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論文

Structural characterization by X-ray analytical techniques of calcium aluminate cement modified with sodium polyphosphate containing cesium chloride

高畠容子; 渡部創; 入澤啓太; 塩飽秀啓; 渡部雅之

Journal of Nuclear Materials, 556, p.153170_1 - 153170_7, 2021/12

https://doi.org/10.1016/j.jnucmat.2021.153170

The long-time experimental activities on pyroprocessing have generated waste eutectic salts contaminated with nuclear materials. After reprocessing tests, waste salts should be appropriately treated, with a focus on Cl disposal considering its corrosive nature. It is important to construct Cl confinement for the waste salts. Chlorapatite (Ca $_{10}$ (PO $_{4}$ ) $_{6}$ Cl $_{2}$ ) has great potential for Cl confinement due to Ca and P. The chemical reactivity of Cl will be drastically reduced if chlorapatite can be synthesized in calcium aluminate cement modified with sodium polyphosphate (CAP) containing CsCl. This study confirms the chemical state of Cl and metal elements in the cement by XRD, XPS, and XANES in the CAP containing CsCl. The analyses results suggest the existence of the Ca-Cl-Cs and Al-Cl-Cs bonds in CAP containing CsCl. The formation of the chemical bonds of Cl with metal elements might be one of important factors for the chlorapatite formation from the CAP containing CsCl.

論文

Mechanistic study on the removal of Cs from contaminated soil by rapid ion exchange in subcritical water

福田達弥*; 高橋亮*; 原卓飛*; 尾原幸治*; 加藤和男*; 松村大樹; 稲葉優介*; 中瀬正彦*; 竹下健二*

Journal of Nuclear Science and Technology, 58(4), p.399 - 404, 2021/04

https://doi.org/10.1080/00223131.2020.1830866

被引用回数：1 パーセンタイル：0.01(Nuclear Science & Technology)

As a result of the Fukushima nuclear power plant accident in March 2011, massive amounts of soil were contaminated with radioactive Cs. To remediate the contaminated soil, we are developing a desorption technique for removing Cs from soil using subcritical water. We found that rapid ion exchange of Cs with multivalent cations in subcritical water is an effective desorption technique. To understand the mechanism and structural aspects of this process, in situ observations of the soil layer in subcritical water were carried out by high-energy X-ray diffraction together with pair distribution function analysis, and extended X-ray absorption fine structure analysis. Both the desorption experiments and structural studies indicated that conformational changes of the layer containing Cs $^{+}$ under subcritical water conditions promoted intercalation of the hydrated Mg and trapped Cs $^{+}$ , which facilitated a rapid ion-exchange reaction of Mg $^{2+}$ and Cs $^{+}$ .

論文

Local Ir dedimerization followed by ligand-hole hopping in X-ray irradiated thiospinel

平賀晴弘*; 松村大樹; 堀金和正*; 水木純一郎*

Journal of Physics and Chemistry of Solids, 150, p.109870_1 - 109870_8, 2021/03

https://doi.org/10.1016/j.jpcs.2020.109870

被引用回数：0 パーセンタイル：0(Chemistry, Multidisciplinary)

The extended X-ray-absorption fine structure of a spinel CuIr $_{2}$ (S $_{0.95}$ Se $_{0.05}$ ) $_{4}$ powder sample, which has the charge-ordered temperature $T_{rm{CO}}$ = 190 K, was determined at the Ir $L_{3}$ edge for a wide temperature range. All the local structure parameters on the Ir-Ir bonds signified the second structural change at $T^{*} sim$ 70 K. Remarkably, the number of Ir dimers decreased by 10% below $T^{*}$ , which indicates partial dedimerization by X-ray irradiation. We also reanalyzed the resistance data of CuIr $_{2}$ S $_{4}$ with the variable-range hopping model by focusing on the density of states. The X-ray-induced decrease in resistance was quantitatively explained as a result of the increase in the density of states, which was attributed to the release of holes from the 10%-dedimerized Ir ions. We suppose that the released holes hop over the ligand chalcogen site.

論文

Coordination number regulation of molybdenum single-atom nanozyme peroxidase-like specificity

Wang, Y.*; Jia, G.*; Cui, X.*; Zhao, X.*; Zhang, Q.*; Gu, L.*; Zheng, L.*; Li, L. H.*; Wu, Q.*; Singh, D. J.*; et al.

Chem, 7(2), p.436 - 449, 2021/02

https://doi.org/10.1016/j.chempr.2020.10.023

被引用回数：13 パーセンタイル：99.48(Chemistry, Multidisciplinary)

Nanozymes are promising alternatives to natural enzymes, but their use remains limited owing to poor specificity. Overcoming this is extremely challenging due to the intrinsic structural complexity of these systems. We report theoretical design and experimental realization of a series of heterogeneous molybdenum single-atom nanozymes (named Mo $_{rm{SA}}$ -N $_{x}$ -C), wherein we find that the peroxidase-like specificity is well regulated by the coordination numbers of single Mo sites. The resulting Mo $_{rm{SA}}$ -N $_{3}$ -C catalyst shows exclusive peroxidase-like behavior. It achieves this behavior via a homolytic pathway, whereas Mo $_{rm{SA}}$ -N $_{2}$ -C and Mo $_{rm{SA}}$ -N $_{4}$ -C catalysts have a different heterolytic pathway. The mechanism of this coordination-number-dependent enzymatic specificity is attributed to geometrical structure differences and orientation relationships of the frontier molecular orbitals.

論文

Speciation of cesium in tree tissues and its implication for uptake and translocation of radiocesium in tree bodies

田中万也; 金指努*; 竹中千里*; 高橋嘉夫*

Science of the Total Environment, 755(Part 2), p.142598_1 - 142598_8, 2021/02

https://doi.org/10.1016/j.scitotenv.2020.142598

被引用回数：3 パーセンタイル：83.41(Environmental Sciences)

本研究では、安定セシウムを樹皮,辺材,心材,樹葉,枝に吸着させてEXAFSスペクトル測定を行った。その結果、すべての部位においてセシウムは外圏型錯体として静電的に吸着していることが明らかとなった。これは酢酸アンモニウムを用いたセシウム脱離実験の結果と整合的であった。また、これらの結果は、常緑樹であるスギ,アカマツと落葉広葉樹であるコナラ,コシアブラのすべての樹種において同様であった。

論文

分散型光学系を用いたXAFS測定による実時間分割構造変化観測

松村大樹; 加藤和男*

放射光, 34(1), p.3 - 11, 2021/01

分散型光学系を用いたX線吸収微細構造(X-ray absorption fine structure: XAFS)分光法は、機械的に動く機構が無いという特徴から、高い実時間分解能と高い相対精度が期待できる。我々は「その場」かつ「時間分解」XAFS測定システムを立ち上げ、多くの反応系に適用させ、化学反応の真の姿を理解するという目的の下、研究開発を行ってきた。分散型光学系によるXAFS測定のこれまでの研究を概説すると共に、手がけたいくつかの研究例を説明する。

論文

XAFS analysis of ruthenium in simulated iron phosphate radioactive waste glass

岡本芳浩; 小林秀和; 塩飽秀啓; 捧賢一; 畠山清司*; 永井崇之

Journal of Non-Crystalline Solids, 551, p.120393_1 - 120393_8, 2021/01

https://doi.org/10.1016/j.jnoncrysol.2020.120393

被引用回数：0 パーセンタイル：0.02(Materials Science, Ceramics)

模擬廃液を含有した鉄リン酸ガラス試料におけるルテニウムの化学状態を、X線吸収微細構造(XAFS)およびイメージングXAFSによって調べた。EXAFS分析の結果、30mol%Fe $_{2}$ O $_{3}$ -P $_{2}$ O $_{5}$ ベースガラスに、廃棄物成分が10wt.%以下の場合では、ルテニウムがガラス相に含まれることを示唆された。他の試料では、ルテニウムは、主に結晶性RuO $_{2}$ として存在することが確認された。イメージングXAFS分析からは、RuO $_{2}$ の析出が確認されたが、全ての試料において、大きさ50m以下の小さいものであった。ホウケイ酸ガラス系で観察されるような、RuO $_{2}$ の凝集体は、本研究における鉄リン酸ガラス試料では確認されなかった。

論文

General synthesis of single-atom catalysts for hydrogen evolution reactions and room-temperature Na-S batteries

Lai, W.-H.*; Wang, H.*; Zheng, L.*; Jiang, Q.*; Yan, Z.-C.*; Wang, L.*; 吉川浩史*; 松村大樹; Sun, Q.*; Wang, Y.-X.*; et al.

Angewandte Chemie; International Edition, 59(49), p.22171 - 22178, 2020/12

https://doi.org/10.1002/anie.202009400

被引用回数：16 パーセンタイル：89.25(Chemistry, Multidisciplinary)

Herein, we report a comprehensive strategy to synthesize a full range of single-atom metals on carbon matrix, including V, Mn, Fe, Co, Ni, Cu, Ge, Mo, Ru, Rh, Pd, Ag, In, Sn, W, Ir, Pt, Pb, and Bi. The extensive applications of various single-atom catalysts (SACs) are manifested via their ability to electro-catalyze typical hydrogen evolution reactions (HER) and conversion reactions in novel room-temperature sodium sulfur batteries (RT-Na-S). The enhanced performances for these electrochemical reactions arisen from the ability of different single active atoms on local structures to tune their electronic configuration. Significantly, the electrocatalytic behaviors of diverse SACs, assisted by density functional theory calculations, are systematically revealed by in situ synchrotron X-ray diffraction and in situ transmission electronic microscopy, providing a strategic library for the general synthesis and extensive applications of SACs in energy conversion and storage.

論文

ウラン含有模擬廃棄物ガラスの評価研究

永井崇之; 秋山大輔*; 桐島陽*; 佐藤修彰*; 岡本芳浩

2019年度「物質・デバイス領域共同研究拠点」および「人・環境と物質をつなぐイノベーション創出ダイナミック・アライアンス」研究成果・活動報告書(CD-ROM), P. 20191107_1, 2020/11

本研究は、ウラン(U)濃度を高めたホウケイ酸ガラス組成中のUの化学状態を把握するため、異なる原料ガラス組成を用いてU含有ガラスを作製し、放射光XAFS測定によりUの原子価等を評価した。ホウケイ酸ガラス組成へのU溶解度はUO $_{3}$ 換算で15wt%以上であり、U含有ガラス中のUはガラス相に概ね6価状態で均一に存在する。

論文

Application of an augmentation method to MCR-ALS analysis for XAFS and Raman data matrices in the structural change of isopolymolybdates

佐伯盛久*; 蓬田匠; 松村大樹; 斉藤拓巳*; 中西隆造*; 辻卓也; 大場弘則*

Analytical Sciences, 36(11), p.1371 - 1378, 2020/11

https://doi.org/10.2116/analsci.20P147

被引用回数：0 パーセンタイル：0(Chemistry, Analytical)

モリブデンイオンMoO $_{4}$ $^{2-}$ 水溶液に酸を加えると、複数のモリブデン原子が酸素を介して結合したポリモリブデン酸が形成され、さらに酸濃度に応じてポリモリブデン酸の化学形態は大きく変化する。我々は、これまで研究例の少なかった高酸性水溶液中(0.15-4.0M)でのポリモリブデン酸の化学形態を、ラマン分光法およびX線吸収微細構造(XAFS)分光法により調べ、測定したスペクトルを多変量スペクトル分解法(MCR-ALS)により解析した。MCR-ALS解析では実験データ解析により得られるスペクトルの任意性が問題になり、XAFSデータのみの解析ではこれが顕著になるが、XAFSデータとラマンデータを同時にMCR-ALS解析することで、信頼性の高い3成分のXAFSスペクトルを得ることに成功した。構造解析の結果から、硝酸濃度が高くなるにつれポリモリブデン酸の化学種が[Mo $_{36}$ O $_{112}$ (H $_{2}$ O) $_{16}$ ] $^{2+}$ [Mo $_{2}$ O $_{5}$ (H $_{2}$ O) $_{6}$ ] $^{2+}$ [HMoO $_{3}$ (H $_{2}$ O) $_{3}$ ] $^{+}$ へと変化する様子を明らかにした。

論文

水素-酸素再結合触媒の長寿命化

松村大樹

触媒の劣化対策,長寿命化, p.205 - 212, 2020/11

東日本大震災に伴う東京電力福島第一原子力発電所での事故においては、原子力格納容器内部にて水素が大量に発生し、それが外部へと漏れ出ることにより水素爆発を誘発させ、放射能物質の環境への拡散を引き起こす要因となった。金属微粒子触媒を利用した水素-酸素再結合反応の利用は、放出された水素と環境中に存在する酸素とを緩やかに反応させ、水素が爆発限界濃度に達する以前に水素ガスを消費させ水素濃度の低減化を図ろうとするもので、外部電源が存在しない環境下においても効果的に水素を除去するシステムを構築できる可能性があり、より幅広い環境下における実用化が求められている。触媒の長寿命化という観点からの開発には、触媒の劣化の要因を知ることが必要である。X線吸収分光(X-ray absorption fine structure: XAFS)法は担持微粒子触媒の構造解析手法として、「その場」測定に最も適した手法と言っても過言ではない。各種雰囲気を制御したXAFS法による「その場」観測を行うことで、反応と構造との関連を付け、触媒劣化の真の構造要因を探り、触媒の長寿命化への道筋を作ることができる。

報告書

軟X線領域のXAFS測定による模擬廃棄物ガラスの構造評価(共同研究)

永井崇之; 岡本芳浩; 山岸弘奈*; 太田俊明*; 小島一男*; 猪瀬毅彦*; 佐藤誠一*; 畠山清司*

JAEA-Research 2020-009, 48 Pages, 2020/09

JAEA-Research-2020-009.pdf:4.53MB

廃棄物ガラス中のガラス成分や廃棄物成分の局所構造は、その廃棄物ガラスの化学組成によって変化する。本研究では原料ガラスや模擬廃棄物ガラス試料を作製し、軟X線領域のXAFS測定によりホウ素(B),酸素(O)及び廃棄物成分のセリウム(Ce)やセシウム(Cs)等の化学的状態及び局所構造を評価した。化学組成や原料ガラス形態等が異なるガラス試料を対象に、BのK吸収端XANESスペクトルを測定した結果、Na $_{2}$ O濃度が高くなるとB-Oの4配位sp $^{3}$ 構造(BO $_{4}$ )の存在比が高まる傾向を確認した。また、OのK吸収端XANESスペクトルを測定した結果、OのK吸収端スペクトルで観察されるプリエッジの高さは、試料中のFe濃度に依存することを確認した。長期化学的耐久性を評価した浸出試験前後のガラス試料表面を対象に、BのK吸収端XANESスペクトルを測定した結果、浸出試験後に試料表面のB-Oの4配位sp $^{3}$ 構造(BO $_{4}$ )の存在比が高まる傾向を確認した。また、CeやCsのM吸収端等のXANESスペクトルを測定した結果、表層に存在するCeは浸出試験により酸化され、表層のCsの多くが浸出試験後に失われていることを確認した。また、XAFS測定に供したガラス試料の状態をラマン分光測定で確認した結果、原料ガラス形態や作製方法によって同様な化学組成であってもラマンスペクトルが異なることを確認した。

論文

Ultra-fine CeO $_{2}$ particles triggered strong interaction with LaFeO $_{3}$ framework for total and preferential CO oxidation

Zheng, Y.*; Xiao, H.*; Li, K.*; Wang, Y.*; Li, Y.*; Wei, Y.*; Zhu, X.*; Li, H.-W.*; 松村大樹; Guo, B.*; et al.

ACS Applied Materials & Interfaces, 12(37), p.42274 - 42284, 2020/09

https://doi.org/10.1021/acsami.0c10271

被引用回数：4 パーセンタイル：51.8(Nanoscience & Nanotechnology)

Interactions between the active components with the support are one of the fundamentally factors in determining the catalytic performance of a catalyst. In this study, we investigated the interaction between CeO $_{2}$ and LaFeO $_{3}$ , the two important oxygen storage materials in catalysis area, by tuning the sizes of CeO $_{2}$ particles and highlight a two-fold effect of the strong oxide-oxide interaction in determining the catalytic activity and selectivity for preferential CO oxidation in hydrogen feeds. It is found that the anchoring of ultra-fine CeO $_{2}$ particles at the framework of three-dimensional-ordered macroporous LaFeO $_{3}$ surface results in a strong interaction between the two oxides that induces the formation of abundant uncoordinated cations and oxygen vacancy at the interface. This discovery demonstrates that in hybrid oxide-based catalysts, tuning the interaction among different components is essential for balancing the catalytic activity and selectivity.

論文

Microscopic analyses on Zr adsorbed IDA chelating resin by PIXE and EXAFS

荒井陽一; 渡部創; 大野真平; 野村和則; 中村文也*; 新井剛*; 瀬古典明*; 保科宏行*; 羽倉尚人*; 久保田俊夫*

Nuclear Instruments and Methods in Physics Research B, 477, p.54 - 59, 2020/08

https://doi.org/10.1016/j.nimb.2019.10.028

被引用回数：0 パーセンタイル：0.02(Instruments & Instrumentation)

Used PUREX process solvent generated from reprocessing process of spent nuclear fuel contains a small amount of U and Pu complexed with tributyl phosphate (TBP) or dibutyl phosphate (DBP). The radioactive nuclides should be removed from the solvent for safety storage or disposal. The iminodiacetic acid (IDA) type chelating resin was proposed as promising procedures for efficient recovery of the trapped cations in the solvent. In order to reveal the distribution and amount of Zr in the particle and local structure of Zr complex formed in the adsorbent, PIXE and EXAFS analyses on the Zr adsorbed chelating resin were carried out. Micro-PIXE analysis proved that it is an effectual method for quantitative analysis of trace adsorbed elements. Moreover, some of the adsorption sites were possibly occupied by the molecules. On the other hand, Zr-K edge EXAFS analysis suggested that extraction mechanism of Zr from the aqueous solution and the solvent was different.

論文

Structural characterization of Eu-HONTA complexes by IBIL and EXAFS analyses

渡部創; 佐野雄一; 岡田諒*; 松浦治明*; 羽倉尚人*; 加田渉*

Nuclear Instruments and Methods in Physics Research B, 477, p.60 - 65, 2020/08

https://doi.org/10.1016/j.nimb.2019.10.004

被引用回数：1 パーセンタイル：39.17(Instruments & Instrumentation)

抽出クロマトグラフィを用いたMA回収技術開発のためのHONTA含侵吸着材中に形成されるEu錯体の局所構造を、EXAFSとIBILとを組み合わせた手法により調査した。本分析により、吸着材中と溶媒中とで形成される錯体構造の微小な変化をとらえることができることが明らかとなった。

論文

Structural significance of nickel sites in aluminosilicate glasses

門力也*; 岸哲生*; Lelong, G.*; Galoisy, L.*; 松村大樹; Calas, G.*; 矢野哲司*

Journal of Non-Crystalline Solids, 539, p.120070_1 - 120070_8, 2020/07

https://doi.org/10.1016/j.jnoncrysol.2020.120070

被引用回数：1 パーセンタイル：0.01(Materials Science, Ceramics)

We use Ni ions as a structural probe to investigate the influence of modifier cations on the structure of aluminosilicate glasses. The color of these glasses varies with the nature of the cations present in glass. Structural origin of this change is investigated by optical absorption and X-ray absorption spectroscopies. Our results reveal pronounced changes in Ni coordination. Tetrahedra Ni $^{2+}$ ins present in all these glasses and Ni $^{2+}$ in 5-fold coordination site also appears. There is a weak contribution from octahedral Ni $^{2+}$ . The concentration of tetrahedral Ni $^{2+}$ deduced from the optical absorption spectroscopy increases with decreasing cation field strength, explaining the variation of color from yellow and brown to purple. This is in line with X-ray absorption spectroscopy data. Cation-oxygen distances and site symmetry indicate a similar structural behavior of Mg $^{2+}$ and Ni $^{2+}$ , being a good structural probe to Mg.

論文

Unusual redox behavior of ruthenocene confined in the micropores of activated carbon

糸井弘行*; Ninomiya, Takeru*; 長谷川英之*; Maki, Shintaro*; Sakakibara, Akihiro*; 鈴木隆太郎*; 笠井湧斗*; 岩田博之*; 松村大樹; 大和田真生*; et al.

Journal of Physical Chemistry C, 124(28), p.15205 - 15215, 2020/07

https://doi.org/10.1021/acs.jpcc.0c02965

被引用回数：4 パーセンタイル：61.86(Chemistry, Physical)

We demonstrate reversible charge/discharge in ruthenocene, RuCp $_{2}$ (Cp = -C $_{5}$ H $_{5}$ ), using activated carbon (AC) as a support. Upon subsequent electrochemical oxidation using an aqueous H $_{2}$ SO $_{4}$ electrolyte, the clusters are disassembled and the RuCp $_{2}$ molecules are finely dispersed in the micropores. The resulting RuCp $_{2}$ has a large contact area with conductive carbon surfaces, thereby realizing rapid charge transfer at the contact interface. Consequently, rapid charge storage occurs via the reversible redox reaction of the supported RuCp $_{2}$ in aqueous H $_{2}$ SO $_{4}$ without dimerization or disproportionation reactions, which is confirmed by X-ray absorption spectroscopy. Since hybridization can produce different properties of the host and guest materials, their infinite combinations would have the possibility to yield properties far surpassing those of existing materials.

論文

Synthesis and characterization of iodovanadinite using PdI $_{2}$ , an iodine source for the immobilisation of radioiodine

Johnstone, E. V.*; Bailey, D. J.*; Lawson, S.*; Stennett, M. C.*; Corkhill, C. L.*; Kim, M.*; Heo, J.*; 松村大樹; Hyatt, N. C.*

RSC Advances (Internet), 10(42), p.25116 - 25124, 2020/07

https://doi.org/10.1039/D0RA04114A

被引用回数：0 パーセンタイル：0(Chemistry, Multidisciplinary)

The synthesis of a palladium-containing iodovanadinite derivative, hypothetically "PdPb $_{9}$ (VO $_{4}$ ) $_{6}$ I $_{2}$ ", was attempted using PdI $_{2}$ as a source of iodine in searching for a novel waste form for radioiodine. The resulting products were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, IR spectroscopy, thermal analysis and Pd K XANES. Results showed that PdI $_{2}$ can function as a sacrificial iodine source for the formation of iodovanadinite, prototypically Pb $_{10}$ (VO $_{4}$ ) $_{6}$ I $_{2}$ , however, the incorporation of Pd into this phase was not definitively observed. Overall, the key novelty and importance of this work is in demonstrating a method for direct immobilisation of undissolved PdI $_{2}$ from nuclear fuel reprocessing, in a composite wasteform in which I-129 is immobilised within a durable iodovandinite ceramic, encapsulating Pd metal.

論文

Porous metal-organic frameworks containing reversible disulfide linkages as cathode materials for lithium-ion batteries

清水剛志*; Wang, H.*; 松村大樹; 光原圭*; 太田俊明*; 吉川浩史*

ChemSusChem, 13(9), p.2256 - 2263, 2020/05

https://doi.org/10.1002/cssc.201903471

被引用回数：9 パーセンタイル：85.53(Chemistry, Multidisciplinary)

Three porous disulfide-ligand-containing metal-organic frameworks (DS-MOFs) and two nonporous coordination polymers with disulfide ligands (DS-CPs) with various structural dimensionalities were used as cathode active materials in lithium batteries. Charge/discharge performance examinations revealed that only porous DS-MOF-based batteries exhibited significant capacities close to the theoretical values, which was ascribed to the insertion of electrolyte ions into the DS-MOFs. Battery reactions were probed by instrumental analyses. The dual redox reactions of metal ions and disulfide ligands in the MOFs resulted in higher capacities, and the presence of reversible electrochemically dynamic S-S bonds stabilized the cycling performance. Thus, the strategy of S-S moiety trapping in MOFs and the obtained correlation between the structural features and battery performance could contribute to the design of high-performance MOF-based batteries and the practical realization of Li-S batteries.

論文

Hydrogen absorption and desorption on Rh nanoparticles revealed by dispersive X-ray absorption fine structure spectroscopy

Song, C.*; Seo, O.*; 松村大樹; 廣井慧*; Cui, Y.-T.*; Kim, J.*; Chen, Y.*; Tayal, A.*; 草田康平*; 小林浩和*; et al.

RSC Advances (Internet), 10(34), p.19751 - 19758, 2020/05

https://doi.org/10.1039/D0RA03322G

被引用回数：0 パーセンタイル：0(Chemistry, Multidisciplinary)

To unveil the origin of the hydrogen-storage properties of rhodium nanoparticles (Rh NPs), we investigated the dynamical structural change of Rh NPs using dispersive X-ray absorption fine structure spectroscopy (XAFS). The variation of the Rh-Rh interatomic distance and Debye-Waller factor of Rh NPs with a size of 4.0 and 10.5 nm during hydrogen absorption and desorption suggested that they have a different mechanism for hydrogen absorption, which is that the hydrogen absorption on the inner site has a greater contribution than that on a surface for Rh 4.0 nm. In the case of Rh 10.5 nm, it is opposed to Rh 4.0 nm. This study demonstrates a powerful XAFS method for observing small local structural changes of metal nanoparticles and its importance for understanding of the hydrogen-absorption properties of Rh NPs with an interesting hydrogenation mechanism.