Randall E. Winans

Increased Silver Activity for Direct Propylene Epoxidation via Subnanometer Size Effects

Silver Cluster Catalysts for Propylene Oxide The formation of ethylene oxide—in which an oxygen atom bridges the double bond of ethylene—can be made directly and efficiently from ethylene and oxygen with the aid of silver catalysts (typically comprising a small silver cluster on aluminum oxide). Similar approaches are not so successful for making propylene oxide—an important starting material for polyurethane plastics, which are made from chlorinated intermediates. Lei et al. (p. 224) report that silver trimers, Ag3, deposited on alumina are active for direct propylene oxide formation at low temperatures with only a low level of formation of CO2 by-product, unlike larger particles that form from these clusters at higher temperatures. Density functional calculations suggest that the open-shell nature of the clusters accounts for the improved reactivity. Clusters of three silver atoms deposited on alumina are active for the low-temperature direct formation of propylene oxide. Production of the industrial chemical propylene oxide is energy-intensive and environmentally unfriendly. Catalysts based on bulk silver surfaces with direct propylene epoxidation by molecular oxygen have not resolved these problems because of substantial formation of carbon dioxide. We found that unpromoted, size-selected Ag3 clusters and ~3.5-nanometer Ag nanoparticles on alumina supports can catalyze this reaction with only a negligible amount of carbon dioxide formation and with high activity at low temperatures. Density functional calculations show that, relative to extended silver surfaces, oxidized silver trimers are more active and selective for epoxidation because of the open-shell nature of their electronic structure. The results suggest that new architectures based on ultrasmall silver particles may provide highly efficient catalysts for propylene epoxidation.

Selective propene epoxidation on immobilized au(6-10) clusters: the effect of hydrogen and water on activity and selectivity.

Epoxidation made easy: Subnanometer gold clusters immobilized on amorphous alumina result in a highly active and selective catalyst for propene epoxidation. The highest selectivity is found for gas mixtures involving oxygen and water, thus avoiding the use of hydrogen. Ab initio DFT calculations are used to identify key reaction intermediates and reaction pathways. The results confirm the high catalyst activity owing to the formation of propene oxide metallacycles. Al green, Au yellow, O red, and C gray.

The nature and fate of natural resins in the geosphere—II. Identification, classification and nomenclature of resinites

Abstract A classification scheme for resinites is proposed. Most resinites may be classified, on the basis of structural characteristics, into one of four classes. In order to exclude the effects of structural changes which reflect differences in the relative maturity of different samples, classifications are based on the structural character of the original resin from which the resinite was derived. In all samples characterized to date, this may be reasonably inferred from analytical data concerning the structure and composition of the individual sample. Class I resinites, which are by far the most abundant form of resinite in the geosphere, are derived from resins based primarily on polymers of labdatriene (diterpenoid) carboxylic acids, especially communic or ozic acids. Class II resinites are derived from resins based on polymers of sesquiterpenoid hydrocarbons, especially various isomers of cadinene. Class III resinites are natural polystyrenes. Class IV resinites are the least well characterized of the four resinite classes defined, but appear to be largely non-polymeric materials, dominated by sesquiterpenoids based on the cedrane carbon skeleton. Resinites belonging to Class I are further subdivided into three sub-classes on the basis of details of their composition. Class Ia resinites, which include succinite and related “Baltic ambers”, are derived from resins based primarily on communic acid and incorporate significant amounts of succinic acid into their macromolecular structure. Class Ib resinites are also derived from resins based primarily on communic acid, but do not contain succinic acid. Class Ic resinites are derived from resins based primarily on labdatrienoic acids of the enantio series, especially ozic and/or zanzibaric acids. The structure, origin, and identification of resinites of each class are discussed. The effects of maturation on the structure of Class I resinites, and the consequences of these changes for the recognition and classification of this form of resinite are also briefly discussed.

Trapped organic compounds and aromatic units in coals

Abstract Some insight into the chemical nature of coals and the coalification process was obtained by detailed analyses of the organic constituents of three coals — a lignite, a bituminous, and an anthracite coal. Organic compounds trapped in the coal matrix, residuals and products of the original coalification process, were isolated by vacuum distillation and solvent extraction. The macromolecular material which constitutes the bulk of coals was degraded by a series of selective oxidations to smaller units which could be identified and measured. The essential aromatic character of coals was demonstrated, with condensation of aromatic rings increasing with increasing rank.

Design and performance of a ASAXS instrument at the Advanced Photon Source

The SAXS instrument on the high brilliance undulator beam line (ID12, BESSRC-CAT) at APS has been designed to produce high-resolution scattering patterns in the millisecond time domain. This instrument is equipped with a 18 cm x 18 cm position sensitive gas detector and a 15 cm x 15 cm high-resolution position sensitive CCD mosaic detector. A photodiode detector mounted on a 3.7 mm diameter beam stop permits quick alignment of the instrument as well as precise measurement of the transmitted beam intensity. The exposure time with the CCD detector varies from 0.1 to 10 seconds depending on the scattering cross-section of the samples. Techniques to interface ancillary equipment for time-resolved studies and software for faster online analysis of the data have also been developed. We have obtained data on the unfolding of proteins in the millisecond time domain and ASAXS of metallic alloys using this instrument.

Experimental Shock Chemistry of Aqueous Amino Acid Solutions and the Cometary Delivery of Prebiotic Compounds

A series of shock experiments were conducted to assess thefeasibility of the delivery of organic compounds to theEarth via cometary impacts. Aqueous solutions containingnear-saturation levels of amino acids (lysine, norvaline,aminobutyric acid, proline, and phenylalanine) were sealedinside stainless steel capsules and shocked by ballisticimpact with a steel projectile plate accelerated along a12-m-long gun barrel to velocities of 0.5–1.9 km sec-1. Pressure-temperature-time histories of the shocked fluidswere calculated using 1D hydrodynamical simulations. Maximum conditions experienced by the solutions lasted0.85–2.7 μs and ranged from 5.1–21 GPa and 412–870 K. Recovered sample capsules were milled open and liquid wasextracted. Samples were analyzed using high performanceliquid chromatography (HPLC) and mass spectrometry (MS). In all experiments, a large fraction of the amino acidssurvived. We observed differences in kinetic behavior andthe degree of survivability among the amino acids. Aminobutyricacid appeared to be the least reactive, and phenylalanine appeared to be the most reactive of the amino acids. The impact process resulted in the formation of peptide bonds; new compounds included amino acid dimers and cyclic diketopiperazines. In our experiments, and in certain naturally occurring impacts, pressure has a greater influencethan temperature in determining reaction pathways. Our resultssupport the hypothesis that significant concentrations of organic material could survive a natural impact process.

Size-dependent subnanometer Pd cluster (Pd4, Pd6, and Pd17) water oxidation electrocatalysis

Water oxidation is a key catalytic step for electrical fuel generation. Recently, significant progress has been made in synthesizing electrocatalytic materials with reduced overpotentials and increased turnover rates, both key parameters enabling commercial use in electrolysis or solar to fuels applications. The complexity of both the catalytic materials and the water oxidation reaction makes understanding the catalytic site critical to improving the process. Here we study water oxidation in alkaline conditions using size-selected clusters of Pd to probe the relationship between cluster size and the water oxidation reaction. We find that Pd4 shows no reaction, while Pd6 and Pd17 deposited clusters are among the most active (in terms of turnover rate per Pd atom) catalysts known. Theoretical calculations suggest that this striking difference may be a demonstration that bridging Pd-Pd sites (which are only present in three-dimensional clusters) are active for the oxygen evolution reaction in Pd6O6. The ability to experimentally synthesize size-specific clusters allows direct comparison to this theory. The support electrode for these investigations is ultrananocrystalline diamond (UNCD). This material is thin enough to be electrically conducting and is chemically/electrochemically very stable. Even under the harsh experimental conditions (basic, high potential) typically employed for water oxidation catalysts, UNCD demonstrates a very wide potential electrochemical working window and shows only minor evidence of reaction. The system (soft-landed Pd4, Pd6, or Pd17 clusters on a UNCD Si-coated electrode) shows stable electrochemical potentials over several cycles, and synchrotron studies of the electrodes show no evidence for evolution or dissolution of either the electrode material or the clusters.

Phenolic ethers in the organic polymer of the Murchison meteorite

Seven phenolic acids and many nonphenolic organic acids, including large amounts of meta-hydroxy (3-hydroxy) benzoic acid and 3-hydroxy-1,5-benzene-dicarboxylic acid, were obtained from the organic polymer of the Murchison C2 chondrite upon oxidation with alkaline cupric oxide. The phenolic acids apparently were derived from phenolic ethers in the polymer, which in turn probably were formed from carbon monoxide and hydrogen by catalytic Fischer-Tropsch type reactions in the solar nebula. In contrast, terrestrial polymers such as lignin, humic acid, and coal yield mainly para-hydroxy (4-hydroxy) benzene derivatives by the same oxidation procedure.

New carbon electrodes for secondary lithium batteries

The authors have synthesized and electrochemically tested carbon samples that are suitable as anodes for lithium secondary batteries. The unique synthesis is based on the use of the inorganic templates and organic precursors. Pyrolysis of these carbons was performed at 500 and 700 C. High reversible capacity (up to 825 mAh/g) was found on samples heated to 700 C. The cells were tested continuously for more than 20 cycles with a drop in capacity of only 10%. X-ray powder diffraction showed that the samples heated to 700 C have a highly disordered structures.

Growth of Metal Oxide Nanowires from Supercooled Liquid Nanodroplets

Nanometer-sized liquid droplets formed at temperatures below the bulk melting point become supercooled as they grow through Ostwald ripening or coalescence and can be exploited to grow nanowires without any catalyst. We used this simple approach to synthesize a number of highly crystalline metal oxide nanowires in a chemical or physical vapor deposition apparatus. Examples of nanowires made in this way include VO(2), V(2)O(5), RuO(2), MoO(2), MoO(3), and Fe(3)O(4), some of which have not been previously reported. Direct evidence of this new mechanism of nanowire growth is found from in situ 2-dimensional GISAXS (grazing incidence small angle X-ray scattering) measurements of VO(2) nanowire growth, which provides quantitative information on the shapes and sizes of growing nanowires as well as direct evidence of the presence of supercooled liquid droplets. We observe dramatic changes in nanowire growth by varying the choice of substrate, reflecting the influence of wetting forces on the supercooled nanodroplet shape and mobility as well as substrate-nanowire lattice matching on the definition of nanowire orientation. Surfaces with defects can also be used to pattern the growth of the nanowires. The simplicity of this synthesis concept suggests it may be rather general in its application.