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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 OSTI2020

The interplay between surface facet and reconstruction on isopropanol conversion over SrTiO 3 nanocrystals

Strontium titanate (SrTiO 3 ) is an extensively investigated perovskite for various applications due to its optical, electrical and chemical properties. To gain an in-depth understanding of the active sites involved in heterogeneous catalysis over the broadly used SrTiO 3 (STO), we studied a model reaction, isopropanol conversion, on three differently shape-controlled nanocrystals: cube, truncated cube and dodecahedra. SEM, XRD and XPS confirmed the morphology, phase and composition of STO shapes. Low energy ion scattering (LEIS) revealed the occurrence of surface reconstruction over STO shapes during O 2 pretreatment at different temperatures. Based on the catalytic activities, scanning transmission electron microscopy images and density functional theory calculations, the step sites on STO derived from surface reconstruction were proposed to be the active sites for isopropanol conversion. This was further confirmed by steady state isotopic kinetic analysis (SSITKA) which demonstrated similar intrinsic turnover frequencies (TOFs) for the differently reconstructed STO shapes. It is concluded that the crystal facets impose an indirect effect on the catalysis of STO via controlling the degrees of surface reconstruction: the less stable STO (1 1 0) facet (dodecahedra) leads to more step sites after reconstruction and hence higher overall reaction rate than the more stable (1 0 0) facet (cube). This work highlights the important interplay between the crystal facet and surface reconstruction in controlling the nature and density of active sties and thus catalysis over complex oxides.

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

Highly selective hydrogenation of phenol to cyclohexanone over a Pd-loaded N-doped carbon catalyst derived from chitosan

A highly stable Pd-loaded N-doped carbon catalyst (ACN pd ) for phenol hydrogenation was prepared from chitosan by hydrothermal carbonization. ACN pd does not require a reduction step before catalytic use due to the Pd in the as-prepared catalyst mainly exists in the form of Pd 0 (80%). The carbon support involves N-containing groups such as pyridinic nitrogen and pyrrolic nitrogen, which could provide basic sites to adsorb phenol effectively. The as-fabricated ACN pd shows high catalytic performance with turnover frequency (TOF) of 29.34 h -1 . Accordingly, a phenol conversion of 100% and a cyclohexanone selectivity of 99.1% are achieved in 5 h at 100 °C and 1 MPa H 2 . This outstanding performance is attributed to the synergetic effects of the Pd particles, the N-functional groups, and the Lewis acid sites on the support. The carbon support presents intrinsic Lewis acid sites due to its electrophilicity, and Pd doping further increases the strength of such acid sites as it causes electron-deficient structural features. Moreover, the Lewis acid sites inhibit the over-hydrogenation from cyclohexanone to cyclohexanol. This study provides new insights into the application of functional biomass-based carbon materials as catalyst supports.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Synergistic Ru Co atomic pair with enhanced activity toward levulinic acid hydrogenation

Development of efficient metal-based catalysts is of great importance for levulinic acid (LA) hydrogenation to γ-valerolactone (GVL). The widely employed Ru-based catalysts are advantageous for H 2 dissociation, however, the steric hindrance for large Ru particles hampers their coordination to C=O moiety in LA, and thereby decreasing the activity. Herein, we report a Ru 1 Co 1 -N-C double single-atom catalyst (DSAC) with synergistic Ru and Co atomic pairs for LA hydrogenation into GVL. The Ru and Co doped zeolitic imidazole frameworks (RuCo-doped ZIF-8) precursor was rationally designed ((Ru+Co)/(Zn+Ru+Co) = 2 at.%), where the Zn node spatially isolates Ru and Co species, expanding the adjacent Ru-Co distance and facilitating the formation of the Ru-Co atomic pair upon pyrolysis, with each atom coordinated with three nitrogen atoms (N 3 -Ru 1 Co 1 -N 3 ). The Ru 1 Co 1 -N-C catalyst exhibits outstanding catalytic activity, with a turnover frequency (TOF) of 1980 h –1 , surpassing previously reported Ru-based catalysts. Experimental investigation and density functional theory (DFT) calculations reveal that the electron-rich Ru induced by less electronegative Co facilitates H 2 dissociation, while atomic Ru in dual-atomic pairs promotes C=O activation, Ru and Co atomic pairs synergistically enhancing LA conversion to GVL. In conclusion, this research will shed light on the precise control of active sites at atomic scale, and also provides a new concept for designing high-performance Ru-based catalysts towards LA hydrogenation to GVL.

Double single-atom catalysts↗
DOE OSTI2022

Vertical gradient freeze growth of detector grade CdZnTeSe single crystals

Here, we report the growth of detector grade Cd 0.9 Zn 0.1 Te 0.97 Se 0.03 (CZTS) single crystals, a recently discovered quaternary semiconductor for room temperature radiation detection, by a vertical gradient freeze (VGF) method. VGF is a comparatively low-temperature growth method and avoids relative motion between the heater and the ampoule containing the precursor materials which minimizes any thermal drift or temperature fluctuations. As a result, CZTS single crystals with superior charge transport properties has been obtained. Growth of detector-grade CZTS single crystals using VGF method has not been reported yet. X-ray spectroscopy based elemental analysis showed that the grown crystals demonstrated the desired stoichiometry required for high resolution radiation detection. Planar detectors fabricated by deposition of gold contacts (~0.07 cm 2 ) demonstrated high bulk resistivity ~10 10 Ω-cm and a very low leakage current density of 2.8 × 10 –8 A/cm 2 at a bias of 100 V when measured at room temperature. The detectors showed excellent radiation response with 100 % charge collection efficiency when exposed to 5486 keV alpha particles. The electron mobility-lifetime (μτ) product was measured to be 3 × 10 –3 cm 2 /V using a single polarity Hecht analysis which is at par with the recently reported values measured in CZTS grown using conventional Bridgman or travelling heater method. The electron mobility has been calculated to be 964 cm 2 V –1 s –1 using a time-of-flight (TOF) method, a substantial improvement over that obtained from conventionally grown CZTS single crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effect of Ni particle size on the production of renewable methane from CO 2 over Ni/CeO 2 catalyst

Production of ‘renewable Methane’ has attracted renewed research interest as a fundamental probe reaction and process for CO 2 utilization through potential use in C1 fuel production and even for future space exploration technologies. CO 2 methanation is a structure sensitive reaction on Ni/CeO 2 catalysts. To precisely elucidate the size effect of the Ni metal center on the CO 2 methanation performance, we prepared 2%Ni/CeO 2 catalysts with pre-synthesized uniform Ni particles (2, 4 and 8 nm) on a high surface area CeO 2 support. Transmission electron microscopy (TEM) and ambient pressure X-ray photo spectroscopy (AP-XPS) characterization have confirmed that the catalyst structure and chemical state was uniform and stable under reaction conditions. The 8 nm sized catalyst showed superior methanation selectivity over the 4 and 2 nm counterparts, and the methanation activity in term of TOF is 10 times and 70 times higher than for the 4 and 2 nm counterparts, respectively. Here, the DRIFTS studies revealed that the larger Ni (8 nm particles) over CeO 2 efficiently facilitated the hydrogenation of the surface formate intermediates, which is proposed as the rate determining step accounting for the excellent CO 2 methanation performance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Uranium Isotopic Ratio Measurements of U3O8 Reference Materials by Atom Probe Tomography

We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural.

Atom Probe Tomography↗
DOE OSTI2020

Evolution of solid electrolyte interphase and active material in the silicon wafer model system

Alloying anode materials for lithium-ion batteries, such as silicon (Si), are an important focus of materials research due to the demand for increased energy density for electric vehicles and stationary grid storage. However, progress towards next generation anode materials has been hindered by poor capacity retention due to the instability of the Si active material and the solid electrolyte interphase (SEI). Herein, the evolution of the active Si material and the SEI are simultaneously investigated from the perspective of chemical, structural, morphological, and electronic evolution in the Si wafer model system through its cycling life, using time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning transmission electron microscopy (STEM), atomic force microscopy (AFM), and scanning spreading resistance microscopy (SSRM). The results illustrate a dynamic evolution of the SEI and active Si material through cycling. Through an improved understanding of evolution of SEI and Si active material within the Si wafer model system, mitigation strategies may be designed to extend the lifetime of Si anodes.

25 ENERGY STORAGE↗
DOE OSTI2014

Toward a better understanding of the magnetocaloric effect: An experimental and theoretical study of MnFe{sub 4}Si{sub 3}

The intermetallic compound MnFe{sub 4}Si{sub 3} has been studied by high-resolution Time of Flight (TOF) neutron powder diffraction. MnFe{sub 4}Si{sub 3} crystallizes in the hexagonal space group P6{sub 3}/mcm with lattice constants of a=b=6.8043(4) Å and c=4.7254(2) Å at 310 K. Magnetic susceptibility measurements show clearly the magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. Magnetic structure refinements based on neutron powder diffraction data with and without external magnetic field reveal strong evidence on the origin of the large magnetocaloric effect (MCE) in this material as a partial reordering of the spins between ∼270 K and 300 K. In addition, electronic structure calculations using the self-consistent, spin-polarized Tight Binding-Linear MuffinTin Orbital (TB-LMTO) method were also accomplished to address the “coloring problem” (Mn/Fe site preference) as well as the unique ferromagnetic behavior of this intermetallic compound. - Graphical abstract: Theoretical and experimental reinvestigation of the magnetic structure of MnFe{sub 4}Si{sub 3} for a better understanding of its large magnetocaloric effect (MCE). - Highlights: • Strong magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. • MCE associated to a partial reordering of the spins between ∼270 K and 300 K. • DFT calculations show strong relation between MCE and spintronic materials.

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

Syntheses, structures, molecular and cationic recognitions and catalytic properties of two lanthanide coordination polymers based on a flexible tricarboxylate

Two lanthanide coordination polymers, namely, ([La(TTTA)(H{sub 2}O){sub 2}]·2H{sub 2}O){sub n} (La-TTTA) and [Nd(TTTA)(H{sub 2}O){sub 2}]·2H{sub 2}O){sub n} (Nd-TTTA) have been hydrothermally synthesized through the reaction of lanthanide ions (La{sup 3+} and Nd{sup 3+}) with the flexible tripodal ligand 2,2′,2″-[1,3,5-triazine-2,4,6-triyltris(thio)]tris-acetic acid (H{sub 3}TTTA). La-TTTA and Nd-TTTA are isostructural and both show three dimensional structures. La-TTTA and Nd-TTTA show good recognition of amine molecules via quenching the luminescent intensities in amines emulsions. They can also recognize Fe{sup 3+}, Cu{sup 2+}, Mg{sup 2+}, Cr{sup 3+} and Co{sup 2+} ions with the quenching the peak around 361 nm when the compounds immersed in ionic solutions. The two compounds act as efficient Lewis acid catalysts for the cyanosilylation of benzaldehyde and derivatives in high yields shortly due to the strong Lewis acidity and the possible open sites of the lanthanide ions. - Graphical abstract: We have synthesized two isostructural 3D compounds based on H{sub 3}TTTA. They are chemical sensor of amine solvents and cations. They have higher yields and TOFs to catalyze cyanosilylation reactions. - Highlights: • The compounds show recognition of amine molecules via quenching luminescent intensities. • The compounds recognize Fe{sup 3+}, Cu{sup 2+}, Mg{sup 2+}, Cr{sup 3+} and Co{sup 2+} ions via quenching the peak around 361 nm. • They act as efficient Lewis acid catalysts for the cyanosilylation reactions in high yields.

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

Effective reduction in the nanoparticle sizes of NiO obtained via the pyrolysis of nickel malonate precursor modified using oleylamine surfactant

Nickel oxide nanoparticles were synthesized via thermal decomposition of two precursors, the first, a simple nickel malonate and the second, a nickel malonate modified by oleylamine, a surfactant, both having been synthesized by precipitation. While FTIR, TGA and ToF-SIMS were used to characterize the two precursors and to show the presence of oleylamine in the modified precursor, XRD, SEM, TEM and BET were employed to investigate the structure, the morphology and the specific surface area of the decomposition products obtained after pyrolysis. The results showed that the modification of nickel malonate by oleylamine was effective. The XRD results, which showed a cubic structure for the NiO obtained, suggest with SEM an important particle size reduction (at least 54%) when oleylamine was used to modify the nickel malonate precursor. The SEM images also showed a well-defined spherical nanoparticle morphology in both cases, not affected by the presence of oleylamine. The TEM also confirmed the reduction of particle size and their spherical nature but at the same time showed that, in the presence of oleylamine, there was no agglomeration resulting in a more uniform particle size distribution. The specific surface area of the NiO obtained by the oleylamine-modified precursor was 4.7 times larger than that obtained with the regular precursor. This again confirms the particle size reduction. - Highlights: • Nickel malonate precursor has been synthesized by precipitation method. • This precursor was successfully modified by a surfactant (oleylamine). • NiO was identified as the decomposition products of the previous precursors. • Oleylamine has provoked around 54% of particle size reduction of the NiO.

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

Hierarchical porous silver metal using Pluronic F-127 and graphene oxide as reinforcing agents for the reduction of o-nitroaniline to 1, 2-benzenediamine

An elegant method is used to prepare silver monoliths with Pluronic F-127(F-127) as sacrificial template by modified sol-gel method. Si nanoparticles (SiNPs) and graphene oxide (GO) are added in situ to Ag/F-127 hydrogel for the reduction of ο-nitroaniline (ο-NA) to 1, 2-benzenediamine. Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetric analysis (TGA), Raman Spectroscopy, Powder X-Ray Diffraction (PXRD) analysis and Brunauer-Emmett-Teller (BET) Nitrogen adsorption techniques were used for characterization of monoliths. An epoch-making catalytic activity of Ag/F-127/GO monoliths is observed in the reduction of ο-NA to 1, 2-benzenediamine in presence of NaBH{sub 4} in aqueous media. The catalyst Ag/F-127/GO took only 2 min which is the minimum time reported so far with significant rate constant claimed itself a leading catalyst for the reduction of ο-NA to 1,2-benzenediamine. Pseudo first order rate constant (k) and Turn over frequency (TOF) values are 0.231 min{sup −1} and 30.053×10{sup 19} molecules min{sup −1} respectively suggest that the catalyst has industrial importance. Recyclability and stability of Ag/F-127/GO catalyst are studied successfully up to 10 cycles. Energy of activation (E{sub a}), and thermodynamic parameters viz. activation enthalpy (ΔH{sup ≠}), activation Gibbs free energy (ΔG{sup ≠}), and entropy of activation (ΔS{sup ≠}) were also ascertained. Catalytic activities of Ag/F-127, Ag/F-127/Dextran, Ag/F-127/Trimethylbenzene (TMB), Ag/F-127/SiNPs, and Ag/F-127/Si/GO monoliths were also studied. - Graphical abstract: Significant catalytic activities of silver monoliths against the reduction of ο-NA to 1,2 benzenediamine. - Highlights: • A new catalyst synthesized Ag/F-127/GO for the reduction of ο- NA to 1, 2- benzenediamine took only 2 min. • Turn over frequency of as synthesized catalyst was 30.053×10{sup 19} molecules min{sup −1} claimed itself a leading catalyst. • Recyclability of the catalyst was up to 10 cycles. • The synthesis is non toxic, economically viable and environmentally benign.

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

Physicochemical and antibacterial characterization of ionocity Ag/Cu powder nanoparticles

Metal ion in bimetallic nanoparticles has shown vast potential in a variety of applications. In this paper we show the results of physical and chemical investigations of powder Ag/Cu nanoparticles obtained by chemical synthesis. Transmission electron microscopy (TEM) experiment indicated the presence of bimetallic nanoparticles in the agglomerated form. The average size of silver and copper nanoparticles is 17.1(4) nm (Ag) and 28.9(2) nm (Cu) basing on the X-ray diffraction (XRD) data. X-ray photoelectron (XPS) and Raman spectroscopies revealed the existence of metallic silver and copper as well as Cu{sub 2}O and CuO being a part of the nanoparticles. Moreover, UV–Vis spectroscopy showed surface alloy of Ag and Cu while Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) and Energy Dispersive X-ray Spectroscopy (EDX) showed heterogeneously distributed Ag structures placed on spherical Cu nanoparticles. The tests of antibacterial activity show promising killing/inhibiting growth behaviour for Gram positive and Gram negative bacteria. - Highlights: • Ag/Cu nanoparticles were obtained in the powder form. • The average size of nanoparticles is 17.1(4) nm (Ag) and 28.9(2) nm (Cu). • Ag/Cu powder nanoparticle shows promising antibacterial properties.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Impact of microstructure on the thermoelectric properties of the ternary compound Ce{sub 3}Cu{sub 3}Sb{sub 4}

We present detailed structural and thermoelectric studies of the ternary compound Ce{sub 3}Cu{sub 3}Sb{sub 4}. This material is of interest due to previously reported considerable thermopower above room temperature (∼ 100 μV/K) and low thermal conductivity (2 W/(m K)). Here, we present detailed studies concerning microstructural and thermoelectric data, their variation across the samples and possible explanations for the observed behaviour. We have used X-ray diffraction, scanning electron microscopy (SEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) for microstructural analysis. The thermoelectric properties were examined using a physical property measurement system (PPMS). We analyse the impact of the sample quality on the thermoelectric properties. The most unstable parameter is the material resistivity which varies between 1.5 and 15 mΩ cm at room temperature. The properties variability is mainly due to structural defects caused by stresses during material preparation and also due to formation of foreign phases CeCuSb{sub 2} and CeSb. The figure of merit ZT is also strongly dependent on the quality of the sample. The largest value ZT ≈ 0.15 at 400 K is determined for the almost stoichiometric sample with small amounts of a impurity phases. - Highlights: •The Ce{sub 3}Cu{sub 3}Sb{sub 4} has considerable thermoelectric properties and potential for further chemical and/or structural modification. •The control over foreign phases formation is challenging. •The defects arising during arc melting process highly deteriorate ZT of material.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A simple and fast preparation of neodymium-substituted nanocrystalline Mn{sub 2}O{sub 3}

Graphical abstract: Synthesis of Mn{sub 2−x}Nd{sub x}O{sub 3} with mixed morphology -- Abstract: Neodymium (Nd) ions were substituted for manganese in the crystal lattice of synthetic Mn{sub 2}O{sub 3}, via oxidation of Mn(NO{sub 3}){sub 2} in basic solution at room temperature. Doping of Nd into the lattice structure of Mn{sub 2}O{sub 3} has been reported for the first time, which resulted in materials with new composition, morphology and optical properties. The synthesized materials were characterized by XRD, SEM, TEM, HRTEM, XPS and TOF-SIMS. Light (2.6%) Nd doping resulted in a mixture of rods, plates and small sheets, while heavy (8.9%) Nd doping resulted in rods, large sheets and large single crystals. The effect of structural doping of Nd ions into Mn{sub 2}O{sub 3} resulted in a red shift in the absorbance.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Fe{sub 3}O{sub 4}@graphene oxide composite: A magnetically separable and efficient catalyst for the reduction of nitroarenes

Highlights: ► The Fe{sub 3}O{sub 4}@GO composite was prepared by a facile co-precipitation method. ► Fe{sub 3}O{sub 4} nanoparticles are well distributed on GO nanosheets. ► Fe{sub 3}O{sub 4}@GO was for the first time explored as a catalyst to reduce nitroarenes. ► Fe{sub 3}O{sub 4}@GO exhibits higher catalytic activity. ► The composite catalyst is easily recycled due to its magnetic separability. - Abstract: We reported a facile co-precipitation method to prepare a highly active Fe{sub 3}O{sub 4}@graphene oxide (Fe{sub 3}O{sub 4}@GO) composite catalyst, which was fully characterized by means of X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and N{sub 2} adsorption–desorption measurements. The results demonstrated that the Fe{sub 3}O{sub 4} nanoparticles (Fe{sub 3}O{sub 4} NPs) with a small diameter of around 12 nm were densely and evenly deposited on the graphene oxide (GO) sheets. The as-prepared Fe{sub 3}O{sub 4}@GO composite was explored as a catalyst to reduce a series of nitroarenes for the first time, which exhibited a great activity with a turnover frequency (TOF) of 3.63 min{sup −1}, forty five times that of the commercial Fe{sub 3}O{sub 4} NPs. The dosages of catalyst and hydrazine hydrate are both less than those reported. Furthermore, the composite catalyst can be easily recovered due to its magnetic separability and high stability.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Syntheses of gold supported on metal oxides and their application in organic transformations

Herein, we report a general and straightforward synthesis method for gold supported on mesoporous and microporous metal oxides. Supported materials, in general, show higher crystallinity compare to unsupported systems as verified through powder X-ray diffraction (XRD). Also, through XRD, most of the metal is observed to be in its oxide form, whereas the gold support was found to be in its metallic state, which has been further confirmed from TEM. In terms of surface area, the catalyst was not found to follow any trend. Morphology wise, there are no changes observed after doping except in few cases. Combined results from XRD, X-ray fluorescence spectroscopy, Auger, and X-ray photoelectron spectroscopy suggest that gold is mainly in the bulk and very little (0.04% in case of gold doped calcium oxide) or non (in case of gold doped mixed manganese-cerium oxide) on the surface. The presence of Au (0) 4f peaks in XPS further confirms the metallic state of the gold. Oxides of indium, magnesium and calcium have been studied for the organic transformation reactions. An enhancement in activity and product selectivity was observed in the case of the gold supported catalysts. Indium serves as a great catalyst for C–C coupling and electrophilic aromatic substitution reactions and gives >99% conversion. Interestingly, 88% selectivity for C–C coupling and >99% selectivity for aromatic substitution have been achieved at 100 °C and room temperature respectively. Magnesium and calcium give Knoevenagel condensation products. At room temperature with very low catalyst loading, >99% conversion and selectivity were observed for the Knoevenagel reaction with as high as 35.30 TOF. Finally, a mechanism for the C–C coupling reaction has been proposed based on these results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗