Atm O2 Research Articles

Benchmarking of oxygen evolution catalysts on porous nickel supports

Summary Active and inexpensive oxygen evolution reaction (OER) electrocatalysts are needed for energy-efficient electrolysis applications. Objective comparison between OER catalysts has been blurred by the use of different supports and methods to evaluate performance. Here, we selected nine highly active transition-metal-based catalysts and described their synthesis, using a porous nickel foam and a new Ni-based dendritic material as the supports. We designed a standardized protocol to characterize and compare the catalysts in terms of structure, activity, density of active sites, and stability. NiFeSe- and CoFeSe-derived oxides showed the highest activities on our dendritic support, with low overpotentials of η100 ≈ 247 mV at 100 mA cm–2 in 1 M KOH. Stability evaluation showed no surface leaching for 8 h of electrolysis. This work highlights the most active anode materials and provides an easy way to increase the geometric current density of a catalyst by tuning the porosity of its support.

Hierarchically Porous Hydrothermal Carbon Microspheres Supported N-Hydroxyphthalimide as a Green and Recyclable Catalyst for Selective Aerobic Oxidation of Alcohols.

A novel metal-free, reusable, and green catalytic system comprising hydrothermal carbon microspheres (HCMSs) supporting N-hydroxyphthalimide (NHPI) was developed and employed in the aerobic oxidation of alcohol. Hierarchically porous HCMSs with good monodispersity were produced by the hydrothermal carbonization of sucrose and designed NaOH-impregnated calcination under a static air atmosphere. The meso- and macroporous pores on HCMSs make up 71% of the total pore volume. The covalent immobilization of NHPI onto HCMSs was first accomplished by grafting hyperbranched polyquaternary amine via repetitive ring-opening reactions of diglycidyl ether and subsequent amidation with 4-carboxy-NHPI. Owing to the cocatalysis of grafted quaternary ammonium salt, a designed heterogeneous catalyst has superior performance to free NHPI in the oxidation of 2-phenylethanol. The established catalytic system achieved 42% conversion and up to 96% selectivity of acetophenone at 90 °C under 1 atm O2 for 20 h and presented a versatile catalytic effect for diversified alcohols. Immobilized NHPI could be facilely recycled via simple filtration and displayed good stability for six cycles without a discernible decrease of reactivity or damage of catalyst morphology in repeated oxidation test.

Modeling Temperature- and Humidity-Dependent Kinetics of Oxygen Reduction Reaction

Designing active catalysts for oxygen reduction reaction (ORR) is one of the major challenges for polymer electrolyte fuel cells. Density functional theory (DFT) calculations have made significant contributions on understanding ORR pathways, rate-limiting step and catalytic activity on various transition metal surfaces 1-5. However, all these theoretical studies are for reactions at room temperature in aqueous liquid electrolytes. The condition is significantly different from actual operation conditions of fuel cells [60 to 80 °C and 30 to 100 % relative humidity (RH)]. Although the DFT models reasonably explain experimental results obtained by the rotating disk electrode (RDE) at room temperature in aqueous liquid electrolytes, the reaction mechanism and catalytic activity at the operating conditions can be significantly different. Here, we examine effects of temperature and RH on the ORR by using a micro-kinetic model. The examination indicates that both the rate-limiting step and material-dependence of the catalytic activity are strongly influenced by both temperature and RH.The theoretical analyses were carried out by extending a micro-kinetic model proposed by Hansen et al5 to higher temperature and lower RH conditions. For the extension, following assumptions were adopted. Free energies for reaction intermediates (adsorbed O, OH and HO2) are independent of temperature and relative humidity (RH) and fixed at the values in the original model.An additional reaction barrier due to the solvent reorganization, which was introduced to explain the experimentally observed prefactor in the original model, is entirely attributed to be enthalpic. The assumption (1) can be partially validated by relatively small entropies of the adsorbed species comparing with gaseous species. Because the assumption (2) is not verified, we also carried out the same simulation assuming that the solvent reorganization barrier is fully entropic [we define this assumption as (3)].Figures 1 (a) and (c) show the calculated ORR current density at 0.9V vs. reversible hydrogen electrode (RHE) under 1 atm O2 under the assumption (2) as a function of the binding energy of OH adsorbate vs. that of Pt (111). Figures 1 (b) and (d) show the calculated ORR current density in the same way as Figures 1 (a) and (c) under the assumption (3). In all conditions, in the right leg of the volcano-plot, where the OH binding energy is larger than the optimal point, the reaction is limited by the formation of the reaction intermediates. On the other hand, in the left leg of the volcano, the reaction is limited by the removal of the OH adsorbate. Regardless the type of the assumption [(2) or (3)], both the optimal catalytic activity and the optimal OH binding energy decrease with the rise in the temperature from 25 to 80 °C [see Figs. 1 (a) and (b)]. The low catalytic activity at high temperature is attributed to the drop in the reversible potential of ORR at high temperature. The shift in the optimal OH binding energy is attributed to the destabilization of OH adsorbate relative to the non-adsorbed species, which hold larger entropies than the adsorbates. The drop in RH enhances the optimal catalytic activity, while the opposite shift is observed for the optimal OH binding energy [see Figs. 1 (c) and (d)]. The both trends stem from the lowering of the water activity, which promotes the OH removal from the surface. All in all, our theoretical analyses indicate that the optimal OH binding energy strongly depends on both temperature and RH, indicating that the optimal catalyst at low temperature and in aqueous liquid electrolytes may not be optimal anymore at high temperature and low RH. Although our theoretical analyses strongly rely on non-verified assumptions (1)-(3) and the DFT model adopting the ice-like water,1 which is unlikely a proper model of the electrolyte at high temperature and low RH, the observation indicates the significance of more precise understanding of temperature-, RH- and material-dependence of ORR.In the presentation, we will present experimental data on temperature- and RH-dependent ORR activity and discuss the validity of the theoretical model. References J. K. Nørskov et al., J. Phys. Chem. B, 108, 17886 (2004).J. Greeley et al., Nat. Chem., 1, 552 (2009).J. X. Wang et al., J. Phs. Chem. A, 111, 12702 (2007).R. Jinnouch et al., Phys. Chem. Chem. Phys., 13, 21070 (2011).H. A. Hansen et al., J. Phys. Chem. C, 118, 6706 (2014). Figure 1

YBa2Cu3O7–δ films prepared by pulsed laser deposition in O2/Ar mixture atmosphere

The YBa2Cu3O7-δ(YBCO) superconducting films were fabricated epitaxially on STO(00 l) substrates by pulsed laser deposition method (PLD) in different O2/Ar mixture atmospheres. The surface morphology of the YBCO film is strongly dependent on the O2/Ar ratio of the ambient atmosphere. The surface particle density decreases and the particle size increases with the O2/Ar ratio decreasing. The lattice parameters and the superconducting transition temperature (Tc0) are almost independent on the O2/Ar ratio and are about the same as 1.168 nm and 90 K, respectively, which can be ascribed to the annealing process in 1 atm O2 for all the YBCO samples. Based on the above results, in O2/Ar ratio of 25:75 atmosphere, YBCO:LaAlO3 superconducting composite films with good performance were prepared by co-deposition of PLD with magnetron sputtering method. The experimental results provide a way to control the surface morphology of the YBCO films deposited by PLD method and provide valuable reference for the preparation of YBCO composite thin films by co-deposition of PLD with magnetron sputtering method in Ar/O2 mixture atmosphere.

Multi-instrument study of the mesosphere-lower thermosphere dynamics at 80°N during the major SSW in January 2019

Contemporaneous multi-instrument ground-based optical and meteor radar observations of OH and O2 airglow, temperature and neutral winds during the winter season of November 2018–February 2019 have been used to investigate the dynamics of the mesosphere/lower thermosphere (MLT) (80–100 km) region in the high Arctic at Svalbard, Norway (78°N, 16°E) and at Eureka, Canada (80°N, 274°E). Temperature observations by the MLS Aura satellite over the 20–90 km height range for the same period were also considered. The period is characterized by an unusual major sudden stratospheric warming (SSW) event that began with a displacement of the polar vortex around December 13, 2018 (DoY 347), followed by the vortex split on January 2, 2019 (DoY 367). The MLS Aura temperature observations outlined four periods of interest: 1) late November – early December (DoY 328–335) with cold temperature anomalies in the mesosphere and warm bursts at the stratopause; 2) December 13, 2018–January 2, 2019 (DoY 347–367) when the stratopause rapidly descended to 45 km and broke down, triggering the onset of a SSW; 3) January 3–20, 2019 (DoY 368–385) during the stratopause recovery phase, and 4) from January 21, 2019 (DoY 386) onward, with the formation of the elevated stratopause and gradual return to its pre-SSW height. Both airglow emissions, OH and O2 Atm, showed simultaneously significant depletion of the integrated emission rates (IER) and temperature decrease of the order of 50–60 K, indicating upwelling, depletion of the atomic oxygen and adiabatic cooling. These cold temperature anomalies were followed by enhancements in the observed airglow IERs on December 13, 2018 (DoY 347) and January 2, 2019 (DoY 367) accompanied by a decrease in the peak altitude of the OH layer suggesting down-welling and influx of atomic oxygen from the lower thermosphere. The observations revealed oscillations with periods of 4.5–7 days, 8–10 days, and 16–21 days consistent with previously reported planetary wave activity in the winter MLT region and during major stratospheric warming events. However, the results presented here show for the first time comparisons of the multi-instrument temperature observations at 78°N – 80°N, providing an indispensable tool in monitoring the dynamics over the polar cap in general, and in describing the regional dynamical response of the MLT region to major large-scale phenomena like stratospheric warmings, in particular.

Ionic liquid-mediated catalytic oxidation of β-caryophyllene by ultrathin 2D metal-organic framework nanosheets under 1 atm O2

An ionic liquid (IL)-mediated facile method was established for the epoxidation of β-caryophyllene with molecular oxygen using ultrathin (∼3−6 nm) 2D Cu-, Co- or Ce-based MOF nanosheets. Under the optimum conditions, high selectivity (92.4%) and excellent yield (86.7%) for β-caryophyllene epoxide were obtained over ultrathin (∼5.5 nm) Cu-TCPP nanosheets (TCPP = tetrakis(4-carboxyphenyl)porphyrin) with the aid of [C12mim]Cl at 313 K and 1 atm O2. Notably, a small amount of [C12mim]Cl (1-dodecyl-3-methylimidazolium chloride, 5.0 mol %) played pivotal roles in forming a favorable microenvironment in-situ, thus significantly improving the catalytic performances of above-mentioned Cu-TCPP nanosheets containing PVP stabilizer. Moreover, ultrathin Cu-TCPP nanosheets showed better stability during β-caryophyllene transformation in the presence of amphiphilic [C12mim]Cl, as supported by TEM and XRD analyses. Importantly, the addition of TBHP (tert-butyl hydroperoxide, 13.0 mol %) initiator is also crucial for the aerobic oxidation of β-caryophyllene viaCu-TCPP nanosheets/[C12mim]Cl/TBHP/O2 nanosystem. Further insights into the synergistic effects and free radical mechanism were achieved by fluorescence, DRUV-Vis, UV-vis and XPS measurements.

Fresh Produce Container Operated with a Routine of Hypobaric Application, CO2 Injection and Diffusion Tube Opening for Keeping Beneficial Modified Atmosphere

A concept of household container to create and keep the modified atmosphere (MA) beneficial for fresh produce mix was devised and tested under typical chilled storage conditions of 3°C. The container system containing mixed products is initialized by applying weak hypobaric condition (0.9 atm) and subsequently injecting CO2 gas at an appropriate low level (0.03 atm). The passive atmosphere modification by produce respiration is then induced to reach a target until gas diffusion tube of proper dimension starts to open. The design was made to attain quasi-steady state mass balance of O2, CO2 and N2 to maintain the desired MA through the storage. Interrupted opening for taking out or placing some products was to reinitialize the loop of control logic. The developed concept was tested by the container which held commodities of spinach, pak choi, oyster mushroom, peeled onion, strawberry and cut carrot. The target optimum MA of 11% O2 and 10% CO2 (0.11 and 0.10 atm, respectively) was set to avoid injurious range of O2 and CO2 concentrations for any commodities. The developed container system could work to reach and maintain beneficial MA of 0.10-0.12 atm O2 and 0.07-0.10 atm CO2 close to the target during the storage contributing to quality retention of products measured in weight loss, chlorophyll content of spinach, ascorbic acid content of pak choi, color of onion, texture of oyster mushroom, bacterial count of strawberry and carotenoids of carrot. The container system shows potential to improve current preservation practice of fresh produce mix on consumers’ level.

Synthesis of salicylaldehyde through oxidation of o-cresol: Evaluation of activity and selectivity of different metals supported on OMS-2 nanorods and kinetics

Octahedral molecular sieve (OMS-2) was synthesized by the hydrothermal method and modified by the impregnation of different metals to give M/OMS-2 catalysts (where M = V, Cr, Fe, Co, and Mo). All these catalysts were tested in the oxidation of o-cresol to 2-hydroxybenzaldehyde (or salicylaldehyde, SAL). Among all M/OMS-2 catalysts, 5% Co/OMS-2 was found to be the most active catalyst for selective oxidation of o-cresol to SAL. Effect of several oxygen sources such as air, hydrogen peroxide (H2O2), molecular oxygen (O2), and tert-butyl hydroperoxide (TBHP) was studied for the oxidation of o-cresol. There was a complete conversion of o-cresol with 98% yield of SAL at 5 atm O2 pressure and 80 °C in 2 h. Additionally, the catalysts (virgin as well as reused forms) were characterized by FESEM, EDS, HR-TEM, XRD, CO2-TPD, TPR, Raman Spectra, BET surface area analysis, XPS, and DSC-TGA. The reaction kinetic model was developed using Mars van Krevelen mechanism. The catalyst was found to be inexpensive, robust, active, and showed very good reusability of 4 cycles, which makes it an attractive choice for o-cresol oxidation to SAL. The atom economy of the oxidation process is 98.15%. Thus, this process is an example of the synthesis of a vital chemical entity, salicylaldehyde, at mild reaction condition by a novel clean and green route.

Electrical characterization of mixed conducting SCY-YDC composite electrolyte

SrCe0.9Y0.1O3-δ-Ce0.9Y0.1O2-δ (SCY-YDC, 1:1 mole ratio), as a novel composite electrolyte, was successfully synthesized and characterized. X-ray diffraction patterns showed that SCY-YDC composite electrolyte is a mixture of SCY and YDC. Besides, no impurity phase emerged after sintering at 1550 °C for 10 h. AC impedance spectroscopy was used to determine the electrical properties of SCY-YDC at 500–800 °C in various atmospheres. Partial conductivities of oxygen vacancies, protons, and electrons (p-type) were calculated using the defect structure model. Results showed that SCY-YDC is a mixed (hole, proton, and oxygen-ion) conductor. Moreover, the contribution of holes is minor at 650–800 °C in high pressure (1 atm) or low pressure (10−4 atm) O2 atmospheres. Dominant carrier switched from protons to oxygen ions as temperature increased at vapor pressure in air of 0.038 atm. Total conductivity for SCY-YDC is 6.19 × 10−3 S cm−1 at 800 °C under pO2 = 1 atm and pH2O = 6 × 10−3 atm, which is higher than that of SCY (2.47 × 10−3 S cm−1). Results also showed that SCY-YDC composite material exhibits higher ionic conductivity and lower electron-hole conductivity than SCY. Electron-hole transference number for SCY-YDC is 0.049 at 800 °C in pO2 = 0.21 atm and pH2O = 0.038 atm. Ultraviolet–visible spectrophotometry results provided evidence that SCY-YDC can suppress electron conduction.

Reactions of POP-pincer rhodium(I)-aryl complexes with small molecules: coordination flexibility of the ether diphosphine

Reactions of the aryl complexes Rh(aryl){κ3-P,O,P-[xant(PiPr2)2]} (1; aryl = 3,5-Me2C6H3 (a), C6H5 (b), 3,5-Cl2C6H3 (c), 3-FC6H4 (d); xant(PiPr2)2 = 9,9-dimethyl-4,5-bis-(diisopropylphosphino)xanthene) with O2, CO, and MeO2CC≡CCO2Me have been performed. Under 1 atm of O2, the pentane solutions of complexes 1 afford the dinuclear peroxide derivatives [Rh(aryl){κ2-P,P-xant(PiPr2)2}]2(μ-O2)2 (2a–2d) as yellow solids. In solution, these species are unstable. In dichloromethane, at room temperature, they are transformed into the dioxygen adducts Rh(aryl)(η2-O2){κ3-P,O,P-[xant(PiPr2)2]} (3a–3d), as a result of the rupture of the double peroxide bridge and the reduction of the metal center. Complex 3b decomposes in benzene, at 50 °C, to give diphosphine oxide, phenol, and biphenyl. Complexes 1 react with CO to give the square-planar mono carbonyl derivatives Rh(aryl)(CO){κ2-P,P-[xant(PiPr2)2]} (4a–4d), which under carbon monoxide atmosphere evolve to benzoyl species Rh{C(O)aryl}(CO){κ2-P,P-[xant(PiPr2)2]} (5a–5d), resulting from the migratory insertion of CO into the Rh-aryl bond and the coordination of a second CO molecule. The transformation is reversible; under vacuum, complexes 5 regenerate the precursors 4. The addition of the activated alkyne to complexes 1b and 1d initially leads to the π-alkyne intermediates Rh(aryl){η2-C(CO2Me)≡C(CO2Me)}{κ3-P,O,P-[xant(PiPr2)2]} (6b, 6d), which evolve to the alkenyl derivatives Rh{(E)-C(CO2Me)=C(CO2Me)aryl}{κ3-P,O,P-[xant(PiPr2)2]} (7b, 7d). The diphosphine adapts its coordination mode to the stability requirements of the different complexes, coordinating cis-κ2-P,P in complexes 2, fac-κ3-P,O,P in compounds 3, trans-κ2-P,P in the mono carbonyl derivatives 4 and 5, and mer-κ3-P,O,P in products 6 and 7.

Selective oxidative esterification of alcohols over Au-Pd/graphene

Direct selective oxidative esterification of readily available alcohols under mild conditions is an attractive approach to synthesis valuable esters. Developing high performance catalyst is the key factor to the efficient esters synthesis. We report graphene supported Au-Pd alloy catalyst exhibits excellent catalytic performance in the synthesis of methyl benzoate from benzyl alcohol and methanol, a turnover frequency (TOF) of 230 h−1 and selectivity of 100% to methyl benzoate were achieved under 1 atm O2 at 25 °C, which is superior to the majority of the state-of-the-art catalysts. Experimentally observed volcano-like reactivity trends and DFT calculations prove the outstanding performance was mainly ascribed to unique electronic structures of AuPd alloy catalyst for the adsorption and activation of reactant molecules. The catalytic reaction mechanism for interpretation of the structure-activity relationships of various catalysts at molecular level was investigated. The present study could help to unravel the synergistic effect of Au-Pd catalyst and provides a mild and efficient route for synthesis high-value esters in terms of green and sustainable chemistry.

The Oxidative Polymerization of Vinyl Monomers in the Presence of N‐Hydroxyphthalimide

AbstractThe oxidation of vinyl compounds such as styrene, α‐methylstyrene, methyl methacrylate, acrylonitrile with molecular oxygen in the presence of N‐hydroxyphthalimide have been studied. It was shown that the N‐hydroxyphthalimide is efficient in initiation of the oxidative polymerization of vinyl monomers. The products of the monomer oxidation at 66 °C and 1 atm of O2 are corresponding polyperoxides and low molecular carbonyl compounds. IR‐ and 1H NMR spectroscopy confirm the alternating copolymer structure of polyperoxides with –O–O– bonds in the main chain. In the oxidative polymerization of vinyl monomers initiated with the mixtures of N‐hydroxyphthalimide and 2,2′‐azobisisobutyronitrile or benzoyl peroxide it was observed a synergistic effect of initiators’ action. N‐hydroxyphthalimide reacts with molecular oxygen, initiator radicals or monomer to form the phthalimide‐N‐oxyl radical, which participates in the chain initiation stage and does not participate in the termination stages, which leads to a synergistic effect.

Cobalt-Free Perovskite-Type Oxygen Reduction Reaction Catalysts for Energy Conversion

Alkaline fuel cells and metal–air batteries are emerging as an alternative energy conversion devices which can use non-precious and earth-abundant materials as electrocatalysts for oxygen reduction reaction (ORR) [1-3]. Perovskite-type oxides have been widely investigated due to their high activity, long durability and low cost [4]. Mn and Co-based perovskites have shown stable and high ORR performance and their electrochemical properties was explained using the molecular orbital theory. It was shown that the transition-metal-oxide electrocatalysts exhibit maximum catalytic activity when the occupancy of the eg orbital is ~1 which is the primary activity descriptor, whereas spin-state and electronegativity are secondary activity descriptors [5]. However, Co-based oxides have several disadvantages such as high volatility, thermal expansion coefficient, and cost [6-8]. Thus, there is need for alternative Co-free materials for next generation fuel cells. Here, we report Co-free perovskite-type Ba0.5Sr0.5Fe0.8Cu0.2O3-δ as ORR electrode for fuel cells. Effect of Cu-doping in Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0-0.2) towards the ORR activity in alkaline media has been studied. Partial substitution of Cu in the Fe-site in (Sr,Ba)FeO3 could influence the transition-metal oxygen covalency which replaces and regenerates OH— ions in alkaline ORR process. Thin film rotating-disk electrode (RDE) method with well-defined oxygen transport was previously developed to study the ORR activity of perovskite catalysts [4, 9]. Evaluating the effects of such molecular level engineering on the desired outcome is challenging, since the ORR process consists of multiple adsorption/desorption step involving oxygen containing species. There are fewer literature on understanding the ORR process on transition metal oxides involving the transfer of four electrons and four OH— ions to O2 with subsequent cleavage of double bond O2. Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0-0.2) powders were prepared through sol gel synthesis method. Powder X-ray diffraction was employed for structural characterization and the activity towards ORR was studied using RDE method. RDE experiments were performed in oxygen saturated electrolyte at 100-1600 rpm. The voltage scan was performed from 0.4-0.9 V vs. RHE. The relation between current and rotational speed was evaluated through a Koutechy-Levich (K-L) plot to deduce the number of electrons (n) involved in the ORR process, i.e. n = (0.62∙F∙D0 2/3∙ v-1/6∙Co∙slope)-1 Where, F is Faraday’s constant, F = 96485 C.mol-1, (Do) diffusion coefficient of oxygen in 0.1M KOH = 1.93x10-5 cm2.s-1, (ν) Kinematic viscosity of 0.1 M KOH = 1.09x10-2 cm2.s-1, (Co) saturation concentration of O2 in 0.1 M KOH at 1 atm O2 pressure = 1.26x10-6 mol.cm-3, and slope – slope from K-L plot. Preliminary results showed that Cu doping in the lattice is affecting the ORR properties of perovskite in alkaline media. The slope of K-L plot gradually increases with increase in Cu content and decreases beyond 0.05 Cu until 0.2 Cu. The number of electron involved in the ORR process is mostly restricted to two. Acknowledgements This research was supported by the Canada First Research Excellence Fund (CFREF) at the University of Calgary. References Lu, J. Pan, A. Huang, L. Zhuang, J. Lu, Proc. Natl. Acad. Sci. U. S. A. 105, 20611 (2008).Pan, C. Chen, L. Zhuang, J. Lu, Acc. Chem. Res. 45, 473 (2012).Oz, K. Singh, D. Gelman, V. Thangadurai, Y. Tsur, J. Phys. Chem. C. 122 (27) 15097 (2018).Ge, A. Sumboja, D. Wuu, T. An, B. Li, F. W.T. Goh, T.S.A. Hor, Y. Zong, Z. Liu, ACS Catal. 5 , 4643 (2015).Suntivich, H. A. Gasteiger, N.Yabuuchi, H. Nakanishi, J.B. Goodenough, Y. Shao-Horn, Nat. Chem. 3, 546 (2011).McIntosh, J.F.Vente, W.G. Haije, D.H.A. Blank, H.J.M. Bouwmeester, Chem. Mater. 18, 2187 (2006).Teraoka, H. Shimokawa, C. Y. Kang, H. Kusaba, K. Sasaki, Solid State Ionics 177 , 2245 (2006).Wang, C. Tablet, A. Feldhoff, J. Caro, Adv. Mater. 17, 1785 (2005).Ge, A. Sumboja, D. Wuu, T. An, B. Li, F. W. T. Goh, et al., ACS Catal. 5, 4643 (2015). Figure 1

Oxygen storage capacity and thermal stability of brownmillerite-type Ca2(Al1-xGax)MnO5+δ oxides

Understanding the oxygen uptake/release mechanism in oxygen storage materials is of great importance in the design of energy-related materials and their corresponding applications. In this work, the effects of Ga doping amount on the oxygen storage capacity and thermal stability of Ca2(Al1-xGax)MnO5+δ (0 ≤ x ≤ 1) with a brownmillerite-type structure were investigated. Ca2AlMnO5+δ can reversibly store/release a large amount of excess oxygen (∼3.0 wt%) at low temperature (between 300 and 600 °C) under oxidative atmospheres. With the increasing Ga doping amount in Ca2(Al1-xGax)MnO5+δ, these materials uptake less oxygen at higher temperature which can be attributed to the difficulty in the oxidation of tetrahedral GaO4 blocks into octahedral GaO6 blocks under 1 atm O2. However, with the increasing of Ga-substitution amount, these Ca2(Al1-xGax)MnO5+δ (0 ≤ x < 1) can start to uptake oxygen at lower temperatures during the cooling process under flowing O2 due to the distorted structure. The results demonstrated that Ca2(Al1-xGax)MnO5+δ (0 ≤ x < 1) can reversibly store/release large amounts of oxygen via just controlling the surrounding temperature and/or oxygen partial pressure but without using reductive gases, which would enable them great potentials in many applications.

Ligand-Free Copper(I)-Catalyzed Benzylic Acyloxylation of 2-Alkylpyridines under Aerobic Conditions.

A ligand-free copper(I)-catalyzed benzylic acyloxylation of 2-alkylpyridines with carboxylic acids was realized by using 1.0 atm of O2 as a green oxidant. The transformation provided a facile access to a wide range of N-heterocyclic esters through C-O bond formation, with broad substrate scope and good functional group tolerance. Preliminary mechanistic investigations showed that this protocol included a radical process.

Poly-β-hydroxybutyrate Production by Methylosinus trichosporium OB3b at Different Gas-phase Conditions.

BackgroundThe utilization of methane for production of Poly-β-hydroxybutyrate (PHB) not only cuts the emissions of greenhouse gases but also greatly reduces PHB production cost.ObjectivesThe aim of this study was to determine the effects of gas-phase conditions on PHB production by Methylosinus trichosporium OB3b.Materials and MethodsBacterial cultivation and PHB production were conducted in a series of sealed serum bottles. Nitrogen-free mineral salts medium was used to induce PHB production in the presence or absence of N2 in the headspace.ResultsIn the absence of N2, the highest PHB content (i.e., 52.9% of the dry cell weight with a PHB concentration of 814.3 mg.L-1) was obtained at a ratio of CH4:O2=2:1. Further study at different O2 concentrations with a fixed CH4 partial pressure in absence of N2 showed that PHB accumulation by methanotroph could be tolerated high oxygen partial pressure and its respond to the variation of the oxygen concentration depends on the methane partial pressure. In presence of N2, with headspace gas replenished only when oxygen was almost depleted, the degradation of intracellular PHB has appeared. In the regimen of updating headspace gas at the point when the PHB content began to decrease, the highest PHB content (i.e., 55.5% of the dry cell weight with 901.8 mg.L-1 PHB concentration and 12.5 mg.L-1.h-1PHB productivity) was obtained at 0.2 atm O2 and PHB accumulation was depressed with an oxygen concentration greater than 0.3 atm.ConclusionsThe methanotroph responses differentially to the increase in the oxygen partial pressure with regard to PHB accumulation either in the presence or in the absence of N2.

Palladium-Catalyzed Aerobic Anti-Markovnikov Oxidation of Aliphatic Alkenes to Terminal Acetals.

Terminal acetals were selectively synthesized from various unbiased aliphatic terminal alkenes and 1,2-, 1,3-, or 1,4-diols using a PdCl2(MeCN)2/CuCl catalyst system in the presence of p-toluquinone under 1 atm of O2 and mild reaction conditions. The slow addition of terminal alkenes suppressed the isomerization to internal alkenes successfully. Electron-deficient cyclic alkenes, such as p-toluquinone, were key additives to enhance the catalytic activity and the anti-Markovnikov selectivity. The halogen groups in the alkenes were found to operate as directing groups, suppressing isomerization and increasing the selectivity efficiently.

Aerobic oxidation of the C–H bond under ambient conditions using highly dispersed Co over highly porous N-doped carbon

Highly dispersed Co in porous N-doped carbon is active for oxidation of the C–H bond to ketones under 60 °C and 1 atm O2, which is 41.3 times more active in comparison to ZIF-67-derived Co catalyst.

On the Theoretical and Experimental Control of Defect Chemistry and Electrical and Photoelectrochemical Properties of Hematite Nanostructures.

Hematite (α-Fe2O3) is regarded as one of the most promising cost-effective and stable anode materials in photoelectrochemical applications, and its performance, like other transition-metal oxides, depends strongly on its electrical and defect properties. In this work, the electrical and thermomechanical properties of undoped and Sn-doped α-Fe2O3 nanoscale powders were characterized in situ at controlled temperatures ( T = 250 to 400 °C) and atmospheres ( pO2 = 10-4 to 1 atm O2) to investigate their transport and defect properties. Frequency-dependent complex impedance spectra show that interfacial resistance between particles is negligible in comparison with particle resistance. Detailed defect models predicting the dependence of electron, hole, and iron and oxygen vacancy concentrations on temperature and oxygen partial pressures for undoped and doped α-Fe2O3 were derived. Using these defect equilibria models, the operative defect regimes were established, and the bandgap energy of undoped α-Fe2O3 and oxidation enthalpy of Sn-doped α-Fe2O3 were obtained from the analysis of the temperature and pO2 dependence of the electrical conductivity. On the basis of these results, we are able to explain the surprisingly weak impact of donor doping on the electrical conductivity of α-Fe2O3. Furthermore, experimental means based on the results of this study are given for successfully tuning hematite to enhance its photocatalytic activity for the water oxidation reaction.

Computational Prediction and Experimental Realization of p-Type Carriers in the Wide-Band-Gap Oxide SrZn1- xLi xO2.

It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1- xLi xO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1- xLi xO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient of 353(4) μV K-1 for SrZn1- xLi xO2, where x = 0.021, confirmed that the compound is a p-type conductor, which is consistent with the pO2 dependence of the electrical conductivity observed in all SrZn1- xLi xO2 samples. The conductivity of SrZn1- xLi xO2 is up to 15 times greater than that of undoped SrZnO2 (for x = 0.028σ = 2.53 μS cm-1 at 600 °C and 1 atm of O2).