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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Steering the methanol steam reforming reactivity of intermetallic Cu–In compounds by redox activation: stability vs . formation of an intermetallic compound–oxide interface

To compare the inherent methanol steam reforming properties of intermetallic compounds and a corresponding intermetallic compound–oxide interface, we selected the Cu–In system as a model to correlate the stability limits, self-activation and redox activation properties with the catalytic performance. Three distinct intermetallic Cu–In compounds – Cu 7 In 3 , Cu 2 In and Cu 11 In 9 – were studied both in an untreated and redox-activated state resulting from alternating oxidation–reduction cycles. The stability of all studied intermetallic compounds during methanol steam reforming (MSR) operation is essentially independent of the initial stoichiometry and all accordingly resist substantial structural changes. The inherent activity under batch MSR conditions is highest for Cu 2 In, corroborating the results of a Cu 2 In/In 2 O 3 sample accessed through reactive metal–support interaction. Under flow MSR operation, Cu 7 In 3 displays considerable deactivation, while Cu 2 In and Cu 11 In 9 feature stable performance at simultaneously high CO 2 selectivity. Here, the missing significant self-activation is most evident in the operando thermogravimetric experiments, where no oxidation is detected for any of the intermetallic compounds. In situ X-ray diffraction allowed us to monitor the partial decomposition and redox activation of the Cu–In intermetallic compounds into Cu 0.9 In 0.1 /In 2 O 3 (from Cu 7 In 3 ), Cu 7 In 3 /In 2 O 3 (from Cu 2 In) and Cu 7 In 3 /Cu 0.9 In 0.1 /In 2 O 3 (from Cu 11 In 9 ) interfaces with superior MSR performance compared to the untreated samples. Although the catalytic profiles appear surprisingly similar, the latter interface with the highest indium content exhibits the least deactivation, which we explain by formation of stabilizing In 2 O 3 patches under MSR conditions.

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

pH dependent reactivity of boehmite surfaces from first principles molecular dynamics

pH dependent interfacial chemistry depends upon the distribution and respective pKa values of different surface active sites. This is highly relevant to the chemistry of nanoparticle morphologies that expose faces with varying surface termination. Recent synthetic advances for nanoparticles of various minerals, including AlO(OH) (boehmite), present an excellent opportunity to compare and contrast predicted surface pKa on low Miller index planes so as to reinterpret reported interfacial properties (i.e., point of zero charge – PZC) and reactivity. This work employs ab initio molecular dynamics and empirical models to predict site-specific pKa values of accurate (benchmarked) surface models of boehmite. Using the different surface site populations, the PZC is determined and the influence this has upon reported interfacial chemistry is described.

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

Reactivity of Zn + aq in high-temperature water radiolysis

For this work, reactivity of transients involving Zn + in high-temperature water radiolysis has been studied in the temperature range of 25–300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn 2+ ions using pulse radiolysis. The Zn + species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, H 2 O 2 and ˙H. We find that the absorption of monovalent zinc is very sensitive to the pH of the medium. An absorption maximum at 306–311 nm is most pronounced at pH 7 and the signal then decreases in acidic media where the reducing electrons are competitively captured by protons. At pH values higher than 7, hydroxo-forms of Zn 2+ are created and the maximum of the absorption signal begins to shift to the red spectral region. We find that the optical spectrum of Zn + aq cannot be fully explained in terms of a charge-transfer to solvent (CTTS) process, which was previously proposed. Reaction rates of most of the recombination reactions investigated follow the empirical Arrhenius relationship at temperatures up to 200 °C and have been determined at higher temperatures for the first time. A bimolecular disproportionation reaction of Zn + aq is not observed under the conditions investigated.

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

A crossed molecular beams and computational study on the unusual reactivity of banana bonds of cyclopropane (c-C 3 H 6 ; X 1 A$^{'}_{1}$ ) through insertion by ground state carbon atoms (C( 3 P j ))

The mechanism and chemical dynamics of the reaction of ground electronic state atomic carbon C( 3 P j ) with cyclopropane c-C 3 H 6 (X 1 A$^{'}_{1}$) have been explored by combining crossed molecular beams experiments with electronic structure calculations of the pertinent triplet C 4 H 6 potential energy surface and statistical computations of product branching ratios under single-collision conditions. The experimental findings suggest that the reaction proceeds via indirect scattering dynamics through triplet C 4 H 6 reaction intermediate(s) leading to C 4 H 5 product(s) plus atomic hydrogen via a tight exit transition state, with the overall reaction exoergicity evaluated as 231 ± 52 kJ mol –1 . The calculations indicate that C( 3 P j ) can easily insert into one of the three equivalent C–C ‘banana’ bonds of cyclopropane overcoming a low barrier of only 2 kJ mol –1 following the formation of a van der Waals reactant complex stabilized by 15 kJ mol –1 . The carbon atom insertion into one of the six C–H bonds is also feasible via a slightly higher barrier of 5 kJ mol –1 . Here, these results highlight an unusual reactivity of cyclopropane's banana C–C bonds, which behave more like unsaturated C–C bonds with a π-character than saturated σ C–C bonds, which are known to be generally unreactive toward the ground electronic state atomic carbon such as in ethane (C 2 H 6 ). The statistical theory predicts the overall product branching ratios at the experimental collision energy as 50% for 1-butyn-4-yl, 33% for 1,3-butadien-2-yl, i-C 4 H 5 , and 11% for 1,3-butadien-1-yl, n-C 4 H 5 , with i-C 4 H 5 (230 kJ mol –1 below the reactants) favored by the C–C insertion providing the best match with the experimentally observed reaction exoergicity. The C( 3 P j ) + c-C 3 H 6 reaction is predicted to be a source of C 4 H 5 radicals under the conditions where its low entrance barriers can be overcome, such as in planetary atmospheres or in circumstellar envelopes but not in cold molecular clouds. Both i- and n-C 4 H 5 can further react with acetylene eventually producing the first aromatic ring and hence, the reaction of the atomic carbon with c-C 3 H 6 can be considered as an initial step toward the formation of benzene.

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

High reactivity of mesoporous CeO 2 to dissociate chemical warfare agent sarin

We perform spectroscopic surface characterization on mesoporous ceria (CeO 2 ) under exposure of sarin gas, also known as GB. We find mesoporous CeO 2 displays extraordinary reactivity towards GB dissociation under high vacuum. The spectroscopic results combined with density functional theory (DFT) calculations suggest that the cleavage of the P–F and P–OR bonds are both possible pathways for GB to dissociate on the CeO 2 surfaces. The modeling reveals differences in dissociation pathways of GB on the crystallographic (111)- and (110)-surfaces of ceria. Here we also report some dissociation of GB on mesoporous CeO 2 under ambient conditions. The finding that mesoporous CeO 2 can degrade GB under mild conditions is encouraging and implies the strong potential of ceria-based materials to be applied in combating chemical warfare agents related to the GB series.

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

Hydrophobic pockets built in polymer micelles enhance the reactivity of Cu 2+ ions

We report the hydrophobicity-enhanced reactivity of Cu2+ ions as an ester hydrolase. Using a dipicolylamine (DPA) containing reversible addition–fragmentation chain transfer agent, the synthetic sequence, either hydrophobic or hydrophilic first in amphiphilic block copolymers of polystyrene-block-poly(N'N-dimethylacrylamide) (PS-b-PDMA), was varied to control the location of the binding motif, DPA, in the hydrophobic core or on the hydrated corona of polymer micelles. The hydrophobicity of Cu 2+ sites showed a significant impact (as large as 60 times more activity) on their catalytic efficiency towards ester hydrolase. With two different kinetic modes, including Michaelis–Menten and the reverse saturation kinetics models, the binding constant Kb of the substrates to Cu 2+ sites were quantitatively analyzed and we demonstrate that hydrophobicity favors the binding of the substrates to Cu2+ sites at polymer micelles with smaller sizes, however, K b decays exponentially with micellar diameters. Despite the diffusion barrier, hydrophobicity shows a profound impact on the catalytic rate constant kc that measures the single conversion rate of bound substrates to products. There is a 16–20 times kinetic enhancement in the hydrolase activity, completely endowed by the hydrophobic microenvironment of Cu 2+ sites compared to micelles with similar sizes. Our results indicate how the hydrophobicity of Cu 2+ -containing micelles can impact the catalytic efficiency and potentially illustrate a promising way toward the design of bioinspired catalysts.

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

Exploring the mobility of Cu in bimetallic nanocrystals to promote atomic-scale transformations under a reactive gas environment

Bimetallic nanocrystals (NCs) often show improved catalytic activities compared to their monometallic counterparts, but to optimize the performance it is crucial to understand how they behave under actual reaction conditions, i.e. in gas environments. Here, in this study, we use powder X-ray diffraction (PXRD), total scattering (TS) with pair distribution function (PDF) analysis and in situ high-resolution transmission electron microscopy (HR-TEM) to provide new insights into the atomic-scale behaviour of NC catalysts under a reactive gas environment. By investigating Au, Cu, Pd, PdCu, AuPd and AuCu NCs, we observe that the properties of bimetallic NCs differ significantly from their monometallic counterparts. While metal oxide phases formed for monometallic Pd and Cu under O 2 -exposure, bimetallic PdCu and AuCu NCs showed loss of metallic Cu in the crystalline phases after exposure to O 2 . However, upon introducing the bimetallic NCs to a reducing atmosphere, the Cu was found to reappear and reincorporate into a crystalline phase, forming the initial bimetallic structures. By combining TS, PDF analysis and in situ HR-TEM, we saw that Cu segregates to the NC surfaces or forms small CuO domains under O 2 -exposure. Our results thus indicate that the Cu mobility promotes segregation and formation of CuO along with the formation of a monometallic phase, which ultimately changes the resulting active surface sites of the nanocatalyst. Understanding the dynamical structure–property relations of nanocatalysts is key to enable rational design of efficient and robust catalysts for controlled catalytic reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The impact of gas purity on observed reactivity with NO using inductively coupled plasma tandem mass spectrometry

Interference removal in inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) is strongly dependent on the gas selected for use within the collision/reaction cell. There has been little investigation on the effects that reaction gas impurities may have on the resulting spectra. The reactivity of 60 elements was evaluated using nitric oxide (NO 99.5%) with and without a gas purifier to reduce H 2 O impurities to <100 pptV. Experiments were performed using V, Ce, Tl and Th to investigate the effects of purified NO at various flowrates (0.22–1.49 mL min -1 ). Purified NO was shown to significantly mitigate oxy-hydride interferences, improve total ion sensitivity (notable at high gas flows), and shift product distributions advantageously. The reduction in oxy-hydride species results in a product distribution favoring the major expected products, where signals were shown to increase by an order of magnitude. Reduced background and increased signal for the major expected products provides avenues for improving various analytical applications of ICP-MS/MS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Chlorine gas and anion radical reactivity in molten salts and the link to chlorobasicity

Next-generation nuclear power plants may include exciting novel designs in which molten salts are the coolant or a combination of the coolant and fuel. Whereas it is straightforward to see why having a low volatility coolant can be advantageous for safety, much is not understood about the production of volatile halogen gases as a result of radiation and even less is known about the distribution of these species at and away from interfaces. Using first principles molecular dynamics simulations, we investigate the product of the disproportionation reaction between chlorine anion radicals (nominally Cl 2 ˙ − ) in the bulk and slab configurations. We find that the product depends on the chlorobasicity of the medium. For example, in ZnCl 2 , Cl 2 forms, but in a eutectic mixture of LiCl and KCl, Cl 3 − is formed as a product. We also find that Cl 3 − prefers to form at the vapor interface and this may have implications for corrosion and reactivity. Furthermore, the mechanisms of the mobility of Cl 2 and Cl 3 − are radically different, the first one being vehicular and the second Grotthus-like. Chlorobasicity is linked to the electronic structure of the host melt; ZnCl 2 forms extended networks along which metal ions and anionic counterions have significant electronic orbital overlap forming long, linear, molecular-like constructs; the opposite is true for the alkali metal eutectic salt.

Nguyen, Hung H. [Univ. of Iowa, Iowa City, IA (Uni↗
DOE OSTI2024

Correction: Impact of lanthanide ion complexation and temperature on the chemical reactivity of N , N , N ′, N ′-tetraoctyl diglycolamide (TODGA) with the dodecane radical cation

Correction for ‘Impact of lanthanide ion complexation and temperature on the chemical reactivity of N , N , N ′, N ′-tetraoctyl diglycolamide (TODGA) with the dodecane radical cation’ by Gregory P. Horne et al. , Phys. Chem. Chem. Phys. , 2023, 25 , 16404–16413, https://doi.org/10.1039/D3CP01119D.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗