 1 ) 頁： 48 - 55 2023年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Surveys from Asia

A combination of two base-metal oxides in tandem configuration can realize three-way reaction without platinum group metals. For this purpose, catalysts for hydrocarbon preferential oxidation (HC-PROX) and for NO reduction by CO are required. For the design of HC-PROX catalysts, competitive oxidation of propene and CO on spinel-type MFe<inf>2</inf>O<inf>4</inf> (M = Co, Cu, Mg, Mn, Ni, Zn) was investigated. MnFe<inf>2</inf>O<inf>4</inf> preferentially oxidized propene in the co-presence of CO showing the best propene oxidation activity. Among the series of MFe<inf>2</inf>O<inf>4</inf>, the activity controlling factor was correlated to the M-O bond energy of the second metal oxides, and the preference for HC oxidation was dependent on the electronegativity of the second ion. A tandem catalyst using MnFe<inf>2</inf>O<inf>4</inf> for HC-PROX and CuCo<inf>2</inf>O<inf>4</inf> for NO-CO reaction showed TWC activity comparable to a Rh/CeO<inf>2</inf>.

DOI： 10.1007/s10563-022-09373-9

Exploring the framework of small pore zeolites for passive NOx adsorption

Amen T.W.M., Washiyama S., Oda A., Ohtsu T., Satsuma A., Tsunoji N.

Microporous and Mesoporous Materials 361 巻 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Microporous and Mesoporous Materials

The use of a passive NOx adsorber (PNA) for NOx storage during the cold-start period is crucial for eliminating NOx emissions from the diesel exhaust. Palladium (Pd)-loaded zeolites have garnered significant attention owing to their high potential as PNA. In this study, small-pore zeolites with different frameworks were synthesized, and their structural characteristics and passive NOx adsorption abilities were investigated. Five zeolites, with CHA, AEI, AFX (low- and high- Si/Al ratio), and LEV framework structures, were synthesized by the hydrothermal conversion of faujasite-type (FAU) zeolite. Pd (1 wt%) was impregnated in combination with hydrothermal treatment. NOx adsorption and desorption behaviors were studied based on breakthrough NO adsorption and subsequent temperature-programmed desorption (TPD) experiments. Pd-loaded CHA, AEI, and LEV zeolites and high-silica AFX zeolites adsorbed approximately 93.88, 107.93, 97.57 and 106.53 μmol-NO g−1, respectively. On the other hand, the incorporation of Pd into AFX zeolite with a low Si/Al ratio led to significant hydrothermal damage and resulted in lower levels of adsorption and desorption capabilities. This demonstrates that hydrothermally stable small-pore zeolites on Pd-incorporation have great potential for passive NOx adsorption. The zeolite with different framework exhibited the different temperature range of NOx release. CHA, AEI, and high-silica AFX zeolites desorbed NOx in the low-temperature region (T < 250 °C), whereas the LEV zeolite showed a relatively high NOx desorption amount in the middle-temperature region (250 °C < T < 350 °C).

DOI： 10.1016/j.micromeso.2023.112746

Surface modification of MCr2O4 (M = Mg and Zn) by Cu-Doping: Theoretical prediction and experimental observation of enhanced catalysis for CO oxidation Open Access

Zhao P., Ueda K., Sakai R., Ehara M., Satsuma A., Sakaki S.

Applied Surface Science 605 巻 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

We theoretically investigated surface modification of MCr<inf>2</inf>O<inf>4</inf> (M = Mg and Zn) by Cu-doping and doping effects on catalytic activity for CO oxidation. DFT + U calculations elucidated that Cu-dopants in MCr<inf>2</inf>O<inf>4</inf>(1 1 1) exist on the surface layer, CO oxidation by Cu-doped MCr<inf>2</inf>O<inf>4</inf>(1 1 1) occurs through Mars van Krevelen mechanism, rate-determining step (RDS) is the first CO<inf>2</inf> desorption with oxygen vacancy (O<inf>V</inf>) formation, and the catalytic activity is enhanced very much by Cu-doping. Also, we experimentally observed that CO conversion was dramatically improved to 70% by the Cu-doped ZnCr<inf>2</inf>O<inf>4</inf> from 5.2% by non-doped ZnCr<inf>2</inf>O<inf>4</inf> at 300 °C. Bader charge analysis and difference density map show that M atom on the MCr<inf>2</inf>O<inf>4</inf> surface receives electron density from the dissociating O atom in the O<inf>V</inf> formation step and the Cu-dopant can receive more electron density than Mg and Zn atoms to facilitate the O<inf>V</inf> formation and accelerate the first CO<inf>2</inf> desorption(RDS). This larger capability of Cu-dopant for receiving electron density results from the facts that the Cu atom has large electronegativity and + I oxidation state besides + II in metal oxide but Mg and Zn have small electronegativity and only + II oxidation state.

DOI： 10.1016/j.apsusc.2022.154681

Highly efficient CO-assisted conversion of methane to acetic acid over Rh-encapsulated MFI zeolite prepared using RhCl3 molten salt

Oda A., Horie M., Murata N., Sawabe K., Satsuma A.

Catalysis Science and Technology 12 巻 ( 18 ) 頁： 5488 - 5494 2022年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

Direct catalytic conversion of methane to value-added chemicals with a high reaction rate and selectivity under mild conditions remains a great challenge. Rh-supported zeolite is one of the promising heterogeneous catalysts capable of selectively oxidizing methane to acetic acid using carbon monoxide and oxygen at low temperatures. However, the difficulty in the preparation of the catalytically active species, i.e., zeolite-confined RhI single-atom sites, has limited the mass activity. Here, we successfully prepared a highly-active Rh-containing zeolite using RhCl<inf>3</inf> molten salt. By high-temperature treatment of the physically-mixed H+-MFI zeolite and bulk RhCl<inf>3</inf>, the RhCl<inf>3</inf> molten salt was formed under in situ conditions and then diffused into the zeolite pores, resulting in being trapped within the zeolite cavity via host-guest interaction and ion-exchange with H+. The encapsulated RhCl<inf>3</inf> species are efficiently dispersed with the formation of RhI single-atom species as the active sites in the catalytic reaction, boosting the direct conversion of methane to acetic acid with a record turnover frequency (592 mol mol<inf>Rh</inf>−1 h−1) and yield (14.6 mmol g<inf>cat</inf>−1 h−1) with high selectivity (76.9%).

DOI： 10.1039/d2cy01471h

Orbital Trap of Xenon: Driving Force Distinguishing between Xe and Kr Found at a Single Ag(I) Site in MFI Zeolite at Room Temperature

Oda A., Kouzai H., Sawabe K., Satsuma A., Ohkubo T., Gotoh K., Kuroda Y.

Journal of Physical Chemistry C 126 巻 ( 19 ) 頁： 8312 - 8326 2022年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

Noble gas (Ng) elements are stable because of their octet electronic configuration, and thus Ng capture and purification are highly challenging. Here, we show a new concept for these applications: an orbital trap for Xe. This concept was found in Xe adsorption/separation processes at room temperature (RT) at the single Ag(I) site in MFI zeolite. Experiments and calculations showed the zeolite lattice-coordinated Ag(I) single ion has excellent electron-accepting nature and thereby induces the Xe 5p → Ag(I) 5s donation orbital interaction, forming a stable σ-bond with Xe even in the lower-pressure region and at RT. By contrast, the stable σ-bond for Kr adsorption is not established at RT because of the instability of the orbital interactions of the Kr 4p → Ag(I) 5s donation, as reflected from the relatively high energy of the Kr 4p orbital. Thus, the single Ag(I) site allows it to distinguish between Xe and Kr at RT; the Xe separation from the Xe/Kr gas mixture was achieved at RT using the Ag/MFI containing a high concentration of single Ag(I) sites. Our findings suggest that the orbital Xe trap using the local structure of porous materials shows promise as an efficient approach to selectively collect Xe (air concentration 0.087 ppm only). It will help to expand the range of applications of the costly Xe.

DOI： 10.1021/acs.jpcc.2c01515

High Pt-mass activity of PtIV1/β-MnO2 surface for low-temperature oxidation of CO under O2-rich conditions Open Access

Nagata T., Oda A., Yamamoto Y., Ichihashi R., Sawabe K., Satsuma A.

Catalysis Science and Technology 12 巻 ( 9 ) 頁： 2749 - 2754 2022年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

A Pt-based CO oxidation catalyst that works even at low temperatures is desirable for industrial applications; however, its development is highly challenging because of Pt's high affinity toward CO. Here, we develop a PtIV single-atom/β-MnO<inf>2</inf> composite metal-oxide surface (PtIV<inf>1</inf>/β-MnO<inf>2</inf>). Single PtIV sites were stably formed on the high surface β-MnO<inf>2</inf> by strong interaction with MnIV defect sites. The resulting PtIV-O-MnIV local structures served the lattice oxygens as an oxidant to catalyze low-temperature oxidation of CO. PtIV<inf>1</inf>/β-MnO<inf>2</inf> was highly resistant to CO poisoning because of the high-valence state of the PtIV single-atom sites. Aided by these geometric and electronic features, the CO oxidation was catalyzed with reaction rates of 0.676 and 0.206 mol<inf>CO</inf> h−1 g<inf>Pt</inf>−1 at 25 °C and 0 °C, respectively, under the O<inf>2</inf>-rich conditions (O<inf>2</inf> : CO ratio of 66.7). These are record rates in the literature for Pt-based catalyst application for low-temperature CO oxidation under near atmospheric conditions.

DOI： 10.1039/d2cy00677d

Preferential oxidation of propene in gasoline exhaust conditions over supported vanadia catalysts Open Access

Sakai R., Ueda K., Ohyama J., Oda A., Deguchi K., Ohki S., Satsuma A.

Journal of Catalysis 408 巻頁： 261 - 269 2022年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Catalysis

For the design of a high-performance platinum group metal-free three-way catalyst, we propose a new C<inf>3</inf>H<inf>6</inf>-preferential oxidation (C<inf>3</inf>H<inf>6</inf>-PROX) catalyst under stoichiometric automobile exhaust gas (NO–CO–C<inf>3</inf>H<inf>6</inf>–O<inf>2</inf>) using supported vanadia catalysts. Among various V<inf>2</inf>O<inf>5</inf> supported catalysts, V<inf>2</inf>O<inf>5</inf>/TiO<inf>2</inf> (anatase, coverage of around one monolayer) showed the best activity for C<inf>3</inf>H<inf>6</inf>-PROX with preferable formation of CO. The tandem catalyst combination using V<inf>2</inf>O<inf>5</inf>/TiO<inf>2</inf> as the upstream C<inf>3</inf>H<inf>6</inf>-PROX catalyst and Cu/CeO<inf>2</inf> as the downstream NO–CO reaction catalyst showed comparable activity for NO reduction as a Rh/ZrO<inf>2</inf> catalyst. The reaction mechanism of C<inf>3</inf>H<inf>6</inf> oxidation was analyzed using in situ Infrared spectroscopy. The C<inf>3</inf>H<inf>6</inf> oxidation progressed with the formation of surface acetate as an intermediate, and acetate consumption was the key step of C<inf>3</inf>H<inf>6</inf> oxidation. It is suggested that the Brønsted acid promoted the cleavage of the C–C bond of acetate, therefore, the number of Brønsted acid sites is one of the critical factors for the higher performance of C<inf>3</inf>H<inf>6</inf>-PROX catalysts.

DOI： 10.1016/j.jcat.2022.03.012

Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al2O3-Supported Silver Nanoparticles: Size, Shape, and Support Effects Open Access

Sawabe K., Satsuma A.

ACS Omega 7 巻 ( 5 ) 頁： 4405 - 4412 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Omega

Nanoparticles (NPs) supported on metal oxides exhibit high catalytic activities for various reactions. The shape and oxidation state of such NPs, which are related to the catalytic activity, are often determined by the support. Herein, we conducted a density functional theory study on isolated silver (Ag) NPs and two types of Ag-NPs supported on gamma-aluminum oxide (γ-Al2O3). First, carbon monoxide (CO) adsorption on the isolated Ag NPs was investigated for decahedra (D5h), icosahedra (Ih), and cuboctahedra (Oh) of various sizes. Ih and Oh NPs showed moderate size dependence, whereas D5h NPs showed high size dependence when the height was below 1.4 nm. The enhancement of CO adsorption on D5h NPs was attributed to the presence of superatomic states. Next, we performed geometrical optimization of Ag54/γ-Al2O3(110) with a decahedral shape. Two types of structures were obtained: amorphous Ag54(A) and locally fivefold symmetrical Ag54(B) structures. Both NPs on γ-Al2O3(110) were found to be positively charged, but electron transfer to the support occurred only from the Ag atoms at the two bottom layers, and the upper part of NPs was relatively neutral. The enhancement of CO adsorption on Ag54(B) disappeared due to loss of the high symmetry. In turn, the moderate size dependence of neutral isolated NPs can be applied.

DOI： 10.1021/acsomega.1c06208

Enhancement of toluene hydrogenation activity of supported Pt nanoparticles with increasing the crystallinity of Pt Open Access

Murata K., Onoda J., Yamamoto Y., Oda A., Ohyama J., Satsuma A.

Applied Catalysis A General 629 巻頁： 118425 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Catalysis A General

The activity of Pt/Al<inf>2</inf>O<inf>3</inf> in the hydrogenation of toluene (TOL) was found to monotonically increase in line with an increase in the Pt particle size from 1.0 to 2.5 nm, but was constant for a size above 2.5 nm. Comparing different crystalline phases of Al<inf>2</inf>O<inf>3</inf>, the activity of Pt/θ-Al<inf>2</inf>O<inf>3</inf> was found to be around 1.5 times higher than that of Pt/γ-Al<inf>2</inf>O<inf>3</inf> for the same Pt particle size. Scanning transmission electron microscopy showed the presence of amorphous Pt nanoparticles (NPs) with a size of < 2.0 nm and Pt nanocrystals (NCs) with a size of ≥ 2.0 nm on Al<inf>2</inf>O<inf>3</inf>. Furthermore, the fraction of amorphous Pt NPs in Pt/γ-Al<inf>2</inf>O<inf>3</inf> was higher than that in Pt/θ-Al<inf>2</inf>O<inf>3</inf>. Pt NCs were shown to be more active than the amorphous Pt NPs in the hydrogenation of TOL owing to them having an abundance of Pt plane.

DOI： 10.1016/j.apcata.2021.118425

Rational design of ZSM-5 zeolite containing a high concentration of single Fe sites capable of catalyzing the partial oxidation of methane with high turnover frequency

Oda A., Aono K., Murata N., Murata K., Yasumoto M., Tsunoji N., Sawabe K., Satsuma A.

Catalysis Science and Technology 12 巻 ( 2 ) 頁： 542 - 550 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

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 g<inf>cat</inf>−1 h−1 yield 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 g<inf>cat</inf>−1 h−1 yield. 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 AlO<inf>4</inf> tetrahedra 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.

DOI： 10.1039/d1cy01987b

Theoretical Study of the Propene Combustion Catalysis of Chromite Spinels: Reaction Mechanism and Relation between the Activity and Electronic Structure of Spinels

Zhao P., Ehara M., Satsuma A., Sakaki S.

Journal of Physical Chemistry C 125 巻 ( 47 ) 頁： 25983 - 26002 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

Oxides of base-metal elements play an important role as catalysts in alkene combustion, but correct knowledge of the reaction mechanism and determination factors for activity remains elusive. Herein, we report a systematic study of propene combustion catalyzed by ZnCr2O4(111) as one example using DFT + U calculations. The combustion occurs through three parallel reaction pathways starting from C-H σ-bond cleavage. In each pathway, acetate, carbonate, or formate is formed as a key intermediate, which is consistent with the experimental detection of several different kinds of intermediates in propene combustion. Effects of tetrahedral metal (MTd) and octahedral metal (MOh) atoms on the catalytic activity are discussed by comparing propene combustion by MgCr2O4(111), Cu-doped ZnCr2O4(111) (named Zn1 - xCuxCr2O4(111)), and Co-doped ZnCr2O4(111) (named ZnCr2 - xCoxO4(111)) with that by ZnCr2O4(111). Catalytic activity increases in the order MgCr2O4(111) < Zn1 - xCuxCr2O4(111) < ZnCr2O4(111) < ZnCr2 - xCoxO4(111). The higher activity of ZnCr2O4(111) than that of MgCr2O4(111) agrees with the experimental findings. ZnCr2 - xCoxO4(111) is computationally predicted here to be more active than ZnCr2O4(111) which has been experimentally used as a good catalyst. Based on computational findings, a discussion is presented on the relation between the activity and electronic structure of spinels.

DOI： 10.1021/acs.jpcc.1c06760

Structure-Property Relationships of Pt-Sn Nanoparticles Supported on Al2O3for the Dehydrogenation of Methylcyclohexane Open Access

Murata K., Kurimoto N., Yamamoto Y., Oda A., Ohyama J., Satsuma A.

ACS Applied Nano Materials 4 巻 ( 5 ) 頁： 4532 - 4541 2021年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Nano Materials

The structure-catalytic property relationships of Al2O3-supported Pt-Sn nanoparticles (Pt-Sn/Al2O3) in the dehydrogenation of methylcyclohexane (MCH) were investigated by varying the Sn/Pt ratios of the catalysts. The initial activity and the deactivation rate of the Pt-Sn/Al2O3 catalysts in the MCH dehydrogenation decreased in line with an increase in the Sn/Pt ratio from 0 to 3. The Pt-Sn/Al2O3 catalyst with a Sn/Pt ratio of 2 showed good activity, durability, and toluene selectivity in the MCH dehydrogenation among the series of catalysts. The dispersion of Pt in the Pt-Sn/Al2O3 catalysts was observed to decrease with an increase in the Sn/Pt ratio. Structural changes in the catalysts from Pt-Sn clusters to intermetallic Pt3Sn and PtSn nanoparticles were also observed using scanning transmission electron microscopy and X-ray diffraction. According to structural analysis using X-ray absorption fine-structure spectroscopy and infrared spectroscopy using carbon monoxide as a probe, the electron density of Pt increased, and the fraction of Pt-Pt adjacent sites decreased with an increase in the Sn/Pt ratio. Comparing the catalytic properties and the structures of the Pt-Sn/Al2O3 catalysts, their initial activities were correlated with the dispersion of Pt. In addition, the durability and selectivity of the catalysts were enhanced due to an increase in the electron density of Pt and a decrease in the number of Pt-Pt adjacent sites. Overall, the properties of the catalysts in the MCH dehydrogenation are determined by the local structure of Pt atoms rather than the crystal structure of the Pt-Sn alloy nanoparticles on Al2O3.

DOI： 10.1021/acsanm.1c00128

Relationship between penta-coordinated Al3+sites in the Al2O3supports and CH4combustion activity of Pd/Al2O3catalysts Open Access

Murata K., Shiotani T., Ohyama J., Wakabayashi R., Maruoka H., Kimura T., Satsuma A.

Catalysis Science and Technology 11 巻 ( 7 ) 頁： 2374 - 2378 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

Pd/Al<inf>2</inf>O<inf>3</inf>catalysts were prepared using various Al<inf>2</inf>O<inf>3</inf>supports with different structural features such as crystalline phase and crystallinity related to Al3+coordination, revealing a significant insight into the methane (CH<inf>4</inf>) combustion activity of Pd nanoparticles with the fraction of penta-coordinated Al3+sites in the Al<inf>2</inf>O<inf>3</inf>supports.

DOI： 10.1039/d1cy00098e

17o-esr evidence for zeolite matrix isolation of a square planar zno3 ring radical with c2v symmetry

Oda A., Kumagai J., Sawabe K., Ohkubo T., Kuroda Y., Satsuma A.

Journal of Physical Chemistry C 125 巻 ( 9 ) 頁： 5136 - 5145 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

Atomic-level insights into the geometric and electronic states of the metal-ozonide sequence remain scarce. We have recently found that a zeolite catalyst has a local environment to isolate the extremely rare mononuclear ZnII- ozonide species. In the present study, each atomic oxygen radical of the ZnII-ozonide species was selectively labeled with 17O, and each local environment was analyzed by electron spin resonance (ESR) spectroscopy at an X-band frequency, computer simulations of ESR spectra, density functional theory (DFT) calculations, and ab initio molecular dynamics (AIMD) simulations. The two types of 17O hyperfine structures assignable to the C2v geometry of a square planar ZnO3 ring radical were obtained experimentally. The DFT calculations ascertained the ground-state C2v geometry of the ZnII-ozonide adduct. This model provides 17O-hyperfine coupling constants that correspond well with the experimental parameters, supporting the generation of the C2v ZnO3 ring radical. The C2v ZnO3 ring radical is stable even at around room temperature, as evidenced by the similarity in the ESR spectra collected at 300 and 4 K. Such an unusual stability was supported by AIMD simulations, where C2v geometry was preserved at least for 50 ps at 300 K. Molecular orbital analyses showed that the ozonide species is stabilized via the highly polarized ZnII-(O3 - ) bonds. These interactions led to the polarization of two O-O bonds in the ozonide adduct, through which both side oxygens becomes anionic states, but the central oxygen becomes a cationic state. The zeolite lattice plays a pivotal role in constraining the effective charge of Zn close to (+2) and thereby stabilizing such a highly polarized ZnII-(O3 - ) bond. These novel findings suggest that the zeolite lattice has the potential as the ligand to create reactive metal-oxygen radicals with an unprecedented shape and ionic states.

DOI： 10.1021/acs.jpcc.1c01042

Kinetic analysis of Ag particle redispersion into ZSM-5 in the presence of coke usingin situXAFS Open Access

Murata K., Ohyama J., Satsuma A.

Catalysis Science and Technology 11 巻 ( 2 ) 頁： 506 - 515 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

In the present study, the redispersion behavior of Ag particles on ZSM-5 in the presence of coke was observed usingin 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 to27Al 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.

DOI： 10.1039/d0cy01989e

Theoretical insight into oxidation catalysis of chromite spinel MCr2O4 (M = Mg, Co, Cu, and Zn): Volcano plot for oxygen-vacancy formation and catalytic activity

Zhao P., Ehara M., Satsuma A., Sakaki S.

Journal of Catalysis 393 巻頁： 30 - 41 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Catalysis

Catalysis of chromite spinel MCr<inf>2</inf>O<inf>4</inf> (M = 3d metal etc.) depends very much on M but the reason is unclear. Herein, CO oxidation by cubic MCr<inf>2</inf>O<inf>4</inf>(1 1 1) (M = Mg, Co, Cu, and Zn) and tetragonal CuCr<inf>2</inf>O<inf>4</inf>(1 0 0) was investigated as one example, using DFT + U. Surface termination of these chromites is determined by available oxidation state of M. Catalytic activity of the most stable surface termination increases following the order cubic CuCr<inf>2</inf>O<inf>4</inf>(1 1 1) < cubic MgCr<inf>2</inf>O<inf>4</inf>(1 1 1) < cubic CoCr<inf>2</inf>O<inf>4</inf>(1 1 1)-A < cubic ZnCr<inf>2</inf>O<inf>4</inf>(1 1 1) < cubic CoCr<inf>2</inf>O<inf>4</inf>(1 1 1)-B < tetragonal CuCr<inf>2</inf>O<inf>4</inf>(1 0 0), where surface termination A is as stable as different termination B. This order agrees with experimental findings. Volcano plot is obtained for catalytic activity against oxygen vacancy formation energy (E<inf>Ov</inf>), which is clearly explained by electronic structure of M. This plot indicates that the E<inf>Ov</inf> is a good descriptor for the CO oxidation activity of chromite spinels.

DOI： 10.1016/j.jcat.2020.11.006

Selective hydrogenation of C=C bond in cinnamaldehyde on Pd step sites of Pd/Al2O3

Murata K., Shiotani T., Ohyama J., Satsuma A.

Chemistry Letters 50 巻 ( 4 ) 2021年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry Letters

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-Al<inf>2</inf>O<inf>3</inf> catalysts with Pd particle size of 510 nm were highly active for the C=C selective hydrogenation of CAL.

DOI： 10.1246/CL.200856

Improvement of hydrogen oxidation reaction in anion exchange membrane fuel cells with ruthenium-based nanoparticle catalysts Open Access

Ohyama J., Satsuma A.

Journal of the Japan Petroleum Institute 64 巻 ( 4 ) 頁： 166 - 171 2021年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Japan Petroleum Institute

Catalysts to improve the hydrogen oxidation reaction (HOR) were developed via control of Ru nanoparticle size, alloying Ru with Ir, and surface modification of metal nanoparticles. The performance of these developed anode catalysts for anion exchange membrane fuel cells had improved, which is dependent on the hydrogen binding energy and the bifunctional mechanism. Surface modification of metal nanoparticles further enhanced the HOR activity based on the bifunctional mechanism. Such surface medication could form reactive OH species and remove surface poisoning of the hydrogen adsorption sites.

DOI： 10.1627/jpi.64.166

Tuning the oxygen release properties of CeO2-based catalysts by metal-support interactions for improved gasoline soot combustion Open Access

Ashikaga R., Murata K., Ito T., Yamamoto Y., Arai S., Satsuma A.

Catalysis Science and Technology 10 巻 ( 21 ) 頁： 7177 - 7185 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

To develop highly active soot combustion catalysts for gasoline direct injection exhausts under low oxygen concentration conditions, CeO2 supported-metal catalysts (M/CeO2, M = Mn, Fe, Co, Ni, Cu, Rh, Pd, and Ag) were examined. Among the catalysts tested, Cu/CeO2 and Rh/CeO2 displayed the highest soot combustion activity. By comparing the activities of Cu-based catalysts with and without a Cu-CeO2 interface, the importance of such an interface for soot combustion was inferred. The oxygen release rate of CeO2-based catalysts, enhanced by metal-CeO2 interactions, 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 CeO2 with 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.

DOI： 10.1039/d0cy01294g

How to Constrain Metal-Oxyl Bonds on a Solid Surface? Lesson from Isovalent Zn(II)-Oxyl and Ga(III)-Oxyl Bonds Isolated in Zeolite Matrix

Oda A., Tanaka T., Sawabe K., Satsuma A.

Journal of Physical Chemistry Letters 11 巻 ( 21 ) 頁： 9426 - 9431 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry Letters

Isolation of the atomic O radical anion bound to a metal ion (metal-oxyl) on solid surfaces is highly desirable for an understanding of how we should design the surface structure for using oxyl as the reactive site. Owing to the analytical difficulty of oxyl, however, even identification of oxyl remains scarce. Herein, we report isovalent ZnII-oxyl and GaIII-oxyl bonds isolated in the zeolite matrix. Close similarities in reactivity, spectroscopic property, and bonding nature were observed between them, but their site requirements were entirely different; the former is generated at the monovalent ion-exchangeable site, whereas the latter at the divalent ion-exchangeable site. This study strongly suggests that tuning the polarization of the metal-oxygen bond using the charge-controlled lattice oxygens is a useful way to constrain surface metal-oxyl bonds.

DOI： 10.1021/acs.jpclett.0c02980

Spectroscopic Evidence of Efficient Generation of Dicopper Intermediate in Selective Catalytic Reduction of NO over Cu-Ion-Exchanged Zeolites

Oda A., Shionoya H., Hotta Y., Takewaki T., Sawabe K., Satsuma A.

ACS Catalysis 10 巻 ( 20 ) 頁： 12333 - 12339 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

The key reactive sites in the selective catalytic reduction (SCR) of NO using ammonia (NH3-SCR) are the Cu(II)/Cu(I) ammine complexes encapsulated within zeolite catalysts. The reaction intermediate in the important CuI → CuII reoxidation step has been proposed as the dicopper species. However, obtaining the definitive spectroscopic probe for the dicopper intermediate under NH3-SCR remains a quite challenging subject. Here we report spectroscopic evidence of the efficient generation of the dicopper intermediate in NH3-SCR over Cu-ion-exchanged zeolites. The state of the Cu ion under the NH3-SCR condition was analyzed using fiber-optic UV-vis-NIR spectroscopy; a distinct spectroscopic fingerprint of the (μ-η2:η2-peroxo)dicopper(II) intermediate was detected. Our spectroscopic assignment was rationalized by density functional theory calculations. The intensity of the spectroscopic fingerprints of dimeric copper was much higher than expected from previous reports, and it was also found that such a spectroscopic probe is observable only under the NH3-SCR conditions. This finding strongly supports the previously suggested Cu dynamic contributions to NH3-SCR catalysis.

DOI： 10.1021/acscatal.0c03425

Methane Combustion over Pd/Al2O3Catalysts in the Presence of Water: Effects of Pd Particle Size and Alumina Crystalline Phase Open Access

Murata K., Ohyama J., Yamamoto Y., Arai S., Satsuma A.

ACS Catalysis 10 巻 ( 15 ) 頁： 8149 - 8156 2020年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

The effects of the Pd particle size and the Al2O3 crystalline phase of Pd/Al2O3 catalysts on the CH4 combustion in the presence of H2O were investigated. According to X-ray absorption fine structure (XAFS) measurements, it was revealed that, during the CH4 combustion, the Pd nanoparticles existed on the Al2O3 support as a PdO phase, while the crystallinity of PdO depended on the Pd particle size. On the basis of X-ray diffraction (XRD), amorphous PdO particles with a size of <7 nm exhibited low activity for CH4 combustion. In contrast, as the Pd particle size increased, larger crystalline PdO particles (>7 nm) were formed, which were highly active for CH4 combustion. Comparing the effects of the different Al2O3 crystalline phases, Pd/α-Al2O3 was proved to be more resistant to deactivation by H2O than Pd/γ-Al2O3 and Pd/θ-Al2O3. Moreover, according to H2O temperature-programmed desorption (TPD) and infrared (IR) measurements, since α-Al2O3 was relatively hydrophobic compared to γ-Al2O3 and θ-Al2O3, a faster and reversible adsorption/desorption of OH/H2O species was achieved, while the H2O poisoning on PdO species in the vicinity was limited.

DOI： 10.1021/acscatal.0c02050

Reductive conversion of 5-hydroxymethylfurfural to 1,2,6-hexanetriol in water solvent using supported Pt catalysts Open Access

Kataoka Hiroto, Kosuge Daichi, Ogura Keiji, Ohyama Junya, Satsuma Atsushi

CATALYSIS TODAY 352 巻頁： 60-65 - 65 2020年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Today

One-pot conversion of biomass derived 5-hydroxymethylfurfural (HMF) to 1,2,6-hexanetriol (1,2,6-HT) in water solvent was performed using Pt catalysts supported on various acid-base metal oxides. Pt catalysts supported on hydrotalcite, MgO, and CeO<inf>2</inf> showed better yield of 1,2,6-HT and 2,5-bis(hydroxymethyl)-tetrahydrofuran (BHF), while ring-rearranged cyclopentanol derivatives were predominant products on the other Pt catalysts. The product distribution with time course on Pt/hydrotalcite revealed that HMF is at first hydrogenated to BHF, then the following parallel reactions proceed; ring-rearrangement to cyclopentanol derivatives, ring-hydrogenation to BHF, and hydrogenolysis to 1,2,6-HT. When pure hydrotalcite, MgO and CeO<inf>2</inf> were physically mixed with Pt/SiO<inf>2</inf>, the selectivity to 1,2,6-HT was almost zero or less than 10 %. It was suggested that the formation of 1,2,6-HT proceeds at metal-support interface. The effect of metal-support interface was examined by means of IR spectra of adsorbed methanol. It was indicated that both basic property of supports and surface monodentate alkoxide formation are essential for the production of 1,2,6-HT. The maximum yield of 1,2,6-HT (42 %) was obtained using Co-promoted Pt/CeO<inf>2</inf> catalysts pre-reduced at 200 °C.

DOI： 10.1016/j.cattod.2019.12.002

Effects of carbon number and bond saturation on hydrocarbon combustion over a diesel oxidation catalyst Open Access

Tsuchiya A., Masaoka S., Ohyama J., Sawabe K., Satsuma A.

Catalysis Science and Technology 10 巻 ( 12 ) 頁： 3868 - 3874 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

One of the problems in a diesel oxidation catalyst is its insufficient activity for injected diesel fuel at low temperatures caused by strong adsorption of hydrocarbons. This study systematically clarified the poisoning effect of various hydrocarbons having carbon numbers from 3 to 16. As the carbon number in alkanes increased, the light-off temperature over a Pt-Pd/Al2O3 catalyst gradually shifted to a lower temperature. While alkenes and aromatics showed an opposite trend, the light-off shifted to a higher temperature as the carbon number increased. In situ FTIR spectra indicated that the amount of adsorbed hydrocarbons on the metal surface increased with the increase in the carbon number of alkanes and alkenes. Kinetic analysis showed that the reaction orders with respect to O2 were below zero in light alkane combustion, while those with respect to hydrocarbons were zero or lower in alkene and aromatic combustion. The shift of the light-off temperatures was rationalized by competitive adsorption of hydrocarbons and oxygen. This journal is

DOI： 10.1039/d0cy00017e

Selective Hydrogenation of Cinnamaldehyde over the Stepped and Plane Surface of Pd Nanoparticles with Controlled Morphologies by CO Chemisorption

Murata K., Ogura K., Ohyama J., Sawabe K., Yamamoto Y., Arai S., Satsuma A., Satsuma A.

ACS Applied Materials and Interfaces 12 巻 ( 23 ) 頁： 26002 - 26012 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

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 SiO2 supports. 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.

DOI： 10.1021/acsami.0c05938

PubMed

In Situ Spectroscopic Studies on the Redox Cycle of NH3-SCR over Cu-CHA Zeolites Open Access

Liu Chong, Kubota Hiroe, Amada Takehiro, Kon Kenichi, Toyao Takashi, Maeno Zen, Ueda Kakuya, Ohyama Junya, Satsuma Atsushi, Tanigawa Takuya, Tsunoji Nao, Sano Tsuneji, Shimizu Ken-ichi

CHEMCATCHEM 12 巻 ( 11 ) 頁： 3050-3059 - 3059 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemcatchem

The selective catalytic reduction of NO with ammonia (NH<inf>3</inf>−SCR) catalyzed by Cu−CHA zeolites is thoroughly investigated using in situ spectroscopic experiments combined with on-line mass spectroscopy (MS) under steady-state NH<inf>3</inf>−SCR conditions and transient conditions for Cu(II)/Cu(I) redox cycles. Quantitative analysis of the in situ XANES spectra of Cu−CHA under steady-state conditions of NH<inf>3</inf>−SCR show that NH<inf>3</inf>-coordinated Cu(II) species is the dominant Cu species at low temperatures (100–150 °C). At higher temperatures, Cu(II) species and [Cu(NH<inf>3</inf>)<inf>2</inf>]+ complex coexist, possibly because the rate of the Cu(II)→Cu(I) reduction step is comparable to that of the Cu(I)→Cu(II) oxidation step. In situ XANES, IR/MS, and UV-vis/MS experiments on the reduction half cycle demonstrate that the reduction of Cu(II) species occurs via the reaction of NH<inf>3</inf>-liganded Cu(II) with NO to yield N<inf>2</inf> and H<inf>2</inf>O. For the oxidation half cycle, in situ XANES experiments of Cu(I) oxidation in 10 % O<inf>2</inf> at 200 °C indicate that an increased density in CHA zeolite exhibits a higher oxidation rate. In situ UV-vis experiments of Cu(I) reoxidation using different mixtures of oxidant feed gas demonstrate the key role of O<inf>2</inf> in the oxidation cycle. It is suggested that the reoxidation of Cu(I) to Cu(II) species occurs with only O<inf>2</inf> as the oxidant, and a high Cu density in CHA zeolite promotes SCR activity by enhancing the oxidative activation of Cu(I) to Cu(II) during the catalytic cycle.

DOI： 10.1002/cctc.202000024

Enhancement of Alkaline Hydrogen Oxidation Reaction of Ru-Ir Alloy Nanoparticles through Bifunctional Mechanism on Ru-Ir Pair Site

Ishikawa Kazutomo, Ohyama Junya, Okubo Keiichi, Murata Kazumasa, Satsuma Atsushi

ACS APPLIED MATERIALS & INTERFACES 12 巻 ( 20 ) 頁： 22771-22777 - 22777 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

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.

DOI： 10.1021/acsami.0c00506

Removal of Surface Poisoning Improves Hydrogen Oxidation Performance of Pt Catalysts under Basic Conditions

Ohyama Junya, Okubo Keiichi, Ishikawa Kazutomo, Saida Takahiro, Yamamoto Yuta, Arai Shigeo, Satsuma Atsushi

ACS APPLIED ENERGY MATERIALS 3 巻 ( 2 ) 頁： 1854-1859 - 1859 2020年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Energy Materials

Anion exchange membrane fuel cells (AEMFCs) have been developed to the extent that the cell performance is nearing that of conventional proton exchange membrane fuel cells. For further improvement of AEMFC cell performance, it is necessary to develop the catalysis of hydrogen oxidation reactions (HORs) under basic conditions at the anode. Here, significant poisoning of Pt/C under basic conditions is demonstrated by electrochemical active surface area (ECSA) analysis using not only electrochemical measurement but also in situ Pt L<inf>3</inf>-edge X-ray adsorption spectroscopy (XAS). Furthermore, the in situ XAS analysis reveals that the surface modification of Pt/C with another metal species improves the ECSA of the Pt nanoparticles by removal of the surface poisoning, which contributes to the enhanced HOR performance of the modified Pt/C catalysts. Therefore, the removal of poisoning is proposed as a mechanism for improving the HOR on Pt-based catalysts.

DOI： 10.1021/acsaem.9b02274

In situ/operando spectroscopic studies on NH3–SCR reactions catalyzed by a phosphorus-modified Cu-CHA zeolite Open Access

Kubota H., Liu C., Amada T., Kon K., Toyao T., Maeno Z., Ueda K., Satsuma A., Tsunoji N., Sano T., Shimizu K.

Catalysis Today 376 巻頁： 73 - 80 2020年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Today

The modification of Cu-exchanged zeolites with phosphorus represents a promising method to enhance their hydrothermal stability, which is of pivotal importance for catalysts that promote the selective catalytic reduction of NO with ammonia (NH<inf>3</inf>–SCR). In this study, we investigated the reaction mechanism of NH<inf>3</inf>–SCR catalyzed by a phosphorus-modified CHA zeolite that contains active Cu species (Cu-P-CHA), and assessed the effect of the phosphorus modification on the hydrothermal stability of the catalyst by employing in situ/operando spectroscopic methods. In their entirety, the combined results from in situ/operando IR, UV–vis, and XANES experiments revealed that the NH<inf>3</inf>–SCR process over Cu-P-CHA proceeds via the reduction of Cu(II) to Cu(I) followed by a reoxidation of Cu(I) to Cu(II). In addition, we found that the phosphorus modification improved the hydrothermal durability of the catalyst by retaining a higher amount of the redox-active Cu species and the zeolite framework.

DOI： 10.1016/j.cattod.2020.07.084

Exploiting Metal-Support Interactions to Tune the Redox Properties of Supported Pd Catalysts for Methane Combustion 査読有り

Murata K., Kosuge D., Ohyama J., Mahara Y., Yamamoto Y., Arai S., Satsuma A.

ACS Catalysis 10 巻 ( 2 ) 頁： 1381 - 1387 2020年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

The redox properties of supported Pd catalysts can directly affect their methane combustion activity. Here, the effect of the support on methane combustion was elucidated using Pd nanoparticles supported on various metal oxides (θ-Al<inf>2</inf>O<inf>3</inf>, γ-Al<inf>2</inf>O<inf>3</inf>, ZrO<inf>2</inf>, CeO<inf>2</inf>, MgO, La<inf>2</inf>O<inf>3</inf>, TiO<inf>2</inf>, SnO<inf>2</inf>, and Nb<inf>2</inf>O<inf>5</inf>). To eliminate the effect of Pd particle size and morphology, uniform Pd particles were synthesized in the liquid phase. Interestingly, the methane combustion activity formed a volcano plot when plotted against the oxide formation enthalpy (Δ<inf>f</inf>H<inf>M-O</inf>°) of the support. Combining X-ray photoelectron spectroscopy and scanning transmission electron microscopy-electron energy loss spectroscopy, the structure of the Pd nanoparticles on the support in an oxidizing atmosphere was identified. Pd particles on θ-Al<inf>2</inf>O<inf>3</inf>, γ-Al<inf>2</inf>O<inf>3</inf>, ZrO<inf>2</inf>, and CeO<inf>2</inf> with moderate Δ<inf>f</inf>H<inf>M-O</inf>° adopted a metal-core-oxide-shell structure and showed the highest activities for methane combustion. In contrast, completely oxidized Pd particles were present on MgO and La<inf>2</inf>O<inf>3</inf>, which have lower Δ<inf>f</inf>H<inf>M-O</inf>° and were not very active. Pd metal particles on TiO<inf>2</inf>, SnO<inf>2</inf>, and Nb<inf>2</inf>O<inf>5</inf> with higher Δ<inf>f</inf>H<inf>M-O</inf>° were not effective catalysts for methane combustion.

DOI： 10.1021/ACSCATAL.9B04524

Gas-phase synthesis of morphology-controlled Pt nanoparticles and their impact on cinnamaldehyde hydrogenation

Kato Sosuke, Ohyama Junya, Machida Masato, Satsuma Atsushi

CATALYSIS SCIENCE & TECHNOLOGY 9 巻 ( 9 ) 頁： 2097-2102 - 2102 2019年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

Gas-phase synthesis of morphology-controlled Pt nanoparticles (PtNPs) is conducted with carbon monoxide as a protective agent. Depending on the preparation temperature, Pt nanocubes with Pt{100} or cuboctahedra with Pt{111} and Pt{100} facets are formed by reducing Pt/C and Pt/SiO2 under a CO/H2 flow, although Pt nanospheres are formed under a H2 flow in the absence of CO. The influence of the Pt nanoparticle morphology on cinnamaldehyde hydrogenation is explored by comparing the hydrogenation performances of Pt nanocubes, cuboctahedrons, and spheres with various particle sizes. The hydrogenation activity and selectivity toward cinnamyl alcohol are enhanced in the order Pt nanocuboctahedra > Pt nanocubes > Pt nanospheres; thus, Pt{111} facets > Pt{100} facets > rounded (stepped) surface with respect to the surface structure.

DOI： 10.1039/c9cy00158a

Tandem Base-Metal Oxide Catalyst: Superior NO Reduction Performance to the Rh Catalyst in NO-C3H6-CO-O-2

Ueda Kakuya, Tsuji Masashi, Ohyama Junya, Satsuma Atsushi

ACS CATALYSIS 9 巻 ( 4 ) 頁： 2866-2869 - 2869 2019年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Catalysis

We developed a high-performance PGM-free three-way catalyst based on a new strategy: a combination of two base-metal oxide catalysts with tandem configuration for hydrocarbon preferential oxidation (PROX) in upstream of exhausted gas and efficient purification of NO by CO in the downstream flow. The effectiveness of the tandem concept is verified by a combination of ZnCr2O4 for C3H6-PROX and CuCo2O4 for NO-CO-O2 reaction. The combination achieved a comparable performance to a Rh/ZrO2 catalyst, in terms of NO conversion (66.9%) and a superior performance regarding N2 yield (59.9%) and N2 selectivity (89.8%) at 300 °C.

DOI： 10.1021/acscatal.9b00526

Surface modification of Pt nanoparticles with other metals boosting the alkaline hydrogen oxidation reaction

Okubo Keiichi, Ohyama Junya, Satsuma Atsushi

CHEMICAL COMMUNICATIONS 55 巻 ( 21 ) 頁： 3101-3104 - 3104 2019年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemical Communications

To enhance the hydrogen oxidation reaction (HOR) activity of Pt/C under alkaline conditions, the catalyst's surface was modified with fifteen metals. The surface modification enhanced the activity of Pt/C for the HOR beyond a change in hydrogen binding energy (HBE), and this can be attributed to a change in the reactivity of surface oxygen species to adsorbed hydrogen species.

DOI： 10.1039/c9cc00582j

Enhanced alkaline hydrogen oxidation reaction by modifying Pt nanoparticle surface with another metal

Ohyama J., Okubo K., Satsuma A.

ECS Transactions 92 巻 ( 8 ) 頁： 733 - 738 2019年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ECS Transactions

The cell performance of anion exchange membrane fuel cells (AEMFCs) has been getting closer to that of proton exchange membrane fuel cells (PEMFCs) by improvement of hydrogen oxidation reaction (HOR) catalysts on anodes with the help of the state-of-the-art AEMs having high ion conductivity. However, development of the alkaline HOR catalysts is still demanded to reduce the usage of precious metals on AEMFC anode. Here, Pt/C catalyst is modified to improve the HOR activity using fifteen metals on the group 4-11 of the 4th and 5th period in the periodic table except for Tc, i.e., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag. In addition, the hydrogen binding energy of modified Pt/C and the oxophilicity of modifying metals are evaluated to reveal the mechanism of improved/lowered HOR activity.

DOI： 10.1149/09208.0733ecst

In situ and operando analysis of environmental catalysts - Studies on reaction mechanism and active site

Murata K., Ueda K., Mahara Y., Ohyama J., Satsuma A.

Catalysis 31 巻頁： 242 - 266 2019年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis

In situ and operando analyses are the methods to observe the real features of catalysts under the reaction conditions. These methods can clarify the dynamics of active species of catalysts and reaction scheme on catalyst surface through transient response method, kinetic study, temperature dependence of catalysts and products, and so on. In this review, progress in in situ and operando analyses is summarized with emphasis on environmental catalysts, i.e., catalysts for combustion, selective reduction of NO, automotive three-way catalysis, and related materials.

DOI： 10.1039/9781788016971-00242

Structure–Activity Relationship of Iron Oxides for NO Reduction in the Presence of C3H6, CO, and O2 査読有り

Ueda K., Ohyama J., Sawabe K., Satsuma A.

Chemistry A European Journal 25 巻 ( 61 ) 頁： 13964 - 13971 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry A European Journal

Spinel-type NiFe<inf>2</inf>O<inf>4</inf> exhibited the highest NO reduction activity among base-metal oxides under simulated exhaust of a gasoline-powered vehicle. The structure–activity relationship of iron oxides has been investigated through both experimental and computational studies. Spinel iron oxide (γ-Fe<inf>2</inf>O<inf>3</inf>) exhibited a much higher NO reduction activity than that of iron oxide with other structures (α-Fe<inf>2</inf>O<inf>3</inf> and LaFeO<inf>3</inf>). Operando IR measurements clarified that the spinel structure facilitated the reaction between NO<inf>x</inf> and adsorbed oxidized hydrocarbon or cyanide species. The high reactivity of the spinel structure was ascribed to the high adsorption energy of NO, as elucidated by DFT calculations. Furthermore, molecular orbital calculations demonstrated that the local coordination structure of the spinel iron oxide induced the involvement of not only σ but also π orbitals during NO adsorption on Fe atoms. This work clarified the origin of the structure-dependent activity of metal oxides, with a focus on their local coordination structures.

DOI： 10.1002/CHEM.201902994

Shape Control Preparation of Supported Platinum Nano-octahedra by Ethylene Treatment for Enhancement of Selective Hydrogenation of Cinnamaldehyde 査読有り

Ohyama J., Kato S., Machida M., Satsuma A.

Chemistry Letters 48 巻 ( 10 ) 頁： 1203 - 1205 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry Letters

The particle shape of a Pt/C catalyst is confined to octahedral by adding ethylene in an H<inf>2</inf> stream during reduction of Pt/C. The Pt nano-octahedra enclosed by Pt{111} show higher catalytic activity for selective C=O hydrogenation of cinnamaldehyde in comparison with Pt nano-cuboctahedron, cube, and sphere.

DOI： 10.1246/CL.190462

Quantum Chemical Computation-Driven Development of Cu-Shell-Ru-Core Nanoparticle Catalyst for NO Reduction Reaction 査読有り

Ohyama J., Shibano J., Satsuma A., Fukuda R., Yamamoto Y., Arai S., Shishido T., Asakura H., Hosokawa S., Tanaka T.

Journal of Physical Chemistry C 123 巻 ( 33 ) 頁： 20251 - 20256 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

A supported Cu-based catalyst is designed for nitrogen oxide (NO) reduction reaction based on the previous exploration of Cu-M alloy nanoparticles by quantum chemical computations, where Cu-shell-Ru-core with incoherent interphase interfaces have been suggested as a candidate structure improving NO reduction activity. Here, such Cu-Ru nanoparticles are actually prepared in Al<inf>2</inf>O<inf>3</inf>-supported form by using electrostatic adsorption method as an adequate preparation method of supported core-shell alloy nanoparticle catalysts. Improved NO reduction activity by Cu-shell-Ru-core nanoparticles is demonstrated by NO-CO reaction activity tests on their Cu0/Ru surface in comparison to monometal surface of Cu and Ru nanoparticles.

DOI： 10.1021/ACS.JPCC.9B03687

Identification of active sites in CO oxidation over a Pd/Al2O3 catalyst 査読有り Open Access

Murata K., Eleeda E., Ohyama J., Yamamoto Y., Arai S., Satsuma A.

Physical Chemistry Chemical Physics 21 巻 ( 33 ) 頁： 18128 - 18137 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Chemistry Chemical Physics

The active sites of Pd/Al<inf>2</inf>O<inf>3</inf> catalysts for CO oxidations were identified by investigating the dependence of CO oxidation activities on the surface structure and morphology of Pd nanoparticles. The maximum catalytic activity was obtained for Pd particles approximately 2 nm in particle size. We performed structural analyses on the Pd surface through infrared (IR) spectroscopy of the adsorbed CO molecules. A positive correlation was obtained between catalytic activity and the fraction of linear CO adsorbed on Pd corner sites and Pd(111) facets, indicating that these sites are highly active for CO oxidation. X-ray absorption fine structure (XAFS) and spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) measurements demonstrated that Pd nanoparticles less than 2 nm in particle size with amorphous-like structures and Pd particles with large, well-ordered structures favor the formation of a high fraction of corner sites and Pd(111) facets, respectively.

DOI： 10.1039/C9CP03943K

Twinned/untwinned catalytic gold nanoparticles identified by applying a convolutional neural network to their Hough transformed Z-contrast images

Yamamoto Yuta, Hattori Mizuki, Ohyama Junya, Satsuma Atsushi, Tanaka Nobuo, Muto Shunsuke

MICROSCOPY 67 巻 ( 6 ) 頁： 321-330 - 330 2018年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Microscopy

In this article, we demonstrate that a convolutional neural network (CNN) can be effectively used to determine the presence of twins in the atomic resolution scanning transmission electron microscopy (STEM) images of catalytic Au nanoparticles. In particular, the CNN screening of Hough transformed images resulted in significantly higher accuracy rates as compared to those obtained by applying this technique to the raw STEM images. The proposed method can be utilized for evaluating the statistical twining fraction of Au nanoparticles that strongly affects their catalytic activity.

DOI： 10.1093/jmicro/dfy036

Synthesis of Supported Bimetal Catalysts using Galvanic Deposition Method

Mahara Y., Ohyama J., Sawabe K., Satsuma A.

Chemical Record 18 巻 ( 9 ) 頁： 1306 - 1313 2018年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemical Record

Supported bimetallic catalysts have been studied because of their enhanced catalytic properties due to metal-metal interactions compared with monometallic catalysts. We focused on galvanic deposition (GD) as a bimetallization method, which achieves well-defined metal-metal interfaces by exchanging heterogeneous metals with different ionisation tendencies. We have developed Ni@Ag/SiO2 catalysts for CO oxidation, Co@Ru/Al2O3 catalysts for automotive three-way reactions and Pd−Co/Al2O3 catalysts for methane combustion by using the GD method. In all cases, the catalysts prepared by the GD method showed higher catalytic activity than the corresponding monometallic and bimetallic catalysts prepared by the conventional co-impregnation method. The GD method provides contact between noble and base metals to improve the electronic state, surface structure and reducibility of noble metals.

DOI： 10.1002/tcr.201700084

Time Resolved in situ DXAFS Revealing Highly Active Species of PdO Nanoparticle Catalyst for CH<inf>4</inf> Oxidation

Mahara Y., Murata K., Ueda K., Ohyama J., Kato K., Satsuma A.

ChemCatChem 10 巻 ( 16 ) 頁： 3384 - 3387 2018年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ChemCatChem

The highly active species of Pd/Al2O3 catalysts for methane combustion was revealed by in situ time-resolved dispersive X-ray absorption fine structure (DXAFS) spectroscopy. By using CH4 as a reduction agent, PdO in Pd/Al2O3 is reduced in a 2-step model involving Pd0 nucleation and growth of Pd0 domain in a PdO particle. Kinetic analysis of the 2-step model reduction of PdO nanoparticles leads to a suggestion that partial formation of Pd0 in a PdO particle accelerates methane combustion.

DOI： 10.1002/cctc.201800573

Formation of Rhodium Metal Ensembles that Facilitate Nitric Oxide Reduction over Rhodium/Ceria in a Stoichiometric Nitric Oxide–Carbon Monoxide–Propene–Oxygen Reaction

Junya Ohyama, Takumi Nishiyama, Atsushi Satsuma

ChemCatChem 10 巻 ( 7 ) 頁： 1651 - 1656 2018年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Wiley Blackwell

A series of ceria-supported Rh nanoparticles (NPs) that have various particle sizes of 2–7 nm was prepared to investigate the size effect of Rh NPs on NO reduction in NO–CO–C3H6–O2 under stoichiometric conditions. The turnover frequency (TOF) for NO reduction on Rh NPs increased drastically according to their particle size. The strong size dependence of the TOF was attributed to the oxidation states of Rh NPs but not to particle geometries, which include fractions of surface local sites (e.g., corner, edge, plane) and the surface crystal structures (e.g., Rh(1 1 1), (1 0 0)). The variation of the TOF with the Rh metal fraction suggested that Rh metal ensembles are highly active species for NO reduction.

DOI： 10.1002/cctc.201701842

Enhanced three way catalytic activity of NiFe2O4 by physically mixed metal oxides

Shiori Nagai, Kakuya Ueda, Junya Ohyama, Atsushi Satsuma

Catalysis Today 303 巻頁： 40 - 45 2018年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier B.V.

The NOx reduction activity of NiFe2O4 in automotive three-way catalysis was enhanced by physical mixing with CeO2, MgO, ZrO2, and Al2O3, while the mixing with TiO2 and Nb2O5 did not promoted the catalytic activity. On both pure NiFe2O4 and the physically mixed catalysts, NO was mainly reduced by C3H6 under the NO-C3H6-CO-O2 reaction conditions, because the temperature dependence of NO conversion in NO-C3H6-CO-O2 reaction was the same as that in NO-C3H6-O2 reaction. The in-situ FT/IR measurement revealed that the NO reduction proceeded with (1) partial oxidation of C3H6 to surface carboxylates, i.e., acetate and formate as good reductants for NO, and (2) reduction of NO by surface carboxylates. The metal oxide additives did not have catalytic activity for partial oxidation of C3H6 nor for NO oxidation to NO2, except CeO2. The main promotion effect was attributed to storage and release of surface carboxylates by metal oxide additives.

DOI： 10.1016/j.cattod.2017.07.026

Direct Synthesis of Lactams from Keto Acids, Nitriles, and H2 by Heterogeneous Pt Catalysts

S. M.A.H. Siddiki, Abeda S. Touchy, Ashvini Bhosale, Takashi Toyao, Yuji Mahara, Junya Ohyama, Atsushi Satsuma, Ken-Ichi Shimizu

ChemCatChem 10 巻 ( 4 ) 頁： 789 - 795 2018年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Wiley Blackwell

We report herein the first general catalytic system for the direct synthesis of N-substituted γ- and δ-lactams by reductive amination/cyclization of keto acids (including levulinic acid) with nitriles and H2 under mild conditions (7 bar H2, 110 °C, solvent free). The most effective catalyst, Pt and MoOx co-loaded TiO2 (Pt-MoOx/TiO2), shows a wide substrate scope, high turnover number (TON), and good reusability.

DOI： 10.1002/cctc.201701355

Dynamic Behavior of Rh Species in Rh/Al<inf>2</inf>O<inf>3</inf> Model Catalyst during Three-Way Catalytic Reaction: An Operando X-ray Absorption Spectroscopy Study

Hiroyuki Asakura, Saburo Hosokawa, Toshiaki Ina, Kazuo Kato, Kiyofumi Nitta, Kei Uera, Tomoya Uruga, Hiroki Miura, Tetsuya Shishido, Junya Ohyama, Atsushi Satsuma, Katsutoshi Sato, Akira Yamamoto, Satoshi Hinokuma, Hiroshi Yoshida, Masato Machida, Seiji Yamazoe, Tatsuya Tsukuda, Kentaro Teramura, Tsunehiro Tanaka

Journal of the American Chemical Society 140 巻 ( 1 ) 頁： 176 - 184 2018年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

© 2017 American Chemical Society. 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.

DOI： 10.1021/jacs.7b07114

The Metal–Support Interaction Concerning the Particle Size Effect of Pd/Al<inf>2</inf>O<inf>3</inf> on Methane Combustion

PubMed

Reductive Conversion of 5-Hydroxymethylfurfural in Aqueous Solutions by Furan Ring Opening and Rearrangement

Ohyama Junya, Satsuma Atsushi

PRODUCTION OF BIOFUELS AND CHEMICALS WITH BIFUNCTIONAL CATALYSTS 頁： 159-185 2017年12月

Murata K., Mahara Y., Ohyama J., Yamamoto Y., Arai S., Satsuma A.

Angewandte Chemie - International Edition 56 巻 ( 50 ) 頁： 15993 - 15997 2017年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Angewandte Chemie - International Edition

The particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion was investigated. Pd/θ, α-Al2O3 with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al2O3 increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration-corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal–support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al2O3 for methane combustion.

DOI： 10.1002/anie.201709124

In Situ XAFS Study of Dynamic Behavior of Cu Species in MFI-Zeolite under Element Gases of Ammonia Selective Catalytic Reduction 査読有り

Kakuya Ueda, Junya Ohyama, Atsushi Satsuma

CHEMISTRY LETTERS 46 巻 ( 9 ) 頁： 1390 - 1392 2017年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CHEMICAL SOC JAPAN

We studied the dynamic redox behavior of Cu species in zeolite matrix under NH3-SCR using in situ XAFS. Cu2+ species were slowly reduced to Cu+ in flowing NH3, and subsequent addition of NO promoted the reduction to Cu+. In the oxidation step, oxygen alone did not fully oxidize Cu+ to Cu2+, but the Cu+ species were completely oxidized to Cu2+ by NO-O-2. The oxidation step was slower than the reduction step, which suggested that the oxidation step (Cu+ -> Cu2+) is the slow step of the NH3-SCR reaction.

DOI： 10.1246/cl.170451

Investigation of Reaction Mechanism of NO-C<inf>3</inf>H<inf>6</inf>-CO-O<inf>2</inf> Reaction over NiFe<inf>2</inf>O<inf>4</inf> Catalyst

Ueda K., Ohyama J., Satsuma A.

ACS Omega 2 巻 ( 7 ) 頁： 3135 - 3143 2017年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Omega

To elucidate the reaction mechanism of NO-C3H6-CO-O2 over NiFe2O4, we investigated the dynamics of the adsorbed and gaseous species during the reaction using operando Fourier transform infrared (FTIR). The NO reduction activity dependent on the C3H6 and CO concentrations suggested that NO is reduced by C3H6 under three-way catalytic conditions. From FTIR measurements and kinetic analysis, it was clarified that the acetate species reacted with NO-O2 to form N2 via NCO, and that the rate-limiting step of NO reduction was the reaction between CH3COO- and NO-O2. The NO reduction mechanism of the three-way catalyst on NiFe2O4 is different to that on platinum-group metal catalysts, on which NO reduction proceeds through N-O cleavage.

DOI： 10.1021/acsomega.7b00165

Glucose Isomerization Using Alkali Metal and Alkaline Earth Metal Titanates

Ohyama J., Zhang Y., Ito J., Satsuma A.

ChemCatChem 9 巻 ( 14 ) 頁： 2864 - 2868 2017年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ChemCatChem

Glucose isomerization was performed using various titanate catalysts, which include SrTiO3, BaTiO3, CaTiO3, Na2Ti6O13, K2Ti6O13, and Sr3Ti2O7, prepared using a conventional solid-phase method. Among the titanates, SrTiO3, CaTiO3, and Na2Ti6O13 offered a relatively high fructose yield (32 %) with a high selectivity (68–78 %). The yields are comparable to yields reported previously using a Sn-modified BEA zeolite, which shows a high efficiency for glucose isomerization as a Lewis acid catalyst. A study of the mechanism of glucose isomerization on a SrTiO3 catalyst surface by using 1H NMR spectroscopy suggested that the titanates catalyze the isomerization as base catalysts. Thus, the effect of the basicity of the titanates on glucose isomerization was investigated in terms of the base quantity and strength. The analysis was performed by using an acid–base titration method and FTIR spectroscopy with CHCl3 as a probe molecule. It is proposed that glucose isomerization on the titanates depends not only on the base amount but also on the base strength.

DOI： 10.1002/cctc.201700068

Hydrogenative ring-rearrangement of biomass derived 5-(hydroxymethyl) furfural to 3-(hydroxymethyl) cyclopentanol using combination catalyst systems of Pt/SiO2 and lanthanoid oxides 査読有り

J. Ohyama, Y. Ohira, A. Satsuma

CATALYSIS SCIENCE & TECHNOLOGY 7 巻 ( 14 ) 頁： 2947 - 2953 2017年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

Combination catalyst systems composed of Pt/SiO2 and lanthanoid oxides (Pt/SiO2 + LOx) efficiently catalyze the hydrogenative ring-rearrangement of 5-(hydroxymethyl) furfural (HMF) in water to produce 3-(hydroxymethyl) cyclopentanol (HCPO), which can be a unique building block for new materials derived from biomass. We investigated the reason for the efficient hydrogenative ring-rearrangement on Pt/SiO2 + LOx in terms of the acid-base properties of reaction systems, since H+ and Lewis acids can affect the rearrangement of the furan ring. It is indicated that the ring-rearrangement efficiently proceeds under slightly acidic conditions (pH = 5-7) with moderate or a little weak Lewis acidity of lanthanoid oxides.

DOI： 10.1039/c7cy00712d

A theoretical insight into enhanced catalytic activity of Au by multiple twin nanoparticles 査読有り

Sawabe K., Koketsu T., Ohyama J., Satsuma A.

Catalysts 7 巻 ( 6 ) 頁： 191 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysts

Recently, it has been reported that the morphology of Au nanoparticles (NPs) affects the catalytic activity of CO oxidation; twin crystal NPs show higher activity for CO oxidation than single-crystal NPs. In this study, density functional calculations have been carried out to investigate the morphology effect of Au NPs using CO as a probe molecule. In the case of Au NPs with a size of more than 2 nm, CO adsorption energy on the Au NPs is mainly determined by a coordination number (CN) of adsorption sites. CO binding to a multiple twin NP with a size of about 1 nm is stronger than that on a single-crystal NP with the same size. A simple CN explanation cannot be applied to the enhancement of CO binding to the small multiple twin NP. This enhancement is related to a deformation of the NP structure before and after CO adsorption. It is suggested that the multiple twin NP with a size of less than 1 nm, which shows the deformation upon CO adsorption, contributes to the higher activity for CO oxidation.

DOI： 10.3390/catal7060191

Methane combustion over Pd/CoAl<inf>2</inf>O<inf>4</inf>/Al<inf>2</inf>O<inf>3</inf> catalysts prepared by galvanic deposition

Mahara Y., Tojo T., Murata K., Ohyama J., Satsuma A.

RSC Advances 7 巻 ( 55 ) 頁： 34530 - 34537 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：RSC Advances

Pd/CoAl2O4/Al2O3 methane combustion catalysts were synthesized using a galvanic deposition (GD) method (PdCoAl-GD). This PdCoAl-GD catalyst showed higher activities and turnover frequencies (TOFs) than conventional Pd/Al2O3. According to X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy (STEM) measurements, PdCoAl-GD was composed of a CoAl2O4 phase supported on γ-Al2O3 and dispersed Pd nanoparticles of 2-7 nm in size on CoAl2O4. Operando Pd K-edge XAFS measurements indicated that the Pd in PdCoAl-GD was oxidized to highly active methane combustion PdO species at low temperatures. PdCoAl-GD also showed high activity (light-off tests) when PdO was initially present on the catalysts. Methane temperature-programmed reaction (CH4-TPR) measurements on PdCoAl-GD revealed that PdO was reduced by CH4 at low temperatures. The GD method used herein achieved PdO species that were effective for C-H activation.

DOI： 10.1039/c7ra06150a

In situ XAFS study of dynamic behavior of cu species in MFI-Zeolite under element gases of ammonia selective catalytic reduction

Ueda K., Ohyama J., Satsuma A.

Chemistry Letters 46 巻 ( 9 ) 頁： 1390 - 1392 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry Letters

We studied the dynamic redox behavior of Cu species in zeolite matrix under NH3-SCR using in situ XAFS. Cu2+ species were slowly reduced to Cu+ in flowing NH3, and subsequent addition of NO promoted the reduction to Cu+. In the oxidation step, oxygen alone did not fully oxidize Cu+ to Cu2+, but the Cu+ species were completely oxidized to Cu2+ by NOO2. The oxidation step was slower than the reduction step, which suggested that the oxidation step (Cu+ ¼ Cu2+) is the slow step of the NH3-SCR reaction.

DOI： 10.1246/cl.170451

Hydrogenative ring-rearrangement of biomass derived 5-(hydroxymethyl)furfural to 3-(hydroxymethyl)cyclopentanol using combination catalyst systems of Pt/SiO<inf>2</inf> and lanthanoid oxides

Ohyama J., Ohira Y., Satsuma A.

Catalysis Science and Technology 7 巻 ( 14 ) 頁： 2947 - 2953 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Catalysis Science and Technology

Combination catalyst systems composed of Pt/SiO2 and lanthanoid oxides (Pt/SiO2 + LOx) efficiently catalyze the hydrogenative ring-rearrangement of 5-(hydroxymethyl)furfural (HMF) in water to produce 3-(hydroxymethyl)cyclopentanol (HCPO), which can be a unique building block for new materials derived from biomass. We investigated the reason for the efficient hydrogenative ring-rearrangement on Pt/SiO2 + LOx in terms of the acid-base properties of reaction systems, since H+ and Lewis acids can affect the rearrangement of the furan ring. It is indicated that the ring-rearrangement efficiently proceeds under slightly acidic conditions (pH = 5-7) with moderate or a little weak Lewis acidity of lanthanoid oxides.

DOI： 10.1039/c7cy00712d

Investigation of controlling factor for combustion of diesel soot - Effect of oxygen containing functional groups Open Access

Hoshi S., Yamashita D., Mahara Y., Ohyama J., Satsuma A.

Comodia 2017 9th International Conference on Modeling and Diagnostics for Advanved Engine Systems 2017年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Comodia 2017 9th International Conference on Modeling and Diagnostics for Advanved Engine Systems

DPF (Diesel Particulate Filter) is effective for trapping diesel soot from diesel engines. The trapped diesel soot is removed by combustion above 600°C using excess fuels, which results in reduction of fuel economy. An effective design of DPF is strongly required to improve DPF regeneration efficiency and fuel economy; however, the internal phenomenon of diesel soot combustion on DPF is still not clarified. For an effective design of DPF, in this study, we investigated the effect of diesel soot structure on combustion temperature using real diesel soot. Soot samples were characterized by means of various physicochemical techniques: XPS (X-ray photoelectron spectroscopy), EELS (Electron Energy Loss Spectroscopy), Raman spectroscopy, TEM (transmission electron microscopy), and elemental analysis. TEM images and Raman spectra of real diesel soot showed that the difference in the crystallinity of soot was small. XPS, EELS, and elemental analysis revealed that oxygen content, which is derived from surface functional groups of - COOH, -OH, and - C=O at defect sites, was strongly affected by the engine operating conditions. The ignition temperature of diesel soot was dependent on O/C ratio measured by elemental analysis. With the increase in oxygen content of diesel soot, combustion temperatures of soot became lower. It was concluded that the concentration of oxygen containing functional groups is an essential factor for the control of the ignition temperature of diesel soot.

DOI： 10.1299/jmsesdm.2017.9.A314