研究者詳細 - 近藤　寛

論文 - 近藤　寛

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Acid-Base Bifunctional Catalysis of the Lewis Acidic Isolated Co(OH)<inf>2</inf> and Basic N Anion Generated from CeO<inf>2</inf> and 2-Cyanopyridine

Tamura M., Haga M., Junkaew A., Asada D., Ichikawa R., Toyoshima R., Nakayama A., Kondoh H., Nakagawa Y., Tomishige K.

ACS Catalysis 14 （ 17 ） 13015 - 13029 2024年09月

Acid-base bifunctional catalysts, which have both acid and base sites that are arranged at an appropriate distance, are one of the effective catalyst categories and have been extensively studied as a simple and effective method for designing heterogeneous and homogeneous catalysts in both the laboratories and industry. Recently, we found that a heterogeneous-homogeneous hybrid strong base site of N- was constructed only by mixing 2-cyanopyridine and CeO2 in the solution, where the N- site was formed by the covalent bonding between the lattice O atom of CeO2 and the C atom of the CN group in 2-cyanopyridine. Herein, an effective acid-base bifunctional catalyst with proximal sites of the heterogeneous-homogeneous hybrid base site and metal species-derived Lewis acid site is presented. The introduction of Co species into CeO2 forms isolated Co(OH)2 on CeO2, and further introduction of 2-cyanopyridine generates the heterogeneous-homogeneous hybrid base site of N- near the Co(OH)2 without the interference of these sites. The acid-base bifunctional sites work cooperatively to provide about 10-fold higher activity to the hydromethoxylation of acrylonitrile than the heterogeneous-homogeneous hybrid base site alone. Catalyst characterizations such as XRD, TEM, UV-vis, NO adsorption, XPS, Raman, XAS, NH3-TPD and in situ XPS, DFT calculations, and kinetic studies show that acrylonitrile and methanol are activated by the Lewis acidic Co(OH)2 and the hybrid base site, respectively, and the cooperative work results in the large rate enhancement.

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In Situ Observation of Charge Transfer in the Cocatalyst-Loaded SrTiO<inf>3</inf>:Al Photocatalyst under UV Irradiation by Conversion-Electron-Yield Soft-X-ray Absorption Spectroscopy

Wang Z., Toyoshima R., Yoshida M., Mase K., Kondoh H.

Journal of Physical Chemistry C 128 （ 22 ） 9193 - 9201 2024年06月

ISSN 19327447

We developed an in situ observation system for photoinduced surface phenomena under ambient-pressure conditions based on conversion-electron-yield soft-X-ray absorption spectroscopy (CEY-SXAS). We applied this technique to in situ observation for photoinduced hole transfer in a highly efficient photocatalyst, Al-doped SrTiO3 (STO:Al), with cocatalysts, Rh/Cr2O3 for the hydrogen evolution reaction (HER) site and the CoOOH oxygen evolution reaction (OER) site. In situ Co L-edge CEY-SXAS measurements under saturated water vapor conditions revealed that UV-vis irradiation readily induces oxidation of Co in the CoOOH OER site, which provides evidence for photoinduced hole transfer from the STO:Al site to the OER site. Interestingly, without loading of the Rh/Cr2O3 HER site or without introducing water vapor, no photoinduced hole transfer to the CoOOH OER site was observed. Coexisting of the Rh/Cr2O3 HER site and water vapor on the STO:Al surface is crucial to the hole transfer to the OER site under photoirradiation.

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Dehydrogenative oxidation of hydrosilanes using gold nanoparticle deposited on citric acid-modified fibrillated cellulose: unveiling the role of molecular oxygen

Suwattananuruk B., Uetake Y., Ichikawa R., Toyoshima R., Kondoh H., Sakurai H.

Nanoscale 16 （ 26 ） 12474 - 12481 2024年05月

ISSN 20403364

Efficient and environmentally friendly synthesis of silanols is a crucial issue across the broad fields of academic and industrial chemistry. Herein, we describe the dehydrogenative oxidation of hydrosilane using a gold nanoparticle catalyst supported by fibrillated citric acid-modified cellulose (F-CAC). Au:F-CAC catalysts with various particle sizes (1.7 nm, 4.9 nm, and 7.7 nm) were prepared using the trans-deposition method, a technique previously reported by our group. These catalysts exhibited significant catalytic activity to produce silanols with high turnover frequency (TOF) of up to 7028 h−1. Recycling experiments and transmission electron microscopy (TEM) observation represented the high durability of Au:F-CAC under the reaction conditions, allowing kinetic studies on size dependency. Mechanistic studies were conducted, including isotope labelling experiments, kinetics, and various spectroscopies. Notably, the near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) of the model catalyst (Au:PVP) revealed the formation of catalytically active cationic Au sites on the surface through the adsorption of molecular oxygen, providing a new insight into the reaction mechanism.

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Understanding of a Pt thin-film H<inf>2</inf> sensor under working conditions using AP-XPS and XAFS

Toyoshima R., Tanaka T., Kato T., Abe H., Uchida K., Kondoh H.

Chemistry Letters 53 （ 2 ） 2024年02月

ISSN 03667022

The operating principle of a Pt thin-film H2 gas sensor was investigated using a combination of surface sensitive ambient-pressure X-ray photoelectron spectroscopy and bulk sensitive X-ray absorption fine structure techniques, which provided chemical and structure information under working conditions, coupled with electric resistivity measurements. It is shown that the sensor response was in a linear relation with both coverages of H and O atoms on the Pt surface. Moreover, the bulk structure of Pt remains unchanged under H2 exposure. These observations support that the resistivity change is associated with electron scattering in the near-surface region.

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Promotional Effect of Ag on the Catalytic Decomposition of N<inf>2</inf>O in the Presence of O<inf>2</inf> over the Al<inf>2</inf>O<inf>3</inf>-Supported Rh Catalyst

Jing Y., He C., Zhang N., Murano Y., Toyoshima R., Kondoh H., Kageyama Y., Inomata H., Toyao T., Shimizu K.I.

ACS Catalysis 13 （ 19 ） 12983 - 12993 2023年10月

Catalytic decomposition of N2O into N2 and O2 is one of the most important techniques for removing N2O from the atmosphere to curb global warming. Supported RhOx catalysts are known to show high efficiency for N2O decomposition, even in the presence of O2, compared with other materials, such as supported metal oxides and Fe-based zeolite catalysts. In this study, the addition of Ag was found to enhance the efficiency of an Al2O3-supported RhOx catalyst (RhOx/Al2O3) for N2O decomposition. The promotional effect of Ag was investigated using various operando spectroscopic methods, including X-ray absorption spectroscopy, diffuse reflectance UV-vis spectroscopy (DR UV-vis), ambient-pressure X-ray photoelectron spectroscopy, and kinetic studies. The results demonstrated that the addition of Ag enhanced the catalytic efficiency of the supported RhOx catalysts by enhancing the thermal reduction of Rh oxide, which was identified as the rate-determining step, especially at low temperatures.

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Bifunctionality of Re Supported on TiO<inf>2</inf> in Driving Methanol Formation in Low-Temperature CO<inf>2</inf> Hydrogenation

Phongprueksathat N., Ting K.W., Mine S., Jing Y., Toyoshima R., Kondoh H., Shimizu K.I., Toyao T., Urakawa A.

ACS Catalysis 13 （ 16 ） 10734 - 10750 2023年08月

Low temperature and high pressure are thermodynamically more favorable conditions to achieve high conversion and high methanol selectivity in CO2 hydrogenation. However, low-temperature activity is generally very poor due to the sluggish kinetics, and thus, designing highly selective catalysts active below 200 °C is a great challenge in CO2-to-methanol conversion. Recently, Re/TiO2 has been reported as a promising catalyst. We show that Re/TiO2 is indeed more active in continuous and high-pressure (56 and 331 bar) operations at 125-200 °C compared to an industrial Cu/ZnO/Al2O3 catalyst, which suffers from the formation of methyl formate and its decomposition to carbon monoxide. At lower temperatures, precise understanding and control over the active surface intermediates are crucial to boosting conversion kinetics. This work aims at elucidating the nature of active sites and active species by means of in situ/operando X-ray absorption spectroscopy, Raman spectroscopy, ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Transient operando DRIFTS studies uncover the activation of CO2 to form active formate intermediates leading to methanol formation and also active rhenium carbonyl intermediates leading to methane over cationic Re single atoms characterized by rhenium tricarbonyl complexes. The transient techniques enable us to differentiate the active species from the spectator one on TiO2 support, such as less reactive formate originating from spillover and methoxy from methanol adsorption. The AP-XPS supports the fact that metallic Re species act as H2 activators, leading to H-spillover and importantly to hydrogenation of the active formate intermediate present over cationic Re species. The origin of the unique reactivity of Re/TiO2 was suggested as the coexistence of cationic highly dispersed Re including single atoms, driving the formation of monodentate formate, and metallic Re clusters in the vicinity, activating the hydrogenation of the formate to methanol.

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Operando Spectroscopic Study of Reduction and Oxidation Half-Cycles in NH<inf>3</inf>-SCR over CeO<inf>2</inf>-Supported WO<inf>3</inf>

Kubota H., Jing Y., Wan L., Tong J., Zhang N., Mine S., Toyao T., Toyoshima R., Kondoh H., Ferri D., Shimizu K.I.

ACS Catalysis 13 （ 13 ） 9274 - 9288 2023年07月

Operando spectroscopies (in situ Ce and W L3-edge X-ray absorption near-edge structure, ultraviolet-visible (UV-vis), and infrared (IR) spectroscopies, combined with online analysis of gas-phase products) were exploited to elucidate reduction/oxidation half-cycles in the selective catalytic reduction of NO with NH3 (NH3-SCR) over WO3-loaded CeO2. The Ce4+ species was reduced by NO + NH3 to yield N2 and Ce3+ species (reduction half-cycle), which was then reoxidized by O2 (oxidation half-cycle). The oxidation state of the W6+ species remained unchanged under redox conditions. IR and theoretical results indicated that the reduction half-cycle started with the reaction of W6+-OH and adjacent Ce4+-O with NO to afford Ce3+ species and gaseous HONO, which was converted to NO+ species on the catalyst. The NO+ species then reacted with NH3 to generate N2

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Promoting effect of basic metal additives on DeNOx reactions over Pt-based three-way catalysts

Jing Y., Wang G., Mine S., Kawai J., Toyoshima R., Kondoh H., Zhang X., Nagaoka S., Shimizu K.i., Toyao T.

Journal of Catalysis （Journal of Catalysis） 416 209 - 221 2022年12月

ISSN 00219517

Pt has been economically favored over Rh and Pd. However, Pt-based three-way catalysts (TWCs) have been studied less than Pd- and Rh-based TWCs; therefore, their properties have not yet been sufficiently evaluated, especially under conditions relevant to modern three-way catalysis operation, wherein deviations from stoichiometric conditions are often encountered. In this study, we examined the promotional effect of basic metal additives in Pt/M/Al2O3 (M = Ba, La, Sr) on the efficiency of three-way catalytic reactions. The catalytic activities of the Pt/M/Al2O3 catalysts for NO, CO, and total hydrocarbons were superior to those of Pt/Al2O3; moreover, Ba enhanced the catalytic activity of Pt-based catalysts more efficiently than La and Sr. The best-performing catalyst, Pt/Ba/Al2O3, was subjected to kinetic studies and various in situ/operando spectroscopic experiments, namely, X-ray absorption spectroscopy, infrared spectroscopy, and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), to investigate the role of Ba in the NO reduction reaction. The Pt0 species loaded on Ba/Al2O3 were more electron-rich than those loaded on Al2O3, thereby promoting NO dissociation into N and O atoms, as revealed by the AP-XPS results. Moreover, the efficient formation of intermediate surface NOx species, including nitrites and nitrates, and their reactivities toward reductant gases, such as H2 or CO, were critical for promoting the effect of Ba on the NO reduction reaction.

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Origin of the High Selectivity of the Pt-Rh Thin-Film H<inf>2</inf>Gas Sensor Studied by Operando Ambient-Pressure X-ray Photoelectron Spectroscopy at Working Conditions

Toyoshima R., Tanaka T., Kato T., Uchida K., Kondoh H.

Journal of Physical Chemistry Letters （Journal of Physical Chemistry Letters） 13 （ 36 ） 8546 - 8552 2022年09月

The Pt-Rh thin-film sensors exhibit excellent sensitivity and selectivity for H2 gas detection. Here, we studied the mechanism of highly selective detection of H2 by the Pt-Rh thin-film sensors with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) measurements at working conditions, which were paralleled with electric resistivity measurements. The elemental composition and chemical state of surface Pt and Rh drastically change depending on the background gas environments, which directly link to the sensor response. It is revealed that surface segregated Pt atoms accelerate dissociative adsorption of H2, resulting in a reduction of the sensor surface and then a decrease of electric resistivity of the film, whereas a thin oxidized Rh layer blocks dissociation of the other reducing agent, that is, NH3. This is supported from the adsorption energetics obtained by the density functional theory (DFT) calculations.

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Substrate Effect of Ir and Rh on Surface ReO<inf>x</inf>Species under a Hydrogen Atmosphere Studied by NAP-XPS

Chen J., Kawai J., Ozawa K., Toyoshima R., Tomishige K., Kondoh H.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 126 （ 28 ） 11544 - 11552 2022年07月

ISSN 19327447

The substrate effect of M-Re (M is a noble metal) bifunctional catalysts for C-O hydrogenolysis has been studied by using single-crystal substrates including Ir(111) and Rh(111) with in situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). Compared with Ir-Re and Rh-Re nanoparticle systems reported in the literature, the single crystals Ir(111) and Rh(111) have shown a more significant substrate effect in determining the surface Re species under a H2 atmosphere at elevated temperatures. It has been found that the hydrogen dissociation and spillover efficiency as the intrinsic property of the noble metals significantly impacts the surface species. A surface that supplies hydrogen more efficiently results in a lower overall oxidation state of Re. Most importantly, the chemical environment of OH species is also closely related to the hydrogen spillover; that is, the more efficient hydrogen spillover, the lower is the oxidation state of Re(-OH). Because the Re-OH sites are commonly considered as the active sites for terminal binding of the reactant molecules, the noble-metal substrates are expected to impact the binding strength of the adsorbate species and hence the overall catalytic activity by tuning the acidity of the Re-OH sites.

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A newly designed compact CEY-XAFS cell in the soft X-ray region and its application to surface XAFS measurements under ambient-pressure conditions without photoinduced side effects

Shimizu H., Toyoshima R., Isegawa K., Mase K., Nakamura J., Kondoh H.

Physical Chemistry Chemical Physics （Physical Chemistry Chemical Physics） 24 （ 5 ） 2988 - 2996 2022年02月

ISSN 14639076

We report a newly designed compact cell to measure XAFS spectra with the conversion electron yield (CEY) method in the soft X-ray region under ambient-pressure gas conditions. Secondary electrons generated from the gas and sample by collision of X-ray-absorption-induced Auger electrons are collected by a positively biased collector electrode to obtain XAFS spectra. It was confirmed that this cell is applicable to soft X-ray surface XAFS measurements for different types of materials such as insulating organic materials and metal oxides under 1 bar gas conditions. During the measurements, photoinduced side effects were observed; i.e. photoinduced degradation of organic materials and photoinduced reduction/oxidation of metal oxides. We found that these photoinduced side effects can be sufficiently suppressed by controlling the measuring conditions. The presented measuring approach will enable surface XAFS spectra to be obtained in the soft X-ray region for various types of functional materials under ambient-pressure working conditions. This journal is

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Ligand effects on surface oxide at RhPd(100) alloy surfaces: A density functional theory calculation study

Shirahata N., Toyoshima R., Yoshida M., Ueda K., Mase K., Mun B.S., Kondoh H.

Surface Science （Surface Science） 716 2022年02月

ISSN 00396028

Density functional theory calculations were applied to a study on ligand effects on a Pd surface oxide formed on RhPd(100) alloy surfaces. It was found that chemical composition of the topmost layer of alloy significantly influences on the electronic structure of the Pd surface oxide. Such interlayer ligand effects are originating from the Rh−O and Pd−O interactions between the topmost layer of alloy and the Pd surface oxide. These effects give rise to substantial changes in binding energies of adsorbates and could change catalytic activity depending on atomic fraction of the Rh−Pd alloy.

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Materials Science Research by Ambient Pressure X-ray Photoelectron Spectroscopy Systems at Synchrotron Radiation Facilities in Japan: Applications in Energy, Catalysis, and Sensors

Yamamoto S., Takagi Y., Koitaya T., Toyoshima R., Horio M., Matsuda I., Kondoh H., Yokoyama T., Yoshinobu J.

Synchrotron Radiation News （Synchrotron Radiation News） 35 （ 3 ） 19 - 25 2022年

ISSN 08940886

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Direct Chlorination of Ethene on ZnO (0001̅) by Hot Chlorine Atoms

Doh W.H., Kondoh H., Ahn E., Park D., Cho D., Kim C.M.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 127 （ 18 ） 8523 - 8528 2022年

ISSN 19327447

The interaction between ethene and Cl2 on ZnO(0001̅) has been investigated using X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. At 110 K, the Cl2 molecule is perpendicularly adsorbed on ZnO(0001̅). Upon heating, Cl2 is dissociated on the surface in the temperature range of 200-230 K. When the surface coadsorbed with Cl2 and ethene is heated, the desorption of 1,2-dichloroethane is observed at ∼230 K. The desorption temperature is comparable to the dissociation temperature of Cl2 on ZnO(0001̅). Ethene does not react with Cl atoms chemisorbed on ZnO(0001̅). We propose that “hot” Cl atoms, which are produced during thermal dissociation of Cl2, promote the direct chlorination of C2H4. The energy of the hot Cl atoms is calculated to be maximum 27.5 kcal/mole higher than the energy of the chemisorbed Cl atoms.

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Assessing nickel oxide electrocatalysts incorporating diamines and having improved oxygen evolution activity using operando UV/visible and X-ray absorption spectroscopy

Miura T., Tsunekawa S., Onishi S., Ina T., Wang K., Watanabe G., Hu C., Kondoh H., Kawai T., Yoshida M.

Physical Chemistry Chemical Physics （Physical Chemistry Chemical Physics） 23 （ 40 ） 23280 - 23287 2021年10月

ISSN 14639076

The electrolysis of water using renewable energy is a promising approach to developing a sustainable hydrogen-based economy. To improve the efficiency of this process, it will be necessary to develop highly active electrocatalysts that promote the oxygen evolution reaction (OER). In the present study, the OER activity of a nickel oxide electrocatalyst was dramatically improved following the addition of a diamine to the electrolyte solution during electrodeposition. Operando UV/vis absorption spectroscopy was used to assess a number of nickel catalysts containing various diamines and other organic compounds. The data indicate that Ni(ii) complexes were formed with the diamines during electrodeposition. Consequently, the catalytic activity of these materials was enhanced based on increased concentrations of active reaction sites for the OER process. Ni K-edge X-ray absorption spectra showed that these catalysts were composed of γ-NiOOH with a Ni3.6+ valence state. The coordination of the diamine molecules to the γ-NiOOH produced structural distortion that contributed to improved OER activity. This structural distortion is likely the most important factor in enhancing the OER activity of inorganic-organic composite catalysts.

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In situ AP-XPS study on reduction of oxidized Rh catalysts under CO exposure and catalytic reaction conditions

Toyoshima R., Ueda K., Koda Y., Kodama H., Sumida H., Mase K., Kondoh H.

Journal of Physics D: Applied Physics （Journal of Physics D: Applied Physics） 54 （ 20 ） 2021年05月

ISSN 00223727

Reduction of oxidized Rh catalysts under carbon monoxide (CO) exposure and reaction conditions were studied by using ambient-pressure x-ray photoelectron spectroscopy. First, Rh powders pressed into a pellet were deeply oxidized and the reduction process under 100 mTorr CO environment was monitored in situ at different temperatures. The oxidized Rh surfaces are composed of Rh2O3 and RhO2, the latter of which is more segregated near the surface. Both oxide species are reduced simultaneously to the metallic state; kinetic analyses indicate that the activation energy of the reduction of the Rh oxides is 1.68 eV, which is a little larger than those for Pd oxides, probably due to a stronger Rh-O interaction. Reduction of oxidized Rh nano-particles deposited on SiO2 under two reaction conditions (CO + O2 and CO + NO + O2) was observed with increasing temperature. It was found that the reduction temperature shifts to the higher temperature in the presence of NO, even though the S-factors are almost the same. The NO molecule more strongly prevents the reduction of oxidized Rh catalyst compared to O2.

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Formation and behavior of carbonates on Ag(110) in the presence of ethylene and oxygen

Isegawa K., Ueda K., Amemiya K., Mase K., Kondoh H.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 125 （ 17 ） 9032 - 9037 2021年05月

ISSN 19327447

Intermediate species formed on Ag(110) surfaces under the presence of ethylene and oxygen in the sub-Torr pressure range were studied by near-ambient-pressure X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) measurements. Carbonates are clearly observed exclusively under an ethylene-rich condition (0.2 Torr ethylene and 0.04 Torr oxygen; ethylene/oxygen = 5) at a high temperature of 500 K or relatively low-temperature conditions (≤470 K) at an oxygen-rich gas ratio (ethylene/oxygen = 1/5). NEXAFS results support the formation of carbonates and indicate that the carbonates are adsorbed almost parallel to the Ag(110) surface. The carbonates coexist with surface oxides with different composition ratios depending on the ethylene/oxygen pressure ratio and surface temperature. From these results we propose that the carbonates are formed by reaction(s) between ethylene and oxygen on the Ag(110) surface.

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Detailed Characterization of MoO<inf>x</inf>-Modified Rh Metal Particles by Ambient-Pressure XPS and DFT Calculations

Toyoshima R., Kawai J., Isegawa K., Kondoh H., Junkaew A., Nakayama A., Asano T., Tamura M., Nakagawa Y., Yabushita M., Tomishige K.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 125 （ 8 ） 4540 - 4549 2021年03月

ISSN 19327447

Characterization of Mo species on Rh metal particles in Rh-MoOx/C catalyst for C-O hydrogenolysis reactions was carried out with in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory (DFT) calculations. The as-prepared Rh-MoOx/C sample with high oxidation states of Rh3+, Rh4+ and Mo6+ was reduced with 0.2 Torr of H2. All the Rh species and most Mo species were reduced to Rh0 and Mo4+ during the heating to 570 K. The thickness of the Mo layers after the reduction was calculated by a numerical analysis based on the XPS intensity ratio and a uniform adlayer stacking model. The calculated averaged thickness was about 0.3 nm, suggesting the formation of Mo species with a monolayer order on the metallic Rh particle surface. The O 1s XPS showed the presence of Mo-OH and Mo-O oxygen species with a ratio of 1.4 in reduced Rh-MoOx/C. Considering the presence of residual Mo6+ species with a large number of Mo6+-O bonds, the ratio of Mo4+-OH to Mo4+-O is estimated to be 2, suggesting the formation of MoO(OH)2. The DFT calculations of various monomeric MoOxHy species on the Rh(111) surface were carried out, and the stability was examined by the ab initio thermodynamic approach. The relative stability is changed when the surface coverage of hydrogen atoms is taken into account. The MoO(OH)2 species is calculated to be the most stable species in the presence of surface hydrogens over a wide range of conditions, including those for the catalytic reaction (ca. 400 K, 100-1 MPa H2).

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Initial oxidation of GaAs(100) under near-realistic environments revealed by: In situ AP-XPS

Toyoshima R., Murakami S., Eguchi S., Amemiya K., Mase K., Kondoh H.

Chemical Communications （Chemical Communications） 56 （ 94 ） 14905 - 14908 2020年12月

ISSN 13597345

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How Rh surface breaks CO<inf>2</inf> molecules under ambient pressure

Kim J., Ha H., Doh W.H., Ueda K., Mase K., Kondoh H., Mun B.S., Kim H.Y., Park J.Y.

Nature Communications （Nature Communications） 11 （ 1 ） 2020年12月

Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO2. The linear geometry of CO2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O‒CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.

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論文 - 近藤　寛