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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Co(salophen)-Catalyzed Aerobic Oxidation of p-Hydroquinone: Mechanism and Implications for Aerobic Oxidation Catalysis

Macrocyclic metal complexes and p-benzoquinones are commonly used as co-catalytic redox mediators in aerobic oxidation reactions. In an effort to gain insight into the mechanism and energetic efficiency of these reactions, we investigated Co(salophen)-catalyzed aerobic oxidation of p-hydroquinone. Kinetic and spectroscopic data suggest that the catalyst resting-state consists of an equilibrium between a CoII(salophen) complex, a CoIII-superoxide adduct, and a hydrogen-bonded adduct between the hydroquinone and the CoIII–O2 species. The kinetic data, together with density functional theory data, suggest that the turnover-limiting step features proton-coupled electron transfer from a semi-hydroquinone species and a CoIII-hydroperoxide intermediate. Additional experimental and computational data suggest that a coordinated H2O2 intermediate oxidizes a second equivalent of hydroquinone. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The NSF provided partial support for the EPR instrumentation (NSF CHE-0741901).

Anson, Colin W.↗
DOE OSTI2019

Structure, Dynamics, and Reactivity for Light Alkane Oxidation of Fe(II) Sites Situated in the Nodes of a Metal–Organic Framework

Metal organic frameworks (MOFs), with their crystalline, porous structures, can be synthesized to incorporate a wide range of catalytically active metals in tailored surroundings. These materials have potential as catalysts for conversion of light alkanes, feedstocks available in large quantities from shale gas that are changing the economics of manufacturing commodity chemicals. Mononuclear high-spin (S = 2) Fe(II) sites situated in the nodes of the MOF MIL-100(Fe) convert propane via dehydrogenation, hydroxylation, and overoxidation pathways in reactions with the atomic oxidant N 2 O. Pair distribution function analysis, N 2 adsorption isotherms, X-ray diffraction patterns, and infrared and Raman spectra confirm the single-phase crystallinity and stability of MIL-100(Fe) under reaction conditions (523 K in vacuo, 378–408 K C 3 H 8 + N 2 O). Density functional theory (DFT) calculations illustrate a reaction mechanism for the formation of 2-propanol, propylene, and 1-propanol involving the oxidation of Fe(II) to Fe(III) via a high-spin Fe(IV)$=$O intermediate. The speciation of Fe(II) and Fe(III) in the nodes and their dynamic interchange was characterized by in situ X-ray absorption spectroscopy and ex situ Mössbauer spectroscopy. Furthermore, the catalytic relevance of Fe(II) sites and the number of such sites were determined using in situ chemical titrations with NO. N 2 and C 3 H 6 production rates were found to be first-order in N 2 O partial pressure and zero-order in C3H8 partial pressure, consistent with DFT calculations that predict the reaction of Fe(II) with N 2 O to be rate determining. DFT calculations using a broken symmetry method show that Fe-trimer nodes affecting reaction contain antiferromagnetically coupled iron species, and highlight the importance of stabilizing high-spin (S = 2) Fe(II) species for effecting alkane oxidation at low temperatures (<408 K).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Methanol Oxidative Dehydrogenation on Oxide Catalysts: Molecular and Dissociative Routes and Hydrogen Addition Energies as Descriptors of Reactivity

The oxidative dehydrogenation (ODH) of alkanols on oxide catalysts is generally described as involving H-abstraction from alkoxy species formed via O–H dissociation. Kinetic and isotopic data cannot discern between such routes and those involving kinetically-relevant H-abstraction from undissociated alkanols. Here, we combine such experiments with theoretical estimates of activation energies and entropies to show that the latter molecular routes prevail over dissociative routes for methanol reactions on polyoxometalate (POM) clusters at all practical reaction temperatures. The stability of the late transition states that mediate H-abstraction depend predominantly on the stability of the O–H bond formed, making H-addition energies (HAE) accurate and single-valued descriptors of reactivity. Density functional theory-derived activation energies depend linearly on HAE values at each O-atom location on clusters with a range of composition (H3PMo12, H4SiMo12, H3PW12, H4PV1Mo11, and H4PV1W11); both barriers and HAE values reflect the lowest unoccupied molecular orbital energy of metal centers that accept the electron and the protonation energy of O-atoms that accept the proton involved in the H-atom transfer. Bridging O-atoms form O–H bonds that are stronger than those of terminal atoms and therefore exhibit more negative HAE values and higher ODH reactivity on all POM clusters. For each cluster composition, ODH turnover rates reflect the reactivity-averaged HAE of all accessible O-atoms, which can be evaluated for each cluster composition to provide a rigorous and accurate predictor of ODH reactivity for catalysts with known structure. These relations together with oxidation reactivity measurements can then be used to estimate HAE values and to infer plausible structures for catalysts with uncertain active site structures.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Design and synthesis of highly active MoVTeNb-oxides for ethane oxidative dehydrogenation

Ethane oxidative dehydrogenation (ODH) is an alternative route for ethene production. Crystalline M1 phase of Mo-V mixed metal oxide is an excellent catalyst for this reaction. Here we show a hydrothermal synthesis method that generates M1 phases with high surface areas starting from poorly soluble metal oxides. Use of organic additives allows control of the concentration of metals in aqueous suspension. Reactions leading to crystalline M1 take place at 190 °C, i.e., approximately 400 °C lower than under current synthesis conditions. The evolution of solvated polyoxometalate ions and crystalline phases in the solid is monitored by spectroscopies. Catalysts prepared by this route show higher ODH activity compared to conventionally prepared catalysts. The higher activity is due not only to the high specific surface area but also to the corrugated lateral termination of the M1 crystals, as seen by atomic resolution electron microscopy, exposing a high concentration of catalytically active sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Benchmarking nanoparticulate metal oxide electrocatalysts for the alkaline water oxidation reaction

Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alkaline water oxidation. However, comparisons of the electrochemical performance of these materials have been challenging due to the different methods of attachment, catalyst loadings, and electrochemical test conditions reported in the literature. Here in this paper, we have leveraged a conventional drop-casting method that allows for the successful adhesion of a wide range of nanoparticulate catalysts to glassy-carbon electrode surfaces. We have applied this adhesion method to prepare catalyst films from 16 crystalline metal-oxide nanoparticles with a constant loading of 0.8 mg cm -2 , and evaluated the resulting nanoparticulate films for the oxygen evolution reaction under conditions relevant to an integrated solar fuels device. In general, the activities of the adhered nanoparticulate films are similar to those of thin-film catalysts prepared by electrodeposition or sputtering, achieving 10 mA cm -2 current densities per geometric area at overpotentials of ~0.35–0.5 V.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hydrothermal synthesis and characterization under dynamic conditions of cobalt oxide nanoparticles supported over magnesium oxide nano-plates

Here, a nano-catalyst comprised of oxidized Co NPs supported on MgO nano-plates was synthesized via a hydrothermal co-precipitation strategy and calcination in O 2 and subsequently in H 2 at 250 °C. Spectro-microscopy characterization was performed by scanning transmission electron microscopy, electron energy loss spectroscopy and scanning X-ray transmission microscopy. Surface measurements under H 2 and H 2 + CO atmospheres were obtained by ambient pressure X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy in the 225–480 °C range. These measurements at the atomic and microscopic levels demonstrated that the oxidized Co nanoparticles uniformly decorated the MgO nano-plates. The surfaces are enriched with Co, and with a mixture of Co(OH) 2 and CoO under H 2 and H 2 + CO atmospheres. Under a H 2 atmosphere, the outermost surfaces were composed of (lattice) O 2- , CO 3 2- and OH - . No inorganic carbonates were observed in the bulk. Chemisorbed CO, likely on the oxidized Co surfaces, was observed at the expense of O 2- under 300 mTorr H 2 + CO (2:1) at 225 °C. Gas phase CO 2 was detected under 32 Torr H 2 + CO (2:1) at 225 °C upon prolonged reaction time, and was attributed to a surface chemical reaction between O 2- and chemisorbed CO. Furthermore, sp 3 like carbon species were detected on the otherwise carbon free surface in H 2 + CO, which remained on the surface under the subsequent reaction conditions. The formation of sp 3 like hydrocarbons was ascribed to a surface catalytic reaction between the chemisorbed CO and OH - as the apparent hydrogen source.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mesoporous xEr 2 O 3 ·CoTiO 3 composite oxide catalysts for low temperature dehydrogenation of ethylbenzene to styrene using CO 2 as a soft oxidant

A series of mesoporous xEr 2 O 3 ·CoTiO 3 composite oxide catalysts have been prepared using template method and tested as a new type of catalyst for the oxidative dehydrogenation of ethylbenzene to styrene by using CO 2 as a soft oxidant. Among the catalysts tested, the 0.25Er 2 O 3 CoTiO 3 sample with a ratio of 1:4:4 content and calcined at 600 oC exhibited the highest ethylbenzene conversion (58%) and remarkable styrene selectivity (95%) at low temperature (450 °C).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Supermetal: SbF 5 -mediated methane oxidation occurs by C–H activation and isobutane oxidation occurs by hydride transfer

Sb V F 5 is generally assumed to oxidize methane through a methanium-to-methyl cation mechanism. Yet, experimentally no H 2 is observed, and the mechanism of methane oxidation has remained unsolved for several decades. To solve this problem, density functional theory calculations with multiple chemical models (mononuclear and dinuclear) were used to examine methane oxidation by Sb V F 5 in the presence of CO leading to the methyl acylium cation ([CH 3 CO] + ). While there is a low barrier for methane protonation by [Sb V F 6 ] - [H] + (the combination of Sb V F 5 and HF) to give the [Sb V F 5 ] - [CH 5 ] + ion pair, H 2 dissociation is a relatively high energy process, even with CO assistance, and so this protonation pathway is reversible. While Sb-mediated hydride transfer has a reasonable barrier, the C–H activation/σ-bond metathesis mechanism with the formation of an Sb V –Me intermediate is lower in energy. This pathway leads to the acylium cation by functionalization of the Sb V –Me intermediate with CO and is consistent with no observation of H 2 . Because this C–H activation/metal-alkyl functionalization pathway is higher in energy than methane protonation, it is also consistent with the experimentally observed methane hydrogen-to-deuterium exchange. This is the first time that evidence is presented demonstrating that Sb V F 5 acts beyond a Bronsted superacid and involves C–H activation with an organometallic intermediate. In contrast to methane, due to the much lower carbocation hydride affinity, isobutane significantly favors hydride transfer to give the tert -butyl carbocation with concomitant Sb V to Sb III reduction. In this mechanism, the resulting highly acidic Sb V –H intermediate provides a route to H 2 through protonation of isobutane, which is constant with experiments and resolves the longstanding enigma of different experimental results for methane versus isobutane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Observing the colloidal stability of iron oxide nanoparticles in situ

Colloidal processes such as nucleation, growth, ripening, and dissolution are fundamental to the synthesis and application of engineered nanoparticles, as well as numerous natural systems. In nanocolloids consisting of a dispersion of nanoparticles in solution, colloidal stability is in?uenced by factors including the particle surface facet and capping layer, and local temperature, chemistry, and acidity. In this paper, we investigate colloidal stability through the real-time manipulation of nanoparticles using in situ liquid cell Scanning Transmission Electron Microscopy (STEM). In a distribution of uniform iron oxide nanoparticles, we use the electron beam to precisely control the local chemistry of the solution and observe the critical role that surface chemistry plays in nanoparticle stability. By functionalizing the nanoparticle surfaces with charged amino acids and peptides, stability can be tuned to promote dissolution, growth, or agglomeration, either permanently or reversibly. STEM imaging is used to quantify kinetics of individual nanoparticles subject to local variations in chemistry. These measurements of dissolution and growth rates of iron oxide nanoparticles provide insights into nanoparticle stability relevant to synthesis and functionalization for biomedical applications.

Hufschmid, Ryan D.↗
DOE OSTI2020

Combined Plasmonic Au-nanoparticle and Conducting Metal Oxide High-temperature Optical Sensing with LSTO

<span style="color: rgba(0, 0, 0, 0.79); font-family: &quot;Source Sans Pro&quot;, source-sans-pro, museo_sans300, museo-sans, Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);">Fiber optic sensor technology offers several advantages for harsh-environment applications. However, the development of optical gas sensing layers that are stable under harsh environmental conditions is an ongoing research challenge. In this work, electronically conducting metal oxide lanthanum-doped strontium titanate (LSTO) films embedded with gold nanoparticles are examined as a sensing layer for application in reducing gas flows at high temperature (600–800 °C). A strong localized surface plasmon resonance (LSPR) based response to hydrogen is demonstrated in the visible region of the spectrum, while a Drude free electron-based response is observed in the near-IR. Characteristics of these responses are studied both on planar glass substrates and on silica fibers. Charge transfer between the oxide film and the gold nanoparticles is explored as a possible mechanism governing the Au LSPR response and is considered in terms of the corresponding properties of the conducting metal oxide-based matrix phase. Principal component analysis is applied to the combined plasmonic and free-carrier based response over a range of temperatures and hydrogen concentrations. It is demonstrated that the combined visible and near-IR response of these films provides improved versatility for multiwavelength interrogation, as well as improved discrimination of important process parameters (concentration and temperature) through application of multivariate analysis techniques.</span>

Wuenschell, Jeffrey K.↗
DOE OSTI2020

Lithium oxidation and electrolyte decomposition at Li-metal/liquid electrolyte interfaces

In this work, we examine the evolution of events occurring when a Li metal surface is in contact with a 2 M solution of a Li salt in a solvent or mixture of solvents, via classical molecular dynamics simulations with a reactive force field allowing bond breaking and bond forming. The main events include Li oxidation and electrolyte reduction along with expansion of the Li surface layers forming a porous phase that is the basis for the formation of the solid-electrolyte interphase (SEI) components. Nucleation of the main SEI components (LiF, Li oxides, and some organics) is characterized. The analysis clearly reveals the details of these physical–chemical events as a function of time, during 20 nanoseconds. The effects of the chemistry of the electrolyte on Li oxidation and dissolution in the liquid electrolyte, and SEI nucleation and structure are identified by testing two salts: LiPF 6 and LiCF 3 SO 3 , and various solvents including ethers and carbonates and mixtures of them. The kinetics and thermodynamics of Li 6 F, the core nuclei in the LiF crystal, are studied by analysis of the MD trajectories, and via density functional theory calculations respectively. The SEI formed in this computational experiment is the “native” film that would form upon contact of the Li foil with the liquid electrolyte. As such, this work is the first in a series of computational experiments that will help elucidate the intricate interphase layer formed during battery cycling using metal anodes.

25 ENERGY STORAGE↗
DOE OSTI2021

Effect of water frustration on water oxidation catalysis in the nanoconfined interlayers of layered manganese oxides birnessite and buserite

The role of geometric frustration of water molecules on the rate of water oxidation in the nanoconfined interlayer of manganese-oxide layered materials (birnessite, buserite) is examined in a well-controlled experiment. Calcium buserite is prepared, and used in a split-batch synthetic protocol to prepare calcium birnessite, sodium buserite, and sodium birnessite, and partially dehydrated sodium birnessite. Thus, four samples are prepared in which features effecting catalytic efficiency (defect density, average manganese oxidation state) are controlled, and the main difference is the degree of hydration of the interlayer (two layers of water in buserites vs one layer of water in birnessite). Here, molecular dynamics simulations predict birnessite samples to exhibit geometric water frustration, which facilitates redox catalysis by lowering the Marcus reorganizaiton energy of electron transfer, while buserite samples exhibit traditional intermolecular hydrogen bonding among the two-layer aqeuous region, leading to slower catalytic behavior akin to redox reactions in bulk water. Water oxdiation activity is investigated using chemical and electrochemical techniques, demonstrating and quantifying the role of water frustration in enhancing catalysis. Calculation and experiment demonstrate dehydrated sodium birnessite to be most effective, and calcium buserite the least effective, with a difference in electrocatlytic overpotential of ~750 mV and a ~20-fold difference in turnover number.

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

FEFOS: a method to derive oxide formation energies from oxidation states

Herein we report an interpretable, computationally efficient method to forecast formation energies from oxidation states of binary oxides from unary oxide entries in Materials Project. This new method is envisioned to guide inverse catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Use of Au@Void@TiO 2 yolk-shell nanostructures to probe the influence of oxide crystallinity on catalytic activity for low-temperature oxidations

A series of Au@Void@TiO 2 yolk-shell structures were synthesized and characterized, and their catalytic activity was tested for the oxidation of carbon monoxide. The target of this study was to evaluate the effects of (1) the crystallinity of the TiO 2 shell and (2) the presence of titanate phases. Transmission electron microscopy and X-ray diffraction data show that increasing calcination temperatures, from 850 to 1250 K, leads to the formation of larger titania crystallites. These crystallites are typically in the form of anatase, but some rutile is also made at high temperatures. The general yolk-shell nanostructures retain their basic characteristics upon calcination and upon treatment with HCl (used to remove the titanate phases), but a few structural and chemical changes do take place: (1) the void-space diameter is reduced by approximately 10% when going from T Calc = 850 K to T Calc = 1250 K, a change that is accompanied by a decrease in the surface area (estimated from N 2 adsorption-desorption isotherms); (2) the shell thickness remains unaffected by either calcination or HCl treatment; (3) the pore volume also remains approximately constant with increasing calcination temperature in the catalysts free of titanates but diminishes significantly in the samples with titanate phases; (4) the mesoporosity is minimal in all yolk-shell nanostructures but more noticeable with the pure TiO 2 shells; (5) the titanates have high Na content (measured by X-ray photoelectron spectroscopy), but that Na is fully removed upon treatment with HCl; (6) no Ti 3+ was detectable in any of the samples, but silica, together with C and (minor amounts of) N, was present in all; (7) all Au is in metallic form; (8) two temperature regimes were observed for the catalytic oxidation of CO, as reported for other similar samples in the past, an Arrhenius regime around or above room temperature, and a cryogenic range going to temperatures as low as 120 K; (9) the latter regime is only seen with the samples containing titanate phases; (10) the titanates seem to also aid in the oxidation at higher temperatures; and (11) in general, increasing titania crystallinity leads to a decrease the catalytic activity.

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

Anoxic photogeochemical oxidation of manganese carbonate yields manganese oxide

The oxidation states of manganese minerals in the geological record have been interpreted as proxies for the evolution of molecular oxygen in the Archean eon. In this paper we report that an Archean manganese mineral, rhodochrosite (MnCO 3 ), can be photochemically oxidized by light under anoxic, abiotic conditions. Rhodochrosite has a calculated bandgap of about 5.4 eV, corresponding to light energy centering around 230 nm. Light at that wavelength would have been present on Earth’s surface in the Archean, prior to the formation of stratospheric ozone. We show experimentally that the photooxidation of rhodochrosite in suspension with light centered at 230 nm produced H 2 gas and manganite (γ-MnOOH) with an apparent quantum yield of 1.37 × 10 –3 moles hydrogen per moles incident photons. Our results suggest that manganese oxides could have formed abiotically on the surface in shallow waters and on continents during the Archean eon in the absence of molecular oxygen.

58 GEOSCIENCES↗