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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Sc2InPd2 by Materials Project

Sc2Pd2In crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are two inequivalent Sc sites. In the first Sc site, Sc is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent In atoms. There are two shorter (2.74 Å) and four longer (2.89 Å) Sc–Pd bond lengths. All Sc–In bond lengths are 3.31 Å. In the second Sc site, Sc is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent In atoms. There are two shorter (2.74 Å) and four longer (2.85 Å) Sc–Pd bond lengths. All Sc–In bond lengths are 3.24 Å. Pd is bonded in a 6-coordinate geometry to six Sc and two equivalent In atoms. Both Pd–In bond lengths are 2.97 Å. In is bonded in a 12-coordinate geometry to eight Sc and four equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb4CdPd by Materials Project

Tb4PdCd crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are three inequivalent Tb sites. In the first Tb site, Tb is bonded in a 3-coordinate geometry to three equivalent Pd and three equivalent Cd atoms. All Tb–Pd bond lengths are 2.89 Å. All Tb–Cd bond lengths are 3.40 Å. In the second Tb site, Tb is bonded in a distorted bent 150 degrees geometry to two equivalent Pd and two equivalent Cd atoms. Both Tb–Pd bond lengths are 2.88 Å. Both Tb–Cd bond lengths are 3.54 Å. In the third Tb site, Tb is bonded in a 4-coordinate geometry to two equivalent Pd and two equivalent Cd atoms. Both Tb–Pd bond lengths are 3.57 Å. Both Tb–Cd bond lengths are 3.29 Å. Pd is bonded in a 6-coordinate geometry to nine Tb atoms. Cd is bonded to nine Tb and three equivalent Cd atoms to form a mixture of distorted face and corner-sharing CdTb9Cd3 cuboctahedra. All Cd–Cd bond lengths are 3.20 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy7(TePd)2 by Materials Project

Dy7(PdTe)2 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. there are four inequivalent Dy sites. In the first Dy site, Dy is bonded in a 4-coordinate geometry to two equivalent Pd and two equivalent Te atoms. Both Dy–Pd bond lengths are 2.94 Å. Both Dy–Te bond lengths are 3.16 Å. In the second Dy site, Dy is bonded in a 3-coordinate geometry to three Te atoms. There are two shorter (3.22 Å) and one longer (3.28 Å) Dy–Te bond lengths. In the third Dy site, Dy is bonded in a 5-coordinate geometry to two equivalent Pd and three Te atoms. Both Dy–Pd bond lengths are 2.90 Å. There are one shorter (3.14 Å) and two longer (3.20 Å) Dy–Te bond lengths. In the fourth Dy site, Dy is bonded in a 4-coordinate geometry to three equivalent Pd and one Te atom. There are two shorter (2.87 Å) and one longer (3.21 Å) Dy–Pd bond lengths. The Dy–Te bond length is 3.20 Å. Pd is bonded in a 7-coordinate geometry to seven Dy atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 8-coordinate geometry to eight Dy atoms. In the second Te site, Te is bonded in a 7-coordinate geometry to seven Dy atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeSiGePd2 by Materials Project

CePd2GeSi crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Pd, four equivalent Ge, and four equivalent Si atoms. There are four shorter (3.26 Å) and four longer (3.37 Å) Ce–Pd bond lengths. All Ce–Ge bond lengths are 3.22 Å. All Ce–Si bond lengths are 3.26 Å. Pd is bonded in a 4-coordinate geometry to four equivalent Ce, two equivalent Ge, and two equivalent Si atoms. Both Pd–Ge bond lengths are 2.57 Å. Both Pd–Si bond lengths are 2.45 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Pd, and one Si atom. The Ge–Si bond length is 2.41 Å. Si is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Pd, and one Ge atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb3Ga9Pd2 by Materials Project

Yb3Pd2Ga9 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Yb sites. In the first Yb site, Yb is bonded to twelve Ga atoms to form YbGa12 cuboctahedra that share edges with two equivalent GaYb4Ga4Pd4 cuboctahedra and faces with two equivalent YbGa12 cuboctahedra. There are eight shorter (3.18 Å) and four longer (3.20 Å) Yb–Ga bond lengths. In the second Yb site, Yb is bonded in a 10-coordinate geometry to two equivalent Pd and twelve Ga atoms. Both Yb–Pd bond lengths are 3.05 Å. There are a spread of Yb–Ga bond distances ranging from 3.08–3.38 Å. Pd is bonded in a distorted q6 geometry to two equivalent Yb and eight Ga atoms. There are two shorter (2.65 Å) and six longer (2.77 Å) Pd–Ga bond lengths. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded in a 10-coordinate geometry to four Yb, two equivalent Pd, and four Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.59–2.73 Å. In the second Ga site, Ga is bonded in a 1-coordinate geometry to four Yb, one Pd, and four Ga atoms. The Ga–Ga bond length is 2.60 Å. In the third Ga site, Ga is bonded to four equivalent Yb, four equivalent Pd, and four equivalent Ga atoms to form distorted GaYb4Ga4Pd4 cuboctahedra that share edges with two equivalent YbGa12 cuboctahedra and faces with two equivalent GaYb4Ga4Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y4CdPd by Materials Project

Y4PdCd crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are three inequivalent Y sites. In the first Y site, Y is bonded in a 3-coordinate geometry to three equivalent Pd and three equivalent Cd atoms. All Y–Pd bond lengths are 2.89 Å. All Y–Cd bond lengths are 3.39 Å. In the second Y site, Y is bonded in a distorted bent 150 degrees geometry to two equivalent Pd and two equivalent Cd atoms. Both Y–Pd bond lengths are 2.88 Å. Both Y–Cd bond lengths are 3.54 Å. In the third Y site, Y is bonded in a 4-coordinate geometry to two equivalent Pd and two equivalent Cd atoms. Both Y–Pd bond lengths are 3.57 Å. Both Y–Cd bond lengths are 3.29 Å. Pd is bonded in a 6-coordinate geometry to nine Y atoms. Cd is bonded to nine Y and three equivalent Cd atoms to form a mixture of distorted face and corner-sharing CdY9Cd3 cuboctahedra. All Cd–Cd bond lengths are 3.20 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La7Pd3 by Materials Project

La7Pd3 crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are three inequivalent La sites. In the first La site, La is bonded in a 3-coordinate geometry to three equivalent Pd atoms. All La–Pd bond lengths are 3.04 Å. In the second La site, La is bonded in a distorted water-like geometry to two equivalent Pd atoms. Both La–Pd bond lengths are 2.98 Å. In the third La site, La is bonded in a 3-coordinate geometry to three equivalent Pd atoms. There are two shorter (3.01 Å) and one longer (3.13 Å) La–Pd bond lengths. Pd is bonded in a 6-coordinate geometry to six La atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ionic Precursors Transformed Into Vinyl Acetate Synthesis Catalyst via Reaction-Driven Restructuring

Conventional preparation of supported bimetallic catalysts relies on solution-mediated metal salt immobilization and pre-formation of alloy nanoparticles before reaction. Here, we report a fundamentally different synthesis strategy of using a physical mixture of salt precursors to generate an active catalyst during reaction. The catalytic structure is generated in situ from Pd3(OAc)6, Au(OH)3, and KOAc through H2 treatment and reaction-driven restructuring under vinyl acetate monomer (VAM) synthesis conditions. Ascertained from in situ X-ray diffraction and operando infrared spectroscopy analyses, reduction treatment produces segregated Pd and Au domains, and subsequent exposure to a VAM reaction mixture triggers dynamic extraction of Pd from the metal surface. This latter process, mediated by acetate-assisted redox cycles, facilitates Pd migration toward Au domains to form a near-surface localized Pd50Au50 alloy phase. Monometallic Pd domains serve as a reservoir of Pd to the alloy phase, leading to and sustaining a more Pd-enriched active surface and a higher population of accessible Pd sites, compared to a conventionally prepared K-PdAu/SiO2 catalyst. Consequently, this leads to a twofold increase in the VAM formation rate, demonstrating highly active bimetallic catalysts can be generated through the gas-phase treatment of physically mixed ionic precursors.

Cha, Byeong Jun [Rice University]↗
DOE OSTI2021

Facile Synthesis of Palladium-Based Nanocrystals with Different Crystal Phases and a Comparison of Their Catalytic Properties

A relatively unexplored aspect of noble-metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Here, in this work, a method is reported for the facile synthesis of Ru@Pd core–shell nanocrystals featuring polymorphism, with the core made of hexagonally close-packed (hcp)-Ru while the Pd shell takes either an hcp or face-centered cubic (fcc) phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than ≈1.4 nm taking the hcp phase whereas the thicker ones revert to fcc. The injection rate provides an experimental knob for controlling the phase, with one-shot and drop-wise injection of the Pd precursor corresponding to fcc-Pd and hcp-Pd shells, respectively. When these nanocrystals are tested as catalysts toward formic acid oxidation, the Ru@Pd hcp nanocrystals outperform Ru@Pd fcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Platinum and Palladium Monolayer Electrocatalysts for Formic Acid Oxidation

The direct formic acid fuel cell holds great promise as a next generation portable power source. In this paper we report an experimental study on Pt and Pd monolayer (Pt* and Pd*) atop the close-packed facet of transition metal substrates (denoted Pt*/M or Pd*/M, where M = Pt, Pd, Ir, Au, Rh and Ru) model catalysts for formic acid oxidation (FAO) and demonstrate a promotional effect on Pt*/Au(111) and Pd*/Pt(111) surfaces. Contrary to findings on monometallic surfaces, in situ infrared reflection adsorption spectroscopy collected during formic acid oxidation at potentials anodic of 375 mV reveal that the poisoning reaction intermediate CO is not formed on the monolayer surfaces, suggesting a promotion of the direct mechanisms of FAO at the expense of the indirect mechanism through CO. Our density functional theory calculations on model surfaces with 1:1 stoichiometry for overlayer to support metal atoms for the thermochemistry of the elementary steps defined by adsorbed CO, OH, COOH, and HCOO on the (111) facet of Pt, PtML/Au, Pd, and PdML/Pt largely attribute the promotional effect observed for the monolayer catalysts to easier removal of CO brought about by easier activation of water, relative to the monometallic catalysts. This synergy between experiments and theory brings us closer to a fundamental understanding of FAO electrocatalysts under reaction conditions, paving the way to achieving more active electrocatalysts possibly with less Pt or Pd; a pre-requisite for the mass commercialization of this technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Out-of-pile and postirradiated examination of lanthanide and lanthanide-palladium interactions for metallic fuel

Palladium is being investigated as a fuel additive to bind with and potentially immobilize lanthanide fission products. A primary cause of fuel-cladding chemical interaction (FCCI) is the lanthanide fission products migrating to the fuel periphery and interacting with the cladding. This interaction will lead to wastage of the cladding and eventually to a cladding breach. Palladium has previously been identified as a promising additive used to prevent or decrease FCCI by reacting with the lanthanide fission products. In the current study, an alloy cast from the four highest abundant lanthanides found in irradiated metallic fuel, Nd, Ce, Pr, and La, with and without Pd, has been characterized using neutron diffraction, scanning electron microscopy, and electron probe microanalysis. In the lanthanide-Pd intermetallic compounds, all of the constituent compounds, i.e. Nd-Pd, Ce-Pd, La-Pd and Pr-Pd are known. There is very good agreement, both structurally and compositionally, between the out-of-pile lanthanide alloy and lanthanide fission products characterized in irradiated fuels. In both cases, the lanthanide elements form a solid solution in a hexagonal crystal structure. The out-of-pile lanthanide alloy follows Vegard's Law, with the measured and calculated (weighted average of constituents) lattice parameters being within 1% for both the a and c parameters. Pd bonds with the lanthanides (Ln) forming the phases LnPd and Ln7Pd3. The results indicate the properties of lanthanide compounds in irradiated metallic fuel can be reliably simulated in out-of-pile experiments.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Reduction of Oxidized Pd/Ag(111) Surfaces by H 2 : Sensitivity to PdO Island Size and Dispersion

Understanding the migration of species across interfaces in bimetallic systems is key to exploiting their bifunctionality for chemical reactivity and heterogeneous catalysis. The present study demonstrates that the sizes and dispersion of oxidized Pd islands present on oxidized Ag(111) in addition to the concentration of active Pd sites have a significant influence on the rate of surface reduction by H 2 . Two distinct types of Pd oxide islands were generated for this investigation and characterized using X-ray photoelectron spectroscopy and scanning tunneling microscopy. Small, uniformly-dispersed PdO x islands (1-5 nm diameter) were created by depositing Pd onto AgO x surfaces, while larger, non-uniformly dispersed PdO x agglomerates (30-50 nm) were produced by depositing Pd on Ag(111) prior to oxidizing. Based on X-ray photoelectron spectroscopy, the small PdO x islands have a higher concentration of undercoordinated Pd atoms than the large agglomerates. Both types of PdO x are found to dramatically enhance the reduction of AgO x by H 2 at 300 K due to the ability of the PdO x to dissociate H 2 ; the pure AgO x surfaces are unreactive toward H 2 . The rate of reduction at 300 K is found to be 2-4 times larger for the AgO x surface covered by small, uniformly dispersed PdO x islands. The higher reactivity of this surface is attributed to enhanced migration of oxygen and hydrogen atoms between the PdO x and AgO x phases due to the sizes and high dispersion of the small PdO islands as well as the higher concentration of active Pd sites on the PdO x . Furthermore, the results of this study demonstrate that reactant migration between co-existing surface phases is highly sensitive to both the intrinsic chemical activity and morphological properties of the active phase (PdO x ) and reveal that these properties can be significantly influenced by the method of synthesizing the oxidized bimetallic surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A Coverage Self-Consistent Microkinetic Model for Vapor-Phase Formic Acid Decomposition over Pd/C Catalysts

An iterative approach utilizing density functional theory (DFT, PW91-GGA)-informed mean-field microkinetic models and reaction kinetics experiments is used to determine the reaction mechanism and the active site for formic acid (HCOOH, FA) decomposition over a Pd/C catalyst. Models parametrized using DFT energetics on clean Pd(100) and Pd(111) required large corrections to the DFT energetics for capturing our experimental data. Further, both Pd(111) and Pd(100) models predicted a high coverage of adsorbed CO (CO*), inconsistent with the assumption of a clean surface at which the rate parameters for these models were calculated. To better represent the active site under reaction conditions and explicitly account for the presence of CO*, subsequent microkinetic models were formulated using DFT energetics that were calculated on partially (5/9 ML) CO*-covered Pd (111) and (100) facets. Upon parameter adjustment, the resultant 5/9 ML CO*-covered Pd(100) model, although consistent in terms of CO* coverage, was unable to capture the dehydration path measured in the experiments and was, therefore, deemed not to offer an accurate representation of the active site for FA decomposition over Pd/C. In contrast, a partially CO*-covered Pd(111) model was better at representing the catalytic active site, as in addition to being consistent in terms of CO* coverages, it required small adjustments of the DFT parameters to accurately capture the experimental data set (both dehydrogenation and dehydration). Our results suggest that the reaction occurs via the spectroscopically elusive carboxyl (COOH*) intermediate and that spectator CO*-assisted decomposition pathways play an important role under typical experimental conditions. In addition, our study highlights the importance of striving for coverage self-consistent microkinetic models and for including spectator-assisted mechanisms in order to develop an improved picture of the active site under reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Design of Dilute Palladium–Indium Alloy Catalysts for the Selective Hydrogenation of CO 2 to Methanol

Adding small amounts of a more reactive dopant metal to a more selective host metal is a well-known strategy for promoting the catalytic reactivity of the latter without sacrificing its selectivity. While substantial attention has been given to coinage metal hosts for activating individual C–H or O–H bonds, less attention has been given to more exotic metals, such as indium, which is highly selective in the complex hydrogenation of CO 2 to methanol. Herein, we describe the synthesis and properties of Pd–In alloys containing Pd in various states of aggregation (isolated atom, small clusters, and extended clusters) assessed through various characterization methods. These materials exhibit unique catalytic behaviors, with Pd promoting both the reaction rate and methanol selectivity in all cases, though its efficacy is highest when Pd is present in small clusters. Here, the inefficiency of high Pd loadings is due in part to losses in Pd accessibility, while the importance of aggregated vs isolated Pd is theorized to result from accelerated H 2 activation. Methods used to synthesize more conventional dilute-limit and single-atom alloy catalysts can, therefore, be extended to non-coinage metal hosts to promote and control more complex chemistries, though the roles of ensemble size may greatly differ.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic Layers of B2 CuPd on Cu Nanocubes as Catalysts for Selective Hydrogenation

The search for highly active and selective catalysts with high precious metal atom utilization efficiency has attracted increasing interest in both the fundamental synthesis of materials and important industrial reactions. Here, in this work, we report the synthesis of Pd–Cu nanocubes with a Cu core and an ordered B2 intermetallic CuPd shell with controllable atomic layers on the surface (denoted as Cu/B2 CuPd), which can efficiently and robustly catalyze the selective hydrogenation of acetylene (C 2 H 2 ) to ethylene (C 2 H 4 ) under mild conditions. The optimized Cu/B2 CuPd with a Pd loading of 9.5 at. % exhibited outstanding performance in the C 2 H 2 semi-hydrogenation with 100% C 2 H 2 conversion and 95.2% C 2 H 4 selectivity at 90 °C. We attributed this outstanding performance to the core/shell structure with a high surface density of active Pd sites isolated by Cu in the B2 intermetallic matrix, representing a structural motif of single-atom alloys (SAAs) on the surface. The combined experimental and computational studies further revealed that the electronic states of Pd and Cu are modulated by SAAs from the synergistic effect between Pd and Cu, leading to enhanced performance compared with pristine Pd and Cu catalysts. This study provides a new synthetic methodology for making single-atom catalysts with high precious metal atom utilization efficiency, enabling simultaneous tuning of both geometric and electronic structures of Pd active sites for enhanced catalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structural Asymmetry and Chiral-Induced Spin Selectivity in Chiral Palladium-Halide Semiconductors

Chiral Pb-free metal-halide semiconductors (MHSs) have attracted considerable attention in the field of spintronics due to various interesting spin-related properties and chiral-induced spin selectivity (CISS) effect. Despite their excellent chemical and structural tunability, the material scope and crystal structure of Pb-free chiral MHSs exhibiting the CISS effect are still limited; chiral MHSs that have metal-halide structures of octahedra and tetrahedra are only reported. Here, we report a new class of chiral MHSs, of which palladium (Pd)-halides are formed in 1D square-pyramidal structures or 0D square-planar structures, with a general formula of ((R/S-MBA) 2 PdBr 4 ) 1-x ((R/S-MBA) 2 PdCl 4 ) x (MBA = methylbenzylammonium; x = 0, 0.25, 0.5, 0.75, and 1) for the first time. The crystals adopt the 1D helical chain of Pd-halide square-pyramid (for x = 0, 0.25, 0.5, and 0.75) and 0D structure of Pd-halide square-plane (for x = 1). All the Pd-halides are distorted by the interaction between the halide and the chiral organic ammonium and arranged in a noncentrosymmetric position. Circular dichroism (CD) for ((R/S-MBA) 2 PdBr 4 ) 1-x ((R/S-MBA) 2 PdCl 4 ) x indicates that chirality was transferred from chiral organic ammonium to Pd-halide inorganics. ((R-MBA) 2 PdBr 4 ) 1-x ((R-MBA) 2 PdCl 4 ) x (x = 0, 0.25, 0.5, and 0.75) shows a distortion index of 0.127-0.128, which is the highest value among the previously reported chiral MHSs to the best of our knowledge. We also find that (R/S-MBA) 2 Pd(Br 1-x Cl x ) 4 crystals grow along the out-of-plane direction during spin coating and have high c-axis orientation and crystallinity, and (R/S-MBA) 2 Pd(Br 1-x Cl x ) 4 (x = 0 and 0.5) crystals exhibit a CISS effect in polycrystalline bulk films. In conclusion, these results demonstrate the possibility of a new metal-halide series with square-planar structures or square-pyramidal structures for future spintronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Quaternary structure independent folding of voltage-gated ion channel pore domain subunits

Every voltage-gated ion channel (VGIC) has a pore domain (PD) made from four subunits, each comprising an antiparallel transmembrane helix pair bridged by a loop. The extent to which PD subunit structure requires quaternary interactions is unclear. In this report we present crystal structures of a set of bacterial voltage-gated sodium channel (BacNa V ) 'pore only' proteins that reveal a surprising collection of non-canonical quaternary arrangements in which the PD tertiary structure is maintained. This context-independent structural robustness, supported by molecular dynamics simulations, indicates that VGIC-PD tertiary structure is independent of quaternary interactions. This fold occurs throughout the VGIC superfamily and in diverse transmembrane and soluble proteins. Strikingly, characterization of PD subunit-binding Fabs indicates that non-canonical quaternary PD conformations can occur in full-length VGICs. Together, our data demonstrate that the VGIC-PD is an autonomously folded unit. This property has implications for VGIC biogenesis, understanding functional states, de novo channel design, and VGIC structural origins.

59 BASIC BIOLOGICAL SCIENCES↗