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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Predicting a Sharp Decline in Selectivity for Catalytic Esterification of Alcohols from van der Waals Interactions

Controlling the selectivity of catalytic reactions is a critical aspect of improving energy efficiency in the chemical industry; thus, predictive models are of key importance. Herein the performance of a heterogeneous, nanoporous Au catalyst is predicted for the complex catalytic self-coupling of the series of C 2 -C 4 alkyl alcohols, based solely on the known kinetics of the elementary steps of the catalytic cycle for methanol coupling, using scaling methods augmented by density functional theory. Notably, a sharp decrease in selectivity for ester formation with increasing molecular weight to favor the aldehyde due to van der Waals interactions of reaction intermediates with the surface was predicted and subsequently verified quantitatively by experiment. Furthermore, the agreement between theory and experiment clearly demonstrates the efficacy of this approach for building a predictive model of catalytic behavior for a homologous set of reactants using a small set of experimental information.

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

Predicting a Sharp Decline in Selectivity for Catalytic Esterification of Alcohols from van der Waals Interactions

Controlling the selectivity of catalytic reactions is a critical aspect of improving energy efficiency in the chemical industry; thus, predictive models are of key importance. Herein the performance of a heterogeneous, nanoporous Au catalyst is predicted for the complex catalytic self-coupling of the series of C 2 –C 4 alkyl alcohols, based solely on the known kinetics of the elementary steps of the catalytic cycle for methanol coupling, using scaling methods augmented by density functional theory. Notably, a sharp decrease in selectivity for ester formation with increasing molecular weight to favor the aldehyde due to van der Waals interactions of reaction intermediates with the surface was predicted and subsequently verified quantitatively by experiment. Further, the agreement between theory and experiment clearly demonstrates the efficacy of this approach for building a predictive model of catalytic behavior for a homologous set of reactants using a small set of experimental information.

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

Quantifying the effect of late bombardment on terrestrial zircons

The first 500 million years of Earth history is thought to be a period of intense planetary bombardment, but the timing and flux of this meteorite bombardment is poorly understood. In particular, on the basis of an inferred lunar impact history, some workers have hypothesized a ~3.9 Ga terminal cataclysm (TC) in which there was marked increase in the impact flux affecting the Moon, the Earth and possibly other terrestrial planets. Minerals that survived this enigmatic period offer a way to test early planetary bombardment models as they may contain telltale micro- to nanoscale shock features. Here, we present results from a numerical modeling calculation that assesses the probability that a zircon residing in the crust would escape shock melting or shock deformation during a TC bombardment event. Even with conservative pressure estimates for zircon shock deformation and intermediate bombardment intensities, we find that only ~6% of ≥4.0 Ga crust would be expected to survive a 3.9 Ga cataclysm without experiencing either complete melting or zircon shock metamorphism. In this study, we couple this modeling with a search for shock effects in the oldest zircons from the Acasta Gneiss Complex, which would have been present in the Earth's crust during a putative 3.9 Ga TC. Spatially correlated electron and NanoSIMS ion microscopy of 4.02 Ga igneous zircons from Acasta reveals no evidence of ancient shock. These data, together with similar results from other Hadean zircon suites, confirm that a post-Hadean TC is unlikely to have occurred. We suggest that the dearth of pre-3.9 Ga terrestrial crust and zircons is instead best explained by endogenic processes related to the mechanisms of early crust formation. Our modeling allows us to evaluate bombardment scenarios from the terrestrial zircon record by applying probabilistic interpretations to zircon shock deformation data. This approach will be valuable for other planetary bodies, allowing broader conclusions to be drawn from geographically limited datasets.

58 GEOSCIENCES↗
DOE OSTI2021

Electronic tuning of confined sub-nanometer cobalt oxide clusters boosting oxygen catalysis and rechargeable Zn–air batteries.

Reasonable design of robust bifunctional oxygen catalysts from an electronic structure perspective is intriguing and challenging for the development of high active rechargeable zinc-air batteries (ZABs). In this study, the favorable regulation of the electronic structure of the cobalt oxide nanoclusters was firstly predicted by density functional theory (DFT) simulation, and then experimentally verified by confining sub-nanometer CoOx clusters (0.86 nm) into the small pore of ZIF-8 derived N-doped nanomaterials (PNC) using a microporous MOFs confinement strategy. The confined effect of the MOF micropores not only enhanced the stability of the subnanometer cobalt oxide clusters, but also make it coupled with Co-Nx to further regulate the electronic structure of the former, synergistic resulting in enhanced ORR/OER actives. As a result, the optimized 0.05CoOx@PNC catalyst demonstrates outstanding bifunctional oxygen performance with a smaller potential gap of 0.67 V. Moreover, the rechargeable Zn-air batteries integrated 0.05CoOx@PNC air cathode displays encouraging performance with a peak power density of 157.1 mW cm(-2), a specific capacity of 887 mAh g(Zn)(-1)at 10 mA cm(-2) and long-term cyclability for over 200 h, significantly outperforming the benchmark electrode couple consisted of Pt/C/RuO2. DFT calculation further revealed that reducing particle size and coupling with Co-N could effectively regulate the charge distribution of CoOx nanoclusters and downshift the D-band center of Co adsorption sites in CoOx nanoclusters, which reduced the reaction barrier of intermediate O-2* and OH* and ORR/ OER over potential, thus accelerating the overall ORR/OER kinetic process. This work offers a novel reference for the construction of a robust sub-nanometer cluster catalysts in the field of ZABs.

Bifunctional oxygen electrocatalysts↗
DOE OSTI2015

Systematic Perturbations of Binuclear Non-heme Iron Sites: Structure and Dioxygen Reactivity of de Novo Due Ferri Proteins

We report that DFsc (single-chain due ferri) proteins allow for modeling binuclear non-heme iron enzymes with a similar fold. Three 4A → 4G variants of DFsc were studied to investigate the effects of (1) increasing the size of the substrate/solvent access channel (G4DFsc), (2) including an additional His residue in the first coordination sphere along with three additional helix-stabilizing mutations [3His-G4DFsc(Mut3)], and (3) the three helix-stabilizing mutations alone [G4DFsc-(Mut3)] on the biferrous structures and their O 2 reactivities. Near-infrared circular dichroism and magnetic circular dichroism (MCD) spectroscopy show that the 4A → 4G mutations increase coordination of the diiron site from 4-coordinate/5-coordinate to 5-coordinate/5-coordinate, likely reflecting increased solvent accessibility. While the three helix-stabilizing mutations [G4DFsc(Mut3)] do not affect the coordination number, addition of the third active site His residue [3His-G4DFsc(Mut3)] results in a 5-coordinate/6-coordinate site. Although all 4A → 4G variants have significantly slower pseudo-first-order rates when reacting with excess O 2 than DFsc (~2 s ₋1 ), G4DFsc and 3His-G4DFsc(Mut3) have rates (~0.02 and ~0.04 s ₋1 ) faster than that of G4DFsc(Mut3) (~0.002 s ₋1 ). These trends in the rate of O 2 reactivity correlate with exchange coupling between the Fe(II) sites and suggest that the two-electron reduction of O 2 occurs through end-on binding at one Fe(II) rather than through a peroxy-bridged intermediate. Finally, UV–vis absorption and MCD spectroscopies indicate that an Fe(III)Fe(III)-OH species first forms in all three variants but converts into an Fe(III)-μ-OH-Fe(III) species only in the 2-His forms, a process inhibited by the additional active site His ligand that coordinatively saturates one of the iron centers in 3His-G4DFsc(Mut3).

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

Pseudomonas sp. Strain 273 Degrades Fluorinated Alkanes

Fluorinated organic compounds have emerged as environmental constituents of concern. We demonstrate that the alkane degrader Pseudomonas sp. strain 273 utilizes terminally monofluorinated C 7 –C 10 alkanes and 1,10-difluorodecane (DFD) as the sole carbon and energy sources in the presence of oxygen. Strain 273 degraded 1-fluorodecane (FD) (5.97 ± 0.22 mM, nominal) and DFD (5.62 ± 0.13 mM, nominal) within 7 days of incubation, and 92.7 ± 3.8 and 90.1 ± 1.9% of the theoretical maximum amounts of fluorine were recovered as inorganic fluoride, respectively. With n-decane, strain 273 attained (3.24 ± 0.14) × 10 7 cells per μmol of carbon consumed, while lower biomass yields of (2.48 ± 0.15) × 10 7 and (1.62 ± 0.23) × 10 7 cells were measured with FD or DFD as electron donors, respectively. The organism coupled decanol and decanoate oxidation to denitrification, but the utilization of (fluoro)alkanes was strictly oxygen-dependent, presumably because the initial attack on the terminal carbon requires oxygen. Fluorohexanoate was detected as an intermediate in cultures grown with FD or DFD, suggesting that the initial attack on the fluoroalkanes can occur on the terminal methyl or fluoromethyl groups. Overall, the findings indicate that specialized bacteria such as Pseudomonas sp. strain 273 can break carbon–fluorine bonds most likely with oxygenolytic enzyme systems and that terminally monofluorinated alkanes are susceptible to microbial degradation. The findings have implications for the fate of components associated with aqueous film-forming foam (AFFF) mixtures.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

The Role of Excited State Proton Relays on the Photochemical Dynamics of Water Nanodroplets

In this work, we applied non-adiabatic excited state molecular dynamics in tandem with ab initio electronic structure theory to illustrate a complete mechanistic landscape underpinning the UV absorption initiated photochemical dynamics in water nanodroplets. The goal is to understand the nonequilibrium excited state molecular dynamics initiated by the relaxation of solvated photoelectron, and consequential photochemical processes. The lowest-lying excited state shows the proton dissociation for a single water molecule forming intermediate hydronium complexes through a proton relay. At approximately 100 femtoseconds, the proton relay process gives rise to the relaxation of the excited state accompanied with a rapid increase in the non-adiabatic coupling strength with the ground state, and the nanodroplet non-radiatively decays. The non-adiabatic transition to the ground state produces excited vibrational states that facilitate the recombination of the dissociated proton and hydroxyl group, eventually leading to the desorption of water molecules from the nanodroplet. Additionally, lifetimes of transient photochemical events are also resolved for the relaxation of solvated electron, excited state proton relay, and non-radiative transition.

Stetina, Torin F.↗
DOE OSTI2018

Guiding Electrochemical Carbon Dioxide Reduction toward Carbonyls Using Copper Silver Thin Films with Interphase Miscibility

Steering the selectivity of Cu-based electrochemical CO2 reduction (CO2R) catalysts toward targeted products will serve to improve the technoeconomic outlook of technologies based on this process. Using physical vapor deposition as a tool to overcome thermodynamic miscibility limitations, CuAg thin films with nonequilibrium Cu/Ag alloying were prepared for CO2R performance evaluation. In comparison to pure Cu, the CuAg thin films showed significantly higher activity and selectivity toward liquid carbonyl products, including acetaldehyde and acetate. Suppressed activity and selectivity toward hydrocarbons and the competing hydrogen evolution were also demonstrated on CuAg thin films, with a greater degree of suppression observed at increasing nominal Ag compositions. Compositional-dependent CO2R trends coupled with physical characterization and density functional theory suggest that significant miscibility of Ag into the Cu-rich phase of the catalyst underpinned the observed CO2R trends through tuning of adsorbate and reaction intermediate binding energies on the surface.

10 SYNTHETIC FUELS↗
DOE OSTI2017

Photo-driven electron transfer from the highly reducing excited state of naphthalene diimide radical anion to a CO 2 reduction catalyst within a molecular triad

The naphthalene-1,4:5,8-bis(dicarboximide) radical anion (NDI - ˙), which is easily produced by mild chemical or electrochemical reduction (-0.5 V vs. SCE), can be photoexcited at wavelengths as long as 785 nm, and has an excited state (NDI - ˙*) oxidation potential of -2.1 V vs. SCE, making it a very attractive choice for artificial photosynthetic systems that require powerful photoreductants, such as CO 2 reduction catalysts. However, once an electron is transferred from NDI - ˙* to an acceptor directly bound to it, a combination of strong electronic coupling and favorable free energy change frequently make the back electron transfer rapid. To mitigate this effect, we have designed a molecular triad system comprising an NDI - ˙ chromophoric donor, a 9,10-diphenylanthracene (DPA) intermediate acceptor, and a Re(dmb)(CO) 3 carbon dioxide reduction catalyst, where dmb is 4,4'-dimethyl-2,2'-bipyridine, as the terminal acceptor. Photoexcitation of NDI - ˙ to NDI - ˙* is followed by ultrafast reduction of DPA to DPA - ˙, which then rapidly reduces the metal complex. The overall time constant for the forward electron transfer to reduce the metal complex is τ = 20.8 ps, while the time constant for back-electron transfer is six orders of magnitude longer, τ = 43.4 μs. Achieving long-lived, highly reduced states of these metal complexes is a necessary condition for their use as catalysts. The extremely long lifetime of the reduced metal complex is attributed to careful tuning of the redox potentials of the chromophore and intermediate acceptor. The NDI - ˙–DPA fragment presents many attractive features for incorporation into other photoinduced electron transfer assemblies directed at the long-lived photosensitization of difficult-to-reduce catalytic centers.

bio-inspired↗
DOE OSTI2015

Quantum calculation of inelastic CO collisions with H. II. Pure rotational quenching of high rotational levels

Carbon monoxide is a simple molecule present in many astrophysical environments, and collisional excitation rate coefficients due to the dominant collision partners are necessary to accurately predict spectral line intensities and extract astrophysical parameters. We report new quantum scattering calculations for rotational deexcitation transitions of CO induced by H using the three-dimensional potential energy surface (PES) of Song et al. State-to-state cross sections for collision energies from 10{sup −5} to 15,000 cm{sup −1} and rate coefficients for temperatures ranging from 1 to 3000 K are obtained for CO (v = 0, j) deexcitation from j=1−45 to all lower j′ levels, where j is the rotational quantum number. Close-coupling and coupled-states calculations were performed in full-dimension for j=1−5, 10, 15, 20, 25, 30, 35, 40, and 45 while scaling approaches were used to estimate rate coefficients for all other intermediate rotational states. The current rate coefficients are compared with previous scattering results using earlier PESs. Astrophysical applications of the current results are briefly discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Chiral spin liquid with spinon Fermi surfaces in the spin-$\frac{1}{2}$ triangular Heisenberg model

Here, we study the interplay of competing interactions in spin-$\frac{1}{2}$ triangular Heisenberg model through tuning the first- ($J_1$), second- ($J_2$), and third-neighbor ($J_ 3$) couplings. Based on a large-scale density-matrix renormalization group calculation, we identify a quantum phase diagram of the system and discover a gapless chiral spin-liquid (CSL) phase in the intermediate $J_2$ and $J_ 3$ regime. This CSL state spontaneously breaks time-reversal symmetry with finite scalar chiral order, and it has gapless excitations implied by a vanishing spin triplet gap and a finite central charge on the cylinder. Moreover, the central charge grows rapidly with the cylinder circumference, indicating emergent spinon Fermi surfaces. To understand the numerical results we propose a parton mean-field spin-liquid state, the U (1) staggered flux state, which breaks time-reversal symmetry with chiral edge modes by adding a Chern insulator mass to Dirac spinons in the U (1) Dirac spin liquid. This state also breaks lattice rotational symmetries and possesses two spinon Fermi surfaces driven by nonzero $J_2$ and $J_3$, which naturally explains the numerical results. This realizes an example of a gapless CSL state with coexisting spinon Fermi surfaces and chiral edge states, demonstrating the rich family of interesting quantum phases emergent from competing interactions in triangular-lattice magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Spin-aligned neutron-proton pair mode in atomic nuclei

Shell-model calculations using realistic interactions reveal that the ground and low-lying yrast states of the N=Z nucleus {sub 46}{sup 92}Pd are mainly built upon isoscalar neutron-proton pairs, each carrying the maximum angular momentum J=9 allowed by the shell 0g{sub 9/2}, which is dominant in this nuclear region. This structure is different from that found in the ground and low-lying yrast states of all other even-even nuclei studied so far. The low-lying spectrum of excited states generated by such correlated neutron-proton pairs has two distinctive features: (i) the levels are almost equidistant at low energies and (ii) the transition probability I{yields}I-2 is approximately constant and strongly selective. This unique mode is shown to replace normal isovector pairing as the dominant coupling scheme in N=Z nuclei approaching the doubly magic nucleus {sup 100}Sn.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1975

The synthesis and transport properties of the complex salt /TMPD/ /TCNQ/2

The syntheses and transport properties of the complex salt /TMPD/ /TCNQ/2 are described. At high temperatures, the complex is a magnetic semiconductor with transport properties intermediate between those found in the highly conducting and poorly conducting TCNQ salts. The complex undergoes a transition below 50-60 K to a state exhibiting singlet-triplet behavior with weakly alternating exchange coupling.

Somoano, R.↗
DOE OSTI2019

Flexible Design for Steam Generation in an SMR Module

The intermediate heat exchanger is a key aspect of the JUMP tertiary loop. An IHX will be required as an interface between the main steam side and secondary side of the NuScale Power Module and coupled TES or energy users. This project examines the preliminary design of the IHX to establish a design range for detailed design and explore the relationships between variables.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

Hidden axion dark matter decaying through mixing with QCD axion and the 3.5 keV X-ray line

Hidden axions may be coupled to the standard model particles through a kinetic or mass mixing with QCD axion. We study a scenario in which a hidden axion constitutes a part of or the whole of dark matter and decays into photons through the mixing, explaining the 3.5 keV X-ray line signal. Interestingly, the required long lifetime of the hidden axion dark matter can be realized for the QCD axion decay constant at an intermediate scale, if the mixing is sufficiently small. In such a two component dark matter scenario, the primordial density perturbations of the hidden axion can be highly non-Gaussian, leading to a possible dispersion in the X-ray line strength from various galaxy clusters and near-by galaxies. We also discuss how the parallel and orthogonal alignment of two axions affects their couplings to gauge fields. In particular, the QCD axion decay constant can be much larger than the actual Peccei-Quinn symmetry breaking.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Triggering C-N Coupling on Metal Oxide Nanocomposite for the Electrochemical Reduction of CO 2 and NO x ⁻ to Formamide

The co-electroreduction of CO 2 and NO x ⁻ (NO 3 ⁻ /NO 2 ⁻ ) to generate formamide (HCONH 2 ) offers an opportunity for downstream chemical and polymer manufacturing decarbonization; however, significant challenges lie in the C-N coupling and the associated low product selectivity. Herein, p-block metal oxides are incorporated in copper oxides to provide more accessible active sites for reactant adsorption and activation, tuning the reaction selectivity toward the formamide production. Through in situ Raman and synchrotron-based infrared spectroscopy measurements, C-N bond formation is demonstrated in real-time with the CuO x /BiO x catalyst, where the C-N bond is detected via a *CHO and *NH 2 intermediates formation, in agreement with the density functional theory calculations. When tested in a flow electrolyzer, a formamide yield rate of 134 ± 11 mmol h -1 g cat -1 is reported, the first report of co-electroreduction of CO 2 and NO x ⁻ to formamide beyond conventional H-cell measurements. These new insights on the C-N coupling mechanisms and scale-up capability provide directions for further development of electrocatalysts for the formamide production.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Comment on “A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states” [J. Chem. Phys. 142 , 124312 (2015)]

In a recent article, Nguyen et al. report the discovery of a new decomposition pathway for small Criegee intermediates. Prior to this publication, the lowest known pathway for decomposition of Criegee intermediates involved ring closure to form a dioxirane followed by ring opening to make a methylenebisoxy biradical, which can then isomerize or decompose via a variety of pathways. The new pathway reported by Nguyen et al. involves the partial cleavage of the OO bond of the Criegee intermediate forming nascent H 2 CO and O( 1 D) fragments. The O( 1 D) fragment then orbits around the H 2 CO fragment in a manner reminiscent of roaming radical reactions and eventually inserts into one of the CH bonds of the H 2 CO fragment leading directly to formic acid. The authors report saddle point geometries for this pathway determined at a number of different levels of theory in which the distance between the oxygen atom and the formaldehyde varies from 2.0 Å to 3.5 Å depending on the level of theory. Density functional theory (DFT) calculations are found to give more compact, planar saddle point structures while coupled cluster, CCSD(T), and complete active space self consistent field, CASSCF, optimizations lead to looser saddle point structures in which the O atom orbits above the plane of the H 2 CO fragment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗