Electrochemical reduction of carbon dioxide to organic chemicals provides a value-added route for mitigating greenhouse gas emissions. We report a family of carbon-supported Sn electrocatalysts with the tin size varying from single atom, ultrasmall clusters to nanocrystallites. High single-product Faradaic efficiency (FE) and low onset potential of CO2 conversion to acetate (FE = 90% @ -0.6 V), ethanol (FE = 92% @ -0.4 V), and formate (FE = 91% @ -0.6 V) were achieved over the catalysts of different active site dimensions. The CO2 conversion mechanism behind these highly selective, size-modulated p-block element catalysts was elucidated by structural characterization and computational modeling, together with kinetic isotope effect investigation.

Direct electrochemical conversion of CO2 to ethanol offers a promising strategy to lower CO2 emissions while storing energy from renewable electricity. However, current electrocatalysts offer only limited selectivity toward ethanol. Here we report a carbon-supported copper (Cu) catalyst, synthesized by an amalgamated Cu–Li method, that achieves a single-product Faradaic efficiency (FE) of 91% at −0.7 V (versus the reversible hydrogen electrode) and onset potential as low as −0.4 V (reversible hydrogen electrode) for electrocatalytic CO2-to-ethanol conversion. The catalyst operated stably over 16 h. The FE of ethanol was highly sensitive to the initial dispersion of Cu atoms and decreased significantly when CuO and large Cu clusters become predominant species. Operando X-ray absorption spectroscopy identified a reversible transformation from atomically dispersed Cu atoms to Cun clusters (n = 3 and 4) on application of electrochemical conditions. First-principles calculations further elucidate the possible catalytic mechanism of CO2 reduction over Cun. Electrocatalytically reducing CO2 to ethanol can provide renewably generated fuel, but catalysts are often poorly selective for this conversion. Here the authors use a Cu catalyst to produce ethanol with high selectivity. Cu dispersion is key to the performance and operando studies indicate that it changes under reaction conditions.

Interfacial liquid-liquid ion transport is of crucial importance to biotechnology and industrial separation processes including nuclear elements and rare earths. A water-in-oil microemulsion is formulated here with density and dimensions amenable to atomistic molecular dynamics simulation, facilitating convergent theoretical and experimental approaches to elucidate interfacial ion transport mechanisms. Lutetium(III) cations are transported from the 5 nm diameter water pools into the surrounding oil using an extractant (a lipophilic ligand). Changes in ion coordination sphere and interactions between the interfacial components are studied using a combination of synchrotron X-ray scattering, spectroscopy, and atomistic molecular dynamics simulations. Contrary to existing hypotheses, our model system shows no evidence of interfacial extractant monolayers, but rather ions are exchanged through water channels that penetrate the surfactant monolayer and connect to the oil-based extractant. Our results highlight the dynamic nature of the oil-water interface and show that lipophilic ion shuttles need not form flat monolayer structures to facilitate ion transport across the liquid-liquid interface.

The applications of H-1 and C-13 nuclear magnetic resonance (NMR) and two-dimensional H-1/C-13 NMR spectroscopy have been shown to be useful techniques for the qualitative and quantitative characterization of hydrotreated recycled lube oils. The addition of hydrogen to aromatic and alkene hydrocarbons can be quantitatively and selectively measured. The decrease of oxygen/nitrogen/sulfur species can also be inferred from the reduction of specific resonances in the NMR spectra. Treated recycled lube oil was subsequently hydrotreated with Pd catalysts deposited by either atomic layer deposition (ALD) or incipient wetness impregnation (IWI) on a SiO2/Al2O3 support. In both cases, much lower hydrogenation temperatures were required than had been observed with typical NiMo or CoMo on Al2O3. In addition, the ALD-deposited catalyst was more effective for the reduction of aromatics and heteroatom components than the IWI catalyst. The lube oil fractions were of high purity (low aromaticity and low heteroatom content) even at low reaction severity.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We report a one-pot method for sequestration, containment, and immobilization of lanthanide (Ln) ions from dilute aqueous waste streams. The approach is based on the use of collapsible, surface modified controlled pore glass (CPG) nanomaterials. We present several approaches for a single-step chemical modification of 3-propylaminated CPGs that yield highly efficient Ln-extracting materials with distribution coefficients exceeding 10000 mL/g. The resulting Ln complexes were studied using X-ray absorption, magnetic resonance, and time-resolved luminescence spectroscopies. One of these CPG materials involving an imidodi(methanediphosphate) moiety demonstrated high extraction efficacy, significant ionic radius sensitivity, and exceptional tolerance to masking agents, which is conducive to its use for removal of traces of radionuclide ions from aqueous TALSPEAK raffinate (trivalent actinide lanthanide separation by phosphorus reagent extraction from aqueous complexes process used in processing of spent nuclear fuel). The glass loaded with the extracted metal ions can be calcined and sintered at 1100 degrees C, yielding fused material that buries Ln ions in the vitreous matrix. This processing temperature is significantly lower than 1700 degrees C that is required for direct vitrification of lanthanide oxides in high-silica glass. X-ray absorption spectroscopy and acid leaching tests indicate that the immobilized ions are isolated and dispersed in the fused glass matrix. Thus, the method integrates Ln ions into the glass network. The resulting glass can be used for temporary storage or as the source of silica for production of borosilicate waste forms that are used for long-term disposal of high level radioactive waste.

An approach directed at rapid sequestration and disposal of technetium-99 from UREX (uranium extraction) liquid waste streams is presented. This stream is generated during reprocessing of light-water-reactor spent fuel to recycle the actinides and separate fission products for waste disposal. U and Tc are co-extracted from a nitric acid solution using tri-n-butylphosphate in dodecane, so that Tc(VII) is present in the strip solution after the actinide separations. The goal is to separate uranyl from the pertechnetate in this U-Tc stream and then sequester Tc in the metallic form. Our approach is based on reductive stripping of pertechnetate either from aqueous solution (for column extractions) or organic solvents (for liquid-liquid extractions). In both of these methods, metallic zinc in the presence of formic acid serves as a reducing agent, and 99Tc is recovered as a co-precipitate of Zn(II) hydroxide and hydrous Tc(IV) oxide, with a Zn:Tc ratio between 1:1 and 2:1 mol/mol. This solid residue can be reduced to a Zn-Tc alloy by high temperature (500–700°C) hydrogenation, and the resulting heterophase alloy can be added to a metallic Fe-Zr-Mo waste form that is processed at 1600°C, with subsequent loss of Zn by evaporation. Alternatively, Zn and Tc can be separated and 99Tc sequestered as NH4TcO4 for further reduction to Tc(0) metal. The aqueous Zn reduction process removes ∼90% of 99Tc per cycle. The nonaqueous Zn reduction in 1:1 methanol – formic acid removes 60–70% of 99Tc per cycle, depending on the extracting agent (such as a tetraalkylammonium nitrate). The extracting agent is recycled in the process. The pertechnetate is extracted from the aqueous phase into 1,2-dichloroethane, which is removed by evaporation and reused. The residue is either calcined and steam reformed to Tc(0) or processed by the nonaqueous Zn reduction method. These methods can be used not only to remove the pertechnetate from the U-Tc product stream, but also to sequester the pertechnetate from aqueous waste streams generated through the processes described in this paper, thereby closing the cycle. The same approaches can be used to close the 99Tc cycle for other methods that are currently being developed at Los Alamos and Argonne National Laboratories.

The source of the regioselectivity in the intramolecular nucleophilic addition of nitrile-stabilized carbanions to arene chromium tricarbonyl complexes was investigated for seven different substitution patterns on the arenes. All of the arenes are 1,4-dioxygenated and the substitution varies in the oxygen substituent and in the substituents of the arene carbons (hydrogen and alkyl). The regioselectivity is correlated with the preferred conformations of the chromium tricarbonyl group which in turn was determined by solution and solid-state 13C NMR spectroscopy, 1H NMR spectroscopy in solution as well as X-ray diffraction. In the four complexes analyzed by X-ray diffraction and the three complexes analyzed by solid-state 13C NMR spectroscopy, there was only one complex where it was found that the preferred conformation of the –Cr(CO)3 is different in solution than it is in the solid-state.

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Though other approaches have positive features and could eventually supplant hydrometallurgical separations, solvent extraction and ion exchange (and related techniques) are technologically the most important methods for actinide processing and analysis, and likely will remain so for the next few decades. From uranium mining to actinide transmutation, increased understanding of the fundamental interactions between actinide cations, chelating agents, oxidizing and reducing agents, and the solvents (aqueous and non-aqueous) that serve as the medium for chemical manipulations is essential if these techniques are to advance in the 21st century. Research continues around the world in this field, principally in those countries actively involved in (or considering) actinide partitioning and recycle. In this presentation, the results of a variety of investigations designed to provide new insights into the nature of actinide interactions with solutes and solvents will be presented. Among the key issues discussed will be aspects of the thermodynamics and kinetics of actinide-ligand interactions, of structural features of actinide complexes in solutions, and of the nature of interactions of free actinide cations and their complexes with solvent molecules. Each of the systems discussed will have some significance in actinide separations science with primary emphasis on solvent extraction and ion exchange. Work performed under the auspices of the US Department of Energy Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences under contract number W-31-109-ENG-38.

As part of a larger study of the structure and behavior of polyterpenoids in sedimentary systems, the structural characteristics of the macromolecular constituents of Dammar resin and a related Class II amber have been reinvestigated. The conclusions drawn from these analyses are inconsistent with the current widely held "polycadinene" model for the macromolecular structure of these materials. Double bond characteristics observed by one and two dimensional NMR spectroscopy do not match those in the proposed "polycadinene" structure. Based on these observations it is suggested that the proposed "polycadinene" structure for these materials is inadequate and requires revision. Elemental and NMR data also suggest a significant contribution from functionalized monomers.

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state 13C- and 1H NMR and 13C-1H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py–GC–MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride–methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py–GC–MS, solid-state 13C CP/MAS and 13C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.

The synthesis and characterization of the Eu-encrypted heteropolyanion [EuP5W30O110](12-) are presented. X-ray absorption near-edge structure experiments were used to determine that Eu is trivalent in the anion. Optical spectra confirm this finding. The unusual cyclic voltammogram obtained for the Eu heteropolyanion is discussed in terms of the stability of Eu-II under reducing conditions. Time delayed optical fluorescence data are only consistent with two structurally inequivalent Eu ions, both inside the heteropoly cavity. Lifetime measurements of the D-5(o) State indicate that the two structurally different Eu sites are not occupied in the same anion. In addition, from complementary measurements on samples made in D2O, it is determined that there are three waters coordinated to Eu in one site and only two waters coordinated to Eu in the second site. P-31 NMR and cyclic voltammetry data, obtained from samples with either one or two sites occupied, are indistinguishable. Possible models to explain the presence of two sites are discussed.

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Recent research on the aliphatic structural elements of bituminous coals is discussed in this presentation. 6 refs., 1 fig., 3 tabs.