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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Cyclotrimerization of Acetylene in Gas Phase V + (C 2 H 2 ) n Complexes: Detection of Intermediates and Products with Infrared Spectroscopy

Infrared laser spectroscopy and mass spectrometry were used to determine the structures of intermediates and products in the single-atom-catalyzed trimerization of acetylene to form benzene. Complexes of the form V + (C 2 H 2 ) n were produced in the gas phase via laser ablation in a pulsed-nozzle source, size-selected with a mass spectrometer, and studied with infrared laser photodissociation spectroscopy. Density Functional Theory (DFT) calculations were performed in support of the experiments. Single- and doub le-acetylene complexes form V + (C 2 H 2 ) n metallacycle structures. Three-acetylene complexes exhibit a surprising dependence on the acetylene concentration, forming V + (C 2 H 2 ) 3 and (C 2 H 2 )V + (C 4 H 4 ) tri- and dimetallacycle ion structures at low concentration, and eventually V + (benzene) at higher concentrations. Finally, these observations reveal intermediates along the reaction path of acetylene cyclotrimerization to benzene.

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

In Situ Characterization of Mesoporous Co/CeO 2 Catalysts for the High-Temperature Water-Gas Shift

Here, mesoporous Co/CeO 2 catalysts were found to exhibit significant activity for the high-temperature water-gas shift (WGS) reaction with cobalt loadings as low as 1 wt %. The catalysts feature a uniform dispersion of cobalt within the CeO 2 fluorite type lattice with no evidence of discrete cobalt phase segregation. In situ XANES and ambient pressure XPS experiments were used to elucidate the active state of the catalysts as partially reduced cerium oxide doped with oxidized cobalt atoms. In situ XRD and DRIFTS experiments suggest facile cerium reduction and oxygen vacancy formation, particularly with lower cobalt loadings. In situ DRIFTS analysis also revealed the presence of surface carbonate and bidentate formate species under reaction conditions, which may be associated with additional mechanistic pathways for the WGS reaction. Deactivation behavior was observed with higher cobalt loadings. XANES data suggest the formation of small metallic cobalt clusters at temperatures above 400 °C may be responsible. Notably, this deactivation was not observed for the 1% cobalt loaded catalyst, which exhibited the highest activity per unit of cobalt.

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

Integrated Reference Electrodes in Anion-Exchange-Membrane Electrolyzers: Impact of Stainless-Steel Gas-Diffusion Layers and Internal Mechanical Pressure

Alkaline-membrane electrolyzers operating in pure water might provide scalable low-cost H 2 production but currently lag in performance and durability compared to commercial technologies. Typically, membrane–electrode assemblies (MEAs) are optimized in electrolyzers by changing one parameter at a time and assessing the resulting system performance via two-electrode polarization and impedance measurements. These approaches are limited in their ability to assign performance changes and durability to specific electrodes or processes. We integrate a reference electrode with the MEA to separate anode and cathode responses in both polarization and impedance measurements. Here we illustrate the power of the approach by showing how the fiber diameter of stainless-steel gas-diffusion layers (GDLs) affects performance solely at the anode, while changing the thickness of the cathode GDL simultaneously affects the performance of the anode and cathode due to changes in internal pressure from mechanical compression. This finding was obscured in conventional two-electrode measurements. The work thus guides both high-performance alkaline-membrane water-electrolyzer development and illustrates a useful strategy to study structure–activity relationships in the MEA.

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

A Structure Function Model Recovers the Many Formulations for Air-Water Gas Transfer Velocity: Air-Water Gas Transfer

Two ideas regarding the structure of turbulence near a clear air-water interface are used to derive a waterside gas transfer velocity kL for sparingly and slightly soluble gases. The first is that k L is proportional to the turnover velocity described by the vertical velocity structure function D ww (r), where r is separation distance between two points. The second is that the scalar exchange between the air-water interface and the waterside turbulence can be suitably described by a length scale proportional to the Batchelor scale lB=ηSc -1/2 , where Sc is the molecular Schmidt number and η is the Kolmogorov microscale defining the smallest scale of turbulent eddies impacted by fluid viscosity. Using an approximate solution to the von Kármán-Howarth equation predicting D ww (r) in the inertial and viscous regimes, prior formulations for k L are recovered including (i) k L =$\sqrt{2/15}$Sc -1/2 $v$, v K is the Kolmogorov velocity defined by the Reynolds number v K η/ν = 1 and ν is the kinematic viscosity of water; (ii) surface divergence formulations; (iii) k L ∝ SC -1/2 u * , where u * is the waterside friction velocity; (iv) k L ∝ Sc -1/2 $\sqrt{gv/u_*}$ for Keulegan numbers exceeding a threshold needed for long-wave generation, where the proportionality constant varies with wave age, g is the gravitational acceleration; and (v) k L = $\sqrt{2/15}$Sc -1/2 (vgβ o q o ) 1/4 in free convection, where qo is the surface heat flux and β o is the thermal expansion of water. The work demonstrates that the aforementioned k L formulations can be recovered from a single structure function model derived for locally homogeneous and isotropic turbulence.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Direct observation of C 60 - nano-ion gas phase ozonation via ion mobility-mass spectrometry

Improved methods to probe the reactivity of nano-ions, such as C 60 -, would find utility in nanochemistry, combustion chemistry, and in generally understanding the behavior of matter at the nanometer scale. Here, we demonstrate that ion mobility-mass spectrometry (IM-MS) with a low-field differential mobility analyzer can be used to probe nano-ion reaction kinetics. We used the developed IM-MS approach to examine the gas phase reactivity of C 60 - ions with ozone at atmospheric pressure. Experimental results show that ozonation of C 60 - mainly leads to the formation of C 60 O n -. The controlled reaction time within the ion mobility instrument enables calculation of ozonation reaction rates and assuming oxygen atoms are added sequentially, we find that the reaction rate between C 60 - and O 3 is near the collision controlled limit. We propose an exponentially decaying reaction rate coefficient expression to describe ozonation leading to the addition of >20 oxygen atoms. At high ozone concentrations, CO or CO 2 loss from C 60 O n - is additionally observed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Solving kinetic equations with adaptive mesh in phase space for rarefied gas dynamics and plasma physics (Invited)

The paper describes an Adaptive Mesh in Phase Space (AMPS) technique for solving kinetic equations with deterministic mesh-based methods. The AMPS technique allows automatic generation of adaptive Cartesian mesh in both physical and velocity spaces using a Tree-of-Trees data structure. We illustrate advantages of AMPS for simulations of rarefied gas dynamics and electron kinetics on low temperature plasmas. In particular, we consider formation of the velocity distribution functions in hypersonic flows, particle kinetics near oscillating boundaries, and electron kinetics in a radio-frequency sheath. AMPS provide substantial savings in computational cost and increased efficiency of the mesh-based kinetic solvers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Dissociative electron attachment to the gas-phase nucleobase hypoxanthine

We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C{sub 5}H{sub 4}N{sub 4}O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp − H) anion (C{sub 5}H{sub 3}N{sub 4}O{sup −}) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp − NH){sup −}, C{sub 4}H{sub 3}N{sub 4}{sup −}/C{sub 4}HN{sub 3}O{sup −}, C{sub 4}H{sub 2}N{sub 3}{sup −}, C{sub 3}NO{sup −}/HC(HCN)CN{sup −}, OCN{sup −}, CN{sup −}, and O{sup −}. Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗