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DOE OSTI2017

Hf-W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26 Al in the solar nebula

The CR chondrites are distinct from most other chondrites in having younger chondrule 26 Al- 26 Mg ages, but the significance of these ages and whether they reflect true formation times or a heterogeneous distribution of 26 Al are not well understood. To better determine the timescales of CR chondrule formation and CR chondrite parent body accretion, we obtained Hf-W isotopic data for metal, silicate, and chondrule separates from four CR chondrites. We also obtained Mo isotopic data for the same samples, to assess potential genetic links among the components of CR chondrites, and between these components and bulk chondrites. The isotopic data demonstrate that metal and silicate in CR chondrites exhibit distinct nucleosynthetic W and Mo isotope anomalies, caused by the heterogeneous distribution of a single presolar s-process carrier. These isotope signatures are akin to the complementary anomalies found previously for chondrules and matrix in CV chondrites and indicate that the major components of CR chondrites are genetically linked and formed from a common reservoir of solar nebula dust. The obtained Hf-W age of 3.6±0.6 million years (Ma) after the formation of Ca-Al-rich inclusions (CAIs) most likely dates metal-silicate separation during chondrule formation and is consistent with Al-Mg and Pb-Pb ages for CR chondrules, indicating that CR chondrules formed ~1–2 Ma later than chondrules from most other chondrite groups. Moreover, chemical, isotopic, and chronological data imply close temporal link between chondrule formation and chondrite accretion, making the CR chondrite parent body one of the youngest meteorite parent bodies. Such a late accretion at ~3.6 Ma after CAIs is consistent with isotopic composition of CR chondrites (e.g., 15 N/ 14 N) that is indicative of a formation at a larger heliocentric distance, probably beyond the orbit of Jupiter. As such, the accretion age of the CR parent body provides the earliest possible time at which Jupiter could have migrated inwards, leading to scattering of carbonaceous meteorite parent bodies into the inner solar system. Finally, the concordant Hf-W and Al- Mg ages for CR chondrules, combined with Hf-W and Al-Mg data for bulk CAIs, angrites, and CV chondrules, provide strong evidence for a disk-wide, homogeneous distribution of 26 Al in the early solar system.

58 GEOSCIENCES↗

DOE OSTI2018

Formation and redox reactivity of ferrihydrite-organic carbon-calcium co-precipitates

Complexation with minerals plays a critical role in regulating the stability of organic matter. The presence of cations is assumed to be important for the complexation between organic matter and minerals, but there is still limited direct analysis for the formation and reactivity of mineral-organic matter-cation ternary complexes, as well as governing factors for the fate of minerals and organic matter in the complexes. In order to close this knowledge gap, we investigated the formation and reactivity of ferrihydrite (Fh)-organic carbon (OC)-calcium (Ca) ternary co-precipitates. We performed microbial anaerobic Fe reduction using Shewanella putrefaciens CN32 on synthesized Fh-OC-Ca co-precipitates and characterized OC and Fe minerals using various spectroscopic and wet chemistry techniques. We discovered that Ca incorporated into the co-precipitate was a function of OC/iron (Fe) ratio, but OC incorporation was not impacted by the Ca content. During the reduction, the presence of Ca favored the formation of green rust but decreased the formation of magnetite and siderite in co-precipitates with high OC content. The reduction of Fe and reductive release of Fe-bound OC were controlled primarily by the C/Fe ratio, rather than Ca/Fe ratio. Phenolic OC was preferentially released or degraded during the reduction compared to aromatic and carboxylic OC. Collectively, C/Ca incorporation data, Fe K-edge extended X-ray absorption fine structure (EXAFS) analysis for co-precipitates before and after reduction, and the reductive release of Ca and OC suggest the formation of Fh-OC-Ca ternary co-precipitates, likely with OC as bridges. The reduction of Fe and reductive release of OC were primarily controlled by the C/Fe ratio, whereas the presence of Ca affected the mineral phase transformation for Fh during the reduction of Fe. Thus, our results provide novel understanding for the formation and reactivity of Ca-based ternary co-precipitates, which can be valuable for building up process-based models for cycles of carbon and metals.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

Ionic conductivity and the formation of cubic CaH{sub 2} in the LiBH{sub 4}–Ca(BH{sub 4}){sub 2} composite

LiBH{sub 4}–Ca(BH{sub 4}){sub 2} composites were prepared by ball milling. Their crystal structures and phase composition were investigated using synchrotron X-ray diffraction and Rietveld refinement, and their ionic conductivity was measured using impedance spectroscopy. The materials were found to form a physical mixture. The composites were composed of α-Ca(BH{sub 4}){sub 2}, γ-Ca(BH{sub 4}){sub 2} and orthorhombic LiBH{sub 4}, and the relative phase quantities of the Ca(BH{sub 4}){sub 2} polymorphs varied significantly with LiBH{sub 4} content. The formation of small amounts of orthorhombic CaH{sub 2} and cubic CaH{sub 2} in a CaF{sub 2}-like structure was observed upon heat treatment. Concurrent formation of elemental boron may also occur. The ionic conductivity of the composites was measured using impedance spectroscopy, and was found to be lower than that of ball milled LiBH{sub 4}. Electronic band structure calculations indicate that cubic CaH{sub 2} with hydrogen defects is electronically conducting. Its formation along with the possible precipitation of boron therefore has an effect on the measured conductivity of the LiBH{sub 4}–Ca(BH{sub 4}){sub 2} composites and may increase the risk of an internal short-circuit in the cells. -- Graphical abstract: An Arrhenius plot of the ionic conductivity of the LiBH{sub 4}–Ca(BH{sub 4}){sub 2} composites (red, blue, green). The ionic conductivity of ball milled (gray) and non-milled (black) LiBH{sub 4} is shown for comparison. The filled symbols are measured during heating runs and the empty symbols are measured during subsequent cooling runs. The conductivity of the composites is in all cases higher during cooling, most probably due to the formation of an electronically conducting layer containing defect-rich cubic CaH{sub 2}. Such layer formation could eventually lead to a short circuit in the cell and reveals a general issue of chemical stability that should be attended to in the development of solid electrolyte materials. Highlights: • The LiBH{sub 4}–Ca(BH{sub 4}){sub 2} composite forms a physical mixture rather than a solid solution. • The formation of defect-rich, cubic CaH{sub 2} in a CaF{sub 2}-like structure is observed. • A new layer containing cubic CaH{sub 2} is conducting and may lead to a short-circuit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Space formations and nonlinear properties of noncentrosymmetric germanates

Space formations of Ge-O polyhedra have been analyzed for 114 noncentrosymmetric germanates. The type of Ge-O polyhedra space formations is dependent on the stoichiometric ratio SR=n(O)/n(Ge), where n(O) is the number of oxygen and n(Ge) is the number of germanium atoms in formal composition of the compound. Individual (Ge-O) polyhedra are found for SR≥3 chains of the polyhedra that exist in the range of SR=3–5. Only framework formations are possible at SR≤2.7. - graphical abstract: Examples of space formations of polyhedra. - Highlights: • Space formations of Ge-O polyhedra have been analyzed. • The dependence of the type of Ge-O polyhedra space formations on the stoichiometric ratio SR=n(O)/n(Ge) was established. • Set of experimental SHG data of noncentrosymmetric germanates was presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Unraveling the formation mechanism of NaCoPO 4 polymorphs

Phosphate compounds are one of the attractive classes of cathodes for their potential application in rechargeable Na-ion batteries (NIBs) due to their high insertion voltages and stabilities. Unlike olivine-LiMPO 4 (M = Fe, Mn, Co, Ni) cathodes, maricite-NaMPO 4 phases are electrochemically inactive due to lack of sodium diffusion channels. Interestingly, cobalt bearing compounds exhibit rich polymorphism (α-, β-, ABW- and Red-NaCoPO 4 ). However, the preparation of NaCoPO 4 single phases is challenging due to their closer enthalpies of formation. In this study, we have attempted to understand the formation mechanism of NaCoPO 4 polymorphs during solid state reaction using two different cobalt precursors (Co(OH) 2 and CoCO 3 ). The temperature dependent in-situ powder X-ray Diffraction (PXRD) studies showed the formation of β-NaCoPO 4 at a much lower temperature compared to the one reported in the literature, whilst we have discovered a new high temperature polymorph gamma-NaCoPO 4 . The choice of precursors was also found to be important for the preparation of ABW-NaCoPO 4 , i.e., the rapid decomposition of Co(OH) 2 has resulted in its formation whilst the high stability of CoCO 3 prohibited the same. The order of the formation of the NaCoPO 4 polymorphs during heating was found to be ABW→β→α →$\gamma$. During normal cooling, gamma-NaCoPO 4 transformed primarily into alpha-polymorph whilst quenching in liquid N-2 resulted in the formation of β-NaCoPO 4 The as-synthesized beta- and ABW-NaCoPO 4 phases exhibited high sodium (de)-intercalation voltages (similar to 4.2 and 4.5 V vs. Na + /Na 0 , respectively), albeit with limited reversible capacities. This study is expected to open new avenues to harvest metastable polymorphs based on other transition metals (Fe, Mn and Ni).

25 ENERGY STORAGE↗

DOE OSTI2014

Initial formation stage and succedent biomineralization of pearls

The initial formation stage and succedent biomineralization of pearls were studied using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy and atomic force microscopy. A new initial formation phase with needle-like structure which is found to be nanocrystallites of aragonite was discovered. As a result, two possible formation modes are proposed to describe the initial formation stage of pearls. As for the succedent mineralization of “brick and mortar” structure, nanostripes were first discovered inside the “brick” (aragonite platelet), compared with the foregoing finding of nanograins. The various nanostructures of aragonite platelet allow us to reconsider the role of the inter- and intracrystalline organic material surrounding CaCO{sub 3}, and a possible biomineralization mechanism was proposed. - Highlights: • A new initial formation mineral phase was discovered in pearl. • Nanograins and nanostripes inside aragonite platelets were found in pearl. • Two possible initial formation stages were proposed for pearl. • A possible biomineralization mechanism of nacre in pearl was proposed.

36 MATERIALS SCIENCE↗

DOE OSTI2018

The role of tungsten phases formation during tungsten metal powder consolidation by FAST: Implications for high-temperature applications

Highlights: • Lowering the sintering temperature of W to 2173 K by using FAST. • Application of electron microscopy for microstructure characterisation. • W{sub 2}C shell formation due to C difussion from graphite tooling. • Identification of co-formed secondary phase, WO{sub 2}. • Influence of WO{sub 2} on high-thermal applications. - Abstract: Tungsten is a candidate material for the demonstration fusion power plant DEMO. To ensure high density and structural stability, Field-Assisted Sintering Technique (FAST) is proposed as a consolidation method. This study discusses the formation of phases during sintering of tungsten by the FAST. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to evaluate the microstructure in tungsten-based materials. The results of microscopic examinations revealed the in-situ formation of tungsten oxide and a formation of tungsten carbide shell around tungsten core. Tungsten carbide-rich shell is formed due to the carbon diffusion from the graphite die used in the FAST into tungsten at high temperatures. In contrast to easy removal of tungsten carbide shell by mechanical grinding, the formation of tungsten oxide in the W-matrix can influence the performance of such material when used as plasma-facing material in the fusion reactor. High-temperature experiments at 1873 K showed that tungsten-oxide phase starts to decompose, which results in material degradation and formation of voids and surface blisters.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Study of hydraulic fracturing processes in shale formations with complex geological settings

Hydraulic fracturing has been applied to extract gas from shale-gas reservoirs. Complicated geological settings, such as spatial variability of the rock mass properties, local heterogeneities, complex in situ stress field, and pre-existing bedding planes and faults, could make hydraulic fracturing a challenging task. In order to effectively and economically recover gas from such reservoirs, it is crucial to explore how hydraulic fracturing performs in such complex geological settings. For this purpose, numerical modelling plays an important role because such conditions cannot be reproduced by laboratory experiments. This study focuses on the analysis of the influence of confining formations and pre-existing bedding planes and faults on the hydraulically-induced propagation of a vertical fracture, which will be called injection fracture, in a shale-gas reservoir. An elastic-brittle model based on material property degradation was implemented in a 2D finite-difference scheme and used for rock elements subjected to tension and shear failure. A base case is considered, in which the ratio SR between the magnitudes of the horizontal and vertical stresses, the permeability k c of the confining formations, the elastic modulus E p and initial permeability k p of the bedding plane and the initial fault permeability k F are fixed at reasonable values. In addition, the influence of multiple bedding planes, is investigated. Changes in pore pressure and permeability due to high pressure injection lasting 2 h were analysed. Results show that in our case during the injection period the fracture reaches the confining formations and if the permeability of those layers is significantly larger than that of the shale, the pore pressure at the extended fracture tip decreases and fracture propagation becomes slower. After shut-in, the pore pressure decreases more and the fracture does not propagate any more. For bedding planes oriented perpendicular to the maximum principal stress direction and with the same elastic properties as the shale formation, results were found not to be influenced by their presence. In such a scenario, the impact of multiple bedding planes on fracture propagation is negligible. On the other hand, a bedding plane softer than the surrounding shale formation leads to a fracture propagation asymmetrical vertically with respect to the centre of the injection fracture with a more limited upward fracture propagation. A pre-existing fault leads to a decrease in fracture propagation because of fault reactivation with shear failure. This results in a smaller increase in injection fracture permeability and a slight higher injection pressure than that observed without the fault. Results of a sensitivity analysis show that fracture propagation is influenced by the stress ratio SR, the permeability k c of the confining formations and the initial permeability k p of the bedding plane more than the other major parameters.

58 GEOSCIENCES↗

DOE OSTI2013

Magnolol inhibits migration of vascular smooth muscle cells via cytoskeletal remodeling pathway to attenuate neointima formation

Background: Increased proliferation and migration of vascular smooth muscle cells (VSMCs) contribute importantly to the formation of both atherosclerotic and restenotic lesions. The objective of this study was to investigate the effect of magnolol on VSMC migration. Methods: The proteolytic activity of matrix metalloproteinases (MMPs) in tumor necrosis factor alpha (TNF-α) stimulated VSMCs was performed by gelatin zymography. VSMC migration was assessed by wound healing and Boyden chamber methods. Collagen induced VSMC adhesion was determined by spectrofluorimeter and stress fibers formation was evaluated by fluorescence microscope. The expression of signaling molecules involved in stress fibers formation was determined by western blot. The phosphorylation of myosin light chain (MLC20) was determined by urea-glycerol polyacrylamide gel electrophoresis. Immunohistochemistry was performed to determine the expression of β1-integrin and collagen type I in the injured carotid arteries of rats on day 35 after vascular injury. Results: VSMC migration was strongly inhibited by magnolol without affecting MMPs expression. Also, magnolol inhibited β1-integrin expression, FAK phosphorylation and RhoA and Cdc42 activation to inhibit the collagen induced stress fibers formation. Moreover, magnolol inhibited the phosphorylation of MLC20. Our in vivo results showed that magnolol inhibited β1-integrin expression, collagen type I deposition and FAK phosphorylation in injured carotid arteries without affecting MMP-2 activity. Conclusions: Magnolol inhibited VSMC migration via inhibition of cytoskeletal remodeling pathway to attenuate neointima formation. General significance: This study provides a rationale for further evaluation of magnolol for the management of atherosclerosis and restenosis. - Highlights: • Magnolol strongly inhibited migration of VSMCs. • Magnolol inhibited stress fibers formation. • MLC20 phosphorylation was also inhibited by magnolol. • Anti-migratory effect of magnolol was cytoskeletal dependent. • Magnolol inhibited β1-integrin and collagen expression in vivo.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2021

Adherens junctions are involved in polarized contractile ring formation in dividing epithelial cells of Xenopus laevis embryos

Highlights: • The actomyosin contractile ring formation is polarized in epithelial cells. • Activation of the contractile ring is polarized in epithelial cells. • Adherens junctions are involved in the kinetics of the contractile ring formation. • Adherens junctions and the contractile ring are linked from the onset of cytokinesis. • High temporal resolution microscopy of epithelial cells in the Xenopus embryos. Cells dividing in the plane of epithelial tissues proceed by polarized constriction of the actomyosin contractile ring, leading to asymmetric ingression of the plasma mem brane. Asymmetric cytokinesis results in the apical positioning of the actomyosin contractile ring and ultimately of the midbody. Studies have indicated that the contractile ring is associated with adherens junctions, whose role is to maintain epithelial tissue cohesion. However, it is yet unknown when the contractile ring becomes associated with adherens junctions in epithelial cells. Here, we examined contractile ring formation and activation in the epithelium of Xenopus embryos and explored the implication of adherens junctions in the contractile ring formation. We show that accumulation of proteins involved in contractile ring formation and activation is polarized, starting at apical cell-cell contacts at the presumptive division site and spreading within seconds towards the cell basal side. We also show that adherens junctions are involved in the kinetics of contractile ring formation. Our study reveals that the link between the adherens junctions and the contractile ring is established from the onset of cytokinesis.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2017

Elucidating the Formation Mechanisms of Silver Nanoparticles from a Comprehensive Simulation Based on First-Principles Calculations

The nucleation and growth of silver nanoparticles are modeled and simulated based on first-principles calculations. The formation energy of single-crystal and multiply twinned particles is calculated to elucidate the thermodynamic properties of particles and modeled as a function of geometric parameters. On the basis of the calculated formation energy and the molecular collision theory, Kinetic Monte Carlo simulations are performed to trace the formation process of silver nanoparticles. In particular, the temporal change of size distribution and morphology are obtained and used to elucidate the governing mechanism in each stage of the formation process. It is demonstrated that the formation process is separated into four phases depending on the power-law time dependence of the particle formation and they are characterized by the size difference between coalescent particles. The temperature dependence of size distribution and morphology is also studied to elucidate the underlying mechanisms. The findings are compared with classical theories quantitatively and a strategy to control the morphology of silver nanoparticles is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Identification of Possible Pathways for C–C Bond Formation during Electrochemical Reduction of CO 2 : New Theoretical Insights from an Improved Electrochemical Model

Here, we have carried out a periodic Kohn-Sham density functional theory investigation of the pathways by which carbon-carbon bonds could be formed during the electrochemical reduction of CO 2 on Cu(100) using a model that includes the effects of the electrochemical potential, solvent, and electrolyte. The electrochemical potential was set by relating the applied potential to the Fermi energy and then calculating the number of electrons required by the simulation cell for that specific Fermi energy. The solvent was included as a continuum dielectric, and the electrolyte was described using a linearized Poisson-Boltzmann model. The calculated potential of zero charge for a variety of surfaces agrees with experiment to within a mean average error of 0.09 V, thereby validating the assumptions of the model. Analysis of the mechanism for C–C bond formation revealed that at low-applied potential, C–C bond formation occurs through a CO dimer. However, at high applied potentials, a large activation barrier blocks this pathway; therefore, C–C bond formation occurs through reaction of adsorbed CHO and CO. Rate parameters determined from our calculations were used to simulate the kinetics of ethene formation during the electrochemical reduction of CO over a Cu(100) surface. An excellent match was observed between previously reported measurements of the partial current for ethene formation as a function of applied voltage and the variation in the partial current for C–C bond formation predicted by our microkinetic model. The electrochemical model reported here is simple, fairly easy to implement, and involves only a small increase in computational cost over calculations neglecting the effects of the electrolyte and the applied field. Therefore, it can be used to study the effects of applied potential and electrolyte composition on the energetics of surface reactions for a wide variety of electrochemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Inhibition of AlF3·3H2O Impurity Formation in Ti3C2Tx MXene Synthesis under a Unique CoFx/HCl Etching Environment

MXenes, most commonly transition metal carbides, are a family of two-dimensional (2D) materials with promising potential in, among other applications, supercapacitors and batteries. MXenes are synthesized by etching of aluminum or gallium layers in its parent MAX phase directly by HF or by HF in situ formation using a fluoride salt and strong acid. A commonly undesired byproduct of MXene synthesis is AlF3·3H2O. To relieve MXenes from AlF3·3H2O impurity, it is important to elucidate the factors that drive its formation. Here, we dually deduce the conditions that lead to AlF3·3H2O formation while exploring etching with cobalt fluorides (CoF2/CoF3). Previously uncharacterized, etching with cobalt fluorides offers a forthright method to etch MXenes while intercalating cobalt cations. The influence of this etching environment and AlF3·3H2O formation on MXene’s structure, morphology, and surface bonding is investigated. Ionic strength of solution used for etching is found to be a critical driving factor in the formation of AlF3·3H2O impurity formation. Specifically, when the ionic strength falls between ~8.5 and 10 M, AlF3 complexation is stable. As a result, Ti3C2Tx MXene phase with AlF3·3H2O impurity is obtained. In contrast, near-pure MXene is the only solid state product when I is smaller than 8.5 M or larger than 10 M. Hence, high purity MXene phase can be synthesized by subtle compositional tuning to manipulate the ionic strength of the etching environment.

Cockerham, Cody B.↗

DOE OSTI2023

Species, Pathways, and Timescales for NH 3 Formation by Low-Temperature Atmospheric Pressure Plasma Catalysis

Species, pathways, and timescales for NH3 production by plasma catalysis over transition-metal wools are determined by measuring plasma-derived species densities [N, H, and N 2 (v)], quantitatively correlating consumption of these species with NH 3 formation, and measuring consumption of plasma-derived species at different residence times. These findings are enabled by a capillary flow through Ar/N 2 /H 2 plasma jet reactor setup that allows for the measurement of gas-phase species densities by molecular beam mass spectrometry. Surface-mediated reactions involving N radicals are responsible for NH 3 formation over Fe, Ni, and Ag surfaces. N reacts to form NH 3 with ~100% selectivity over Ni and Ag when H/N > 3 and % H 2 ≥ 0.5. The selectivity to ammonia drops as H and H 2 densities decrease for each catalyst. A comparison between amounts of NH 3 formed and N consumed with and without catalysts present shows that surface reactions enable higher and more selective conversion of N to NH 3 than gas-phase reactions alone. The conversion of N to NH 3 is negligible in the absence of H, demonstrating that H is required to produce NH 3 at these operating conditions. The consumption of N occurs on the same timescale as NH 3 formation, further confirming that reactions involving N contribute to NH 3 formation. Though vibrationally excited N 2 [N 2 (v)] is produced in quantities exceeding N by 100-fold, consumption of N 2 (v) on the catalytic surface does not contribute to NH 3 formation. Furthermore, these findings show that for low-temperature atmospheric pressure plasma catalysis, surface- mediated reactions among radical N and H species drive NH 3 formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2016

Reaction Mechanisms for the Electrochemical Reduction of CO 2 to CO and Formate on the Cu(100) Surface at 298 K from Quantum Mechanics Free Energy Calculations with Explicit Water

Copper is the only elemental metal that reduces a significant fraction of CO 2 to hydrocarbons and alcohols, but the atomistic reaction mechanism that controls the product distributions is not known because it has not been possible to detect the reaction intermediates on the electrode surface experimentally, or to carry out Quantum Mechanics (QM) calculations with a realistic description of the electrolyte (water). We carry out QM calculations with an explicit description of water on the Cu(100) surface (experimentally shown to be stable under CO 2 reduction reaction conditions) to examine the initial reaction pathways to form CO and formate (HCOO – ) from CO 2 through free energy calculations at 298 K and pH 7. We find that CO formation proceeds from physisorbed CO 2 to chemisorbed CO 2 (*CO 2 δ- ), with a free energy barrier of ΔG ‡ = 0.43 eV, the rate-determining step (RDS). The subsequent barriers of protonating *CO 2 δ- to form COOH* and then dissociating COOH* to form *CO are 0.37 and 0.30 eV, respectively. HCOO– formation proceeds through a very different pathway in which physisorbed CO 2 reacts directly with a surface H* (along with electron transfer), leading to ΔG ‡ = 0.80 eV. Thus, the competition between CO formation and HCOO – formation occurs in the first electron-transfer step. On Cu(100), the RDS for CO formation is lower, making CO the predominant product. Therefore, to alter the product distribution, we need to control this first step of CO 2 binding, which might involve controlling pH, alloying, or changing the structure at the nanoscale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

Activation of dioxygen (O 2 ) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O 2 -activation reaction, has been the focus of current research. Herein, we report the O 2 -activation and O–O bond formation reactions by manganese corrole complexes. In the O 2 -activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O 2 in the presence of base (e.g., OH – ) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O 2 -activation reaction did not occur in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O 2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present paper reports the first example of using the same manganese complex in both O 2 -activation and O–O bond formation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

Increasing Gas Hydrate Formation Temperature for Desalination of High Salinity Produced Water with Secondary Guests

We suggest a new gas hydrate-based desalination process using water-immiscible hydrate formers; cyclopentane (CP) and cyclohexane (CH) as secondary hydrate guests to alleviate temperature requirements for hydrate formation. The hydrate formation reactions were carried out in an isobaric condition of 3.1 MPa to find the upper temperature limit of CO2 hydrate formation. Simulated produced water (8.95 wt % salinity) mixed with the hydrate formers shows an increased upper temperature limit from -2 °C for simple CO2 hydrate to 16 and 7 °C for double (CO2 + CP) and (CO2 + CH) hydrates, respectively. The resulting conversion rate to double hydrate turned out to be similar to that with simple CO2 hydrate at the upper temperature limit. Hydrate formation rates (Rf) for the double hydrates with CP and CH are shown to be 22 and 16 times higher, respectively, than that of the simple CO2 hydrate at the upper temperature limit. Such mild hydrate formation temperature and fast formation kinetics indicate increased energy efficiency of the double hydrate system for the desalination process. Dissociated water from the hydrates shows greater than 90% salt removal efficiency for the hydrates with the secondary guests, which is also improved from about 70% salt removal efficiency for the simple hydrates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

An Investigation of Hydrate Formation in Unsaturated Sediments Using X-Ray Computed Tomography

Physical properties of hydrate–bearing sediments are often correlated with hydrate saturation with little or no information on hydrate distribution uniformity in the specimens. This study focuses on water redistribution and sediment skeleton shift depending on various hydrate formation conditions in unsaturated systems, as well as on the resulting hydrate distribution patterns. Using X–ray computed tomography, we investigate the factors such as fines content and the pressure–temperature path on mass migration during carbon dioxide hydrate formation. The experiments show water migration, preferential hydrate formation toward the core periphery, localized patchy hydrate distribution, and sediment particle movement toward the core center. Sediment particle movement can be impeded in densely packed specimens. Furthermore, the overall mass migration due to hydrate formation can be significantly suppressed by adding 5% by mass of kaolinite. Hydrate formation initiated by pressurization and then cooling causes less mass migration than the cases where hydrate is formed using cooling followed by pressurization or pressurizing frozen cores followed by heating methods. Freezing can induce water migration and particle pushing in a similar manner as hydrate formation. Image analyses show that the pressure–temperature path and the rates of heat transfer during hydrate nucleation and growth govern the uniformity of hydrate distribution in sediments.

58 GEOSCIENCES↗