Добірка наукової літератури з теми "Double Oxygen Reduction"

Molybdenum carbide (Mo2C)-based electrocatalysts were prepared using two different carbon supports, commercial carbon nanotubes (CNTs) and synthesised carbon xerogel (CXG), to be studied from the point of view of both capacitive and electrocatalytic properties. Cation type (K+ or Na+) in the alkaline electrolyte solution did not affect the rate of formation of the electrical double layer at a low scan rate of 10 mV s−1. Conversely, the different mobility of these cations through the electrolyte was found to be crucial for the rate of double-layer formation at higher scan rates. Molybdenum carbide supported on carbon xerogel (Mo2C/CXG) showed ca. 3 times higher double-layer capacity amounting to 75 mF cm−2 compared to molybdenum carbide supported on carbon nanotubes (Mo2C/CNT) with a value of 23 mF cm−2 due to having more than double the surface area size. The electrocatalytic properties of carbon-supported molybdenum carbides for the oxygen reduction reaction in alkaline media were evaluated using linear scan voltammetry with a rotating disk electrode. The studied materials demonstrated good electrocatalytic performance with Mo2C/CXG delivering higher current densities at more positive onset and half-wave potential. The number of electrons exchanged during oxygen reduction reaction (ORR) was calculated to be 3, suggesting a combination of four- and two-electron mechanism.

This paper describes a facile solution route to the synthesis of CoCuPt hollow nanoparticles that readily form chain-like structures in solution. The formation of porous CoCuPt nanostructure is through galvanic replacement with cobalt-containing cores as the templates. This approach does not require the further removal of templates and greatly simplifies the synthetic procedures. These porous CoCuPt nanoparticles can be used as supportless electrocatalysts that exhibit enhanced mass- and area-specific activities in the oxygen reduction reaction (ORR) over commercial Pt black catalysts. The highest ORR specific activity achieved so far for this ternary Pt-alloy catalyst is 0.37 mA cm −2 Pt which is more than double that for Pt black.

The impact of hydrocarbon-molecular (C3H6)-ion implantation in an epitaxial layer, which has low oxygen concentration, on the dark characteristics of complementary metal-oxide-semiconductor (CMOS) image sensor pixels was investigated by dark current spectroscopy. It was demonstrated that white spot defects of CMOS image sensor pixels when using a double epitaxial silicon wafer with C3H6-ion implanted in the first epitaxial layer were 40% lower than that when using an epitaxial silicon wafer with C3H6-ion implanted in the Czochralski-grown silicon substrate. This considerable reduction in white spot defects on the C3H6-ion-implanted double epitaxial silicon wafer may be due to the high gettering capability for metallic contamination during the device fabrication process and the suppression effects of oxygen diffusion into the device active layer. In addition, the defects with low internal oxygen concentration were observed in the C3H6-ion-implanted region of the double epitaxial silicon wafer after the device fabrication process. We found that the formation of defects with low internal oxygen concentration is a phenomenon specific to the C3H6-ion-implanted double epitaxial wafer. This finding suggests that the oxygen concentration in the defects being low is a factor in the high gettering capability for metallic impurities, and those defects are considered to directly contribute to the reduction in white spot defects in CMOS image sensor pixels.

As fossil fuel resources become more and more scarce, attention has been turned to alternative sources of fuels and energy. One promising prospect is the conversion of methane (natural gas) to methanol, which requires an initial activation of a C-H bond and subsequent formation of a C-O bond. The most well studied methodologies for both C-H activation and C-O bond formation involve oxidation of the metal center. Metal complexes with facile access to oxidation states separated by four charge units, required for two subsequent oxidations, are rare. Non-oxidative methods to perform C-H bond activation or C-O bond formation must be pursued in order for methane to methanol to become a viable strategy. In this dissertation studies on redox and non-redox methods for both C-H activation and C-O bond formation are discussed. In the early chapters C-O bond formation in the form of reductive functionalization is modeled. Polypyridine ligated rhodium complexes were studied computationally to determine the properties that would promote reductive functionalization. These principles were then tested by designing an experimental complex that could form C-O bonds. This complex was then shown to also work in acidic media, a critical aspect for product stabilization. In the later chapters, non-oxidative C-H activation is discussed with Ir complexes. Both sigma bond metathesis and concerted metalation deprotonation were investigated. For the former, the mechanism for an experimentally known complex was elucidated and for the latter the controlling factors for a proposed catalyst were explored.

La reduction de l'oxygene est une reaction complexe; elle fait intervenir deux chemins reactionnels a deux ou quatre electrons pouvant se derouler simultanement. La technique employee pour etudier ce type de mecanisme est la cellule electrochimique a flux d'electrolyte et a double electrode (cfde). Dans ce type de dispositif hydrodynamique, la solution circule dans un canal ou sont fixees deux electrodes de travail: generatrice et collectrice. Les dimensions de la cellule sont fixees par les lois de l'hydrodynamique et par les limitations imposees par les problemes d'effets de bord. L'etude des facteurs hydrodynamiques et du comportement electrochimique de la cellule a montre que les caracteristiques geometriques de la cellule correspondent aux exigences necessaires au regime d'ecoulement laminaire. Le schema reactionnel de la reduction de l'oxygene considere est celui propose par wroblowa. Conformement a ce modele, nous avons etabli les equations permettant de determiner les constantes de vitesse relatives a la reduction directe (k#1) et a la reduction constituee de deux etapes avec formation de l'intermediaire peroxyde (k#2). Ces equations sont appliquees a la reduction de l'oxygene sur platine et sur les manganites de cuivre. Les resultats montrent que ce dispositif est utilisable pour detecter et quantifier l'espece intermediaire formee lors de la reaction. L'etude du mecanisme reactionnel de la reduction de l'oxygene est ensuite etudie sur les cobaltites mixtes et de nickelate de lanthane. L'utilisation de la cfde permet de determiner la quantite d'especes peroxydes formees pendant la reaction et les constantes cinetiques. De maniere independante, le nombre d'electrons echanges par molecule d'oxygene est determine en se basant sur les travaux de koutecky-levich. Finalement, nous comparons les differents oxydes etudies

博士
國立臺灣科技大學
化學工程系
107
Developing advanced nanomaterials and catalytically active materials is a substantial area of research to meet the growing global energy demand, given the central role that electrocatalytic reactions play in green sustainable energy generation, storage and conversion. However, development of catalytically active, operationally stable and inexpensive materials for the bifunctional oxygen evolution (OER) and reduction reaction (ORR) is one of the grand challenges in renewable energy storage and conversion technologies such as metal-air batteries and fuel cells due to the sluggish reaction kinetics of OER and ORR even when noble metal catalysts such as platinum with carbon support (Pt/C for ORR), ruthenium oxide (RuO2), and iridium oxide (IrO2) toward OER are applied. Consequently, a critical feature is to develop robust materials that have outstanding catalytic activity, cost-effective and promising durability for the more difficult ORR/OER process. Currently, transition metal hydroxides/oxides and Ni-based layered double hydroxides (LDHs) electrocatalysts are an interesting alternative to the novel metal-based electrodes in alkaline solutions due to their low cost, abundance, proven ability to catalyze the OER/ORR and operationally stable in high pH values of the electrolytes. To accelerate the development of Ni-based LDHs electrocatalysts with improved catalytic activities for the OER/ORR, it is essential to increase the understanding of the mechanisms, active sites at a fundamental level, and surface properties at relevant potentials during the OER and ORR operation and remains of great importance to the design of new electrocatalysts. This dissertation aims to develop endurable, inexpensive, and efficient bifunctional electrocatalysts for the OER and ORR operated under alkaline conditions at room temperature; investigate the mechanisms, active sites, and surface properties during the OER process using in situ spectro-electrochemical techniques. Accordingly, new classes of Ni-based LDHs electrocatalysts (NiRu-LDHs and NiMn-LDHs nanosheets) were developed and integrated with conductive supports (silver nanoparticles (Ag NPs) and silver nanowires (Ag NWs)) using decoration action and core-shelling strategies as efficient bifunctional electrocatalysts for OER and ORR. This approaches will have great benefits to design highly active and stable bifunctional electrocatalysts for the next-generation reversible oxygen electrodes involve the combination of less-expensive single-function OER and ORR electrocatalysts into one hybrid system. The first approach (Chapter 4) investigated in this dissertation “Site activity and population engineering of NiRu-layered double hydroxide nanosheets decorated with conductive silver nanoparticles for oxygen evolution and reduction reaction”. This work focuses on the development of new electrocatalyst; NiRu-LDHs decorated with Ag NPs (Ag NP/NiRu-LDHs) as efficient and stable bifunctional electrocatalyst toward the OER and ORR and intended to distinguish the site activity and site population associated to the overall catalytic activity. The higher ORR activity of Ag NP/NiRu-LDHs was mainly attributed to the increased Ag site activity and accessible Ag site populations. The increased Ag site activity is extensively contributed from the charge polarization occurring on the Ag sites responsible for weakening the adsorption of OH on the Ag sites and the presence of LDHs helps to remove the adsorbed OH from the surface of Ag. Furthermore, the decoration strategy enhances the dispersion of Ag and considerably increased the accessible site populations. These strong synergetic effects between Ag and LDHs significantly enhanced the catalytic activity of the ORR. Interestingly, engineering multiple vacancies (metal and oxygen vacancies) which causes the structural disorder and defects through the introduction of Ru and decorating NiRu-LDHs nanosheets with conductive Ag NPs (improve the intrinsically poor conductivity of LDHs) tunes the intrinsic properties of the Ni sites which in turn enhances the OER site activity and site populations. The strong synergetic effects of silver nanoparticles and metal LDHs engineer the active site activity and populations on both Ag and Ni in the bifunctional electrocatalysts for ORR and OER, respectively. The as-prepared Ag NP/NiRu-LDH shows substantially marvelous catalytic activity toward both OER and ORR features with low onset overpotential of 0.21 V and -0.27 V, respectively, with 0.76 V overvoltage difference between OER and ORR with excellent durability, demonstrating the preeminent bifunctional electrocatalyst reported to date. This work provides a new strategy to improve the intrinsic properties of LDHs and engineering multivacancies to enhance the site activity and populations associated with the overall bifunctional activity of the electrocatalysts. The second study (Chapter 5) aims to develop “hierarchical 3D NiMn-layered double hydroxide (NiMn-LDHs) shells grown on conductive silver nanowires (Ag NWs) cores as efficient ORR/OER bifunctional electrocatalysts”. As a result, the hierarchical 3D architectured Ag NW@NiMn-LDHs catalysts exhibit superb OER/ORR activities in alkaline condition. The outstanding bifunctional activities of Ag NW@NiMn-LDHs are essentially attributed to the synergistic contributions from the hierarchical 3D open-pores structure of the LDHs shells, improved electrical conductivity and small thickness of the LDHs shells associated to more accessible site populations. Moreover, the charge transferring effect between Ag cores and metals of LDHs shells, the formation of less coordinated Ni and Mn sites causes defective and distorted sites that strongly tune the intrinsic activity of the site activity and hence attaining enhanced catalytic activities. Thus, Ag NW@NiMn-LDH hybrids exhibit 0.75 V overvoltage difference between ORR and OER with excellent durability for 30 h, demonstrating the distinguished bifunctional electrocatalyst reported to date. Thus, the concept of the hierarchical 3D architecture of Ag NW@NiMn-LDHs considerably advances comprehensive research towards water electrolysis and oxygen electrocatalyst. The third approach (chapter 6) of this dissertation is to investigate the mechanisms, probe the active sites and surface properties of NiMn-LDHs and β-Ni(OH)2 electrocatalysts during the OER operation using in situ spectro-electrochemical techniques. Ni-based layered double hydroxides (LDHs) materials are highly active and cost-effective electrocatalysts that can be potentially used for efficient water oxidation process and extensively used toward sustainable energy generation. However, the mechanisms at a fundamental level, active phases and the processes occurring on the surface of Ni-based LDHs materials during the OER operation are not clearly known. Accordingly, the evidence from in situ Raman features provide that the Ni(OH)2 phases in both NiMn-LDHs and β-Ni(OH)2 get oxidized to NiOOH species as the electrode voltage increasing and NiOOH intermediate species deprotonated and get charged prior to the real water oxidation, suggesting that the formation of “active oxygen” species and hence acts as a precursors for the OER. We therefore propose that the identity of the “active oxygen” species is nickel superoxidic or peroxidic nature. The in situ XANES spectra provides the evidence that the Ni K-edge significantly shifted to higher energy upon the electrode potential increased, suggesting the redox transition of Ni(OH)2 in NiMn-LDHs to NiOOH upon anodization that constitutes the catalytic activity of OER active center. The in situ EXAFS spectra of Ni K-edge indicates that the intensity of both Ni−O (R =1.53 Å) and Ni−M (R =2.73 Å) coordination spheres gradually decreases as the applied electrode potentials increase prior to the OER whereas the formation of new peaks at 1.44 Å and 2.42 Å corresponding to the coordination sphere of Ni−O and Ni−M, suggesting the formation of new phases existing in different environment due to the redox transition of Ni(OH)2 to NiOOH occurs. The intensity of these peaks substantially increased as the voltage of electrode increased. However, the intensity and peak positions of Mn K-edge collected at different potentials are almost similar and remain unchanged, suggesting no transformation of Mn sites during the OER process. We therefore conclude that Ni constitutes the active center and evidently the active site for the OER whereas the introduction of Mn atom promotes synergistically the OER activity. We also present a systematic studies of guest anion effect on the number of active sites and site activity of NiMn-LDHs and Ni(OH)2 catalysts during the OER process using electrochemical, in situ spectro-electrochemical techniques and in situ XRD measurements, which in turn used to probe the active sites and structural change during the OER process. Evidently, the NiMn-LDHs exhibited incredible OER activity after guest anions (bromide and chloride) introduced and the OER activity gradually increased as the concentration of guest anions increased. These observations suggest that the active site activity originated from the less-stacking and plentiful exposed active edge sites due to the expansion of interlayer spaces of LDHs structure (confirmed by the in situ XRD measurement) promotes the OER activity. Unlike NiMn-LDHs, both the redox transition of Ni(OH)2/NiOOH and the OER activity of β-Ni(OH)2 catalyst is significantly affected after guest anions introduced and suppressed to higher overpotential. These results suggest that since β-Ni(OH)2 is structurally close-packed, the guest anions have only one possibility to interact with Ni(OH)2 and that is attacking the Ni sites which certainly accounts for the declined OER activity. In general, integrating LDHs with conductive Ag NPs and Ag NWs through decoration and core-shelling strategies engineers multiple vacancies which cause the structural disorder and defects essentially enhances bifunctional properties of the hybrids, conductivity, stability during OER and ORR operation. The discussed in situ spectro-electrochemical characterization of NiMn-LDHs catalysts with high OER activity demonstrates that the Ni sites constitute the active center and the presence of Mn atom promotes synergistically the OER activity. Although the recent studies are limited to investigate the active sites and surface properties of LDHs for oxygen electrocatalysis, these considerations are also anticipated to extend to other LDHs catalysts and electrochemical reactions.

博士
國立臺灣科技大學
應用科技研究所
106
Abstract We are in the era of seeking renewable energy to substitute fossil fuels due to the increasing demand for energy of the modern society, global warming, and depletion of natural sources. Therefore, globalization of advanced energy conversion technologies like rechargeable metal-air batteries (MAB’s), water-splitting, and regenerated fuel cells (RFCs) devices are highly regarded by the scientists as an environmentally friendly power source with global commercial viability. One of the most important challenges for electrochemically energy conversion and storage devices is to increase the efficiencies of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which will require the development of efficient and stable electrocatalysts. So far, Pt, Pd, IrO2, and RuO2 noble metal catalysts have acceptable kinetics. However, other electrocatalysts usually have high overpotential and sluggish kinetics and they give unsatisfactory ORR/OER performance. Further, limited reserves of noble-metal-based catalysts have precluded these renewable energy technologies from large-scale commercial applications. In many cases, how to improve both the activity and stability of an electrocatalyst is still an important challenge, especially under harsh alkaline conditions. The objectives of this dissertation are to tackle the challenge by developing new electrocatalysts and introducing robust and conductive support. The introduced materials are robust and conductive Magnéli phase Ti4O7 decorated in 3D-FL-NiRu-LDH and NiFe-LDH as ORR and OER electrocatalyst, respectively. This will have a great impact on lengthening the lifetime and reduce cost in energy conversion devices. The first part of the dissertation emphasizes “Robust and conductive Magnéli Phase Ti4O7 decorated on 3D-nanoflower NiRu-LDH (3D-FL-NiRu-LDH/Ti4O7) as high-performance oxygen reduction electrocatalyst”. This work has intended to discuss two basic issues and challenges in ORR electrocatalysts, namely increasing site population and enhancing the stability. The site population of the NiRu-LDH increased by engineering the morphology from 2D to 3D flowerlike material and the approach resulted in more surfaces exposed to the electrolyte. The second main challenge is to improve the intrinsically poor conductivity of LDHs and their short durability. In order to address this issue, we introduce robust, conductive and stable Magnéli phase Ti4O7 nano-pillar into flower-like NiRu-LDH through an easy in situ growth approach for the first time. The decoration of Magnéli phase Ti4O7 not only significantly improves the activity but also the stability of LDH nanosheet catalyst. The as-synthesized materials retain 98% of the activity after 45 h which surpasses all the reported LDH catalysts for oxygen reduction reaction under alkaline media. The key roles of Ti4O7 are to provide the effective charge transfer networks of LDH catalyst and prevent agglomeration of LDH catalysts though strongly coupled interactions evidenced by XPS. Therefore, the developed catalyst demonstrates promising conductivity, together with durability. The reported approach of introducing a robust and conductive pillar coupled with LDH catalysts provides a novel pathway for developing a highly efficient and durable electrocatalyst. The second part of this work is mediate extension of the first work but with some modification material for the application. Based on this, it is concerned with NiFe-LDH decorated by Magnéli phase Ti4O7 for OER electrocatalyst. An earth-abundant and highly efficient electrocatalyst are essential for OER due to its poor kinetics. NiFe-LDH is most promising OER catalysts, which perform best in alkaline electrolytes. However, the poor conductivity and the stacking structure of LDH limit its activity and exposure of active site, respectively. Therefore, we decorate LDH with highly conductive and robust Magnéli phase Ti4O7 in order to both boost conductivity and generate more dangling bonds and disordered structure that would result in vacancy and expose more active site on NiFe-LDH. In this work, a series of analyses reveal that the improved OER performances of NiFe-LDH-Ti4O7 compared to previously published works. This series improved performance is originated from the charge transfer effect, and strain effect between Ti4O7 and NiFe-LDH that results in structural deformation. Based on this, the as-synthesized NiFe-LDH-Ti4O7 nano-sheet exhibit an excellent catalytic activity for OER with ultra-small onset potential of only 1.42 and retain 100% of the current density after 30 hr. Furthermore, the presence of Fe3+ ions in the solution could bond with the Ti4O7 generating heterogeneous NiFe-LDH sites decorated with Ti4O7. These NiFe-LDH-Ti4O7 sites exhibited markedly an improved OER activity. In general, the use of Ti4O7 to decorate LDHs mainly enhances conductivity, stability (relative to carbon supports) and stacking between LDH layers during OER and ORR measurement. Additionally, it can also electronic and strain effect in the material that will result in vacancy and disordered in a structure of LDHs.

碩士
國立臺灣科技大學
化學工程系
107
Recently years, the rechargeable zinc-air batteries have its attracted much attention owing to high energy density and economic viability. In air electrode, a bifunctional electrocatalyst is desirable since the dual functionality of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are required on the same electrode under charging and discharging processes, respectively. Unfortunately, both commonly used catalysts: Pt/C in ORR and IrO2 in OER have no bifunctional property while the scarcity and cost of the metals limit its large-scale application for the electrolysis. In this work, the NiFe layered double hydroxides (Ni3Fe LDH) decorated with Ag nanowires (Ag NWs), as a bifunctional catalyst, was applied in oxygen reduction reaction and oxygen evolution reaction under alkaline media. First, the Ag nanowires were prepared via a polyol reduction method, and to optimize their linewidth and shape by changing the stirring rate and the precursor dropping rate. The Ni3Fe LDH was then deposited on the Ag nanowires by a hydrothermal process. As the results in surface morphology, the linewidth of Ag NWs was shortened with increasing stirring rate and precursor dropping rate. In FTIR analysis, a few residual PVP was still observed on Ag NWs while the intercalation anions of CO32- and NO3- were identified. As characterized in XPS and XAS, it was found that Fe sites in decorated Ni3Fe LDH were strongly influenced by Ag NWs, including the electronic effect (binding energy positively shifts) and the local structure environment (shorter Fe-O and Fe-M bond length). In OER performance, a mass activity of 432 mA mg-1LDH was reached by S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL, much better than Ni3Fe LDH (121 mA mg-1LDH) and IrO2 (149 mA mg-1catalyst), attributed to a large number of accessible active sites on the catalytic surface. However, the ORR activities of the Ni3Fe LDH/Ag NWs catalysts showed no advantage compared to as-synthesized Ag NWs and commercial Pt/C catalyst, which may be attributed to a few residual of PVP and too thick of LDH layer on Ag surface thereby inhibit O2 diffusion. In OER stability test, a chronoamperometric method was used for 24 hours, S-Ni3Fe LDH/Ag NWs-F(2:1)-10mL showed current retention by 92.6%, better than Ni3Fe LDH (76.3%) and IrO2 (91.6%), more suitable as an OER catalyst.

A citrate pyrolysis technique is a unique route to prepare reactive precursor mixtures through an ignition process of concentrated aqueous solution. This procedure enables to synthesize highly homogeneous and fine powders for functional materials. The double-chain based superconductor Pr2Ba4Cu7O15−δ and double perovskite photocatalytic semiconductor Ba2Tb(Bi,Sb)O6 were synthesized by using the citrate pyrolysis technique. For the present sample with a reduction treatment for 72 h, a sharp superconducting transition appeared at an onset temperature Tc,on=26 K accompanied by a zero-resistance state at Tc,zero=22 K. The superconducting volume fraction estimated from the magnetization measurement showed an excellent value of ∼58%. Both reduction treatment in a vacuum and subsequent quenching procedure are needed to realize higher superconductivity due to further oxygen defects. The polycrystalline samples for Ba2Tb(Bi1−x,Sbx)O6 (x=0 and 0.5) were formed in the monoclinic and cubic crystal structures. We conducted the gaseous 2-propanol (IPA) and methylene blue (MB) degradation experiments under a visible light irradiation, to evaluate photocatalytic activities of the powder samples. For the Sb50% substituted sample, the highest performance of MB degradation was observed. The effect of Sb-substitution on the photocatalytic degradation of MB is in direct contrast to that on the IPA decomposition under visible light irradiation. The enhanced photocatalytic properties in the citrate samples are attributed to their morphology, where fine particles are homogeneously distributed with a submicron order.

Phytosterols and related derivatives phytostanols are naturally occurring bioactive compounds present mainly in plant cell membranes. These lipophilic steroid alcohols contain a tetracyclic cyclopenta [a] phenanthrene structure which is substituted with a hydroxyl group at position C3 and have a side chain at position C17, usually containing one or more double bonds in the steroid skeleton. Phytosterols derived from isopentenyl pyrophosphate belong to the terpene family and are generally synthesized by the mevalonate pathway. They have similar structural and biological functions to cholesterol. It is not possible to synthesize by a human; as a result of their intake in diet, they are present in the human body as cereals, legumes, vegetables, fruits, nuts, vegetable oils, oilseeds, cereal grains, cereal-based products and related products which contain phytosterols in relatively high amount, consumed daily by the whole world population. Phytosterols are known as part of the normal human diet. Increasing interest has been given to phytosterols in recent years as epidemiological and experimental studies suggest that they have an important role in the protection from cancer besides their several beneficial effects, such as anti-inflammatory, antioxidative, anticarcinogenic, antifungal, antibacterial, antipyretic, antineoplastic, anti-ulcerative activity and cholesterol-lowering capacity. Inhibition tumor cell growth, multiplication, invasion and metastasis; reducing cell proliferation and increasing apoptosis; decreasing tumor size; inhibition of carcinogen production; reduction of angiogenesis and adhesion of cancer cells; inhibition of reactive oxygen species production and oxidative stress and increased antioxidant enzymes have been suggested as responsible mechanisms for anticancer activity of phytosterols. The current review aims to summarize the occurrence, safety, toxicity and chemistry of phytosterols to explain their potential activities in cancer with suggested mechanisms in detail. Furthermore, epidemiological and experimental studies related to treating the activity of phytosterols in gastrointestinal system cancers have been described.

Control of the absolute configuration of adjacent alkylated stereogenic centers is a classic challenge in organic synthesis. In the course of the synthesis of (–)-hybridalactone 4, Alois Fürstner of the Max-Planck-Institut Mülheim effected (J. Am. Chem. Soc. 2011, 133, 13471) catalytic enantioselective conjugate addition to the simple acceptor 1. The initial adduct, formed in 80% ee, could readily be recrystallized to high ee. In an alternative approach to high ee 2,3-dialkyl γ-lactones, David M. Hodgson of the University of Oxford cyclized (Org. Lett. 2011, 13, 5751) the alkyne 5 to an aldehyde, which was condensed with 6 to give 7. Coupling with 8 then delivered (+)-anthecotulide 9. The enantiomerically pure diol 10 is readily available from acetylacetone. Weiping Tang of the University of Wisconsin dissolved (Org. Lett. 2011, 13, 3664) the symmetry of 10 by Pd-mediated cyclocarbonylation. The conversion of the lactone 11 to (–)-kumausallene 12 was enabled by an elegant intramolecular bromoetherification. Shoji Kobayshi of the Osaka Institute of Technology developed (J. Org. Chem. 2011, 76, 7096) a powerful oxy-Favorskii rearrangement that enabled the preparation of both four-and five-membered rings with good diastereocontrol, as exemplified by the conversion of 13 to 14. With the electron-withdrawing ether oxygen adjacent to the ester carbonyl, Dibal reduction of 14 proceeded cleanly to the aldehyde. Addition of ethyl lithium followed by deprotection completed the synthesis of (±)-communiol E. En route to (–)-exiguolide 18, Karl A. Scheidt of Northwestern University showed (Angew. Chem. Int. Ed. 2011, 50, 9112) that 16 could be cyclized efficiently to 17. The cyclization may be assisted by a scaffolding effect from the dioxinone ring. Dimeric macrolides such as cyanolide A 21 are usually prepared by lactonization of the corresponding hydroxy acid. Scott D. Rychnovsky of the University of California Irvine devised (J. Am. Chem. Soc. 2011, 133, 9727) a complementary strategy, the double Sakurai dimerization of the silyl acetal 19 to 20.

Obesity carries a unique set of physiological changes and increased risks that impact thoracic surgery. Obese patients have reductions in expiratory reserve volume and functional residual capacity, decreased lung and chest wall compliance, and increased work of breathing. Preoperative assessment should include evaluation for signs of difficult airway management and review of studies assessing pre-thoracotomy respiratory function. Invasive lines may be required in addition to standard American Society of Anesthesiologists monitors. Positive pressure ventilation, optimal positioning, and passive oxygen may assist in adequate preoxygenation before induction. Lung isolation may be achieved via double-lumen tube or bronchial blocker placement through a single-lumen tube, or via exchange to a double-lumen tube. Lateral decubitus positioning can be challenging and carries a risk of brachial plexus injury. Hypoxaemia during one-lung ventilation may be managed with continuous positive airway pressure, positive end-expiratory pressure, or periodic re-inflation of specific lungs. Thoracic epidural analgesia or paravertebral block may assist postoperative pain management. Hypoxaemia, dysrhythmias, haemorrhage, and acute kidney injury must be monitored for postoperatively.

This chapter defines a core set of central metabolites that are thermodynamically activated but sufficiently stable kinetically to serve as diffusible molecules that power coupled reaction equilibria to drive biosynthesis in both primary and secondary pathways. Three such molecules are adenosine triphosphate (ATP), acetyl-coenzyme A (CoA), and the reduced nicotinamide coenzymes NADH and NADPH, which serve as cellular currencies for phosphoryl-, acetyl-, and electron transfers, respectively. ATP's thermodynamic activation arises from its kinetically stable side chain phosphoric anhydride linkages; acetyl-CoA from its acyl thioester grouping, and NAD(P)H from the dihydropyridinium ion linkage. S-Adenosylmethionine, with its activated sulfonium cation group, can transfer methyl, aminobutyryl, and adenosyl groups to cosubstrates as electrophilic or as radical fragments. Carbamoyl phosphate is a biologic carbamoylating reagent due to its mixed acyl phosphoric anhydride core. UDP-glucose and congeneric NDP-hexoses are fragmentable enzymatically into C1-glucosyl electrophiles for capture by cosubstrate nucleophiles. The delta 2- and 3-double bonds in isopentenyl-PP isomers serve as electrophilic and nucleophilic partners, respectively, for C–C bond-forming alkylations at the start of all isoprenoid biosynthetic pathways. Adenosine-5′-phosphosulfate is activated for sulfuryl group transfer via its mixed sulfuric-phosphoric acid side chain linkage. Molecular oxygen (O2) is kinetically stable enough to comprise 21% of Earth's atmosphere, but is thermodynamically activated to be the terminal electron acceptor in aerobic metabolism. Its controlled reductive cleavage is the driving force for introduction of diverse oxygen functional groups in a plethora of natural product maturations.

Weiping Tang at the University of Wisconsin, Madison reported (J. Am. Chem. Soc. 2013, 135, 12434) the total synthesis of the tropone-containing norditerpenes hain­anolidol 6 and harringtonolide 7 by making use of a strategic [5+2] oxidopyrylium cycloaddition. First, the known ketone 1 was converted through a number of steps to cycloaddition precursor 2. Treatment with DBU then effected the key cycloaddition to furnish the complex polycyclic compound 3. Additional manipulations revealed struc­ture 4 with the lactone ring in place. The tropone ring of the natural structures was con­structed by reaction of the cycloheptadiene moiety of 4 with singlet oxygen followed by Kornblum- DeLaMare rearrangement with DBU to afford ketone 5. Double elimination using TsOH then produced hainanolidol 6. The free hydroxyl of 6 was engaged in a C–H-functionalizing cyclization using Pd(OAc)₄ to yield harringtonolide 7 as well. Hanfeng Ding at Zhejiang University developed (Angew. Chem. Int. Ed. 2013, 52, 13256) a concise route to indoxamycin F 12 (as well as the related indoxamy­cins A and C). The complex intermediate 9 was accessed in only four steps from the bicyclic ketone 8, which in turn was prepared by a route involving an Ireland–Claisen rearrangement and a reductive 1,6-enyne cyclization (not shown). An impressive oxa-conjugate addition/methylenation reaction to produce 11 was accomplished by treat­ment of 9 with Grignard 10 followed by Eschenmoser’s salt. Some final decorative work then led to indoxamycin F 12. The strained polycyclophane natural product cavicularin 18 was synthesized in enantioenriched form by an innovative strategy reported (Angew. Chem. Int. Ed. 2013, 52, 10472) by Keisuke Suzuki at the Tokyo Institute of Technology.

Abstract In the continuing progress of fuel cell technology, CeO2 double doped electrolytes appears to be promising for lowering the SOFC's working temperatures. Ceria electrolytes have better ionic conductivities than YSZ but, at low oxygen partial pressures, the chemical reduction of ceria leads to increasing electronic conduction. Double doping of the ceria increases the electrolytic conduction range without changing its conductivity. To avoid stress development within the ceria crystallographic structure, the dopants mix must have a mean ionic radius as close as possible to the critical ionic radius. Ceria electrolytes with various compositions and dopant concentrations are synthesized with a combinatorial chemistry approach. To synthesize new electrolytes, solution plasma spraying with nitrate salt precursor is used. The reaction is completed and nanocrystalline thin layers of ceramic are formed in the plasma. Comparative studies of plasma spraying techniques, with YSZ powder plasma spraying as electrolyte reference, were performed. Also, comparative impedance spectroscopy measurements are to be performed to validate the double doping hypothesis and thence to identify the best electrolytes in the suite of over 300 new materials.

Abstract This paper presents an unparalleled engineering assessment conducted to evaluate the feasibility of pre-investing in O2 enrichment technology, with the purpose of increasing the processing capacities of conventional air-based sulfur recovery units (SRUs). Ultimately, the goal is to minimize the overall number of required SRUs for a greenfield gas plant and, consequently, capture a significant cost-avoidance opportunity. The technology review revealed that a high-level O2 enrichment can double the processing capacity of air-based SRU, depending on the H2S content in acid gas. As H2S mole fraction in feed increases, the debottlenecking capability increases. For the project under assessment, the processing capacity of air-based SRUs showed a maximum increase of 80%. On the contrary, operating with high O2 levels, will elevate SRU reaction furnace temperature, and mandates installing high-intensity burners, along with special control and ESD functions, to manage potential risk and ensure safe operation. Additionally, the liquid handling section of SRUs (condensers, collection vessels, degassing vessels, sulfur storage tanks) should be enlarged to accommodate more sulfur production. Typically, the enriched oxygen can be supplied from air separation units (ASUs), which entails significant capital cost. Apart from these special design considerations, there are several advantages for adopting this technology. Oxygen enrichment removes significant nitrogen volumes, which reduces loads on Claus, tail gas treatment, and thermal oxidizer units. Hence, lower capital cost for new plants is acquired due to equipment size reduction. In addition, higher HP steam production and less fuel gas consumption are achieved. Conventionally, O2 enrichment technology is employed in the initial design stage or used to retrofit operating SRUs facilities. However, it is unique to consider O2 enrichment-design requirements as part of new air-based SRUs design for phased program development. The objective is to enable smooth transition to fully O2 enrichment operated SRUs at a later phase of the project without the need for any design modification. This exceptional pre-investment strategy has resulted into reducing the required number of SRUs at phase II from eight to five units; and accordingly, a significant cost avoidance was captured.

Fatigue crack propagation (FCP) rates for 304 stainless steel (304SS) were determined in 24°C and 288°C air and 288°C water using double-edged notch (DEN) specimens of 304 stainless steel (304 SS). Tests performed at matched loading conditions in air and water at 288°C with 20–60 cc H2/kg H2O provided a direct comparison of the relative crack growth rates in air and water over a wide range of crack growth rates. The DEN crack extension ranged from short cracks (0.03–0.25 mm) to long cracks up to 4.06 mm beyond the notch, which are consistent with conventional deep crack tests. Crack growth rates of 304 SS in water were about 12 times the air rate. This 12X environmental enhancement persisted to crack extensions up to 4.06 mm, far outside the range associated with short crack effects. The large environmental degradation for 304 SS crack growth is consistent with the strong reduction of fatigue life in high hydrogen water. Further, very similar environmental effects were reported in fatigue crack growth tests in hydrogen water chemistry (HWC). Most literature data in high hydrogen water show only a mild environmental effect for 304 SS, of order 2.5 times air or less, but the tests were predominantly performed at high cyclic stress intensity or equivalently, high air rates. The environmental effect in low oxygen environments at low stress intensity depends strongly on both the stress ratio, R, and the load rise time, Tr, as recently reported for austenitic stainless steel in BWR water. Fractography was performed for both tests in air and water. At 288°C in water, the fracture surfaces were crisply faceted with a crystallographic appearance, and showed striations under high magnification. The cleavage-like facets on the fracture surfaces suggest that hydrogen embrittlement is the primary cause of accelerated cracking.

Development of reliable and precise methods for measuring the ratios of the isotopes of oxygen, 18O/16O and 17O/16O, in silicate minerals with spatial resolution on the order of tens of microns is of considerable interest to the geochemical community. Laser healing or ablation in a F2 atmosphere releases O2 tram small volumes of mineral material and so affords considerable reduction in sample size relative to conventional methods. A distinct advantage of laser treatment over other methods of microanalysis is that die liberated oxygen can be analysed using highly precise multicollector, magnetic sector mass spectrometers.

The efforts for reducing the emissions into the atmosphere start already in the furnace and are completed by an effective flue gas cleaning system. This implies the necessity for design developments of key components for a modern EfW plant. For the core component of the firing system — the grate — Fisia Babcock Environment (FBE) is using forward moving grates as well as roller grates. The moving grate, which is used in the great majority of all our plants, has specific characteristics for providing uniform combustion and optimal burnout. These include, amongst others: - Uniform air supply by means of specific grate bar geometry. - Two grate steps in direction of waste transport for optimum burnout. - Flexible adaptation of the combustion process to the respective conditions and requirements by zone-specific air distribution and transport velocity of waste on grate. - Combustion control adapted to the specific plant for ensuring a consistent combustion process and production of energy. In addition to these features influencing the emissions the moving grate exhibits also specific characteristics regarding the mechanical aspects allowing low-maintenance and reliable operation. For optimum flue gas burnout a good oxygen distribution after leaving the combustion zone is required. For ensuring this, the injection of secondary air is designed to produce a double-swirl, developed by FBE. Final reduction of the nitrogen constituents NO and NO2 to the stipulated emission value is achieved by the SNCR process. As well in this respect, there is a great amount of experience available. Besides these measures regarding the combustion process, this paper also reports about flue gas cleaning systems. In this field the FBE CIRCUSORB® process is presented and compared with the known dry absorption process. CIRCUSORB® is a lime-based flue gas cleaning process with continuous recirculation of the moistened reaction product and simultaneous addition of fresh hydrated lime. The flue gas temperature downstream of the economizer can be selected very low and permits in this way maximized utilization of the energy. The evaporation of the moisture from the reaction product (flash evaporation) effects final cooling down of the flue gas to optimum process temperature and improves at the same time SO2 separation. This reduces the technical investment required for the flue gas cleaning process. The total of all measures taken and the robust design of all components permit economical plant operation while complying with the stipulated emission limit values.

Abstract Reactive Plasma Spraying (RPS) with a hydrocarbon gas has been studied as a method to improve the mechanical properties of a commercially available 80:20 Ni/Cr alloy and subsequently as a method to reduce the oxygen content of MCrA1Y coatings. A conventional d.c. plasma torch has been modified by attaching a conical graphite tube (reactor) onto the end of the gun. The powder is then sprayed through the reactor with injected reactive hydrocarbon gas. The reactor shrouds the plasma flame from the external atmosphere and contains the desirable inner atmosphere necessary for RPS. When using a reactor and reactive gas the plasma environment is changed significantly, making it necessary to alter the spraying parameters from those recommended by the manufacturer for a particular powder. Work has been carried out to establish the effect various spray parameters have on the final coating such that new parameters can be selected which maximise the coatings quality and performance. Significant improvements have been achieved in terms of both objectives with hardnesses being doubled for the 80/20 Ni/Cr alloy and an order of magnitude reduction in the oxygen content for the MCrA1Y alloy.