研究者詳細 - 薩摩　篤

論文 - 薩摩　篤

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Design of platinum group metal-free automotive three-way catalyst: MgMn2O4 and CuCo2O4 in tandem layout Open Access

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

Applied Catalysis A General 700 巻 2025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：Applied Catalysis A General

Platinum group metal (PGM)-free and Cr-free automotive three-way catalyst (TWC) was examined using two types of base-metal oxides for hydrocarbon preferential oxidation (HC-PROX) and NO reduction by CO in tandem configuration. MnOx-based binary mixed metal oxides (X1Mn2, X = Ba, Ca, Co, Cu, Fe, Mg, Ni, Zn, Zr) were investigated for the design of HC-PROX catalysts. Mg1Mn2 achieved both high propene oxidation activity and low CO oxidation activity, and the catalyst phase was determined as MgMn<inf>2</inf>O<inf>4</inf> having the spinel structure. A tandem TWC composed of MgMn<inf>2</inf>O<inf>4</inf> for HC-PROX and CuCo<inf>2</inf>O<inf>4</inf> for NO-CO reaction showed comparable NO reduction activity and higher oxidation activity of propene and CO compared to Rh/ZrO<inf>2</inf> as a benchmark. In-situ FTIR study clarified that the suppression of CO oxidation over MgMn<inf>2</inf>O<inf>4</inf> is caused by strongly adsorbed acetate and formate on the catalyst surface.

DOI： 10.1016/j.apcata.2025.120305

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 M<sup>2+</sup>−(CO<inf>2</inf>)<inf>n</inf>−M<sup>2+</sup> (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 Ba<sup>2+</sup> pair site exhibits higher thermodynamic stability for multiple adsorptions due to the optimal binding mode of Ba<sup>2+</sup>−O<inf>t</inf>−Ba<sup>2+</sup>. Through high-accuracy energy calculations, we have established the relationship among structure, CO<inf>2</inf> uptake, and operating temperature/pressure, demonstrating that the Ba<sup>2+</sup> 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 Pt<sup>0</sup> nanoparticles of 2-3 nm with a high fraction of the surface Pt<sup>δ+</sup> 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<sup>-1</sup>. 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 Al<sup>3+</sup> 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 Al<sup>3+</sup> 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<sup>−1</sup>, 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 Rh<sup>I</sup> 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<sup>+</sup>-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<sup>+</sup>. The encapsulated RhCl<inf>3</inf> species are efficiently dispersed with the formation of Rh<sup>I</sup> 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><sup>−1</sup> h<sup>−1</sup>) and yield (14.6 mmol g<inf>cat</inf><sup>−1</sup> h<sup>−1</sup>) 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 Pt<sup>IV</sup> single-atom/β-MnO<inf>2</inf> composite metal-oxide surface (Pt<sup>IV</sup><inf>1</inf>/β-MnO<inf>2</inf>). Single Pt<sup>IV</sup> sites were stably formed on the high surface β-MnO<inf>2</inf> by strong interaction with Mn<sup>IV</sup> defect sites. The resulting Pt<sup>IV</sup>-O-Mn<sup>IV</sup> local structures served the lattice oxygens as an oxidant to catalyze low-temperature oxidation of CO. Pt<sup>IV</sup><inf>1</inf>/β-MnO<inf>2</inf> was highly resistant to CO poisoning because of the high-valence state of the Pt<sup>IV</sup> 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<sup>−1</sup> g<inf>Pt</inf><sup>−1</sup> 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

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