Search NASA⌕ Search

SEARCH · Search NASA

Results for “synthesis (scalable processing)”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Adipic Acid Production via Metal-Free Selective Hydrogenolysis of Biomass-Derived Tetrahydrofuran-2,5-Dicarboxylic Acid

Biomass-derived furans offer sustainable routes to adipic acid (AA), a key chemical in Nylon-6,6 synthesis. In this work, we show that tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) is a viable precursor for AA production, achieving up to 89% yield in a metal-free system containing HI and molecular H 2 in a propionic acid solvent at 160 °C. Reactivity studies demonstrate that the interplay between HI, H 2 , and the solvent is essential for effective THFDCA ring opening. By measuring the reaction orders of HI and molecular H 2 and calculating an acid–base equilibrium constant in a nonaqueous solvent, we show that HI plays a multifaceted role in the reaction by acting both as a proton source and an iodide source to selectively cleave C–O bonds without overhydrogenation of carboxylic acid groups. Using reactivity studies, kinetic measurements, and first-principles computational insights, we demonstrate that metal-free activation of molecular H 2 plays a key role in the reaction, following HI-mediated cleavage of the etheric C–O bond in THFDCA.

09 BIOMASS FUELS↗
DOE OSTI2018

Redox-Mediator-Assisted Electrocatalytic Hydrogen Evolution from Water by a Molybdenum Sulfide-Functionalized Metal–Organic Framework

The Zr 6 -based metal–organic framework NU-1000 was successfully functionalized with candidate catalysts—MoS x units—via SIM (solvothermal deposition in MOFs) of molybdenum(VI), followed by reaction with H2S gas. The structure of the material, named MoS x - SIM, was characterized spectroscopically and through a single-crystal X-ray diffraction measurement. These measurements and others established that the catalyst is monometallic, with mixed oxygen and sulfur coordination, and that it forms from a MOF-node-supported molybdenum-based cluster featuring only oxy ligands. Notably, the formal potential for the MOF-grafted complex, like that for the metal–sulfur active site of hydrogenase, is nearly coincident with the formal potential for the hydrogen couple. Its effective concentration within the mesoporous MOF is several hundred millimolar, and its porous-framework-based immobilization/heterogenization obviates the need for aqueous solubility as a condition for use as a well-defined catalyst. MoS x - SIM was evaluated as an electrocatalyst for evolution of molecular hydrogen from aqueous acid. Although the MoS x - functionalized framework exhibits catalytic behavior, the highly insulating nature of the support inhibits high electrocatalytic performance. Introduction of an archetypal redox mediator (RM), methyl viologen (MV 2+ ), resulted in more than 20-fold enhancement in its catalytic performance on a turnover frequency basis, implying efficient RM-assisted electron transfer to otherwise electrochemically non-addressable MoS x moieties. Electrochemical kinetic studies with additional viologens as mediators reveal an unexpected square-root dependence of overall reaction rate on mediator concentration, as well as sensitivity to the strength of RM •+ as a reductant. These observations, together with observations of potential-dependent H/D isotope effects and potential-dependent pH effects, provide useful insights into the catalysis mechanism and help to explain how the MOF-affixed monometallic catalyst can effectively catalyze a two-electron reduction reaction, i.e., hydrogen evolution from acidified water.

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

Synergy between Ceria Oxygen Vacancies and Cu Nanoparticles Facilitates the Catalytic Conversion of CO 2 to CO under Mild Conditions

The performance of supported metal catalysts can depend on many factors, including metal particle size and dispersion and metal–support interactions, and differentiation of these effects is challenging because of their interwoven relationship. Copper/ceria catalysts are well-known redox catalysts studied in the conversion of CO and CO 2 via oxidation and/or reduction pathways. The redox behaviors of each species, Cu-CuO and CeO x -CeO 2 , are often suggested to be interlinked, allowing ceria-supported copper domains to outperform copper species on other, nonredox active supports. In this work, the catalytic activity of nanosized Cu supported on either cerium oxide or mesoporous silica is explored using samples where the Cu weight loading, particle size, and dispersion of Cu are held constant to highlight the impact of the two supports on catalytic performance without additional influencing factors. The Cu/CeO 2 catalysts are synthesized via a space-confined method to limit the growth of CeO 2 particles and to achieve a high dispersion of Cu. Through in situ XRD and XAS, it is shown that the presence of Cu nanoparticles on the CeO 2 support lowers the reduction temperature of CeO 2 , allowing formation of oxygen vacancies at low temperatures <300 °C. The Cu/CeO x catalyst demonstrates 100% CO selectivity in the low temperature (300 °C) and ambient pressure conversion of CO 2 to CO, even when approaching equilibrium conversion. Moreover, this catalyst is approximately 4 times more active than the corresponding Cu/SiO 2 catalyst with otherwise similar structural attributes. The potential reaction pathways are probed by in situ FTIR and in situ XAS at various temperatures, identifying Cu + -CO species and oxygen vacancies forming under some conditions. The collected experimental evidence also suggests a reaction sequence for CO 2 hydrogenation over Cu/CeO x catalysts, consistent with DFT reports in the literature.

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

Selective Production of Aromatics by Catalytic Fast Pyrolysis of Furan with In Situ Dehydrogenation of Propane

Catalytic fast pyrolysis (CFP) of furan was studied with the co-feeding of propane over ZSM-5, CrOx/Al2O3, and mixed catalysts with both ZSM-5 and CrOx/Al2O3 to combine the dehydrogenation of propane and CFP of furan in the presence of in situ generated propylene. With 15 vol % propane co-feeding, a slight increase in aromatic yield was observed over ZSM-5 catalyst. These enhancement was further improved by using mixed catalysts consisting of CrOx/Al2O3 and ZSM-5 with different weight ratios. Over the best mixed catalyst with CrOx/Al2O3 to ZSM-5 weight ratio of 2, a nearly 2-fold increase in the aromatic yield was obtained. The toluene selectivity was also increased from 37% to 50%. The increase in aromatic yield is directly dependent on the propane to total flow volume ratio. Moreover, the coke formation within ZSM-5 was also reduced, leading to a slower catalyst deactivation. From mechanistic studies, a two-step cascade reaction pathway was observed over the bifunctional mixed catalysts. It was proposed that propane dehydrogenates to propylene over CrOx/Al2O3. The propylene then reacts with furan within ZSM-5 catalyst to selectively form aromatics. This work demonstrates a simple and economical strategy to further improve the CFP technique.

bio-inspired↗
DOE OSTI2017

Collateral Advantages of a Gel Electrolyte for MnO 2 Nanowire Capacitors: Higher Voltage and Reduced Volume

Recently we demonstrated that symmetric, all Au@δ-MnO 2 core@shell nanowire capacitors can achieve cycle stability to 100 000 cycles and beyond in a poly(methyl methacrylate) (PMMA) gel electrolyte. Here we examine the limits of the PMMA gel to confer this extraordinary stability, in terms of the accessible maximum voltage, Vmax, and the thickness of the PMMA gel electrolyte layer. Two conclusions are (1) the PMMA gel permits the Vmax to be increased by 50% from 1.2 V to 1.8 V, allowing the specific energy to be increased 5–6 fold, and (2) the PMMA gel layer thickness can be reduced from 180 μm (previously) to 2 μm while simultaneously utilizing two layers of nanowires and patterning nanowires in each layer at 5× higher density. For this nanowire “sandwich” architecture, a net increase in volumetric capacity of 600× up to 500 mF/cm3 can be achieved while retaining cycle stability to 100 000 cycles.

25 ENERGY STORAGE↗
DOE OSTI2018

Dynamic Hosts for High-Performance Li–S Batteries Studied by Cryogenic Transmission Electron Microscopy and in Situ X-ray Diffraction

Developing a high-performance sulfur host is central to the commercialization and general development of lithium–sulfur batteries. Here, for the first time, we propose the concept of dynamic hosts for lithium–sulfur batteries and elucidate the mechanism through which TiS 2 acts in such a fashion, using in situ X-ray diffraction and cryogenic scanning transmission electron microscopy (cryo-STEM). A TiS 2 –S composite electrode delivered a reversible capacity of 1120 mAh g –1 at 0.3 C after 200 cycles with a capacity retention of 97.0% and capacities of 886 and 613 mAh g –1 at 1.0 C up to 200 and 1000 cycles, respectively. Finally, our results indicate that it is Li x TiS 2 (0 < x ≤ 1), rather than TiS 2 , that effectively traps polysulfides and catalytically decomposes Li 2 S.

25 ENERGY STORAGE↗
DOE OSTI2019

Manifesto on the Thermochemistry of Nanoscale Redox Reactions for Energy Conversion

Advancements in the use of nanoscale materials for energy conversions will rely on a clear understanding of reaction thermochemistry. While band edge and Fermi energies can be rigorous thermodynamic descriptors of bulk materials, we show here that their application to nanoscale systems is problematic. A change of one electron at a 1000 atom nanoparticle or a localized surface site on a catalyst/electrode causes significant nuclear reorganization of the system. Electron transfer is often coupled with solvent reorganization and/or with the transfer of ions, including ion intercalation, surface binding, and movement within the surrounding double layer. These effects can be significant (even for some bulk materials). However, Fermi and band energies, as typically used, do not include the energetics of nuclear reorganizations or cation coupling. A comprehensive approach to nanoscale charge transfer thermodynamics must explicitly consider these effects in order to have a more complete understanding and greater control of nanoscale redox reactivity.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Semiconductor Quantum Dots Are Efficient and Recyclable Photocatalysts for Aqueous PET-RAFT Polymerization

This Letter describes the use of CdSe quantum dots (QDs) as photocatalysts for photoinduced electron transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization of a series of aqueous acrylamides and acrylates. In this work, the high colloidal solubility and photostability of these QDs allowed polymerization to occur with high efficiency (>90% conversion in 2.5 h), low dispersity (PDI < 1.1), and ultralow catalyst loading (<0.5 ppm). The use of protein concentrators enabled the removal of the photocatalyst from the polymer and monomer with tolerable metal contamination (8.41 ug/g). These isolated QDs could be recycled for four separate polymerizations without a significant decrease in efficiency. By changing the pore size of the protein concentrators, the QDs and polymer could be separated from the remaining monomer, allowing for the synthesis of block copolymers using a single batch of QDs with minimal purification steps and demonstrating the fidelity of chain ends.

36 MATERIALS SCIENCE↗