研究者詳細 - 薩摩　篤

論文 - 薩摩　篤

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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><sup>−1</sup> h<sup>−1</sup> 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><sup>−1</sup> h<sup>−1</sup> 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 Al<sup>3+</sup>coordination, revealing a significant insight into the methane (CH<inf>4</inf>) combustion activity of Pd nanoparticles with the fraction of penta-coordinated Al<sup>3+</sup>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 to<sup>27</sup>Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), the Ag<sup>+</sup>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

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>]<sup>+</sup> 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<sup>-</sup> 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

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