Showing papers on "Oxygen published in 2013"
TL;DR: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-Electron processes, which feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.
Abstract: The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.
Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3
However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.
Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.
A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.
1,326 citations
TL;DR: Both experimental and computational studies indicate that the catalytic activity of MnO(2) towards oxygen reduction is enhanced by introducing a modest concentration of oxygen vacancies.
Abstract: Oxygen-vacant nanocrystalline MnO(2) has been prepared by the simple process of annealing pristine oxide in Ar or O(2) . Both experimental and computational studies indicate that the catalytic activity of MnO(2) towards oxygen reduction is enhanced by introducing a modest concentration of oxygen vacancies.
625 citations
TL;DR: A self-assembly-formed triglycylcylglycine macrocyclic ligand (TGG(4-)) complex of Cu(II) efficiently catalyzes water oxidation in a phosphate buffer at pH 11 at room temperature by a well-defined mechanism.
Abstract: A self-assembly-formed triglycylglycine macrocyclic ligand (TGG(4-)) complex of Cu(II), [(TGG(4-))Cu(II)-OH(2)](2-), efficiently catalyzes water oxidation in a phosphate buffer at pH 11 at room temperature by a well-defined mechanism. In the mechanism, initial oxidation to Cu(III) is followed by further oxidation to a formal "Cu(IV)" with formation of a peroxide intermediate, which undergoes further oxidation to release oxygen and close the catalytic cycle. The catalyst exhibits high stability and activity toward water oxidation under these conditions with a high turnover frequency of 33 s(-1).
393 citations
TL;DR: A promotor for lithium batteries: nanocrystalline cobalt(II,III) oxide supported on graphene enhances the transport kinetics for both oxygen reduction and oxygen evolution in the lithium-oxygen cell.
Abstract: A promotor for lithium batteries: nanocrystalline cobalt(II,III) oxide supported on graphene enhances the transport kinetics for both oxygen reduction and oxygen evolution in the lithium-oxygen cell. On cycling the lithium-oxygen cell, the effect of the promoter is, however, eventually overwhelmed by side reactions in the cell, such as, the deposition of carbonates.
385 citations
TL;DR: Maintenance of the cellular redox balance is crucial for cell survival and has the potential to mediate extensive yet fully reversible structural and functional changes, rapidly adjusting the protein's activity to the prevailing oxidant levels.
328 citations
TL;DR: Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on commercial carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co3O4-N@C materials.
Abstract: Novel cobalt-based heterogeneous catalysts have been developed for the direct oxidative esterification of alcohols using molecular oxygen as benign oxidant. Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on commercial carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co3O4-N@C materials. By applying these catalysts in the presence of oxygen, the cross and self-esterification of alcohols to esters proceeds in good to excellent yields.
311 citations
TL;DR: In this article, hierarchical functionalized multiwalled carbon nanotube (MWNT)/graphene structures with thicknesses up to tens of micrometers and relatively high density (> 1 g cm−3) are synthesized using vacuum filtration for the positive electrode of lithium batteries.
Abstract: Hierarchical functionalized multiwalled carbon nanotube (MWNT)/graphene structures with thicknesses up to tens of micrometers and relatively high density (>1 g cm−3) are synthesized using vacuum filtration for the positive electrode of lithium batteries. These electrodes, which are self-standing and free of binder and current collectors, utilize oxygen functional groups for Faradaic reactions in addition to double-layer charging, which can impart high gravimetric (230 Wh kg−1 at 2.6 kW kg−1) and volumetric (450 Wh L−1 at 5 kW L−1) performance. It is demonstrated that the gravimetric and volumetric capacity, capacitance, and energy density can be tuned by selective removal of oxygen species from as-prepared functionalized MWNT/graphene structures with heat treatments in H2/Ar, potentially opening new pathways for the design of electrodes with controlled surface chemistry.
310 citations
TL;DR: In this paper, the authors investigated the role of oxygen and manganese in the redox process in charge and showed that oxygen is significantly more involved in the reduction process than O2.
Abstract: Materials prepared by chemical Li deintercalation with NO2BF4 from Li1.20Mn0.54Co0.13Ni0.13O2 and chemical Li reinsertion with LiI show very similar chemical composition, oxidation state of each transition metal ion, structural properties and electrochemical performance to those of the material recovered after the 1st electrochemical cycle. Investigations combining redox titration, magnetic measurement, neutron diffraction and chemical analyzes reveal that uncommon redox processes are involved during the first charge at high voltage and explain the charge overcapacity and large reversible discharge capacity obtained for this material. This further assesses our proposal that oxygen, in addition to nickel and cobalt, participates to the redox processes in charge: within the bulk oxygen is oxidized without oxygen loss, whereas at the surface oxygen is oxidized to O2 and irreversibly lost from the structure. During the subsequent discharge, in addition to nickel, cobalt and oxygen, manganese is also slightly involved in the redox processes (reduction) to compensate for the initial surface oxygen loss.
303 citations
TL;DR: Pits confined in an atomically thin sheet as a platform to evaluate carbon monoxide catalytic oxidation at various sites are proposed and it is disclosed that the four- and five-fold coordinated pit-surrounding cerium sites assume their respective role in carbon mon dioxide adsorption and oxygen activation, which lowers the activation barrier and avoids catalytic poisoning.
Abstract: Finding ideal material models for studying the role of catalytic active sites remains a great challenge. Here we propose pits confined in an atomically thin sheet as a platform to evaluate carbon monoxide catalytic oxidation at various sites. The artificial three-atomic-layer thin cerium(IV) oxide sheet with approximately 20% pits occupancy possesses abundant pit-surrounding cerium sites having average coordination numbers of 4.6 as revealed by X-ray absorption spectroscopy. Density-functional calculations disclose that the four- and five-fold coordinated pit-surrounding cerium sites assume their respective role in carbon monoxide adsorption and oxygen activation, which lowers the activation barrier and avoids catalytic poisoning. Moreover, the presence of coordination-unsaturated cerium sites increases the carrier density and facilitates carbon monoxide diffusion along the two-dimensional conducting channels of surface pits. The atomically thin sheet with surface-confined pits exhibits lower apparent activation energy than the bulk material (61.7 versus 122.9 kJ mol(-1)), leading to reduced conversion temperature and enhanced carbon monoxide catalytic ability.
296 citations
TL;DR: In this article, a MoO3-based catalyst is proposed for C-O bond cleavage and operates with low H2 pressures (≤1 bar). But it is shown that deactivation can be minimised by tuning hydrogen partial pressure, original activity can be recovered by calcination, and that catalytic activation can be maintained in the presence of water.
Abstract: Effective hydrodeoxygenation of biomass-derived oxygenates is achieved with MoO3 to produce unsaturated hydrocarbons, converting linear ketones and cyclic ethers to olefins, and cyclic ketones and phenolics to aromatics with high yields. The catalyst is selective for C–O bond cleavage and operates using low H2 pressures (≤1 bar). We show that deactivation can be minimised by tuning hydrogen partial pressure, that original activity can be recovered by calcination, and that catalytic activity can be maintained in the presence of water. Theoretical calculations are used to elucidate reaction pathways and highlight the role of oxygen vacancies in the deoxygenation process.
289 citations
TL;DR: An alternative dehydrogenative pathway effected by water and base with the concomitant generation of hydrogen gas is described, which could be a safer and cleaner process for the synthesis of carboxylic acids and their derivatives at both laboratory and industrial scales.
Abstract: The development of a catalytic, mild and atom-economical transformation of alcohols to carboxylic acid salts and hydrogen gas is described. The reaction uses water as a source of oxygen, with a homogenous Ru catalyst at low (0.2 mol%) catalyst loadings in basic aqueous solution.
TL;DR: A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL).
Abstract: A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL). The oxygen vacancy plays an essential role for TMOs when they are employed as HTLs: TMO films with excess oxygen are highly undesirable for their application in organic electronics.
TL;DR: In this paper, a reaction mechanism of vinyl chloride oxidation over LaMnO 3 -based perovskite oxides was proposed, which was found to be strongly related to the low-temperature reducibility of the B site and the amount of adsorbed oxygen species and vacancies on the surface.
Abstract: The LaMnO 3 and LaB 0.2 Mn 0.8 O 3 (B = Co, Ni, Fe) perovskite-type oxides were prepared by the conventional co-precipitation method and studied as catalysts for the oxidation of vinyl chloride emission in the temperature range of 50–350 °C. Their physicochemical properties were characterized by ICP-AES, N 2 adsorption, XRD, H 2 -TPR, O 2 -TPD and XPS. Catalytic performances were evaluated for the oxidation of 1000 ppm of VC in air at a GHSV of 15,000 h −1 . The substituted LaB 0.2 Mn 0.8 O 3 samples showed higher catalytic activity than pure LaMnO 3 . Characterization results revealed that the catalytic activity of the perovskite oxides was greatly related to the low-temperature reducibility of the B site and the amount of adsorbed oxygen species and vacancies on the surface. The surface adsorbed oxygen species played a key role in the catalytic reaction and oxygen vacancies promoted the oxygen mobility. A reaction mechanism of vinyl chloride oxidation over LaMnO 3 -based perovskite oxides was proposed.
TL;DR: Co3O4/Co2MnO4 nanocomposites, derived from a single-source CoMn-layered double hydroxide precursor, exhibit excellent bifunctional oxygen electrode activities for both oxygen reduction and evolution reactions, which can be attributed to the large specific surface area and well-dispersed heterogeneous structure of the nanocom composites.
Abstract: Co3O4/Co2MnO4 nanocomposites, derived from a single-source CoMn-layered double hydroxide precursor, exhibit excellent bifunctional oxygen electrode activities for both oxygen reduction and evolution reactions, which can be attributed to the large specific surface area and well-dispersed heterogeneous structure of the nanocomposites.
TL;DR: In this article, the aprotic polar solve is used to solve the problem of oxygen reduction in nonaqueous electrolyte solutions containing Li salts, which is a complex field of research involving solution reactions with oxygen radicals and lithium oxides.
Abstract: Oxygen reduction in nonaqueous electrolyte solutions containing Li salts is a complex field of research involving solution reactions with oxygen radicals and lithium oxides. The aprotic polar solve...
TL;DR: In this article, a multiplicity of experimental and theoretical techniques were used to study the electrochemical evolution of oxygen on gold, the metal on which water splitting was initially discovered more than two centuries ago, and the evidence obtained with a combination of in situ surfaceenhanced Raman spectroscopy, online electrochemical mass spectrometry and density functional theory calculations suggests the existence of several mechanisms for the evolution of O2 on Au electrodes, depending on the electrode potential.
Abstract: In this paper we study through a multiplicity of experimental and theoretical techniques the electrochemical evolution of oxygen on gold, the metal on which water splitting was initially discovered more than two centuries ago. The evidence obtained with a combination of in situ surface-enhanced Raman spectroscopy, online electrochemical mass spectrometry and density functional theory calculations suggests the existence of several mechanisms for the evolution of O2 on Au electrodes, depending on the electrode potential. Significantly, at approximately 2.0 V vs. RHE the first O2 that is evolved consists of two oxygens from the surface oxide, suggesting an oxide decomposition or oxide disproportionation step. At somewhat higher potentials, O2 is formed by a combination of oxygen from the oxide lattice and oxygen provided by water. The oxide decomposition step implies a more three-dimensional mechanism for oxygen evolution than suggested in previous mechanisms, which involve only surface-adsorbed intermediates.
TL;DR: In volume-responders, unlike markers of anaerobic metabolism, central venous oxygen saturation did not allow the prediction of whether a fluid-induced increase in oxygen delivery would result in an increase inoxy consumption, which suggests that along with indicators of volume-responsiveness, the indicators of an aerobic metabolism should be considered instead of central venOUS oxygen saturation for starting hemodynamic resuscitation.
Abstract: Objectives:During circulatory failure, the ultimate goal of treatments that increase cardiac output is to reduce tissue hypoxia. This can only occur if oxygen consumption depends on oxygen delivery. We compared the ability of central venous oxygen saturation and markers of anaerobic metabolism to pr
TL;DR: Chlorination of NOM during disinfection is selective toward components with relatively high double bond equivalency and number of oxygen atoms per carbon, resulting in distinct patterns in the occurrence of DBP formulas.
Abstract: Natural organic matter (NOM) serve as precursors for disinfection byproducts (DBPs) in drinking water production making NOM removal essential in predisinfection treatment processes. We identified molecular formulas of chlorinated DBPs after chlorination and chloramination in four Swedish surface water treatment plants (WTPs) using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Chlorine-containing formulas were detected before and after disinfection and were therefore classified to identify DBPs. In total, 499 DBPs were detected, of which 230 have not been reported earlier. The byproducts had, as a group, significantly lower ratio of hydrogen to carbon (H/C) and significantly higher average carbon oxidation state (COS), double bond equivalents per carbon (DBE/C) and ratio of oxygen to carbon (O/C) compared to Cl-containing components present before disinfection and CHO formulas in samples taken both before and after disinfection. Electrophilic substitution, the proposed most significant reaction pathway for chlorination of NOM, results in carbon oxidation and decreased H/C while O/C and DBE/C is left unchanged. Because the identified DBPs had significantly higher DBE/C and O/C than the CHO formulas we concluded that chlorination of NOM during disinfection is selective toward components with relatively high double bond equivalency and number of oxygen atoms per carbon. Furthermore, choice of disinfectant, dose, and predisinfection treatment at the different WTPs resulted in distinct patterns in the occurrence of DBP formulas.
TL;DR: The study suggests that surface passivation is important for MoS(2)-based electronic devices and recommends that polymethyl methacrylate-passivated devices should be considered as a preferred material for FETs.
Abstract: We investigated the effects of passivation on the electrical characteristics of molybdenum disulfide (MoS(2)) field effect transistors (FETs) under nitrogen, vacuum, and oxygen environments. When the MoS(2) FETs were exposed to oxygen, the on-current decreased and the threshold voltage shifted in the positive gate bias direction as a result of electrons being trapped by the adsorbed oxygen at the MoS(2) surface. In contrast, the electrical properties of the MoS(2) FETs changed only slightly in the different environments when a passivation layer was created using polymethyl methacrylate (PMMA). Specifically, the carrier concentration of unpassivated devices was reduced to 6.5 × 10(15) cm(-2) in oxygen from 16.3 × 10(15) cm(-2) in nitrogen environment. However, in PMMA-passivated devices, the carrier concentration remained nearly unchanged in the range of 1-3 × 10(15) cm(-2) regardless of the environment. Our study suggests that surface passivation is important for MoS(2)-based electronic devices.
TL;DR: The convergent evolution of high myoglobin net surface charge in mammalian divers increases intermolecular electrostatic repulsion, permitting higher muscle oxygen storage capacities without potentially deleterious self-association of the protein.
Abstract: Hemoglobin and myoglobin are widely responsible for oxygen transport and storage (see the Perspective by [Rezende][1] ). The ability of diving mammals to obtain enough oxygen to support extended dives and foraging is largely dependent on muscle myoglobin (Mb) content. Mirceta et al. (p. [1234192][2]) found that in mammalian lineages with an aquatic or semiaquatic lifestyle, Mb net charge increases, which may represent an adaptation to inhibit self-association of Mb at high intracellular concentrations. Epistasis results from nonadditive genetic interactions and can affect phenotypic evolution. Natarajan et al. (p. [1324][3]) found that epistatic interactions were able to explain the increased hemoglobin oxygen-binding affinity observed in deer mice populations at high altitude. In mammals, the offloading of oxygen from hemoglobin is facilitated by a reduction in the blood's pH, driven by metabolically produced CO2. However, in fish, a reduction in blood pH reduces oxygen carrying capacity of hemoglobin. Rummer et al. (p. [1327][4]) implanted fiber optic oxygen sensors within the muscles of rainbow trout and found that elevated CO2 levels in the water led to acidosis and elevated oxygen tensions.
[1]: /lookup/doi/10.1126/science.1240631
[2]: http://www.sciencemag.org/content/340/6138/1234192.full
[3]: /lookup/doi/10.1126/science.1236862
[4]: /lookup/doi/10.1126/science.1233692
TL;DR: In this paper, the authors reviewed the pertinent literature regarding oxygen transfer and consumption in subsurface flow treatment wetlands, and discussed the factors that influence oxygen availability, and provided first results from a pilot-scale research facility in Langenreichenbach, Germany.
TL;DR: In this article, the complex chemistry in both the neutral and ionic systems of a radio-frequency-driven atmospheric-pressure plasma in a helium?oxygen mixture (He?0.5% O2) with air impurity levels from 0 to 500?ppm of relative humidity from 0% to 100% using a zero-dimensional, time-dependent global model is clarified.
Abstract: We unravel the complex chemistry in both the neutral and ionic systems of a radio-frequency-driven atmospheric-pressure plasma in a helium?oxygen mixture (He?0.5% O2) with air impurity levels from 0 to 500?ppm of relative humidity from 0% to 100% using a zero-dimensional, time-dependent global model. Effects of humid air impurity on absolute densities and the dominant production and destruction pathways of biologically relevant reactive neutral species are clarified. A few hundred ppm of air impurity crucially changes the plasma from a simple oxygen-dependent plasma to a complex oxygen?nitrogen?hydrogen plasma. The density of reactive oxygen species decreases from 1016 to 1015?cm?3, which in turn results in a decrease in the overall chemical reactivity. Reactive nitrogen species (1013?cm?3), atomic hydrogen and hydroxyl radicals (1011?1014?cm?3) are generated in the plasma. With 500?ppm of humid air impurity, the densities of positively charged ions and negatively charged ions slightly increase and the electron density slightly decreases (to the order of 1011?cm?3). The electronegativity increases up to 2.3 compared with 1.5 without air admixture. Atomic hydrogen, hydroxyl radicals and oxygen ions significantly contribute to the production and destruction of reactive oxygen and reactive nitrogen species.
TL;DR: In this article, Density functional theory plus U (DFT+U) calculations are used to investigate how the Sr concentration affects the processes that govern oxygen ion transport in La1-xSrxFeO3δ (LSF, x = 0, 0.25, and 0.50).
Abstract: Incorporating mixed oxygen-ion-electron conducting (MIEC) cathode materials is a promising strategy to make intermediate-temperature solid oxide fuel cells (IT-SOFCs) viable; however, a lack of fundamental understanding of oxygen transport in these materials limits their development. Density functional theory plus U (DFT+U) calculations are used to investigate how the Sr concentration affects the processes that govern oxygen ion transport in La1‑xSrxFeO3‑δ (LSF, x = 0, 0.25, and 0.50). Specifically, we show that oxygen vacancies compensate holes introduced by Sr and that this compensation facilitates oxygen vacancy formation in LSF. We also find that oxygen migration in LaFeO3 is accompanied by electron transfer in the opposite direction. Our results explicitly identify and clarify the role of electron-deficient substitutions in promoting oxygen diffusion in LSF. This atomic level insight is important for enabling rational design of iron-based SOFC cathode materials.
TL;DR: In this paper, high-quality silicon oxide (SiO2) thin films are formed by plasma-enhanced atomic layer deposition (PEALD) using bis(diethylamino)silane as a Si precursor and ammonia/oxygen plasmas at a substrate temperature of 150 ◦ C.
Abstract: High-quality silicon oxide (SiO2) thin films are deposited by plasma-enhanced atomic layer deposition (PEALD) using bis(diethylamino)silane as a Si precursor and ammonia/oxygen plasmas at a substrate temperature of 150 ◦ C. The SiO2 films are formed at a growth rate of ∼0.137 nm/cycle in high purity. The overall quality of the PEALD-SiO2 films are assessed by infrared spectroscopy, wet etch rate in 0.5% hydrofluoric solution, Auger electron spectroscopy, and current-voltage analysis. The quality of the films formed at low temperature using the combination of ammonia/oxygen plasmas compares well with deposition at higher temperatures (350 ◦ C) using oxygen plasma only.
TL;DR: In this paper, the role of gas phase oxygen on the ignition of nanothermite reactions was investigated, and it was concluded that the presence of free molecular oxygen cannot be a prerequisite to initiation for many other nanothermites.
TL;DR: In this paper, the synthesis of perovskite-type oxides was investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, temperature-programmed reduction (TPR), and Fourier transformed infrared spectroscopy (FTIR).
TL;DR: In this paper, the authors used FeZSM-5 zeolite with increased concentration of α-sites (100μmol/g) for the oxidation of methane by α-oxygen predeposited from nitrous oxide.
TL;DR: In this article, the selective catalytic oxidation of ammonia to nitrogen (NH 3 -SCO) has been studied over CuO-CeO 2 mixed oxides, and the active Cu component was doped into the CeO 2 by surfactant-templated method.
Abstract: The selective catalytic oxidation of ammonia to nitrogen (NH 3 -SCO) has been studied over CuO-CeO 2 mixed oxides. The active Cu component was doped into the CeO 2 by surfactant-templated method. The finely dispersed CuO, Cu-O-Ce solid solution and bulk CuO species were detected in CuO-CeO 2 mixed oxides. When the Cu loading was 10 wt% and the calcination temperature was 500 °C, CuO-CeO 2 catalyst exhibited the highest molar ratio of the finely dispersed CuO species and the smallest CeO 2 particles in size, and simultaneously possessed the highest level of activity. The finely dispersed CuO species was the main adsorbed sites of NH 3 molecules, and the NH 3(ad) could be further activated and transformed into NH x species by ceria under the roles of quick change of chemical state in near-surface region and the strong electron state interaction in CuO-CeO 2 catalysts. The synergetic interaction between the two components played an important role in NH 3 activation and oxidation. In addition, the activated intermediates (NH x ) could also react with lattice oxygen provided by Cu-O-Ce solid solution to form N 2 , N 2 O and H 2 O, which was confirmed by XPS, EPR and NH 3 -TPR analysis. Moreover, gas oxygen could refill the oxygen vacancies to replenish the lattice oxygen consumed by NH x species. The Cu-O-Ce solid solution promoted the activation of gas oxygen as well as the formation and migration of lattice oxygen in NH 3 -SCO reaction, and the formed rapid reduction–oxidation cycle was essential for the higher activity of NH 3 oxidation.
TL;DR: Various theoretical and empirical models of high-temperature dissociation were tested, including the empirical model proposed in the present work, and the oxygen dissociation rate constants were obtained for thermal equilibrium and thermal non-equilibrium conditions.
Abstract: The oxygen absorbance was studied at wavelengths 200–270 nm in Schumann-Runge system behind the front of a strong shock wave. Using these data, the vibrational temperature Tv behind the front of shock waves was measured at temperatures 4000–10 800 K in undiluted oxygen. Determination of Tv was based on the measurements of time histories of absorbance for two wavelengths behind the shock front and on the results of detail calculations of oxygen absorption spectrum. Solving the system of standard quasi-one-dimensional gas dynamics equations and using the measured vibrational temperature, the time evolution of oxygen concentration and other gas parameters in each experiment were calculated. Based on these data, the oxygen dissociation rate constants were obtained for thermal equilibrium and thermal non-equilibrium conditions. Furthermore, the oxygen vibrational relaxation time was also determined at high temperatures. Using the experimental data, various theoretical and empirical models of high-temperature d...