Oxygen

About: Oxygen is a research topic. Over the lifetime, 48149 publications have been published within this topic receiving 1113788 citations. The topic is also known as: O & Oxygen.

Oxygen complexes and oxygen activation by transition metals

Abstract: Opening Remarks- Dioxygen Complexes with Transition Metals- Bonding of Dioxygen to Transition Metals- Oxygen Binding by the Metalloproteins Hemerythrin, Hemocyanin, and Hemoglobin- Metal Oxo Complexes and Oxygen Activation- Kinetics of Formation of Biological Oxygen Carriers- Synthetic Dioxygen Carriers for Dioxygen Transport- Formation and Degradation of Cobalt Dioxygen Complexes- Reversible Complexes for the Recovery of Dioxygen- Summary - Dioxygen Complexes with Transition Metals- Oxygen Activation by Transition Metals- Summary - Oxygen Activation by Transition Metals- The Chemistry and Activation of Dioxygen Species (02, 02-, and H00H) in Biology- Oxygen Activation by Neutrophils- Mechanisms of Dioxygen Activation in Metal-Containing Monooxygenases: Enzymes and Model Systems- Radical Cation Pathways for Selective Catalytic Oxidation by Molecular Oxygen- Vanadium Catalyzed Autoxidation of Hydrogen Sulfide- Copper Catalyzed Oxidative Carbonylation of Methanol to Dimethyl Carbonate- Dependence of Reaction Pathways and Product Distribution on the Oxidation State of Palladium Catalysts for the Reactions of Olefinic and Aromatic Substrates with Molecular Oxygen- Oxygen Activation and Oxidation Reactions on Metal Surfaces- Methane Oxidation at Metal Oxide Surfaces- The Activation of Oxygen by Metal Phosphorus Oxides - The Vanadium Phosphorus Oxide Catalyst- The Oxidation of Organic Compounds by Metal Complexes in Zeolites- Abstracts of Posters- Kinetics and Mechanisms of Degradation of Binuclear Cobalt Dioxygen Complexes- Methane Activation over Lanthanide Oxides- Dioxygen Affinities of Some Synthetic Cobalt Schiff Base Complexes- Temporal Analysis of Products (TAP): A Unique Catalyst Evaluation System with Sub-Millisecond Time Resolution- Dioxygen Insertion into Metal-Carbon Bonds of Metalloporphyrins: Formation and Characterization of Alkylperoxy Metalloporphyrins- Iron Porphyrin Catalyzed Air Oxidation of Aldehydes and Alkenes- Oxidative Dimerization of Methane over Sodium-Promoted Calcium Oxides- Synthesis and Metal Ion Affinities of a Binucleating Polyamine: Reversible Formation of a Cobalt Dioxygen Complex- Potentiometric Determination of Stabilities of Cobalt(II) Complexes of Polyamine Schiff Bases and Their Dioxygen Adducts- Catalysis of Cobalt Schiff Base Complexes for the Oxygenation of Olefins Mechanisms for the Ketonization Reaction- Selective Oxidation of Saturated Hydrocarbons by the Gif and Gif-Orsay Systems- The Formation, Characterization, and Reactivity of the Oxene Adduct of Tetrakis(2,6-dichlorophenyl)porphinato-Iron(III) Perchlorate in Acetonitrile- Preparation and Characterization of a Binuclear Iron(III)- Hydroxo-y-hydroperoxy Complex [(Ph3PO)4(HO)FeIII(HOOH)FeIII(OH)(OPPh3)4](C1O4)4- Autoxidation of FeII(dihydroxyphenanthroline)3- Phosphine-Ruthenium(II)-Aquo Redox Chemistry: The Aerobic Catalytic Oxidation of Cyclohexene- The Oxidation of Organic Substrates by Molecular Oxygen Catalysis by Ru(III) and Ru(III)-EDTA- Oxygenation of Tryptophane Catalyzed by Polyamine Cobalt Dioxygen Complexes- Resonance Raman Spectroscopy of the Fe(IV)=0 Group in Peroxidase Intermediates- Reaction of Dioxygen with Synthetic Copper(I) Compounds of Biological Relevance- Thorough Elucidation of Oxygenation- and Oxidation-Mechanisms of Iron(II) Porphyrin on the Basis of a New Hypothesis for an Electron-Transfer Pathway- IUCCP Description

Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface

Abstract: Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (for example, ) by the positively charged oxygen vacancies () enriched at the surface. Here we show that reducing the surface concentration improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while reducing the concentration of and making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 °C achieved by Hf addition onto LSC. Finally, the results revealed a 'volcano' relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss.

Phosphorescent Complexes of Porphyrin Ketones: Optical Properties and Application to Oxygen Sensing

Abstract: A new class of dyes, platinum(II) and palladium(II) complexes of the porphyrin ketones (or oxochlorins), exhibiting strong phosphorescence at room temperature is described. Several representative compounds were prepared and studied by spectral luminescence methods in solution. Compared to the related porphyrin and chlorin complexes, the new dyes display high photochemical stability, long wave spectral characteristics, and good compatibility with semiconductor optoelectronics (e.g., excitation by light-emitting diodes). These properties make the new dyes promising for a number of relevant applications, such as quenched phosphorescence sensing and phosphorescence probing (e.g., in binding assays). Analytical application of the porphyrin ketone complexes to phosphorescence lifetime-based sensing of molecular oxygen is described. Platinum(II) octaethylporphine ketone was dissolved in a polystyrene layer to give an oxygen-sensitive film. Oxygen measurements were performed with a prototype fiber-optic instrument based on solid-state components, such as light-emitting diodes and photodiodes. The instrument measured phosphorescence lifetime via changes in phase shift. The phosphorescence lifetime was determined to change from about 61.4 μs at zero oxygen to 16.3 μs in air (210 hPa of oxygen) at 22 °C. The analytically useful range of the sensor was 0-210 hPa of oxygen partial pressure, with a detection limit of 1.5 hPa. The precision of the device was 1.0 hPa at 210 hPa of oxygen and 0.5 hPa at zero oxygen.

Measurement of fragmentation and functionalization pathways in the heterogeneous oxidation of oxidized organic aerosol

Abstract: The competition between the addition of polar, oxygen-containing functional groups (functionalization) and the cleavage of C–C bonds (fragmentation) has a governing influence on the change in volatility of organic species upon atmospheric oxidation, and hence on the loading of tropospheric organic aerosol. However the relative importance of these two channels is generally poorly constrained for oxidized organics. Here we determine fragmentation–functionalization branching ratios for organics spanning a range of oxidation levels, using the heterogeneous oxidation of squalane (C30H62) as a model system. Squalane particles are exposed to high concentrations of OH in a flow reactor, and measurements of particle mass and elemental ratios enable the determination of absolute elemental composition (number of oxygen, carbon, and hydrogen atoms) of the oxidized particles. At low OH exposure, the oxygen content of the organics increases, indicating that functionalization dominates, whereas for more oxidized organics the amount of carbon in the particles decreases, indicating the increasing importance of fragmentation processes. Once the organics are moderately oxidized (O/C ≈ 0.4), fragmentation completely dominates, and the increase in O/C ratio upon further oxidation is due to the loss of carbon rather than the addition of oxygen. These results suggest that fragmentation reactions may be key steps in the formation and evolution of oxygenated organic aerosol (OOA).

Gold-catalyzed aerobic oxidation of 5-hydroxymethylfurfural in water at ambient temperature.

Abstract: The aerobic oxidation of 5-hydroxymethylfurfural, a versatile biomass-derived chemical, is examined in water with a titania-supported gold-nanoparticle catalyst at ambient temperature (30 °C). The selectivity of the reaction towards 2,5-furandicarboxylic acid and the intermediate oxidation product 5-hydroxymethyl-2-furancarboxylic acid is found to depend on the amount of added base and the oxygen pressure, suggesting that the reaction proceeds via initial oxidation of the aldehyde moiety followed by oxidation of the hydroxymethyl group of 5-hydroxymethylfurfural. Under optimized reaction conditions, a 71% yield of 2,5-furandicarboxylic acid is obtained at full 5-hydroxymethylfurfural conversion in the presence of excess base.