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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Enhanced CO 2 Methanation Activity of Sm 0.25 Ce 0.75 O 2-δ –Ni by Modulating the Chelating Agents-to-Metal Cation Ratio and Tuning Metal–Support Interactions

Highly active and selective CO 2 methanation catalysts are critical to CO 2 upgrading, synthetic natural gas production, and CO 2 emission reduction. Wet impregnation is widely used to synthesize oxide-supported metallic nanoparticles as the catalyst for CO 2 methanation. However, as the reagents cannot be homogeneously mixed at an atomic level, it is challenging to modulate the microstructure, crystal structure, chemical composition, and electronic structure of catalysts via wet impregnation. In this work, a scalable and straightforward catalyst fabrication approach has been designed and validated to produce Sm 0.25 Ce 0.75 O 2-δ -supported Ni (SDC–Ni) as the CO 2 methanation catalyst. By varying the chelating agents-to-total metal cations ratio (C/I ratio) during the catalyst synthesis, we can readily and simultaneously modulate the microstructure, metallic surface area, crystal structure, chemical composition, and electronic structure of SDC–Ni, consequently fine-tuning the oxide–support interactions and CO 2 methanation activity. The optimal C/I ratio (0.1) leads to an SDC–Ni catalyst that facilitates C–O bond cleavage and significantly improves CO 2 conversion at 250 °C. A CO 2 -to-CH 4 yield of >73% has been achieved at 250 °C. Furthermore, a stable operation of >1500 hours has been demonstrated, and no degradation is observed. Extensive characterizations were performed to fundamentally understand how to tune and enhance CO 2 methanation activity of SDC–Ni by modulating the C/I ratio. The correlation of physical, chemical, and catalytic properties of SDC–Ni with the C/I ratio is established and thoroughly elaborated in this work. This study could be applied to tune the oxide–support interactions of various catalysts for enhancing the catalytic activity.

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

Thin Cation-Exchange Layers Enable High-Current-Density Bipolar Membrane Electrolyzers via Improved Water Transport

With suitable water dissociation (WD) catalysts, bipolar membranes (BPMs) can efficiently dissociate water into H + and OH – at the junction between anion- and cation-exchange layers (AEL and CEL, respectively). First, however, water must be transported through the AEL or CEL and thus against the outward flow of hydrated H + and OH – . This is a challenge intrinsic to the BPM architecture and limits operation to current densities typically less than ~0.5 A·cm –2 . Here we explore how water transport affects durability and performance in reference alkaline and acidic membrane electrolyzers, and we use the insight gained to design BPMs with improved water transport. We demonstrate a thin-CEL BPM (2-μm Nafion CEL|~200 nm TiO 2 |~200 nm NiO + ionomer|50 μm Sustainion AEL) which maintains a pH difference of ~14 units between the anode and cathode for current densities of up to 3.4 A·cm –2 with a total water electrolysis voltage of ~4 V and an estimated WD overpotential of ~1.5 V. Finally, such high-current-density operation is crucial for key emerging BPM applications, including in water and carbon-dioxide electrolyzers and in (regenerative) fuel cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mechanistic studies of NH 3 -assisted reduction of mononuclear Cu(ii) cation sites in Cu-CHA zeolites

Cu-Exchanged zeolites catalyze various redox reactions including the selective catalytic reduction (SCR) of NO x with NH 3 and the partial oxidation of hydrocarbons. The reduction of Cu(II) cations to Cu(I) by NH 3 alone has been observed experimentally, yet fundamental details regarding the Cu active site requirements, reaction stoichiometry, and reaction mechanism remain incompletely understood. Here, we synthesized model Cu-exchanged chabazite (Cu-CHA) zeolites with varying Cu ion densities and distributions of mononuclear Cu(II) ion site types (Cu 2+ , (CuOH) + ) and studied NH 3 -assisted Cu(II) reduction reactions using a combination of spectroscopic, titrimetric, and gas-phase product analysis methods. In situ UV-visible and X-ray absorption spectroscopies were used to monitor and quantify the transient reduction of Cu(II) to Cu(I) during exposure to NH 3 (473 K), in concert with titration methods that use NO and NH 3 co-reductants to fully reduce to the Cu(I) state any residual Cu(II) ions that remained after treatments in NH 3 alone for a given time period. The techniques provide quantitative evidence that both mononuclear Cu(II) site types are able to reduce in NH 3 alone, and do so to similar extents as a function of time. NH 3 temperature programmed reduction (TPR) revealed that the reaction stoichiometry of NH 3 -assisted reduction forms approximately one equivalent of N 2 per 6 Cu sites, regardless of Cu speciation or density, consistent with a six-electron reduction process whereby two NH 3 molecules react with six Cu(II) species to produce one N 2 molecule and six Cu(I) species. Furthermore, these findings provide new insights into the reaction pathways and mechanisms by which NH 3 alone reduces mononuclear Cu(II) sites in zeolites, which are undesired side-reactions that occur during steady-state NO x SCR and can unintentionally influence SCR-relevant spectroscopic or titrimetric characterization experiments.

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

The Influence of Current Density on Transport of Vanadium Acetylacetonate through a Cation-Exchange Membrane

Fluxes of negatively charged, neutral, and positively charged vanadium acetylacetonates through the cation-exchange membrane Nafion® 211 were measured as functions of current density. Fluxes increase in order V(C 5 H 7 O 2 ) 3 – < V(C 5 H 7 O 2 ) 3 0 < V(C 5 H 7 O 2 ) 3 + as expected for a membrane with fixed negative charges. Furthermore, the dependence of these fluxes on current density is quantitatively consistent with predictions made using independently measured conductivities in Nernst-Planck-Einstein transport equations. However, differences between the three fluxes are smaller than predicted by Donnan equilibrium calculations for Nafion 211 immersed in V(C 5 H 7 O 2 ) 3 solutions. Furthermore, specific interactions between sorbed species appear to be responsible for the relatively rapid transport of V(C 5 H 7 O 2 ) 3 – compared to V(C 5 H 7 O 2 ) 3 + .

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

Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains

We used X-ray diffraction and molecular dynamics simulations to probe the structures of two families of ionic liquids containing oligoether tails on the cations. Imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)amide ILs with side chains ranging from 4 to 10 atoms in length, including both linear alkyl and oligo-ethylene oxide tails, were prepared. Furthermore, their physical properties, such as viscosity, conductivity and thermal profile, were measured and compared for systematic trends. Consistent with earlier literature, a single ether substituent substantially decreases the viscosity of pyrrolidinium and imidazolium ILs compared to their alkyl congeners. Remarkably, as the number of ether units in the pyrrolidinium ILs increases there is hardly any increase in the viscosity, in contrast to alkylpyrrolidinium ILs where the viscosity increases steadily with chain length. Viscosities of imidazolium ether ILs increase with chain length but always remain well below their alkyl congeners. To complement the experimentally determined properties, molecular dynamics simulations were run on the two ILs with the longest ether chains. Our results point to specific aspects that could be useful for researchers designing ILs for specific applications.

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

Sigma bond activation of deuterium mediated by atomic cerium cations: Experiment and theory

Reaction of ground-state Ce + (5d 2 4f 1 ) with deuterium in a reaction cell at a pressure of 1.5–4.0 Torr and temperatures ranging from approximately 265–515 K is studied. Rate constants for formation of CeD 2 + are acquired and vary from approximately 2.8 × 10 -14 to 2.1 ×10 -13 cm 3 /s. A negative temperature dependence is observed for the measured rate constants, indicating the reaction becomes less efficient as the temperature increases, consistent with an exothermic reaction. Electronic structure calculations were performed using density functional theory (DFT) at the PBE0 level to characterize all reactant and product species as well as to generate potential energy surfaces (PESs) for the insertion reaction. This combination of experimental and theoretical results suggest that Ce + inserts into the deuterium sigma bond in an overall exothermic and barrierless process.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Naphthylbipyrrole-Containing Amethyrin Analogue: A New Ligand for the Uranyl (UO 2 2+ ) Cation

Using naphthobipyrrole as a functional building block, a new expanded porphyrin, naphtho-isoamethyrin, was prepared in 85% yield under acid catalyzed [4+2] MacDonald coupling conditions. Here, treatment of naphtho-isoamethyrin with the non- aqueous uranyl silylamide salt, [UO 2 [N(SiMe 3 ) 2 ] 2 ·2THF], yielded the corresponding uranyl complex. Upon metalation, naphtho-isoamethyrin undergoes a 2-electron oxidation to yield a formal 22 π-electron aromatic species, as inferred from 1H NMR and UV-vis spectroscopy, as well as cyclic voltammetry.

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

Redox-active on-surface polymerization of single-site divalent cations from pure metals by a ketone-functionalized phenanthroline

Metallic iron, chromium, or platinum mixing with a ketone-functionalized phenanthroline ligand on a single crystal gold surface demonstrates redox activity to a well-defined oxidation state and assembly into thermally stable, one dimensional, polymeric chains. The diverging ligand geometry incorporates redox-active sub-units and bi-dentate binding sites. The gold surface provides a stable adsorption environment and directs growth of the polymeric chains, but is inert with regard to the redox chemistry. These systems are characterized by scanning tunnelling microscopy, non-contact atomic force microscopy, and X-ray photoelectron spectroscopy under ultra-high vacuum conditions. The relative propensity of the metals to interact with the ketone group is examined, and it is found that Fe and Cr more readily complex the ligand than Pt. The formation and stabilization of well-defined transition metal single-sites at surfaces may open new routes to achieve higher selectivity in heterogeneous catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗