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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Flexible Zirconium Metal‐Organic Frameworks as Bioinspired Switchable Catalysts

Abstract Flexible metal–organic frameworks (MOFs) are highly desirable in host–guest chemistry owing to their almost unlimited structural/functional diversities and stimuli‐responsive pore architectures. Herein, we designed a flexible Zr‐MOF system, namely PCN‐700 series, for the realization of switchable catalysis in cycloaddition reactions of CO 2 with epoxides. Their breathing behaviors were studied by successive single‐crystal X‐ray diffraction analyses. The breathing amplitudes of the PCN‐700 series were modulated through pre‐functionalization of organic linkers and post‐synthetic linker installation. Experiments and molecular simulations confirm that the catalytic activities of the PCN‐700 series can be switched on and off upon reversible structural transformation, which is reminiscent of sophisticated biological systems such as allosteric enzymes.

Yuan, Shuai↗
DOE OSTI2017

Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts

Although well known in the material science field, surface reconstruction of perovskites has not been implemented in heterogeneous catalysis. In this work, we employ multiple surface sensitive techniques to characterize the surface reconstruction of SrTiO3 (STO) after thermal pretreatment (Sr-enrichment) and chemical etching (Ti-enrichment). We show, using the conversion of 2-propanol as a probe reaction, that the surface reconstruction of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivities in a wide range, which are inaccessible using single metal oxides, either SrO or TiO2. Density functional theory (DFT) calculations well explain the selectivity tuning and reaction mechanism on differently reconstructed surfaces of STO. Similar catalytic tunability is also observed on BaZrO3, highlighting the generality of the finding from this work.

Polo-Garzon, Felipe↗
DOE OSTI2016

Pillared Sn‐MWW Prepared by a Solid‐State‐Exchange Method and its Use as a Lewis Acid Catalyst

Abstract Pillared Sn‐MWW (Sn‐MWW(SP)‐SSE) was prepared through a solid‐state‐exchange (SSE) route. The pillared structure was inherited from pillared B‐MWW, and Sn was inserted in the framework by boron leaching and solid‐state‐exchange with tin tetrachloride pentahydrate. The Sn‐MWW(SP)‐SSE with framework Sn sites exhibits Lewis acidity and good catalytic performance for the Baeyer–Villiger oxidation, and mono‐ and disaccharide isomerizations.

Ren, Limin↗
DOE OSTI2017

Fluoropolymer‐Stabilized Chromophore–Catalyst Assemblies in Aqueous Buffer Solutions for Water‐Oxidation Catalysis

Abstract Here, the application of the fluorinated polymer [Dupont AF, a copolymer of 4,5‐difluoro‐2,2‐bis(trifluoromethyl)‐1,3‐dioxole and tetrafluoroethylene] is described in stabilizing phosphonate‐derivatized molecular assemblies on oxide electrodes. In the procedure, the polymer was dip‐coated onto the surfaces of oxide electrodes with pre‐bound, phosphonate‐derivatized chromophores and assemblies, including assemblies for water oxidation. The results of the experiments showed a high degree of stabilization by the added polymer and a demonstration of its use in stabilizing surface‐bound assemblies for water‐oxidation catalysis.

Eberhart, Michael S.↗
DOE OSTI2017

Oxidative Hydrophenylation of Ethylene Using a Cationic Ru(II) Catalyst: Styrene Production with Ethylene as the Oxidant

The complex [(MeOTTM)Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr' 4 ] (MeOTMM = 4,4',4"-(methoxymethanetriyl)-tris(1-benzyl-1H-1,2,3-triazole), BAr' 4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) is used to catalyze the hydrophenylation of ethylene to produce styrene and ethylbenzene. The selectivity of styrene versus ethylbenzene varies as a function of ethylene pressure, and replacing the MeOTTM ligand with tris(1-phenyl-1H-1,2,3-triazol-4-yl)methanol reduces the selectivity toward styrene. For styrene production ethylene serves as the oxidant to produce ethane, as determined by both 1 H NMR spectroscopy and GC-MS. The Ru(III/II) potentials of [(MeOTTM)Ru[P(OCH 2 ) 3 CEt](NCMe)Ph][BAr' 4 ] (0.86 V) and [(HC(pz 5 ) 3 )Ru[P(OCH 2 ) 3 CEt](NCMe)Ph][BAr' 4 ] (0.82 V) (HC(pz 5 ) 3 = tris(5-methyl-pyrazolyl)methane) are nearly identical. Since catalytic conversion of ethylene and benzene by [(HC(pz 5 ) 3 )Ru[P(OCH 2 ) 3 CEt](NCMe)Ph][BAr' 4] is known to selectively produce ethylbenzene, the formation of styrene using [(MeOTTM)Ru[P(OCH 2 ) 3 CEt](NCMe)Ph][BAr' 4 ] is attributed to the substituents on the triazole rings of the MeOTTM ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗