X-ray Absorption Fine Structure Research Articles

Ferrocene‐Based Nickel Metal–Organic Framework Nanosheets as Efficient, Long‐Cycle Cathode Catalyst for Li‐CO2 Battery

AbstractLi‐CO2 batteries, as a novel type of secondary battery, show great potential for energy conversion and storage. However, challenges such as large electrode polarization and poor cycling performance, stemming from difficulties in decomposing discharge products, limit their practical application. Here, Ferrocene‐based nickel metal–organic framework (Ni‐Fc) nanosheets structure to act as cathode catalysts, prepared via a one‐pot solvothermal reaction. X‐ray absorption fine structure (XAFS) analysis shows that Ni metal forms abundant catalytic active centers with O coordination of carboxylic acid groups in ferrocene units. The Ni‐Fc‐based battery demonstrates a high discharge capacity of 18636 mAh g−1 and exhibits a cycle life exceeding 2000 h at a current of 200 mA g−1. Density functional theory (DFT) calculations indicate that the stronger interaction of Ni‐Fc with discharge intermediates and enhanced Li adsorption accelerate battery reaction kinetics. This study introduces novel catalyst design concepts aimed at achieving high‐performance CO2 reduction and oxidation, thereby advancing Li‐CO2 batteries toward practical application.

Investigation of short-term chemical changes in stable ruthenium added to soil by using X-ray absorption fine-structure analysis.

Radioactive ruthenium may be accidentally released from spent nuclear fuel reprocessing plants to the surrounding environment. However, research on the chemical behavior of radioactive Ru in the environment is limited, and the complex chemical properties of this element complicate the application of extraction methods for the analyses of its chemical forms. To obtain basic information regarding the outcome of radioactive Ru in the environment, we investigated the changes in the form of stable Ru added to soil through X-ray absorption fine-structure (XAFS) analysis. This study uses ruthenium tetroxide (RuO4), ruthenium dioxide (RuO2), ruthenium nitrosyl nitrate (Ru(NO)(NO3)3) and ruthenium chloride (RuCl3) as test sources. These are added to ultrapure water, soil solution or fresh soil samples, which are analyzed using XAFS immediately or 5 days after Ru addition. The Ru K-edge X-ray absorption near edge structure spectra acquired immediately after Ru addition differed with respect to the source. The XAFS results suggest that RuO4 immediately changes to tetravalent form after deposition from air to soil. For RuCl3, the ionic structure in the vicinity of Ru is affected by the soil even if the valence does not change immediately. By contrast, RuO2 and Ru(NO)(NO3)3 are highly stable in soil. The results show that the chemical forms of RuO2 and Ru(NO)(NO3)3 added to the soil solution and soil are retained for 5 days, whereas those of RuCl3 and RuO4 are affected by the soil solution and soil within a short period. These results emphasize the need to focus on the chemical form of Ru deposits and the form change after Ru addition when investigating the environmental fate of radioactive Ru.

NEXAFS spectroscopy of alkylated benzothienobenzothiophene thin films at the carbon and sulfur K-edges.

Alkylated benzothienobenzothiophenes are an important class of organic semiconductors that exhibit high performance in solution-processed organic field-effect transistors. In this work, we study the near-edge x-ray absorption fine-structure (NEXAFS) spectra of 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) at both the carbon and sulfur K-edges. Angle-resolved experiments of thin films are performed to characterize the dichroism associated with molecular orientation. First-principles calculations using the density functional theory-based many-body x-ray absorption spectroscopy (MBXAS) method are also performed to correlate the peaks observed and their dichroism with transitions to specific antibonding molecular orbitals. Interestingly, the dichroism of the dominant, lowest energy peak is opposite at the carbon and sulfur K-edges. While the low-energy peak at the carbon K-edge is assigned to carbon 1s → π* transitions with transition dipole moment (TDM) perpendicular to the planar BTBT core, the dominant low energy peak at the sulfur K-edge is assigned to sulfur 1s → σ* transitions with TDM oriented along the long axis of the BTBT core. These differences at the sulfur and carbon K-edges are understood through the MBAXS simulations that find a reordering of the energy of the lowest energy π* and σ* transitions at the sulfur K-edge due to the strong localization of the σ* orbital over the sulfur atom. This work highlights differences in the NEXAFS spectra of organic semiconductors at carbon and sulfur K-edges and provides new insights into peak assignment and x-ray dichroism relevant for studying the molecular orientation of organic semiconductor films.

Visualizing the Structure and Dynamics of Transition Metal-Based Electrocatalysts Using Synchrotron X-Ray Absorption Spectroscopy.

As the global energy structure evolves and clean energy technologies advance, electrocatalysis has become a focal point as a critical conversion pathway in the new energy sector. Transitional metal electrocatalysts (TMEs) with their distinctive electronic structures and redox properties show great potential in electrocatalytic reactions. However, complex reaction mechanisms and kinetic limitations hinder the improvement of energy conversion efficiency, highlighting the necessity for comprehensive studies on structure and performance of electrocatalysts. X-ray Absorption Fine Structure (XAFS) spectra stand out as a robust tool for examining the electrocatalyst's structures and performance due to its atomic selectivity and sensitivity to local environments. This review delves into the application of XAFS technology in characterizing TMEs, providing in-depth analyses of X-ray Absorption Near-Edge Structure (XANES) spectra, and Extended XAFS (EXAFS) spectra in both R-space and k-space. These analyses reveal intrinsic structural information, electronic interactions, catalyst stability, and aggregation morphology. Furthermore, the paper examines advancements in in-situ XAFS techniques for real-time monitoring of active site changes, capturing critical intermediate and transitional states, and elucidating the evolution of active species during electrocatalytic reactions. These insights deepen our understanding on structure-activity relationship of electrocatalysts and offer valuable guidance for designing and developing highly active and stable electrocatalysts.

MAPO-5 molecular sieves from alkylimidazolium bromide ionic liquids

The ionic liquids diisopropylimidazolium bromide (DIPI) and diisobutylimidazolium bromide (DIBU) were used both as solvents and structure-directing agents (SDAs) to obtain AlPO4-5 and MnAPO-5 (Mn-AFI) molecular sieves. For increasing level of manganese, DIBU always yielded pure-phase Mn-AFI whereas DIPI led to amorphous product when more than 0.13 eq of Mn was added. Varying amounts of water, HF and metal led to AFI, cristobalite or tridymite phases. We also explored the use of nickel as the metal dopant, and although AFI phase were obtained under certain conditions, no framework incorporation of the metal was observed. Because of the vanishingly low vapor pressure of the ILs, the synthesis does not carry the risk of pressure build-up. The ILs were easily and fully recyclable and used for multiple syntheses. The MnAPO-5 material was characterized with powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), electron paramagnetic resonance (EPR), multinuclear solid-state nuclear magnetic resonance (SS-NMR) and X-ray absorption fine structure (XAFS). These findings provide new insight into the ionothermal synthesis of metal-doped AFI frameworks with possible implications in catalytic applications.

Formation of β-U3O8 from UCl3 Salt Compositions under Oxygen Exposure.

Complementary X-ray absorption fine structure (XAFS) and Raman spectroscopy studies were conducted on various UCl3 concentrations in alkali chloride salt compositions. The samples were 5 mol % UCl3 in LiCl (S1), 5 mol % UCl3 in KCl (S2), 5 mol % UCl3 in LiCl-KCl eutectic (S4), 50 mol % UCl3 in KCl (S5), and 20 mol % UCl3 in KCl (S6) molar concentrations. Samples were heated to 800 °C and allowed to cool to room temperature with measurements performed at selected temperatures; the highest temperatures showed the most stability and will be primarily referenced for conclusions. The processing and interpretation of the Raman and extended X-ray absorption fine structure (EXAFS) peaks revealed several uranium-oxygen bond lengths and symmetries in the samples before, during, and after heating. Based on published thermodynamic data of similar systems, X-ray absorption fine structure spectroscopy, and identification of Raman peaks, a β variation of α-U3O8, typical at room temperature, is the suspected dominant phase of all samples at high temperatures (800 °C). In the existing literature, this β structure of U3O8 was synthesized by slow cooling of uranium oxides from 1350 °C. This paper suggests the rapid formation of the compound due to the decomposition of the uranium chlorides or oxychlorides at increasing temperatures and O2 reaction kinetics.

Formation of Na-O bonds in NaZn(BH4)3·xTHF for enhancing sodium conductivity

Developing high-performance solid-state batteries requires solid electrolytes with high ionic conductivity and excellent electrode compatibility. This study focuses on bimetallic borohydride NaZn(BH4)3·xTHF, revealing a room temperature sodium conductivity of 1.89 × 10−5 S cm−1 due to the formation of Na-O bonds. This THF-involved NaZn(BH4)3 was synthesized in a THF solution without ball milling. Our investigation highlights the key role of THF in determining the crystal structure of NaZn(BH4)3·xTHF, which adopts a space group of P2/m. In-situ X-ray diffraction reveals that removing THF from NaZn(BH4)3 under dynamic vacuum conditions leads to a gradual transformation of the crystal structure from space group P2/m to P21/c. X-ray Absorption Fine Structure (XAFS), Pair Distribution Function (PDF), and Far-Infrared analysis illustrate the coordination of THF to NaZn(BH4)3 in the form of Na-O bonds. The DSC results suggest that dynamic desorption and adsorption of THF play an active role in Na+ migration, with the movement of THF creates sodium defects/vacancies that promote Na+ migration. This outstanding property offers attractive prospects for designing bimetallic borohydrides as novel solid-state sodium ion conductors.

Enhanced plasticization resistance of hollow fiber membranes via metal ion coordination for advanced helium recovery

Plasticization can significantly impair the gas separation performance of gas separation membranes, especially for hollow fiber membranes (HFMs) with ultrathin skin layer. While conventional thermal crosslinking is an effective method to address this issue, it often leads to the transition layer collapse in HFMs, resulting in a significant decrease in gas permeance. Herein, we fabricate polyimide-cerium (PI-Ce) complex HFMs using a carboxylic group-containing 6FDA-mPDA0.65-DABA0.3-TFMB0.05 copolyimide through metal ion coordination to achieve plasticization-resistance helium recovery from natural gas. We optimized dope compositions and spinning conditions to produce defect-free hollow fiber membranes with a skin layer as thin as 300 nm. The coordination between carboxyl groups and cerium ions was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The polymer-metal coordinated membranes exhibited enhanced gas selectivities compared to the pristine HFMs due to the tailored microporosity achieved through polymer-metal coordination. Furthermore, the PI-Ce HFMs demonstrated only a 10.8% decline in mixed-gas He/CH4 selectivity, which is significantly lower than the 55.4% decline observed in pristine HFMs when exposed to CO2-containing feed pressures below 400 PSIA. Molecular dynamics simulations confirmed that coordination confined molecular chain swelling, thereby suppressing plasticization caused by CO2. The exceptional plasticization resistance of the PI-Ce complex HFMs provides a novel strategy for recovering helium from aggressive natural gas environments.

Covalent Organic Framework Stabilized Single CoN4Cl2 Site Boosts Photocatalytic CO2 Reduction into Tunable Syngas

AbstractSolar carbon dioxide (CO2) reduction provides an attractive alternative to producing sustainable chemicals and fuel. However, the construction of a highly active photocatalyst was challenging because of the rapid charge recombination and sluggish surface CO2 reduction. Herein, a unique Co−N4Cl2 single site was fabricated by loading Co species into the 2,2′‐bipyridine and triazine‐containing covalent organic framework (COF) for CO2 conversion into syngas under visible light irradiation. The resulting champion catalyst TPy‐COF‐Co enabled a record‐high CO production rate of 426 mmol g−1 h−1, associated with the unprecedented turnover number (TON) and turnover frequency (TOF) of 2095 and 1607 h−1, respectively. The catalyst also exhibited favorable recycling performance and widely adjustable syngas production (CO/H2 ratio: 1.8 : 1–1 : 16). A systematical investigation including operando synchrotron X‐ray absorption fine structure (XAFS) spectroscopy, in situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS), and theoretical calculation indicated that the triazine‐based COF framework promoted the charge transfer towards the single Co−N4Cl2 sites that greatly promoted the CO2 activation by lowering the energy barrier of *COOH generation, facilitating the CO2 transformation. This work highlights the great potential of the molecular regulation of COF‐derived single‐atom catalysts to boost CO2 photoreduction efficiency.

Introducing strong metal–oxygen bonds to suppress the Jahn-Teller effect and enhance the structural stability of Ni/Co-free Mn-based layered oxide cathodes for potassium-ion batteries

Mn-based layered oxides (KMO) have emerged as one of the promising low-cost cathodes for potassium-ion batteries (PIBs). However, due to the multiple-phase transitions and the distortion in the MnO6 structure induced by the Jahn-Teller (JT) effect associated with Mn-ion, the cathode exhibits poor structural stability. Herein, we propose a strategy to enhance structural stability by introducing robust metal–oxygen (M–O) bonds, which can realize the pinning effect to constrain the distortion in the transition metal (TM) layer. Concurrently, all the elements employed have exceptionally high crustal abundance. As a proof of concept, the designed K0.5Mn0.9Mg0.025Ti0.025Al0.05O2 cathode exhibited a discharge capacity of approximately 100 mA h g−1 at 20 mA g−1 with 79% capacity retention over 50 cycles, and 73% capacity retention over 200 cycles at 200 mA g−1, showcased much better battery performance than the designed cathode with less robust M–O bonds. The properties of the formed M–O bonds were investigated using theoretical calculations. The enhanced dynamics, mitigated JT effect, and improved structural stability were elucidated through the in-situ X-ray diffractometer (XRD), in-situ electrochemical impedance spectroscopy (EIS) (and distribution of relaxation times (DRT) method), and ex-situ X-ray absorption fine structure (XAFS) tests. This study holds substantial reference value for the future design of cost-effective Mn-based layered cathodes for PIBs.

Automatic Identification of X-ray Absorption Fine Structure Spectra via Machine Learning

Automatic Identification of X-ray Absorption Fine Structure Spectra via Machine Learning

Rationally tailored configuration of multifunctional scavengers by encapsulating nanoscale Fe0 and FeS into zeolite imidazole framework–8 with reinforced perrhenate/pertechnetate confinement

In order to probe into the potential application prospects of multifunctional scavengers in remediating nuclear wastewater, we combined versatile functionality of nanoscale Fe0 and FeS with tailorable porosity of zeolitic imidazole frameworks–8 (ZIF–8) to manufacture two multifunctional scavengers for ReO4– confinement i.e., NZVI@ZIF–8 by reduction approach and FeS@ZIF–8 by coprecipitation approach. Batch approaches unveiled that as–manufactured scavengers illustrated an reinforced performance towards ReO4– confinement. The pseudo-second-order model was well simulated with the kinetic of ReO4– confinement. Thermodynamic analysis unraveled that ReO4– confinement was endothermic and spontaneous. The mechanism was explored via characterization alters of structure and composition of NZVI@ZIF–8 and FeS@ZIF–8 before and after ReO4– confinement. Specifically, fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD) indicated that NZVI and FeS were successfully encapsulated into ZIF–8, and NZVI@ZIF–8 and FeS@ZIF–8 remained stable after ReO4– confinement. X–ray absorption fine structure (XAFS) unveiled that various Fe mineral phases were formed on the scavenger surfaces under various reaction conditions. X-ray photoelectron spectroscopy (XPS) unraveled existence of Re(VI)/Re(IV) on scavengers surfaces, unveiling ReO4– was initially enriched NZVI@ZIF–8 and FeS@ZIF–8 surfaces with subsequent reduction into Re(VI)/Re(IV). This work proposed an innovative perspective to tailored multifunctional scavengers in nuclear waste management.

Catalytic degradation of stable benzene molecules under room temperature conditions over Pt-loaded boron-carbon-nitride (Pt/BCN) catalysts

The catalytic degradation of volatile organic compounds (VOCs) such as benzene via ring-opening at room temperature is challenging due to the presence of π-bonds in the ring-forming carbon atoms. This study involved the preparation of a novel Pt-loaded boron-carbon-nitride (Pt/BCN) catalyst containing single-atom active sites for efficient catalysis of benzene degradation at room temperature in air. The micromorphology, surface structure, and coordination environment of the catalyst were analyzed using characterization techniques including aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC–HAADF–STEM) and X-ray absorption fine structure (XAFS). The degradation mechanism was investigated using electron paramagnetic resonance (EPR) and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The experimental results demonstrate that Pt/BCN contains many Pt-N4 single-atom active sites that can generate hydroxyl radicals under room-temperature air conditions, leading to the oxidation of benzene to CO2 and H2O. Containing atomically dispersed active-site catalysts developed in this study offer a theoretical foundation for designing catalyst active centers in related fields and advancing the industrial application of room-temperature, low-carbon VOCs treatment technologies.

Measurements of K-edge and L-edge extended x-ray absorption fine structure at the national ignition facility (invited).

High-energy-density laser facilities and advances in dynamic compression techniques have expanded access to material states in the Terapascal regime relevant to inertial confinement fusion, planetary science, and geophysics. However, experimentally determining the material temperature in these extreme conditions has remained a difficult challenge. Extended X-ray Absorption Fine Structure (EXAFS), referring to the modulations in x-ray absorption above an absorption edge from photoelectrons' interactions with neighboring atoms, has proven to be a versatile and robust technique for probing material temperature and density for mid-to-high Z elements under dynamic compression. The current platform at the National Ignition Facility has developed six configurations for EXAFS measurements between 7 and 18keV for different absorption edges (Fe K, Co K, Cu K, Ta L3, Pb L3, and Zr K) using a curved-crystal spectrometer and a bright, continuum foil x-ray source. In this work, we describe the platform geometry, x-ray source performance, spectrometer resolution and throughput, design considerations, and data in ambient and dynamic-compression conditions.

Using synchrotron based ATR-FTIR, EXAFS, and XRF to characterize the chemical compositions of TSP in industrial estate area

In Thailand, the Map Ta Phut Industrial Estate (MTPIE), a prominent industrial hub, has substantial environmental and health issues caused by industrial pollution. This study uses advanced synchrotron-based techniques, such as Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR), Extended X-ray Absorption Fine Structure (EXAFS), and X-ray Fluorescence (XRF), to fully examine the chemical make-up of total suspended particulate (TSP) in the given area. Notable findings include the detection of remarkably high enrichment factors for magnesium and sulfur, indicating the presence of industrial operations. Additionally, we found that magnetite, which accounts for an average of 40 % of the total iron oxides in the samples, is the main iron oxide. The study also highlights about how calcium carbonate and different organic functional groups are found in large amounts, which shows that industrial emissions and natural sources are connected in a complex way. The findings underscore the susceptibility of children to TSP exposure, revealing increased rates of inhalation and significant health hazards. In order to safeguard public health in industrial areas such as MTPIE, it is imperative to implement more sophisticated pollution control techniques and maintain ongoing environmental monitoring.

Insight into the complexation of uranium with Bacillus sp. dwc-2 by multi-spectroscopic approaches: FT-IR, TRLF and XAFS spectroscopies

The micromechanisms of the interactions between uranium and microorganisms, especially chemical bonds and bonding numbers between uranium and microbe are not yet clear. In this work, uranium coordination with functional groups in/on Bacillus sp. dwc-2 has been rationally explored by X-ray absorption fine structure (XAFS), Fourier transform infrared (FT-IR), time-resolved laser-induced fluorescence (TRLF) spectroscopies. The results indicate that under acidic condition, 66.8 % of O atoms in coordination shell of U(VI) equatorial plane are provided by organic phosphoryl groups via monodentate coordination, 18.8 % and 15.5 % are provided by water molecules and carboxyl groups via monodentate and bidentate coordination, respectively. While under alkaline condition, these proportions change to 53.1 %, 34.4 % and 22.0 %, respectively. Under neutral condition, U(VI) is mainly deposited by complexing with inorganic phosphates released by microbial cells. Under anaerobic condition, partial U(VI) can be reduced to U(IV) which primarily complex with phosphorus containing groups via monodentate and bidentate coordination, existing as amorphous solids or coordination polymers. This is the first exploration of the binding mechanism between uranium and microorganisms at a semi-quantitative level under different conditions. Our studies will further enhance the contribute to the understanding of coordination mechanism of uranium with microorganism, and demonstrate the potential bioremediation value of this bacterium.

Manipulating d-Band Center of Nickel by Single-Iodine-Atom Strategy for Boosted Alkaline Hydrogen Evolution Reaction.

Ni-based electrocatalysts have been predicted as highly potential candidates for hydrogen evolution reaction (HER); however, their applicability is hindered by an unfavorable d-band energy level (Ed). Moreover, precise d-band structural engineering of Ni-based materials is deterred by appropriative synthesis methods and experimental characterization. Herein, we meticulously synthesize a special single-iodine-atom structure (I-Ni@C) and characterize the Ed manipulation via resonant inelastic X-ray scattering (RIXS) spectroscopy to fill this gap. The complex catalytic mechanism has been elucidated via synchrotron radiation-based multitechniques (SRMS) including X-ray absorption fine structure (XAFS), in situ synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy, and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). In particular, RIXS is innovatively applied to reveal the precise regulation of Ni Ed of I-Ni@C. Consequently, the role of such single-iodine-atom strategy is confirmed to not only facilitate the moderate Ed of the Ni site for balancing the adsorption/desorption capacities of key intermediates but also act as a bridge to enhance the electronic interaction between Ni and the carbon shell for forming a localized polarized electric field conducive to H2O dissociation. As a result, I-Ni@C exhibits an enhanced alkaline hydrogen evolution performance with an overpotential of 78 mV at 10 mA/cm2 and superior stability, surpassing the majority of the reported Ni-based catalysts. Overall, this study has managed to successfully tailor the d-band center of materials from the SRMS perspective, which has crucial implications for nanotechnology, chemistry, catalysis, and other fields.

Understanding the evolution of molybdenum-nitrogen doped carbon with long-term durability for efficient oxygen reduction reaction

The performance and durability of catalyst for Oxygen Reduction Reaction (ORR) still are challenges for fuel cell applications. Mo-NC catalyst system was established and showed the activity comparable with commercial Pt/C in alkaline conditions. An activation phenomenon during longer operation was confirmed with an obvious positive shift after 30 k cycles in accelerated degradation tests, which is rarely observed in the ORR process. The X-ray absorption fine structure (XAFS) indicated a coordination structure transform in electrochemical conditions cause the activated performance. The Density Function Theory (DFT) calculation reveals the transformation of the coordination structure is thermodynamically feasible and also conducive to lower the energy barriers of the key steps in the ORR performance, explaining the origin of the activate phenomenon. These findings give potential guidance to improve both activity and stability of catalyst.

Ga-doped spinel-typed Co-Al catalysts for CO2-assisted ethane dehydrogenation

A series of Ga-doped spinel-typed Co-Al catalysts were prepared via one-step evaporation-induced self-assembly (EISA) method. These catalysts present promising catalytic performance for CO2-assisted ethane dehydrogenation, which can be ascribed to the conjunction effect of cobalt and gallium species. The incorporation of Ga into the structure of Co-Al spinel has been recognized for enhancing CO2 conversion via reverse water-gas shift reaction, leading to a favorable equilibrium shift towards ethylene, along with an improved catalyst stability as a result of coexisting Boudouard reaction. Through X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), NH3 and CO2 temperature-programmed desorption (TPD) characterizations, coordinatively unsaturated Co2+ and Ga3+ cations were identified as collaborative catalytic active sites, with gallium species taking the prominent role. These sites were closely associated with the formation of acid-base pairs on the catalyst surface, which were crucial for the adsorption and activation of the reactants.

Alloying and Segregation in PdRe/Al2O3 Bimetallic Catalysts for Selective Hydrogenation of Furfural

X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed reduction (TPR), and temperature-programmed hydride decomposition (TPHD) were employed to elucidate the structures of a series of PdRe/Al2O3 bimetallic catalysts for the selective hydrogenation of furfural. TPR evidenced low-temperature Re reduction in the bimetallic catalysts consistent of the migration of [ReO4]− (perrhenate) species to hydrogen-covered Pd nanoparticles on highly hydroxylated γ-Al2O3. TPHD revealed a strong suppression of β-PdHx formation in the reduced catalysts prepared by (i) co-impregnation and (ii) [HReO4] impregnation of the reduced Pd/Al2O3, indicating the formation of Pd-rich alloy nanoparticles; however, reduced catalysts prepared by (iii) [Pd(NH3)4]2+ impregnation of calcined Re/Al2O3 and subsequent re-calcination did not. Re LIII X-ray absorption edge shifts were used to determine the average Re oxidation states after reduction at 400 °C. XAFS spectroscopy and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) revealed that a reduced 5 wt.% Re/Al2O3 catalyst contained small Re clusters and nanoparticles comprising Re atoms in low positive oxidation states (~1.5+) and incompletely reduced Re species (primarily Re4+). XAFS spectroscopy of the bimetallic catalysts evidenced Pd-Re bonding consistent with Pd-rich alloy formation. The Pd and Re total first-shell coordination numbers suggest that either Re is segregated to the surface (and Pd to the core) of alloy nanoparticles and/or segregated Pd nanoparticles are larger than Re nanoparticles (or clusters). The Cowley short-range order parameters are strongly positive indicating a high degree of heterogeneity (clustering or segregation of metal atoms) in these bimetallic catalysts. Catalysts prepared using the Pd(NH3)4[ReO4]2 double complex salt (DCS) exhibit greater Pd-Re intermixing but remain heterogeneous on the atomic scale.