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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Trends in Formic Acid Decomposition on Model Transition Metal Surfaces: A Density Functional Theory Study

We present a first-principles, self-consistent periodic density functional theory (PW91-GGA) study of formic acid (HCOOH) decomposition on model (111) and (100) facets of eight fcc metals (Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh) and (0001) facets of four hcp (Co, Os, Ru, and Re) metals. The calculated binding energies of key formic acid decomposition intermediates including formate (HCOO), carboxyl (COOH), carbon monoxide (CO), water (H2O), carbon dioxide (CO2), hydroxyl (OH), carbon (C), oxygen (O), and hydrogen (H; H2) are presented. Using these energetics, we develop thermochemical potential energy diagrams for both the carboxyl-mediated and the formate-mediated dehydrogenation mechanisms on each surface. We evaluate the relative stability of COOH, HCOO, and other isomeric intermediates (i.e., CO + OH, CO2 + H, CO + O + H) on these surfaces. These results provide insights into formic acid decomposition selectivity (dehydrogenation versus dehydration), and in conjunction with calculated vibrational frequency modes, the results can assist with the experimental search for the elusive carboxyl (COOH) surface intermediate. Results are compared against experimental reports in the literature.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2017

Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium–Nitrate Example

The influence of countercations (A(n+)) in directing the composition of monomeric metalligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A(n+) in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A(+) hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A(+) counterions. Analyses of their chemical composition and solid-state structures demonstrate that A(+) not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A(+) hydration enthalpies, such that the A(+) with smaller hydration enthalpies associate with less hydrated and more anionic Th-nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of A(n+), opens a new avenue for the design and synthesis of targeted metal-ligand complexes.

Jin, Geng Bang↗
DOE OSTI2014

Rigidifying Fluorescent Linkers by Metal-Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 +/- 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

Wei, ZW↗
DOE OSTI2014

Increasing the Aromatic Selectivity of Quinoline Hydrogenolysis Using Pd/MOx–Al2O3

Catalysts consisting of Pd nanoparticles supported on highly dispersed TiOx–Al2O3, TaOx–Al2O3, and MoOx–Al2O3 are studied for catalytic quinoline hydrogenation and selective C–N bond cleavage at 275 °C and 20 bar H2. The Pd/MOx–Al2O3 materials exhibit significantly greater aromatic product selectivity and thus 10–15 % less required H2 for a given level of denitrogenation relative to an unmodified Pd/Al2O3 catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗