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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Diverse hydrocarbon biosynthetic enzymes can substitute for olefin synthase in the cyanobacterium Synechococcus sp. PCC 7002

Cyanobacteria are among only a few organisms that naturally synthesize long-chain alkane and alkene hydrocarbons. Cyanobacteria use one of two pathways to synthesize alka/enes, either acyl-ACP reductase (Aar) and aldehyde deformylating oxygenase (Ado) or olefin synthase (Ols). The genomes of cyanobacteria encode one of these pathways but never both, suggesting a mutual exclusivity. We studied hydrocarbon pathway compatibility using the model cyanobacterium Synechococcus sp. PCC 7002 (S7002) by co-expressing Ado/Aar and Ols and by entirely replacing Ols with three other types of hydrocarbon biosynthetic pathways. We find that Ado/Aar and Ols can co-exist and that slower growth occurs only when Ado/Aar are overexpressed at 38 °C. Furthermore, Ado/Aar and the non-cyanobacterial enzymes UndA and fatty acid photodecarboxylase are able to substitute for Ols in a knockout strain and conditionally rescue slow growth. Production of hydrocarbons by UndA in S7002 required a rational mutation to increase substrate range. Expression of the non-native enzymes in S7002 afforded unique hydrocarbon profiles and alka/enes not naturally produced by cyanobacteria. This suggests that the biosynthetic enzyme and the resulting types of hydrocarbons are not critical to supporting growth. Exchanging or mixing hydrocarbon pathways could enable production of novel types of CO 2 -derived hydrocarbons in cyanobacteria.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

A two-stage strategy for upcycling chlorine-contaminated plastic waste

Abstract Chemical upcycling of polyolefin plastic waste to lubricant, wax and fuel-range hydrocarbons over metal-based catalysts is a crucial technological solution to the enormous environmental threat posed by plastic waste. However, currently available methods are incompatible with chlorine-contaminated feedstocks. Here we report a two-stage strategy for upcycling chlorine-contaminated polypropylene. First, magnesia–alumina mixed oxide at 30 bar H 2 and 250 °C serves as a chlorine trap by rapidly forming solid chloride, resulting in nearly complete chlorine extraction from the polyolefin melt. This enables the upcycling of plastic waste with up to 10% polyvinyl chloride content to lubricants over ruthenium-based catalysts, in the second stage. The strategy is also applicable to chlorinated aromatics and alkanes. The proposed strategy renders hydrocracking and hydrogenolysis catalysts less sensitive to the chlorine impurities in feedstocks while eliminating HCl emissions and chlorine contamination in products. It could incentivize further progress in plastics upcycling.

Environmental Sciences & Ecology↗
DOE OSTI2015

Temperature effects on nanostructure and mechanical properties of single-nanoparticle thick membranes.

In this study, the properties of mechanically stable single-nanoparticle (NP)-thick membranes have largely been studied at room temperature. How these membranes soften as nanoparticle ligands disorder with increasing temperature is unknown. Molecular dynamics simulations are used to probe the temperature dependence of the mechanical and nanostructural properties of nanoparticle membranes made of 6 nm diameter Au nanoparticles coated with dodecanethiol ligands and terminated with either methyl (CH 3 ) or carboxyl (COOH) terminal groups. For methyl-terminated ligands, interactions along the alkane chain provide mechanical stiffness, with a Young's modulus of 1.7 GPa at 300 K. For carboxyl-terminated chains, end-group interactions are significant, producing stiffer membranes at all temperatures, with a Young's modulus of 3.8 GPa at 300 K. For both end-group types, membrane stiffness is reduced to zero at about 400 K. Ligand structure and mechanical properties of membranes at 300 K that have been annealed at 400 K are comparable to samples that do not undergo thermal annealing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Gamma-radiolytic stability of new methylated TODGA derivatives for minor actinide recycling

The stability against gamma radiation of MeTODGA (methyl tetraoctyldiglycolamide) and Me2TODGA (dimethyl tetraoctyldiglycolamide), derivatives from the well-known extractant TODGA (N,N,N',N';-tetraoctyldiglycolamide), were studied and compared. Solutions of MeTODGA and Me2TODGA in alkane diluents were subjected to 60Co γ-irradiation in the presence and absence of nitric acid and analyzed using LC-MS to determine their rates of radiolytic concentration decrease, as well as to identify radiolysis products. The results of product identification from three different laboratories are compared and found to be in good agreement. The diglycolamide (DGA) concentrations decreased exponentially with increasing absorbed dose. The MeTODGA degradation rate constants (dose constants) were uninfluenced by the presence of nitric acid, but the acid increased the rate of degradation for Me2TODGA. The degradation products formed by irradiation are also initially produced in greater amounts in acid-contacted solution, but products may also be degraded by continued radiolysis. As a result, the identified radiolysis products suggest that the weakest bonds are those in the diglycolamide center of these molecules.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides

The well-defined single-site silica-supported tungsten complex [( Si–O–)W(Me) 5 ], 1 , is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at -78 °C into a partially alkylated tungsten hydride, 4 , as characterized by 1 H solid-state NMR and IR spectroscopies. Species 4 , upon warming to 150 °C, displays the highest catalytic activity for propane metathesis yet reported. DFT calculations using model systems support the formation of [( Si–O–)WH 3 (Me) 2 ], as the predominant species at -78 °C following several elementary steps of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer). Rearrangement of 4 occuring between -78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [( Si–O–)WH 3 ( CH 2 )], as determined by solid-state 1 H and 13 C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Highly dispersed buckybowls as model carbocatalysts for C–H bond activation

Buckybowl fractions dispersed on mesoporous silica constitute an ideal model for studying the catalysis of graphitic forms of carbon since the dispersed carbon nanostructures contain a high ratio of edge defects and curvature induced by non-six-membered rings. Dispersion of the active centers on an easily accessible high surface area material allowed for high density of surface active sites associated with oxygenated structures. This report illustrates a facile method of creating model polycyclic aromatic nano-structures that are not only active for alkane C-H bond activation and oxidative dehydrogenation but also can be practical catalysts to be eventually used in industry.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Direct photoisomerization of CH 2 I 2 vs. CHBr 3 in the gas phase: a joint 50 fs experimental and multireference resonance-theoretical study

Femtosecond transient absorption measurements powered by 40 fs laser pulses reveal that ultrafast isomerization takes place upon S1 excitation of both CH2I2 and CHBr3 in the gas phase. The photochemical conversion process is direct and intramolecular, i.e., it proceeds without caging media that have long been implicated in the photo-induced isomerization of polyhalogenated alkanes in condensed phases. Using complete active space second order perturbation theory (CASPT2) calculations, we investigate the structure of the photochemical reaction paths connecting the photoexcited species to their corresponding isomeric forms. Unconstrained minimum energy paths computed starting from the S1 Franck-Condon points lead to S1/S0 conical intersections, which directly connect the parent CHBr3 and CH2I2 molecules to their isomeric forms. Changes in the chemical bonding picture along the S1/S0 isomerization reaction path are described using multireference average coupled pair functional (MRACPF) calculations in conjunction with natural resonance theory (NRT) analysis. These calculations reveal a complex interplay between covalent, radical, ylidic, and ion-pair dominant resonance structures throughout the nonadiabatic photochemical isomerization processes described in this work.

Borin, Veniamin A.↗
DOE OSTI2016

Understanding oxidative dehydrogenation of ethane on Co 3 O 4 nanorods from density functional theory

Co 3 O 4 is a metal oxide catalyst with weak, tunable M–O bonds promising for catalysis. Here, density functional theory (DFT) is used to study the oxidative dehydrogenation (ODH) of ethane on Co 3 O 4 nanorods based on the preferred surface orientation (111) from the experimental electron-microscopy image. The pathway and energetics of the full catalytic cycle including the first and second C–H bond cleavages, hydroxyl clustering, water formation, and oxygen-site regeneration are determined. We find that both lattice O and Co may participate as active sites in the dehydrogenation, with the lattice-O pathway being favored. Here, we identify the best ethane ODH pathway based on the overall energy profiles of several routes. We identify that water formation from the lattice oxygen has the highest energy barrier and is likely a rate-determining step. This work of the complete catalytic cycle of ethane ODH will allow further study into tuning the surface chemistry of Co 3 O 4 nanorods for high selectivity of alkane ODH reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Functionality and molecular weight distribution of red oak lignin before and after pyrolysis and hydrogenation

In this paper, three red oak derived lignin samples: 1. lignin extracted from red oak chips using γ-valerolactone (GVL lignin), 2. lignin extracted from the pyrolysis oil of red oak chips by fractionation and water extraction (pyrolytic lignin) and 3. pyrolytic lignin hydrogenated over Ru/C (hydrogenated pyrolytic lignin), were analyzed by FT-ICR MS, NMR, and GPC. More than 1100 distinct molecular weights were observed by FT-ICR MS of the lignin streams while changes in the O/C and H/C ratios suggested the dehydration of hydroxylated sidechains from pyrolysis and partial saturation of the compounds from hydrogenation. The relative average molecular weight of the lignin determined by GPC decreased five-fold after pyrolysis. Quantitative 13 C, HSQC, and HMBC NMR revealed a decrease in the C–O aliphatics from pyrolysis potentially forming alkane, alkene, and carbonyl functionalities. Finally, the aldehydes and ketones were highly reactive during hydrogenation and may potentially be responsible for coke formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Selective Conversion of Bio-Derived Ethanol to Renewable BTX over Ga-ZSM-5

Selective conversion of bio-derived ethanol to benzene, toluene and xylenes (BTX) is desirable for producing renewable BTX. Here in this work, we show that addition of Ga to H-ZSM-5 leads to two-fold increase in the BTX yield as compared with H-ZSM-5 when ethanol is converted over these zeolites at 450 °C and ambient pressure. Besides promoting BTX formation, Ga also plays an important role in enhancing molecular hydrogen production and suppressing hydrogen transfer reactions for light alkane formation. The ion exchange synthesis of Ga-ZSM-5 results in the majority of Ga at the outer surface of zeolite crystals as extra-zeolitic Ga 2 O 3 particles and only a small fraction of Ga exchanging with the Brønsted acid sites which appears to be responsible for higher ethanol conversion to BTX. The interface between H-ZSM-5 and Ga 2 O 3 particles is not active since H-ZSM-5 and physical mixture of β-Ga 2 O 3 /H-ZSM-5 furnish almost identical product distribution. Hydrogen reduction of the physical mixtures facilitates movement of Ga to ion exchange locations and dramatically increases BTX yield becoming comparable to those obtained over ion-exchanged Ga-ZSM-5, suggesting that exchanged Ga(III) cations are responsible for the increased BTX production. Linear correlation between BTX site time yield and exchanged Ga sites further confirms that Ga occupying cationic sites are active sites for enhancing BTX formation. Reduction of physical mixtures (β-Ga 2 O 3 /H-ZSM-5) also provides an economical and environmentally friendly non-aqueous method for large scale catalyst synthesis without sacrificing catalyst performance for ethanol conversion application.

09 BIOMASS FUELS↗
DOE OSTI2017

Identifying the first folded alkylbenzene via ultraviolet, infrared, and Raman spectroscopy of pentylbenzene through decylbenzene

The conformational preferences of pentyl- through decylbenzene are studied under jet-cooled conditions in the gas phase. Laser-induced fluorescence excitation spectra, fluorescence-dip infrared spectra in the alkyl CH stretch region, and Raman spectra are combined to provide assignments for the observed conformers. Density functional theory calculations at the B3LYP-D3BJ/def2TZVP level of theory provide relative energies and normal mode vibrations that serve as inputs for an anharmonic local mode theory introduced in earlier work on alkylbenzenes with n = 2–4. This model explicitly includes anharmonic mixing of the CH stretch modes with the overtones of scissors/bend modes of the CH 2 and CH 3 groups in the alkyl chain, and is used to assign and interpret the single-conformation IR spectra. In octylbenzene, a pair of LIF transitions shifted -92 and -78 cm -1 from the all-trans electronic origin have unique alkyl CH stretch transitions that are fit by the local model to a g1g3g4 conformation in which the alkyl chain folds back over the aromatic ring π cloud. Its calculated energy is only 1.0 kJ mol -1 above the all-trans global minimum. This fold is at an alkyl chain length less than half that of the pure alkanes (n = 18), consistent with a smaller energy cost for the g1 dihedral and the increased dispersive interaction of the chain with the π cloud. Local site frequencies for the entire set of conformers from the local mode model show ‘edge effects’ that raise the site frequencies of CH 2 (1) and CH 2 (2) due to the phenyl ring and CH 2 (n - 1) due to the methyl group. The g1g3g4 conformer also shows local sites shifted up in frequency at CH 2 (3) and CH 2 (6) due to interaction with the π cloud.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Mapping a stable solvent structure landscape for aprotic Li–air battery organic electrolytes

Electrolyte instability is one of the greatest impediments that must be overcome for the practical development of rechargeable aprotic Li–air batteries. In this work, we establish a comprehensive framework for evaluation of the stability of potential organic electrolytes for aprotic Li–air batteries that is based on four key descriptors: Bond dissociation energy, deprotonation free energy (i.e., Acidity), Nucleophilic substitution free energy, and Electrochemical oxidation/reduction. These parameters were calculated for several classes of organic compounds. The chemical stability of the molecules was studied experimentally under conditions designed to mimic the aprotic Li–air battery environment (heating in the presence of excess KO2 and Li2O2). In general, the calculated and experimental data agreed well for alkanes, alkenes, ethers, aromatics, carbonates, and S-containing and N-containing compounds. Using this dataset, we identified functional groups and other structural features of organic molecules that may be suitable for aprotic Li–air battery electrolyte design.

Feng, Shuting↗
DOE OSTI2018

Ethane dehydrogenation on pristine and AlO x decorated Pt stepped surfaces

In this work, ethane dehydrogenation on pristine and AlO x decorated Pt surfaces was studied using density functional theory (DFT) calculations and reaction kinetics experiments. Following the study of adsorption of fourteen distinct C 2 H x and CH x species, the whole reaction network for ethane dehydrogenation on the terrace and the step of the pristine Pt(433) surface was systematically analyzed using DFT. We show that the under-coordinated step edge sites bind C 2 H x and CH x species more strongly than terrace sites. These under-coordinated step sites facilitate deep dehydrogenation, resulting in accumulation of coke precursors on the surface and catalyst deactivation. We demonstrate that by decorating the step with AlO x species the step edge sites can be blocked, leading to substantial suppression of deep dehydrogenation and coke formation. These findings were corroborated by reaction kinetics experiments where a four-fold enhancement of the turnover frequency for ethylene formation was measured on 10-cycle atomic layer deposited (ALD) alumina overcoated Pt/γ-Al 2 O 3 catalyst compared to Pt/γ-Al 2 O 3 without decoration with ALD-alumina. Our results suggest that AlO x decorated Pt is a promising catalyst for alkane dehydrogenation and could have applications, including in endothermic cooling in hypersonic flights.

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

Porous liquid zeolites: hydrogen bonding-stabilized H-ZSM-5 in branched ionic liquids

Porous liquids, as a newly emerging type of porous material, have great potential in gas separation and storage. However, the examples and synthetic strategies reported so far likely represent only the tip of the iceberg due to the great difficulty and challenge in engineering permanent porosity in liquid matrices. By taking advantage of the hydrogen bonding interaction between the alkane chains of branched ionic liquids and the Brønsted sites in H-form zeolites, as well as the mechanical bond of the long alkyl chain of the cation penetrated into the zeolite channel at the interface, the H-form zeolites can be uniformly stabilized in branched ionic liquids to form porous liquid zeolites, which not only significantly improve their gas sorption performance, but also change the gas sorption–desorption behavior because of the preserved permanent porosity. Furthermore, such a facile synthetic strategy can be extended to fabricate other types of H-form zeolite-based porous liquids by taking advantage of the tunability of the counter-anion (e.g., NTf 2 - , BF 4 - , EtSO 4 - , etc.) in branched ionic liquids, thus opening up new opportunities for porous liquids for specific applications in energy and environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Carbon chain shape selectivity by the mouse olfactory receptor OR-I7

The rodent OR-I7 is an olfactory receptor exemplar activated by aliphatic aldehydes such as octanal. Normal alkanals shorter than heptanal bind OR-I7 without activating it and hence function as antagonists in vitro. We report a series of aldehydes designed to probe the structural requirements for aliphatic ligand chains too short to meet the minimum approximate 6.9 Å length requirement for receptor activation. Experiments using recombinant mouse OR-I7 expressed in heterologous cells show that in the context of short aldehyde antagonists, OR-I7 prefers binding aliphatic chains without branches, though a single methyl on carbon-3 is permitted. The receptor can accommodate a surprisingly large number of carbons (e.g. ten in adamantyl) as long as the carbons are part of a conformationally constrained ring system. A rhodopsin-based homology model of mouse OR-I7 docked with the new antagonists suggests that small alkyl branches on the alkyl chain sterically interfere with the hydrophobic residues lining the binding site, but branch carbons can be accommodated when tied back into a compact ring system like the adamantyl and bicyclo[2.2.2]octyl systems.

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

Real-time degradation dynamics of hydrated per- and polyfluoroalkyl substances (PFASs) in the presence of excess electrons

Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals that are harmful to both the environment and human health. In this work, using self-interaction-corrected Born–Oppenheimer molecular dynamics simulations, we provide the first real-time assessment of PFAS degradation in the presence of excess electrons. In particular, we show that the initial phase of the degradation involves the transformation of an alkane-type C–C bond into an alkene-type C[double bond, length as m-dash]C bond in the PFAS molecule, which is initiated by the trans elimination of fluorine atoms bonded to these adjacent carbon atoms.

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

Synthesis of aviation fuel from bio-derived isophorone

Using photochemical [2 + 2] cycloaddition, a cyclobutane dione was generated from isophorone, a condensate of bio-acetone. Additionally, hydrodeoxygenation of the dione yielded a mixture of polycyclic alkanes, whose high energy density is appropriate for high perfomance aviation applications. This work outlines a light-based approach to increase the energy density of a potential renewable carbon aviation fuel in high yields and high carbon efficiency without sacrificing performance.

09 BIOMASS FUELS↗
DOE OSTI2020

The effect of strong metal–support interaction (SMSI) on Pt–Ti/SiO 2 and Pt–Nb/SiO 2 catalysts for propane dehydrogenation

In this study, we show how strong metal–support interaction (SMSI) oxides in Pt–Nb/SiO 2 and Pt–Ti/SiO 2 affect the electronic, geometric and catalytic properties for propane dehydrogenation. Transmission electron microscopy (TEM), CO chemisorption, and decrease in the catalytic rates per gram Pt confirm that the Pt nanoparticles were partially covered by the SMSI oxides. X-ray absorption near edge structure (XANES), in situ X-ray photoelectron spectroscopy (XPS), and resonant inelastic X-ray scattering (RIXS) showed little change in the energy of Pt valence orbitals upon interaction with SMSI oxides. The catalytic activity per mol of Pt for ethylene hydrogenation and propane dehydrogenation was lower due to fewer exposed Pt sites, while turnover rates were similar. The SMSI oxides, however, significantly increase the propylene selectivity for the latter reaction compared to Pt/SiO 2 . In the SMSI catalysts, the higher olefin selectivity is suggested to be due to the smaller exposed Pt ensemble sites, which result in suppression of the alkane hydrogenolysis reaction; while the exposed atoms remain active for dehydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗