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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Assessing factors that determine adatom migration and clustering on a thin film oxide; Pt 1 and Rh 1 on the “29” Cu x O/Cu(1 1 1) surface

The dynamical nature of single-site catalysts under non-equilibrium conditions poses significant challenges in the full characterization of their active sites. The “29” oxide is a thin Cu x O film grown on Cu(111) which provides a well-defined surface on which to study the structure and chemistry of atomically dispersed precious metals. A combination of experimental and first-principles approaches is used to investigate the factors that influence the mobility of metal adatoms and their clustering tendencies. Our work elucidates how a homogenous coordination environment of neutral single-atoms can be obtained when its tendency to break oxide bonds within its vicinity is low. Herein we demonstrate that this in turn affects the chemical atomically dispersed species on thin-film oxides, as defects on the oxide would in fact allow such species to be more accessible to CO. We thus highlight the importance of understanding the relationship between defects and atomically dispersed active sites upon designing single-site catalysts.

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

Heterogeneous hydroformylation of alkenes by Rh-based catalysts

Heterogeneously catalyzed hydroformylation reactions avert the problems of separation in homogeneous reactions, reduce the discharge of phosphorus-containing wastes, and prevent the loss of precious metals. This review summarizes the developments of catalysts for heterogeneous hydroformylation in the last decade and proposes potential modification methods for future improvements. The hydroformylation properties of different reactants are compared in order to emphasize the fact that various olefins face unique challenges. The hydroformylation of ethylene requires the enhancement of catalytic activity and chemoselectivity, whereas that of propylene needs improvements in both chemoselectivity and regioselectivity. The hydroformylation of longer-chain olefins and styrene seeks further improvement in regioselectivity. The catalytic properties of activity, selectivity, and stability can be tuned through electronic effects (bimetallic effects, phosphine ligands, and single-atom catalysts), steric hindrance (encapsulation structures, diphosphine ligands, and local functional groups), and reaction condition optimization (temperature, pressure, and solvents). Furthermore, the understanding of these effects is critical in future catalyst design for heterogeneous hydroformylation reactions.

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

Elastic properties of a Sc–Zr–Nb–Ta–Rh–Pd high-entropy alloy superconductor

Here, we report a comprehensive study on the elastic properties of a hexanary high-entropy alloy superconductor (ScZrNbTa) 0.685 [RhPd] 0.315 at room and cryogenic temperatures, by Resonant Ultrasound Spectroscopy experiments. The derived elastic constants are bulk modulus K=132.7 GPa, Young’s modulus E=121.0 GPa, shear modulus G=44.9 GPa, and Poisson’s ratio v= 0.348 for room temperature. The Young’s and shear moduli are ~ 10% larger than those in NbTi superconductor with similar T c , while the ductility is comparable. Moreover, the mechanical performance is further enhanced at cryogenic temperature. Our work confirms the advantageous mechanical properties of high-entropy alloy superconductors and suggests the application prospects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Emergence of Subsurface Oxygen on Rh(111)

Oxygen atoms on transition metal surfaces are highly mobile under the demanding pressures and temperatures typically employed for heterogeneously catalyzed oxidation reactions. This mobility allows for rapid surface diffusion of oxygen atoms, as well as absorption into the subsurface and reemergence to the surface, resulting in variable reactivity. Subsurface oxygen atoms play a unique role in the chemistry of oxidized metal catalysts, yet little is known about how subsurface oxygen is formed or returns to the surface. Furthermore, if oxygen diffusion between the surface and subsurface is mediated by defects, there will be localized changes in the surface chemistry due to the elevated oxygen concentration near the emergence sites. We observed that oxygen atoms emerge preferentially along the boundary between surface phases and that subsurface oxygen is depleted before the surface oxide decomposes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Rh → Sb Interactions Supported by Tris(8-quinolyl)antimony Ligands

The study of ambiphilic systems combining L-type and Z-type ligands within the same construct has emerged as a field of active investigation, especially in the cases of ligands containing a group 13 element as a σ-acceptor for transition metals. (1) Parallel to these developments, several groups have investigated more atypical systems in which the Z-type ligand is a group 15 element. (2) Our contributions to this area have focused on the use of phosphinostibine ligands for the generation of transition metal complexes in which the antimony moiety acts as a Z-type ligand. (1d,3) We have shown that the magnitude of the resulting M → Sb interaction can be readily modulated by the oxidation state of the antimony atom (4) as well as its charge which can be manipulated by abstraction of anionic ligands. (5) Our work has also shown that these effects can be leveraged to enhance the catalytic properties of the transition metal center. (4,5) Some of the simplest systems that we have investigated are those resulting from the reaction of platinum dichloride with the bis- or tris-phosphinostibines ClSb(o-dppp) 2 and Sb(o-dppp) 3 , respectively (o-dppp = o-(Ph 2 P)C 6 H 4 ). These reactions proceed by oxidative insertion of the stibine into a Pt- Cl bond to produce complexes A and B, (6) respectively (Chart 1). Reasoning that the properties of these complexes may also be influenced by the nature of the L-type buttresses, we have now questioned whether stibines featuring nitrogen donor ligands could also display the redox noninnocence of their phosphine counterparts and support the formation of such complexes. Following up on some of our work with ambiphilic tellurium-quinoline ligands, (7) we now report on the reaction of tris-(8-quinolyl)stibines (8) toward (MeCN) 3 RhCl 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Development of Half-Sandwich Ru, Os, Rh, and Ir Complexes Bearing the Pyridine-2-ylmethanimine Bidentate Ligand Derived from 7-Chloroquinazolin-4(3H)-one with Enhanced Antiproliferative Activity

Kinesin spindle protein (KSP) inhibitors are one of the most promising anticancer agents developed in recent years. Herein, we report the synthesis of ispinesib-core pyridine derivative conjugates, which are potent KSP inhibitors, with half-sandwich complexes of ruthenium, osmium, rhodium, and iridium. Conjugation of 7-chloroquinazolin-4(3H)-one with the pyridine-2-ylmethylimine group and the organometallic moiety resulted in up to a 36-fold increased cytotoxicity with IC 50 values in the micromolar and nanomolar range also toward drug-resistant cells. All studied conjugates increased the percentage of cells in the G 2 /M phase, simultaneously decreasing the number of cells in the G 1 /G 0 phase, suggesting mitotic arrest. Additionally, ruthenium derivatives were able to generate reactive oxygen species (ROS); however, no significant influence of the organometallic moiety on KSP inhibition was observed, which suggests that conjugation of a KSP inhibitor with the organometallic moiety modulates its mechanism of action.

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