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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Ag Isotopic Evolution of the Mantle During Accretion: New Constraints from Pd and Ag Metal-Silicate Partitioning

Decay of (sup 107) Pd to (sup 107) Ag has a half-life of 6.5 times 10 (sup 6) mega-annums. Because these elements are siderophile but also volatile, they offer potential constraints on the timing of core formation as well as volatile addition. Initial modelling has shown that the Ag isotopic composition of the bulk silicate Earth (BSE) can be explained if accretion occurs with late volatile addition. These arguments were tested for sensitivity for pre-cursor Pd/Ag contents, and for a fixed Pd/Ag ratio of the BSE of 0.1. New Ag and Pd partitioning data has allowed a better understanding of the partitioning behavior of Pd and Ag during core formation. The effects of S, C and Si, and the effect of high temperature and pressure has been evaluated. We can now calculate D(Ag) and D(Pd) over the wide range of PT conditions and variable metallic liquid compositions that are known during accretion. We then use this new partitioning information to revisit the Ag isotopic composition of the BSE during accretion.

Righter, K.↗
DOE OSTI2020

Methods related to a structure of high-affinity human PD-1/PD-L2 complex

Variants of human PD-1 comprising one or more of amino acid substitutions in residues corresponding to N74, T76 and A132 of SEQ ID NO:1 are described. Also described are structures, obtained using X-ray crystallography, of the human PD-1/PD-L2 complex and mutant PD-1 variants. The structures of human PD-1 described in the present disclosure are useful in drug discovery, including small-molecule drug discovery. Accordingly, methods of using the structures in drug discovery are also described.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Demonstrate Improved Ag Diffusion and Describe the Basis for Pd Penetration Modeling in SiC

In past work, an effective diffusivity coefficient was determined for Ag transport through the silicon carbide layer of a tristructural isotropic fuel particle. The effective diffusivity coefficient accounts for the microstructure of the silicon carbide and includes both bulk diffusion and grain boundary diffusion of Ag. In this report, the model has been improved by accounting for the enhanced concentration of vacancies in the bulk due to irradiation, which substantially influence bulk diffusivity at low temperatures. To improve the BISON model and make it fission rate dependent, effective diffusivity calculations have been performed that incorporate the radiation modified bulk diffusivity. The microstructure and irradiation-dependent effective diffusivity has also been implemented into BISON, and its predictions for Ag release from tristructural isotropic fuel have been successfully compared to AGR-1 post irradiation measurements. Moreover, a new feature has been developed in the Multiphysics Object-Oriented Simulation Environment (MOOSE) to account for different grain boundary types. The Ag diffusivity in 5 (210)/[001] grain boundaries has been computed and was found to be greater than in random high-angle grain boundaries. The presence of the fission product Pd can also have an important effect on the properties of the silicon carbide layer in tristructural isotropic particles. The penetration of Pd into the silicon carbide layer causes a corrosion reaction that can lead to the failure of the silicon carbide layer; however, this corrosion reaction is not well understood. To enable an improved understanding of the mechanism, ab-initio molecular dynamics simulations of Pd interaction with bulk silicon carbide have been performed. The improved understanding of the reaction will form a basis for future improvements to the BISON’s Pd penetration failure model

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on Pd(Se4Cl)2 by Materials Project

Pd(Se4Cl)2 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Pd4+ is bonded in a square co-planar geometry to two equivalent Se+0.25- and two equivalent Cl1- atoms. Both Pd–Se bond lengths are 2.45 Å. Both Pd–Cl bond lengths are 2.33 Å. There are four inequivalent Se+0.25- sites. In the first Se+0.25- site, Se+0.25- is bonded in a 1-coordinate geometry to one Pd4+, two Se+0.25-, and one Cl1- atom. There are one shorter (2.40 Å) and one longer (2.46 Å) Se–Se bond lengths. The Se–Cl bond length is 3.26 Å. In the second Se+0.25- site, Se+0.25- is bonded in a distorted rectangular see-saw-like geometry to two Se+0.25- and two equivalent Cl1- atoms. The Se–Se bond length is 2.38 Å. There are one shorter (3.18 Å) and one longer (3.39 Å) Se–Cl bond lengths. In the third Se+0.25- site, Se+0.25- is bonded in a distorted water-like geometry to two Se+0.25- atoms. The Se–Se bond length is 2.33 Å. In the fourth Se+0.25- site, Se+0.25- is bonded in a 4-coordinate geometry to two Se+0.25- and two equivalent Cl1- atoms. There are one shorter (3.45 Å) and one longer (3.96 Å) Se–Cl bond lengths. Cl1- is bonded in a distorted single-bond geometry to one Pd4+ and five Se+0.25- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pd(SN)4 by Materials Project

Pd(NS)4 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight Pd(NS)4 clusters. Pd4+ is bonded in an L-shaped geometry to two S2- atoms. Both Pd–S bond lengths are 2.25 Å. There are four inequivalent N1+ sites. In the first N1+ site, N1+ is bonded in a bent 120 degrees geometry to two S2- atoms. There is one shorter (1.62 Å) and one longer (1.63 Å) N–S bond length. In the second N1+ site, N1+ is bonded in a single-bond geometry to one S2- atom. The N–S bond length is 1.55 Å. In the third N1+ site, N1+ is bonded in a bent 120 degrees geometry to two S2- atoms. There is one shorter (1.62 Å) and one longer (1.63 Å) N–S bond length. In the fourth N1+ site, N1+ is bonded in a single-bond geometry to one S2- atom. The N–S bond length is 1.54 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a bent 120 degrees geometry to two N1+ atoms. In the second S2- site, S2- is bonded in a bent 120 degrees geometry to two N1+ atoms. In the third S2- site, S2- is bonded in a water-like geometry to one Pd4+ and one N1+ atom. In the fourth S2- site, S2- is bonded in a water-like geometry to one Pd4+ and one N1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pd(NCl)2 by Materials Project

Pd(NCl)2 crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of one Pd(NCl)2 ribbon oriented in the (1, 0, 0) direction. Pd2+ is bonded in a distorted rectangular see-saw-like geometry to four N atoms. There are three shorter (2.01 Å) and one longer (2.02 Å) Pd–N bond lengths. There are two inequivalent N sites. In the first N site, N is bonded in a trigonal planar geometry to two equivalent Pd2+ and one Cl1- atom. The N–Cl bond length is 1.66 Å. In the second N site, N is bonded in a trigonal planar geometry to two equivalent Pd2+ and one Cl1- atom. The N–Cl bond length is 1.66 Å. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one N atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one N atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pd(SN)4 by Materials Project

Pd(NS)4 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four Pd(NS)4 clusters. Pd4+ is bonded in an L-shaped geometry to two S2- atoms. There are one shorter (2.24 Å) and one longer (2.25 Å) Pd–S bond lengths. There are four inequivalent N1+ sites. In the first N1+ site, N1+ is bonded in a bent 120 degrees geometry to two S2- atoms. Both N–S bond lengths are 1.62 Å. In the second N1+ site, N1+ is bonded in a bent 120 degrees geometry to two S2- atoms. There is one shorter (1.62 Å) and one longer (1.63 Å) N–S bond length. In the third N1+ site, N1+ is bonded in a single-bond geometry to one S2- atom. The N–S bond length is 1.54 Å. In the fourth N1+ site, N1+ is bonded in a single-bond geometry to one S2- atom. The N–S bond length is 1.54 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a water-like geometry to one Pd4+ and one N1+ atom. In the second S2- site, S2- is bonded in a water-like geometry to one Pd4+ and one N1+ atom. In the third S2- site, S2- is bonded in a bent 120 degrees geometry to two N1+ atoms. In the fourth S2- site, S2- is bonded in a bent 120 degrees geometry to two N1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Formation enthalpies of Al–Mn–Pd and the structure of the i-AlMnPd quasicrystal

Abstract This paper reports formation enthalpies of phases in the Al–Mn–Pd ternary alloy system as calculated from first principles using electronic density functional theory. We consider all crystal structures as reported in the assessed phase diagrams of the ternary and its binary alloy subsystems (Al–Mn, Al–Pd, and Mn–Pd), as well as additional reported or hypothetical structures. Icosahedral and decagonal quasicrystalline approximants are among the structures that we predict to be stable, or nearly so. Our results suggest the need for careful experimental reexamination of phase stability in each of the alloy systems, in tandem with further efforts to refine crystallographic and ab-initio structures.

17 WIND ENERGY↗
DOE OSTI2022

Synthesis of amorphous Pd-based nanocatalysts for efficient alcoholysis of styrene oxide and electrochemical hydrogen evolution

Amorphous nanomaterials with long-range disordered structures could possess distinct properties and promising applications, especially in catalysis, as compared with their conventional crystalline counterparts. It is imperative to achieve the controlled preparation of amorphous noble metal-based nanomaterials for the exploration of their phase-dependent applications. Here, in this work, we report a facile wet-chemical reduction strategy to synthesize various amorphous multimetallic Pd-based nanomaterials, including PdRu, PdRh, and PdRuRh. The phase-dependent catalytic performances of distinct Pd-based nanomaterials towards diverse catalytic applications have been demonstrated. Specifically, the usage of PdRu nanocatalysts with amorphous and crystalline face-centered cubic (fcc) phases can efficiently switch the ring-opening route of styrene oxide to obtain different products with high selectivity through alcoholysis reaction and hydrogenation reaction, respectively. Moreover, when used as an electrocatalyst for hydrogen evolution reaction (HER), the synthesized amorphous PdRh nanocatalyst exhibits low overpotential and high turnover frequency values, outperforming its crystalline fcc counterpart and most of the reported Pd-based HER electrocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Zeolite supported Pd catalysts for the complete oxidation of methane: A critical review

This review summarizes the recent literature reports on the development of zeolite supported Pd catalysts for the complete oxidation of methane. In-depth analysis reveals that different types of zeolite framework structures, regardless of the dimensionality, pore opening structure, and channel size, have little influence on the methane oxidation activity or the on-stream stability of the supported Pd catalysts. In contrast, the Si/Al ratio of a zeolite support plays a critical role. Both the catalytic activity and the on-stream stability of a Pd/zeolite catalyst increase with the increase of the Si/Al ratio. Catalysts supported on siliceous zeolites consistently show excellent light-off activity and remarkable on-stream stability whether in a dry or wet feed. Silanol nest defect sites in a siliceous zeolite are proposed to be the anchoring sites promoting the formation and minimizing the sintering of finely dispersed Pd nanoparticles. Remaining challenges in overcoming the sulfur poisoning effect are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A refined design concept for sulfur-tolerant Pd catalyst supported on zeolite by shape-selective exclusion and hydrogen spillover for hydrogenation of aromatics

Sulfur poisoning of noble metal catalysts has been a major challenge for decades. This work demonstrates the superior sulfur tolerance of a hybrid zeolite-supported Pd catalyst for hydrogenation of tetralin containing benzothiophene. The hybrid catalyst consists of Pd supported on a large-pore acidic zeolite Y (Pd/HY) and a small-pore zeolite A without (Pd/HA) or with surface metal passivation by chemical vapor deposition of SiO 2 (SiO 2 -Pd/HA) and with potassium ion exchange (SiO 2 -Pd/KA). Pd/HY is very active for tetralin hydrogenation but quickly deactivates after exposure to benzothiophene at high concentration of 100 ppm sulfur. The SiO 2 -coated Pd/HA shows no activity for tetralin hydrogenation, but continues to activate H 2 and serve as a source of hydrogen spillover from Pd/HA since these metal sites are protected from thiophenic sulfur due to size-selective exclusion. Adding K ion-exchanged and SiO 2 -coated catalyst SiO 2 -Pd/KA to Pd/HY is even more effective for enhancing sulfur tolerance, both for tetralin hydrogenation and for isomerization of cis-decalin to trans-decalin in the presence of benzothiophene. The turnover frequencies (TOF) of all the catalysts are similar at the exposed sulfur/Pd atomic ratio of around 0.5. With further increase in sulfur/Pd ratio, rapid decline in TOF was observed on Pd/HY, but SiO 2 -Pd/KA + Pd/HY hybrid catalyst shows a significantly higher TOF than that over Pd/HY, even though SiO 2 -Pd/KA or SiO 2 -Pd/HA alone shows no TOF for tetralin hydrogenation. Even after high-dose poisoning at 400 ppm sulfur, the SiO 2 -Pd/KA + Pd/HY hybrid recovered activity more quickly than SiO 2 -Pd/HA + Pd/HY, while the latter in turn is much better than Pd/HY alone. These results point to the higher activity for hydrogen spillover from SiO 2 -Pd/KA where Pd metal sites are protected from not only thiophenic sulfur but also inorganic sulfur H 2 S by shape-selective exclusion. The present work further establishes the validity of shape-selective exclusion and hydrogen spillover in the design concept proposed for a sulfur-tolerant bimodal acidic zeolite-supported metal catalyst for hydrogenation of naphthalene [C.S. Song, Chemtech, 29 (1999) 26–30], and refines the design concept further for limiting the size of small pore in hybrid catalysts to~3 Å for restricting access of H 2 S but allowing entrance of H 2 . Further, this refined design concept is applicable to other supported monometallic and bimetallic catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Modulating Operational Conditions to Mitigate Deactivation in Formate Dehydrogenation on Pd Phases

In heterogeneous catalysis, poisoning by surface-bound intermediates poses a major barrier to sustained catalyst performance in (de)hydrogenation reactions. Formate/bicarbonate systems, as liquid organic hydrogen carriers (LOHCs), offer a CO 2 -integrated, low-temperature pathway for hydrogen storage and release, making them attractive for circular energy applications. However, their lower hydrogen density and susceptibility to catalyst deactivation limit their competitiveness compared to conventional LOHCs like methylcyclohexane. Here, this study investigates the mechanistic origins of formate (HCOO – ) dehydrogenation and associated deactivation on Pd interfaces. Using density functional theory (DFT) simulations, we show that under thermocatalytic conditions, strongly bound formate accumulates on the catalyst surface (Pd(111)), blocking active sites, raising activation barriers, and leading to progressive performance loss. Because formate adsorption involves charge transfer, we exploit its sensitivity to electronic structure by modulating the electrochemical potential of the catalyst. Our results reveal that hydrogen transfer from water and formate exhibits opposing potential dependencies, providing insights into the opposing driving forces behind both catalytic activity and poisoning. To further probe this phenomenon, we examine electrochemically induced phase transitions in Pd, focusing on PdO(100) and PdH(110), which are stable under oxidizing and reducing potentials, respectively, and demonstrate enhanced dehydrogenation activity between −0.4 and 0.2 V vs standard hydrogen electrode (SHE). Complementary thermal treatments help decouple kinetic and thermodynamic contributions to intermediate binding. These findings underscore the critical role of the catalyst phase and external stimuli in dictating poison-active site interactions and highlight phase engineering as a promising strategy to mitigate deactivation. This work offers mechanistic insights and design principles for developing more resilient and efficient catalysts for LOHC applications under realistic operating conditions.

Pd phase↗
DOE OSTI2022

Surface oxygenation induced strong interaction between Pd catalyst and functional support for zinc–air batteries

Employing the strong metal-support interaction (SMSI) effect for promoting the catalyst's activity toward the oxygen reduction reaction (ORR) is promising due to the electronic structure optimization and high utilization efficiency of platinum group metal (PGM) catalysts. Metal oxides as alternative supports for PGMs facilitate intrinsic activity and improve durability as compared to conventional carbon supports. However, the restricted mass and electron transfer at the metal/support interface need to be addressed. Herein, to strengthen the interaction at the metal/support interfaces and improve the utilization efficiency of PGM, an ultralow loading of Pd was embedded in a surface-oxygenated PdNiMnO porous film. The Mn-doping was designed to promote surface oxygenation using a facile anodization process that created sufficiently exposed interfaces between Pd and the support, strengthening the SMSI effects at the Pd/oxygenated support interface for enhancing ORR performance. Furthermore, the Ni-containing oxygenated catalyst served as both the active component for the oxygen evolution reaction (OER) and the functional support for stabilizing Pd, making PdNiMnO a bifunctional catalyst for zinc–air flow batteries (ZAFB). As a proof-of-concept, the ZAFB (PdNiMnO) shows a maximal power density of 211.6 mW cm –2 and outstanding cycling stability for over 2000 h with a minimal voltage gap of 0.69 V at a current density of 10 mA cm –2 , superior to the state-of-the-art catalysts.

25 ENERGY STORAGE↗
DOE OSTI2024

Complete Development of Critical Capabilities for TRISO Fission Product Source Term Calculations and Quantify Mechanisms for Pd Penetration of SiC

Overall fission product (FP) release will be an important consideration for the licensing and deployment of advanced reactors utilizing tristructural isotropic (TRISO) fuels. This work focuses on enhancing and applying the BISON models needed to predict FP transport within TRISO particles and particle failure probability, both of which factor directly into release predictions. Specifically, this report details (1) the development of the models needed to predict palladium (Pd) conservation at the engineering scale and the application of those models to characterize Pd fluxes for input into a mechanistic multiscale model for Pd penetration; (2) the refinement of sorption mass transfer models and the development of models for trapping in porous layers, which were applied and compared to particle scans from AGR-2 to provide proof of concept for a method of particle-scale validation that may reduce uncertainties compared to compact-scale validation using data from integral effects tests; (3) the development of a failure-statistics-informed, mesh-independent methodology for applying smeared cracking, enabling further study of the localized multiphysics behaviors associated with cascading particle failure mechanisms; and (4) the preliminary characterization of those coupled multiphysics particle failure behaviors using smeared, nonretentive diffusivities to provide a baseline for future study and to guide ongoing engineering applications.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Direct Catalytic Conversion of Ethanol to C 5+ Ketones: Role of Pd–Zn Alloy on Catalytic Activity and Stability

Abstract Ethanol can be used as a platform molecule for synthesizing valuable chemicals and fuel precursors. Direct synthesis of C 5+ ketones, building blocks for lubricants and hydrocarbon fuels, from ethanol was achieved over a stable Pd‐promoted ZnO‐ZrO 2 catalyst. The sequence of reaction steps involved in the C 5+ ketone formation from ethanol was determined. The key reaction steps were found to be the in situ generation of the acetone intermediate and the cross‐aldol condensation between the reaction intermediates acetaldehyde and acetone. The formation of a Pd–Zn alloy in situ was identified to be the critical factor in maintaining high yield to the C 5+ ketones and the stability of the catalyst. A yield of >70 % to C 5+ ketones was achieved over a 0.1 % Pd‐ZnO‐ZrO 2 mixed oxide catalyst, and the catalyst was demonstrated to be stable beyond 2000 hours on stream without any catalyst deactivation.

Subramaniam, Senthil↗
DOE OSTI2024

Modifikation eines Cu‐Pd‐Schaufelrad‐Metall‐Organischen Gerüsts für die selektive CO 2 ‐Elektroreduktion

Abstract Die Optimierung der Bindungsenergie zwischen dem Intermediat und dem aktiven Zentrum ist ein entscheidender Faktor, um die katalytische Produktselektivität und Aktivität bei der elektrochemischen Kohlendioxidreduktion (CO 2 RR) zu steuern. Es ist bekannt, dass Kupferatome als aktive Zentren CO 2 zu Kohlenwasserstoffen und Sauerstoffverbindungen reduzieren, jedoch unter schlechter Produktselektivität leiden, da mehrere Intermediate nur moderate Bindungsenergien aufweisen. Hier berichten wir über eine Ionenaustauschstrategie zur Konstruktion von Cu−Pd‐Schaufelrad‐Dimeren innerhalb von Cu‐basierten metallorganischen Gerüsten (MOFs), [Cu 3‐x Pdx(BTC) 2 ] (BTC=1,3,5‐Benzoltricarbonsäure), ohne die strukturellen Eigenschaften des MOFs zu verändern. Im Vergleich zum reinen Cu‐MOF ([Cu 3 (BTC) 2 ], HKUST‐1) verlagert der Cu−Pd‐MOF die Produkte der CO 2 ‐Elektroreduktion von einer Vielzahl chemischer Spezies hin zu einer selektiven CO‐Erzeugung. Eine in situ‐Röntgenabsorptions‐Feinstrukturanalyse der Oxidationsstufe des Katalysators und der lokalen Geometrie, kombiniert mit theoretischen Berechnungen, zeigt, dass die Einfügung von Pd in die Knotenpunkte der Cu‐Schaufelradstruktur des MOFs die Adsorption des Schlüsselintermediats COOH* am Cu‐Zentrum fördert. Dies ermöglicht CO‐selektive katalytische Mechanismen und verbessert somit unser Verständnis über das Zusammenspiel von Struktur und Aktivität bei der elektrochemischen CO 2 ‐Reduktion unter Verwendung molekularer Katalysatoren.

Zhang, Ruirui↗
DOE OSTI2020

Deformation-enhanced hierarchical multiscale structure heterogeneity in a Pd-Si bulk metallic glass

Here, the multiscale structures in a Pd 82 Si 18 binary bulk metallic glass before and after deformation were studied using electron microscopies, high-energy synchrotron X-ray diffraction, and small-angle scattering techniques. The experimental results revealed an enhancement of hierarchical structure heterogeneities on multiple length scales after deformation. Hierarchical multiple shear bands of high number density were observed after bending, introducing complex but periodically distributed residual strain. Pair distribution function analysis revealed that the connectivity of the short-range clusters on the medium-range scale determines the packing density difference between the tension side and the compression side in the sample after bending. In-situ synchrotron X-ray diffraction study also revealed a transformation of connection modes among short-range clusters under uniaxial tension and compression, which is consistent with those of triaxial tension/compression parts upon bending in Pd 82 Si 18 glassy alloys. The nanoscale heterogeneities for metallic glasses after deformation observed by small-angle scattering and transmission electron microscopy may be attributed to the nanoscale amorphous phase separation and interacting multiple shear bands enhanced by plastic deformation. Our findings suggested that the enhancement of hierarchical heterogeneous structure on multiple length scales may explain the excellent plasticity of Pd-Si glassy alloys, deepening the understanding of structure-property relation during plastic deformation in metallic glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fine-tuning catalytic selectivity by modulating catalyst-environment interactions: CO 2 hydrogenation over Pd-based catalysts

Capturing catalytic behaviors under operational conditions is pivotal to gaining a mechanistic understanding and promoting the design of robust catalysts. The challenge lies in the difficulty of monitoring real-time surface dynamics driven by catalyst-environment interactions. Here, in this work, we introduce a framework based on density functional calculations and kinetic modeling. This framework significantly improves the accuracy of theoretical models’ descriptions of experimental observations by quantifying environmental impacts on surface phases and active sites. CO 2 hydrogenation over Pd-based catalysts is taken as a showcase. The observed selectivity variations of Pd and Pd-M bimetallic catalysts strongly correlate with hydrogen coverage maintained under typical CO 2 hydrogenation conditions. By reducing the amount of surface hydrogen, the selectivity tuned effectively from formic acid toward CO and methanol. This study not only deepens the comprehension of dynamics of active sites under active chemical conditions but also introduces an alternative opportunity for catalytic tuning by modulating catalyst-environment interactions.

03 NATURAL GAS↗