論文 - 薩摩　篤

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

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

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

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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 ZrO2 (m-ZrO2). In the catalyst designs, m-ZrO2 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-ZrO2. 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 H2 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

Open Access

Scopus

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

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

ACS Sustainable Chemistry and Engineering     2025年

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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 H2. 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 H2 evolution rate normalized with a surface Pt content of 1343 mmolH2/gPt/min. The structure-catalytic property relationship of PtSn@S-1 catalysts was systematically studied. Upon Sn introduction, PtOx 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

Scopus

Reversible Multi-Complexation of CO<inf>2</inf> to Alkaline Earth Metal Ion-Pair at 400 ppm and 298 K 査読有り

Oda A., Sawabe K., Satsuma A.

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

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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 CO2 remains a significant challenge due to the lack of established multi-complexation of CO2 to active sites in microporous materials. In this study, we introduce a novel concept of reversible multi-complexation of CO2 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 CO2 molecules, forming M2+−(CO2)n−M2+ (n=0–4, M=Ca, Sr, Ba) complexes, where each CO2 molecule is stabilized by interactions between terminal oxygen (Ot) in CO2 and the AEM ions. Notably, the Ba2+ pair site exhibits higher thermodynamic stability for multiple adsorptions due to the optimal binding mode of Ba2+−Ot−Ba2+. Through high-accuracy energy calculations, we have established the relationship among structure, CO2 uptake, and operating temperature/pressure, demonstrating that the Ba2+ pair site can capture four CO2 molecules even at concentrations as low as 400 ppm and at 298 K. Three of the four molecules of CO2 trapped were removable at room temperature and under vacuum. The findings in the present study provide a new direction for developing efficient CO2 adsorbents.

DOI： 10.1002/anie.202411969

Scopus

Rutile TiO<inf>2</inf>-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol 査読有り

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

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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 TiO2-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 H2O2, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H2O2 to activate ethane, where the C2H5OOH intermediate is formed through a nonradical mechanism and subsequently converted to C2H5OH. 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

Scopus

Pt single atom alloyed sub-1 nm thick Fe overlayer on supported Cu nanoparticles for methylcyclohexane dehydrogenation 査読有り 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

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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 H2-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

Open Access

Scopus

Unveiling Static and Dynamic Structures of Pd Clusters Influenced by Al<inf>2</inf>O<inf>3</inf> Surfaces: DFT and AIMD Studies 査読有り

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

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

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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 Al2O3 surfaces. The MSIs of the Pd clusters with different Al2O3 surfaces resulted in different morphologies of the clusters. The shape of Pd clusters on α-Al2O3(0001) were deformed to oblate and on γ-Al2O3(110) to prolate. On the other hand, the shape of Pd clusters on γ-Al2O3(100) did not change from that in a vacuum. The migration rate of Pd clusters was also affected by the MSI, which was higher on γ-Al2O3(110) than on α-Al2O3(0001) and γ-Al2O3(100). To evaluate the interactions between Pd clusters and Al2O3 surfaces, we calculated the interaction energies for Pd clusters with various sizes on Al2O3 surfaces. The interaction energy of Pd/Al2O3 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-Al2O3(110) surface than that of α-Al2O3(0001) and γ-Al2O3(100) surfaces, the number of bonds formed between Pd clusters and γ-Al2O3(110) was greater than that of α-Al2O3(0001) and γ-Al2O3(100). According to AIMD simulations and perpendicular displacements of Al and O atoms bound to the Pd cluster on the Al2O3 surface from the bare Al2O3 surface, coordinatively unsaturated Al3+ sites on γ-Al2O3(110) were more flexible than those on α-Al2O3(0001) and γ-Al2O3(100). The flexibility of γ-Al2O3(110) facilitated the formation of bonds with the Pd cluster, resulting in stronger MSIs. When the coordinatively unsaturated Al3+ sites were hydrated, the MSIs were found to be weakened.

DOI： 10.1021/acs.jpcc.3c02483

Scopus

Self-organized defect-rich RuMO<inf>x</inf> epitaxial layers (M = Mn, Fe, Co, Ni, Cu) for catalytic applications 査読有り

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

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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 RuOx on a rutile TiO2 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 (RuMOx-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 RuOx 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 RuMOx-ELs even on a powder substrate without any special procedures. The RuMOx-ELs feature a high aspect ratio, and selectively exposed specific facets with abundant Ru-Olatt/Ovac-M local structures as the reactive sites. The surface concentration of Ru-Olatt/Ovac-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

Scopus

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

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

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

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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 H2-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/H2, 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/gPt/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 LIII-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

Scopus

Active coordination sites of Co spinel oxides for NO reduction by CO 査読有り

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

Catalysis Today   411-412 巻   2023年3月

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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 (Oh) and tetrahedral (Td) 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 CoOh/CoTd ratio. Comparing the CoOh/CoTd 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 CoOh sites: The cobalt spinel oxides with high CoOh fraction were more easily reduced by CO to form oxygen vacancies than those with low CoOh fraction, and resulted in the higher activity for NO reduction by CO.

DOI： 10.1016/j.cattod.2022.06.031

Scopus

Enhanced CO oxidation by reversible structural variation of supported Ag nanoparticle catalyst from single to twin by CO treatment 査読有り

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

Catalysis Today   411-412 巻   2023年3月

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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/Al2O3 by H2 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 H2 and CO gas treatment to Ag/Al2O3. 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

Scopus

Tandem Base-Metal Oxide Catalyst for Automotive Three-way Reaction: MnFe<inf>2</inf>O<inf>4</inf> for Preferential Oxidation of Hydrocarbon 査読有り 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

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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 MFe2O4 (M = Co, Cu, Mg, Mn, Ni, Zn) was investigated. MnFe2O4 preferentially oxidized propene in the co-presence of CO showing the best propene oxidation activity. Among the series of MFe2O4, 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 MnFe2O4 for HC-PROX and CuCo2O4 for NO-CO reaction showed TWC activity comparable to a Rh/CeO2.

DOI： 10.1007/s10563-022-09373-9

Scopus

Exploring the framework of small pore zeolites for passive NOx adsorption 査読有り

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

Microporous and Mesoporous Materials   361 巻   2023年

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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

Scopus

Surface modification of MCr<inf>2</inf>O<inf>4</inf> (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

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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 MCr2O4 (M = Mg and Zn) by Cu-doping and doping effects on catalytic activity for CO oxidation. DFT + U calculations elucidated that Cu-dopants in MCr2O4(1 1 1) exist on the surface layer, CO oxidation by Cu-doped MCr2O4(1 1 1) occurs through Mars van Krevelen mechanism, rate-determining step (RDS) is the first CO2 desorption with oxygen vacancy (OV) 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 ZnCr2O4 from 5.2% by non-doped ZnCr2O4 at 300 °C. Bader charge analysis and difference density map show that M atom on the MCr2O4 surface receives electron density from the dissociating O atom in the OV formation step and the Cu-dopant can receive more electron density than Mg and Zn atoms to facilitate the OV formation and accelerate the first CO2 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

Scopus

Highly efficient CO-assisted conversion of methane to acetic acid over Rh-encapsulated MFI zeolite prepared using RhCl<inf>3</inf> 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

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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 RhCl3 molten salt. By high-temperature treatment of the physically-mixed H+-MFI zeolite and bulk RhCl3, the RhCl3 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 RhCl3 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 molRh−1 h−1) and yield (14.6 mmol gcat−1 h−1) with high selectivity (76.9%).

DOI： 10.1039/d2cy01471h

Scopus

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

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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

Scopus

High Pt-mass activity of Pt^IV<inf>1</inf>/β-MnO<inf>2</inf> surface for low-temperature oxidation of CO under O<inf>2</inf>-rich conditions

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

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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-MnO2 composite metal-oxide surface (PtIV1/β-MnO2). Single PtIV sites were stably formed on the high surface β-MnO2 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. PtIV1/β-MnO2 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 molCO h−1 gPt−1 at 25 °C and 0 °C, respectively, under the O2-rich conditions (O2 : 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

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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

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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 C3H6-preferential oxidation (C3H6-PROX) catalyst under stoichiometric automobile exhaust gas (NO–CO–C3H6–O2) using supported vanadia catalysts. Among various V2O5 supported catalysts, V2O5/TiO2 (anatase, coverage of around one monolayer) showed the best activity for C3H6-PROX with preferable formation of CO. The tandem catalyst combination using V2O5/TiO2 as the upstream C3H6-PROX catalyst and Cu/CeO2 as the downstream NO–CO reaction catalyst showed comparable activity for NO reduction as a Rh/ZrO2 catalyst. The reaction mechanism of C3H6 oxidation was analyzed using in situ Infrared spectroscopy. The C3H6 oxidation progressed with the formation of surface acetate as an intermediate, and acetate consumption was the key step of C3H6 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 C3H6-PROX catalysts.

DOI： 10.1016/j.jcat.2022.03.012

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Theoretical Study on Carbon Monoxide Adsorption on Unsupported and γ-Al<inf>2</inf>O<inf>3</inf>-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

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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

Open Access

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

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

Applied Catalysis A: General   629 巻   頁： 118425   2022年1月

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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/Al2O3 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 Al2O3, the activity of Pt/θ-Al2O3 was found to be around 1.5 times higher than that of Pt/γ-Al2O3 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 Al2O3. Furthermore, the fraction of amorphous Pt NPs in Pt/γ-Al2O3 was higher than that in Pt/θ-Al2O3. 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

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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

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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 gcat−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 gcat−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 AlO4 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

Web of Science

Scopus