Complete Reoxidation Research Articles

Fluorinated Mn(III)/(II)-Porphyrin with Redox-Responsive 1 H and 19 F Relaxation Properties.

A new fluorinated manganese porphyrin, (Mn-TPP-p-CF3 ) is reported capable of providing, based on the Mn(III)/Mn(II) equilibrium, dual 1 H relaxivity and 19 F NMR response to redox changes. The physical-chemical characterization of both redox states in DMSO-d6 /H2 O evidenced that the 1 H relaxometric and 19 F NMR properties are appropriate for differential redox MRI detection. The Mn(III)-F distance (dMn-F =9.7-10 Å), as assessed by DFT calculations, is well tailored to allow for adequate paramagnetic effect of Mn(III) on 19 F T1 and T2 relaxation times. Mn-TPP-p-CF3 has a reversible Mn(II)/Mn(III) redox potential of 0.574 V vs. NHE in deoxygenated aqueous HEPES/ THF solution. The reduction of Mn(III)-TPP-p-CF3 in the presence of ascorbic acid is slowly, but fully reversed in the presence of air oxygen, as monitored by UV-Vis spectrometry and 19 F NMR. The broad 1 H and 19 F NMR signals of Mn(III)-TPP-p-CF3 disappear in the presence of 1 equivalent ascorbate replaced by a shifted and broadened 19 F NMR signal from Mn(II)-TPP-p-CF3 . Phantom 19 F MR images in DMSO show a MRI signal intensity decrease upon reduction of Mn(III)-TPP-p-CF3 , retrieved upon complete reoxidation in air within ~24 h. 1 H NMRD curves of the Mn(III)/(II)-TPP-p-CF3 chelates in mixed DMSO/water solvent have the typical shape of Mn(II)/Mn(III) porphyrins.

Oxidation rates and redox stabilization of ferrous iron in trioctahedral smectites

Iron(II)-bearing trioctahedral smectites (saponites) form during anoxic alteration of basaltic rock. They are predicted to have been widespread on the early Earth and are observed in the oceanic subsurface today. Smectite structures, including the occupancy of sites in the octahedral sheet, affect iron redox behavior but the rates and products of trioctahedral smectite oxidation have been largely unexplored to date. In this study we synthesized two Fe(II)-bearing trioctahedral smectites, one moderate (22 wt% Fe) and one high (27 wt% Fe) in iron content. We then examined the rate, extent, and products of their oxidation by dissolved oxygen, nitrite, and hydrogen peroxide. Dissolved oxygen caused partial oxidation of Fe(II) in the smectites with 14 to 43% of Fe(II) unoxidized after 20 to 30 days of exposure. The rate and extent of oxidation correlated with the dissolved oxygen concentration and the Fe(II) content of the clay. The incomplete oxidation in these experiments is consistent with the mixed-valent trioctahedral smectites observed in oxidized natural samples but contrasts with the complete reoxidation by oxygen shown by chemically- or microbially-reduced dioctahedral smectites. Oxidation of structural Fe(II) by 5 mmol L−1 nitrite was negligible for the moderate-iron smectite and yielded only ∼17% oxidation after 54 days of reaction for the high-iron smectite. Hydrogen peroxide caused rapid and near-complete oxidation of both clays. Powder X-ray diffraction, variable-temperature Mössbauer spectroscopy, and extended X-ray absorption fine structure spectroscopy together detected no crystalline or short-range-ordered secondary phases and show that oxidized iron remained in the trioctahedral smectite structure. The recalcitrant Fe(II) pool in oxidized trioctahedral smectites exists in less distorted sites than Fe(II) in the initial clays. Its unreactive nature at prolonged reaction times indicates an elevated redox potential generated by the local coordination environment. Slower oxidation rates create a larger recalcitrant Fe(II) pool, suggesting kinetic competition between oxidation and a process involved in redox stabilization, such as electron exchange between octahedral iron sites or deprotonation of hydroxyl groups in the structure. The resistance to complete oxidation of trioctahedral ferrous smectites and their full retention of iron demonstrates that transitions from anoxic to oxic conditions generate mixed-valence smectites rather than a mixture of new phases. Identifying the diagenetic products of mixed-valent trioctahedral smectites may provide an indicator in the rock record of past redox cycling. Substantial portions of structural Fe(II) in trioctahedral smectites display slow abiotic oxidation kinetics and represent potential electron donors for both microaerophilic iron oxidizing and nitrate-reducing, iron-oxidizing microorganisms in altered mafic rocks and related settings.

Photo-epoxidation of α-pinene catalyzed by a MoVI oxo-diperoxo complex modified Ti-based metal-organic framework

An oxo-diperoxo molybdenum (VI) complex was anchored on a MIL-125-NH2 Metal-Organic Framework (MOF), and its Oxygen Atom Transfer (OAT) catalytic performance in the photo-epoxidation of α-pinene was evaluated. MIL-125-NH2 was modified with salicylaldehyde and pyridine-2-aldehyde by a post-synthetic approach to produce Schiff base ligands. Then, a MoVI complex was incorporated into the resulting MOFs. Bulk and surface characterization evidenced the incorporation of the Shiff base ligands and the MoO(O2)2 complex inside the Ti-MOF by studying the effect on the properties of each post-synthetic step. The final MOFs effectively achieved the transfer of 4 oxygen atoms to 4 olefin molecules during the irradiation but without the presence of any oxidant. The complete reoxidation of the oxo-Mo-center with O2 was reached since it presented the same catalytic activity after the oxygenation cycle. Also, α-pinene oxide resulted as the main product of photoinduced OAT long-term reaction, showing high performance in the epoxidation of olefins.

Synthesis, Experimental, and Theoretical Study of Co3-x Ni x O4 Mixed Oxides: Potential Candidates for Hydrogen Production via Solar Redox Cycles.

Recently, green hydrogen production via solar thermochemical water splitting (STWS) as a clean and sustainable method is becoming a subject of interest to many researchers. Great efforts are being made to develop materials for STWS with suitable operating conditions, low cost, and good cycling stability. In this context, the study of mixed cobalt and nickel oxides with the general formula Co3-x Ni x O4 (0 ≤ x ≤ 1) was carried out, where four mixed metal oxides Co2.75Ni0.25O4, Co2.5Ni0.5O4, Co2.25Ni0.75O4, and Co2NiO4 have been successfully synthesized through the sol-gel method modified Pechini route. The structural investigation demonstrated that pure spinel structures were obtained for 0 ≤ x ≤ 0.75. A deep study was carried out with the main goal of finding the best phase that provides low redox temperature. Interesting reduction temperatures for all the compositions have been found, and the lowest values of 675 and 710 °C have been reported for Co2.25Ni0.75O4 and Co2.5Ni0.5O4, respectively. The thermal cycling results of this latest material using TGA measurement have proven attractive cycling stability of which the complete reoxidation of the samples was achieved. In addition, thermodynamic analysis of a reduction step was performed and good agreement of the theoretical reduction temperature of Co2.25Ni0.75O4 with the experimental one has been found.

Investigation of reactive perovskite materials for solar fuel production via two-step redox cycles: Thermochemical activity, thermodynamic properties and reduction kinetics

The investigation and optimization of solar fuels production by H2O and CO2 splitting reactions using non-stoichiometric redox materials as oxygen carriers relies on materials-related studies. The thermochemical cycles performance strongly rely on the thermodynamics and kinetics of redox reactions, as well as the chemical composition and morphology of the reactive redox materials commonly based on ceria and perovskites. This study focusses on the evaluation and selection of suitable non-stoichiometric metal oxides for two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. The redox activities of different A- and B-site substituted perovskite materials (ABO3) were experimentally investigated (with A = La, Sr, Y, Ca, Ce, Pr, Sm and B = Mn, Co, Fe, Mg, Al, Ga, Cr). The reactive powders were synthesized via modified Pechini methods providing a porous microstructure especially suitable for thermochemical cycles, while their redox activity was evaluated by thermogravimetric analysis. This experimental screening highlighted the difficulty to combine high reduction extent (δ) achievable by the reactive material with complete re-oxidation extent and fast reaction rates. From the redox activity study of manganite perovskites, La0.5Sr0.5Mn0.9Mg0.1O3 (LSMMg) was pointed out as a good compromise between CO2 splitting activity and thermal stability, possibly competing with ceria as a promising material for two-step thermochemical cycles. Both thermodynamic and kinetic studies were also performed to provide a better understanding of the mechanisms involved in thermochemical cycles. Thermodynamic properties derived from experimental δ(T,pO2) diagrams were used to predict the upper bounds for both reduction extent and fuel production performance at equilibrium. Regarding kinetics, the activation energy during LSMMg reduction was shown to increase with the increase of the non-stoichiometry extent.

Manganese oxide coated TiO2 nanotube-based electrode for efficient and selective electrocatalytic sulfide oxidation to colloidal sulfur

Manganese oxide-coated TiO2 nanotube array (NTA) was synthesized and applied for the (electro) catalytic oxidation of sulfide. By setting the electrodeposition parameters and calcination temperature, the coating obtained was MnO2 or Mn2O3, with rod or needle like morphology. Excellent catalytic activity of the Ti/TiO2 NTA/MnxOy anodes resulted in robust and selective oxidation of sulfide to elemental sulfur via an inner sphere complex between the sulfide ion and Mn-oxide. The penetration of the MnxOy inside the NTA improved adhesion and enhanced the electron transfer, thus enabling complete and rapid electrocatalytic re-oxidation of the Mn-oxide coating. At pH 8, the final product of sulfide oxidation was colloidal sulfur, S8, which prevented anode passivation and enabled a stable (electro) catalytic activity in the subsequent applications. This was observed in both synthetic electrolyte and real sewage, thus demonstrating the efficiency of the Ti/TiO2 NTA/MnxOy anode for sulfide oxidation in complex waste streams.

Continuous Production of Formic Acid from Biomass in a Three-Phase Liquid–Liquid–Gas Reaction Process

In this contribution, we present for the first time a continuous production of formic acid under industrially relevant conditions using real biomass as a feedstock. A scale up to 2 L of reaction volume including product separation and catalyst recycling in an automated continuous miniplant has been realized and demonstrated for 670 h time-on-stream using sucrose as a feedstock with space-time yields of 1.1 gFA L–1 h–1, a turnover number (TON) of 840, and an average turnover frequency (TOF) of 1.3 h–1. Very remarkably, by performing a sensitivity analysis, a maximum space-time yield of 1.7 gFA L–1 h–1 was achieved. Moreover, we could demonstrate that oxygen pressures of only 0.5 bar are sufficient for complete catalyst reoxidation in our miniplant. This shows great potential for simply using air as the oxidant in a large-scale application. Very importantly, an experiment with molasses as the substrate showed the use of a technically relevant biomass for a long-term economic application of the continuous OxFA process. By using optimized conditions from the sensitivity analysis, a total amount of 1.2 g h–1 of formic acid could be continuously produced by our miniplant.

Solar chemical looping reforming of methane combined with isothermal H2O/CO2 splitting using ceria oxygen carrier for syngas production

Abstract The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle (CeO2/CeO2−δ) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and methane to syngas in the temperature range 900–1050 °C. Experiments were carried out with different ceria shapes via two-step redox cycling composed of endothermic partial reduction of ceria with methane and complete exothermic re-oxidation of reduced ceria with H2O/CO2 at the same operating temperature, thereby demonstrating the capability to operate the cycle isothermally. A parametric study considering different ceria macrostructure variants (ceria packed powder, ceria packed powder mixed with inert Al2O3 particles, and ceria reticulated porous foam) and operating parameters (methane flow-rate, reduction temperature, or sintering temperature) was conducted in order to unravel their impact on the bed-averaged oxygen non-stoichiometry (δ), syngas yield, methane conversion, and solar reactor performance. The ceria cycling stability was also experimentally investigated to demonstrate repeatable syngas production by alternating the flow between CH4 and H2O (or CO2). A decrease in sintering temperature of the ceria foam was beneficial for increasing syngas selectivity, methane conversion, and reactor performance. Increasing both CH4 concentration and reduction temperature enhanced δ with the maximum value up to 0.41 but concomitantly favored CH4 cracking reaction. The ceria reticulated porous foam showed better performance in terms of effective heat transfer, due to volumetric absorption of concentrated solar radiation and uniform heating with lower solar power consumption, thereby promoting the solar-to-fuel energy conversion efficiency that reached up to 5.60%. The energy upgrade factor achieved during cycle was up to 1.19. Stable patterns in the δ and syngas yield for consecutive cycles with the ceria foam validated material performance stability.

Hydrogen production via a novel two-step solar thermochemical cycle based on non-volatile GeO2

Encouraged by recent advances in solar-chemical fuel production, a moderately high-temperature solar thermochemical cycle based on GeO2/Ge is investigated thermodynamically. Since the GeO2/Ge redox has a great oxygen exchange capacity and suffers unfavorable phase change at high temperature, methanothermal reduction is introduced to lower the operation temperature below melting point of redox. The calculated results indicate that reduction conditions of 875 K ⩽ Tred ⩽ 1200 K and CH4:GeO2 = 2:1 are conducive to achieving high selectivities of H2 and CO. As for the oxidation step, the H2O:Ge ratio of 8:1 is found abundant enough to ensure complete reoxidation of Ge. Isothermal and non-isothermal solar-to-fuel efficiency (ηsolar-fuel) are compared, where Roxi=2 and Roxi=8 are suggested to pursue highest non-isothermal ηsolar-fuel of 0.47 and isothermal ηsolar-fuel of 0.28 respectively. In addition, the preferred site of CH4 adsorbing on GeO2 is predicted, and the calculated adsorption energy is lower than that of SnO2, indicating that GeO2 could be a suitable material for substrate before methanothermal reduction.

Oxide removal and stabilization of bismuth thin films through chemically bound thiol layers.

Bismuth has been identified as a material of interest for electronic applications due to its extremely high electron mobility and quantum confinement effects observed at nanoscale dimensions. However, it is also the case that Bi nanostructures are readily oxidised in ambient air, necessitating additional capping steps to prevent surface re-oxidation, thus limiting the processing potential of this material. This article describes an oxide removal and surface stabilization method performed on molecular beam epitaxy (MBE) grown bismuth thin-films using ambient air wet-chemistry. Alkanethiol molecules were used to dissolve the readily formed bismuth oxides through a catalytic reaction; the bare surface was then reacted with the free thiols to form an organic layer which showed resistance to complete reoxidation for up to 10 days.

Low-Temperature Reducibility of MxCe1–xO2 (M = Zr, Hf) under Hydrogen Atmosphere

Redox cycles utilize the reversible oxygen release/uptake of cerium oxide in a variety of renewable energy applications such as fuel cells, water gas shift reactions, and solar thermochemical fuel production. For all applications the degree of reduction/oxidation determines the overall performance. In this study we report on the redox behavior of MxCe1–xO2−δ (M = Zr, Hf; x = 0, 0.15, 0.2) solid solutions monitored by high-temperature in situ X-ray diffraction. During reduction in H2 at 600 °C and the successive formation of Ce3+ and oxygen vacancies, the lattice of ceria expands up to 0.3%. The lattice expansion of hafnium-doped ceria samples is 4 times larger than in zirconium-doped or undoped ceria, indicating drastically higher extents of oxygen vacancy formation. The same trends are validated using temperature-programmed reduction measurements. Complete reoxidation of the MxCe1–xO2−δ solid solutions in air at 600 °C is reflecting the reversibility of the redox process. Scanning electron microscopy and...

Radical Propagation in E. coli Class Ia Ribonucleotide Reductase Initiated by a 2,3,5‐trifluorotyrosyl Radical Cofactor

Escherichia coli class Ia ribonucleotide reductase (RNR) catalyzes the formation of all four deoxynucleoside 5′‐diphosphates from their corresponding nucleoside 5′‐diphosphates. Class Ia RNRs are composed of two homodimeric subunits, α2 and β2, that form the active complex. A stable tyrosyl radical (Y122•) in the β2 subunit generates a transient cysteine radical (C439•) located 35 Å away in the α2 subunit by a mechanism that is proposed to involve the concerted movement of protons and electrons (proton‐coupled electron transfer or PCET) through several aromatic amino acid residues (Y122 ‐ [W48] ‐ Y356 in β2 to Y731 ‐ Y730 ‐ C439 in α2). 2,3,5‐trifluorotyrosine (2,3,5‐F3Y) has been site‐specifically inserted at Y122 using a polyspecific aminoacyl tRNA synthetase to modulate the driving force of radical propagation. The diferric‐2,3,5‐F3Y• radical cofactor self assembles in vitro producing 0.8‐1.0 F3Y•/β2. The reaction of Y122(2,3,5)F3Y‐β2, α2, substrate and effector generates 0.3‐0.5 equiv. of a putative Y356• that is kinetically and chemically competent in nucleotide reduction. At 5°C, complete re‐oxidation of 2,3,5‐F3Y by Y356• is recorded and represents our first observation of the disappearance and reappearance of the stable radical at position 122. Altering the driving force for radical propagation by simply 10 mV partially lifts the protein conformational gate that governs radical transport allowing mechanistic insight into the details of PCET.

Exploitation of thermochemical cycles based on solid oxide redox systems for thermochemical storage of solar heat. Part 1: Testing of cobalt oxide-based powders

Thermochemical storage of solar heat exploits the enthalpy effects of reversible chemical reactions for the storage of solar energy. Among the possible reversible gas–solid chemical reactions, utilization of a pair of reduction–oxidation (redox) reactions of solid oxides of multivalent metals can be directly coupled to Concentrated Solar Power (CSP) plants employing air as the heat transfer fluid avoiding thus the need for separate heat exchangers. The redox pair of cobalt oxides Co3O4/CoO in particular, is characterized by high reaction enthalpies and thus potential heat storage capacity.Parametric testing of cobalt oxide-based powder compositions via Thermo-Gravimetric Analysis/Differential Scanning Calorimetry was performed to determine the temperature range for cyclic reduction–oxidation and optimize the process parameters for maximum reduction and re-oxidation extent. The heating/cooling rate is an important means to control the extent of the oxidation reaction which is slower than reduction. Complete re-oxidation was achieved within reasonable times by performing the two reactions at close temperatures and by controlling the heating/cooling rate. Under proper operating conditions Co3O4 powders exhibited long-term (30 cycles), complete and reproducible cyclic reduction/oxidation performance within the temperature range 800–1000°C. No benefits occurred by using Ni, Mg and Cu cobaltates instead of “pure” Co3O4. The Co3O4 raw material’s specific surface area is an influential factor on redox performance to which observed differences among powders from various sources could be attributed. Presence of Na was also shown to affect significantly the evolution of the products’ microstructure, though not necessarily combined with improved redox performance.

Dissolved inorganic carbon and alkalinity fluxes from coastal marine sediments: model estimates for different shelf environments and sensitivity to global change

Abstract. We present a one-dimensional reactive transport model to estimate benthic fluxes of dissolved inorganic carbon (DIC) and alkalinity (AT) from coastal marine sediments. The model incorporates the transport processes of sediment accumulation, molecular diffusion, bioturbation and bioirrigation, while the reactions included are the redox pathways of organic carbon oxidation, re-oxidation of reduced nitrogen, iron and sulfur compounds, pore water acid-base equilibria, and dissolution of particulate inorganic carbon (calcite, aragonite, and Mg-calcite). The coastal zone is divided into four environmental units with different particulate inorganic carbon (PIC) and particulate organic carbon (POC) fluxes: reefs, banks and bays, carbonate shelves and non-carbonate shelves. Model results are analyzed separately for each environment and then scaled up to the whole coastal ocean. The model-derived estimate for the present-day global coastal benthic DIC efflux is 126 Tmol yr−1, based on a global coastal reactive POC depositional flux of 117 Tmol yr−1. The POC decomposition leads to a carbonate dissolution from shallow marine sediments of 7 Tmol yr−1 (on the order of 0.1 Pg C yr−1. Assuming complete re-oxidation of aqueous sulfide released from sediments, the effective net flux of alkalinity to the water column is 29 Teq. yr−1, primarily from PIC dissolution (46%) and ammonification (33%). Because our POC depositional flux falls in the high range of global values given in the literature, the reported DIC and alkalinity fluxes should be viewed as upper-bound estimates. Increasing coastal seawater DIC to what might be expected in year 2100 due to the uptake of anthropogenic CO2 increases PIC dissolution by 2.3 Tmol yr−1and alkalinity efflux by 4.8 Teq. yr−1. Our reactive transport modeling approach not only yields global estimates of benthic DIC, alkalinity and nutrient fluxes under variable scenarios of ocean productivity and chemistry, but also provides insights into the underlying processes.

Mechanical Properties of Ni-YSZ Cermet Anode under SOFC Operating Condition by Using In-Situ Mechanical Testing Method

Ni-YSZ composites are widely used as SOFC anode materials for electrochemical devices. The mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method under SOFC operating condition. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol.%, 15:85 vol.%, 30:70 vol.%, and 50:50 vol.%. Electrical resistivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol.%. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of NiO-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

Effect of Redox Cycling on Mechanical Properties of Ni-YSZ Cermets for SOFC Anodes

Effects of redox cycling on the mechanical properties of Ni-YSZ cermets were investigated by using an in-situ small punch (SP) testing method. The Ni contents in the Ni-YSZ cermets tested in this study were 0, 15, 30 and 50 vol. %. Electrical conductivity measurements suggested that the Ni particles formed a network-like structure at the Ni contents greater than 20 vol. %. Experimental results obtained from the in-situ SP tests at 800åC demonstrated that ductile-like deformation was induced under reducing environment (at an oxygen partial pressure of 10-18atm) for the Ni contents of 30 and 50vol. %. The ductile-like behavior was attributable to the formation of Ni network. The first complete re-oxidation of Ni-YSZ cermets then caused critical damage and resulted in drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ cermets under reducing environments.

Unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds: Implications for oceanic isotope cycles and the sedimentary record

Sedimentary S cycling is usually conceptualized and interpreted within the context of steadily accreting (1-D) transport–reaction regimes. Unsteady processes, however, are common in many sedimentary systems and can result in dramatically different S reaction balances and diagenetic products than steady conditions. Globally important common examples include tropical deltaic topset and inner shelf muds such as those extending from the Amazon River ∼1600 km along the Guianas coast of South America. These deposits are characterized by episodic reworking of the surface seabed over vertical depths of ∼0.1–3 m. Reworked surface sediments act as unsteady, suboxic batch reactors, unconformably overlying relict anoxic, often methanic deposits, and have diagenetic properties largely decoupled from net accumulation of sediment. Despite well-oxygenated water and an abundant reactive organic matter supply, physical disturbance inhibits macrofauna, and benthic communities are dominated by microbial biomass across immense areas. In the surficial suboxic layer, molecular biological analyses, tracer experiments, sediment C/S/Fe compositions, and δ 34S, δ 18O of pore water SO 4 2 - indicate close coupling of anaerobic C, S, and Fe cycles. δ 18O– SO 4 2 - can increase by 2–3‰ during anaerobic recycling without net change in δ 34S– SO 4 2 - , demonstrating SO 4 2 - reduction coupled to complete anaerobic reoxidation to SO 4 2 - and a δ 18O– SO 4 2 - reduction + reoxidation fractionation factor⩾12‰ (summed magnitudes). S reoxidation must be coupled to Fe-oxide reduction, contributing to high dissolved Fe 2+ (∼1 mM) and Fe mobilization-export. The reworking of Amazon–Guianas shelf muds alone may isotopically alter δ 18O– SO 4 2 - equivalent in mass to⩾25% of the annual riverine delivery of SO 4 2 - to the global ocean. Unsteady conditions result in preservation of unusually heavy δ 34S isotopic compositions of residual Cr reducible S, ranging from 0‰ to >30‰ in physically reworked deposits. In contrast, bioturbated facies adjacent to physically reworked regions accumulate isotopically light S (δ 34S to −20‰) in otherwise similar decomposition regimes. The isotopic patterns of both physically and biologically reworked regions can be simulated with simple diagenetic models. Heavy S isotopic signatures are largely a consequence of unsteady diffusion and progressive anaerobic burndown into underlying deposits, whereas isotopically depleted bioturbated deposits predominantly reflect biogenic diffusive scaling and isotopic distillation/diffusive pumping associated with reoxidation in burrow walls immediately adjacent to reduced zones. The S isotopic transition from unsteady physically controlled regions of the Amazon delta moving laterally into bioturbated facies mimics the transition of S isotopic patterns temporally in the geologic record during the rise of bioturbation. No special role for S disproportionation is required to explain these differences. The potential role of unsteady, suboxic diagenesis and dynamic reworking of sediments has been largely ignored in models of the evolution of surficial elemental cycling and interpretations of the geologic record.

Quantitative solid-state NMR investigation of V5+ species in VPO catalysts upon sequential selective oxidation of n-butane

Abstract Bulk VPO catalysts (VPO/bulk) and VPO catalysts supported on mesoporous SBA-15 material (VPO/SBA-15) were treated sequentially in a flow of nitrogen loaded with n -butane and of synthetic air loaded with n -butane in order to reach a complete reduction and reoxidation, respectively, of the catalyst surface. The V 5+ species on these VPO catalysts were quantitatively investigated by solid-state NMR spectroscopy and correlated with the catalytic activities of the corresponding materials in the selective oxidation of n -butane to maleic anhydride. By 31 P{ 1 H} cross-polarization MAS NMR experiments on the n -butane-loaded VPO/SBA-15 catalyst was evidenced that n -butane is preferentially adsorbed at surface sites of δ -VOPO 4 -like phases. Based on the number of P/V 5+ species in δ -VOPO 4 -like phases as determined by MAS NMR spectroscopy, the turnover frequency of the surface sites on the VPO/SBA-15 catalyst was estimated to be about 0.2 s −1 .

J0802-4-5 SOFC燃料極用Ni-YSZの強度特性に及ぼすRedoxサイクルの影響([J0802-4]SOFC,PV,キャパシタ)

Effects of redox cycling on the mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol. %, 15:85 vol. %, 30:70vol. %, and 50:50 vol. %. Electrical conductivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol. %. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment (at oxygen partial pressure 1 × 10^<-18>atm) for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of Ni-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

Synthesis and Crystal Structure of a Bixbyite‐Type Solid Solution Zr0.43Er0.57O1.07N0.43

AbstractA powder of the composition 40 mol‐% Er2O3 and 60 mol‐% ZrO2 has been prepared. The anion deficient fluorite related compound Zr3Er4O12 [R\bar{3}: a = 971.79(7) pm and c = 907.976(0) pm] was produced. This precursor was treated with gaseous ammonia at temperatures between 25 and 1200 °C. The reaction was followed in situ by X‐ray diffraction in a high temperature reaction chamber under a constant flow of ammonia. The nitridation of Zr3Er4O12 led to a nitride oxide of the solid‐solution‐type with an apparent composition Zr0.43Er0.57O1.07N0.43 The compound crystallizes isostructural to bixbyite due to vacancy ordering [Ia\bar{3}: a = 1036.37(4) pm]. The reoxidation of the nitride oxide was monitored in DTA/TG experiments exhibiting an almost complete reoxidation to the starting composition except for some inclusions of dinitrogen.