David A. Bruce

Design and synthesis of copper-cobalt catalysts for the selective conversion of synthesis gas to ethanol and higher alcohols.

Combining quantum-mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoO(x) catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non-petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu-Co alloy sites, at Co-enriched surfaces, as ideal for the selective production of long-chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu(2+) and Co(2+) cations in a wide range of compositions. As revealed by energy-dispersive X-ray nanospectroscopy and temperature-resolved X-ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co-rich surface compositions, for which Cu phase segregation is prevented.

An improved replica-exchange sampling method: Temperature intervals with global energy reassignment

In a molecular dynamics (MD) simulation, representative sampling over the entire phase space is desired to obtain an accurate canonical distribution at a given temperature. For large molecules, such as proteins, this is problematic because systems tend to become trapped in local energy minima. The extensively used replica-exchange molecular dynamics (REMD) simulation technique overcomes this kinetic-trapping problem by allowing Boltzmann-weighted configuration exchange processes to occur between numerous thermally adjacent and compositionally identical simulations that are thermostated at sequentially higher temperatures. While the REMD method provides much better sampling than conventional MD, there are two substantial difficulties that are inherent in its application: (1) the large number of replicas that must be used to span a designated temperature range and (2) the subsequent long time required for configurations sampled at high temperatures to exchange down for potential inclusion within the low-temperature ensemble of interest. In this work, a new method based on temperature intervals with global energy reassignment (TIGER) is presented that overcomes both of these problems. A TIGER simulation is conducted as a series of short heating-sampling-quenching cycles. At the end of each cycle, the potential energies of all replicas are simultaneously compared at the same temperature using a Metropolis sampling method and then globally reassigned to the designated temperature levels. TIGER is compared with regular MD and REMD methods for the alanine dipeptide in water. The results indicate that TIGER increases sampling efficiency while substantially reducing the number of central processing units required for a comparable conventional REMD simulation.

The synthesis and structure of a chiral layered aluminophosphate containing the template Co(tn)33

A chiral layered aluminophosphate Co(tn)3·Al3P4O16·2H2O containing only one enantiomer of the metal complex is synthesized using racemic Co(tn)3Cl3 as the templating agent and its structure determined using single-crystal X-ray diffraction.

Design and Feasibility of Creating Gas-Storage Caverns by Using Acid to Dissolve Carbonate Rock Formations

The feasibility of creating gas-storage caverns by dissolving carbonate rock formations was examined based on process design, geologic factors, and preliminary economic analysis. The method involves drilling one or more wells, pumping acid into the formation, and then removing and treating the waste fluid. To enhance acid transport into the formation, the rock may be hydraulically fractured prior to pumping the acid. To analyze the requirements for creating storage volume, the following were examined: weight and volume of rock to be dissolved; gas storage pressure, temperature, and volume at depth; solubility of acid-rock reaction products; and acid costs. Design considerations and economic calculations indicate that the new method will be applied most advantageously to carbonate formations deeper than approximately 4000 feet, with limestone at depths between 6000 and 9000 feet preferred. In order to identify potential sites for applying the new method to creating storage volume, a large amount of data from carbonate formations was compiled for six states: Ohio, Kentucky, Indiana, West Virginia, Pennsylvania, and New York. Based on GIS analysis, large areas of West Virginia, Pennsylvania, and New York were identified as potentially suitable for developing carbonate-cavern storage. Smaller areas that may be suitable were identified in Indiana, Ohio, and Kentucky.

The synthesis, characterization, and X-ray crystal structure of trans-bis(1,3-diamino-2-propanolato-N,N′,O)- cobalt(III) perchlorate trihydrate

The crystal structure of [Co(C3H9N2O)2]ClO4⋅3H2O was established by single-crystal X-ray diffraction techniques. The compound crystallized in the monoclinic space group P21 with unit cell dimensions a = 6.715(2) Å, b = 12.097(3) Å, c = 9.904(3) Å, β = 100.80(3)○, and z = 2. The final R value for 1359 reflections was 0.039. The 1,3-diamino-2-propanolato ligands are tridentately coordinated to cobalt atoms that have slightly distorted octahedral coordination. The five-membered chelate rings exhibit conformations between pure twist and pure envelope, while the six-membered ring adopts a boat confirmation.

The enigma of Au21(SC2H4Ph)14 nanocluster: a synthetic challenge

Abstract Recent investigations into atomically precise gold clusters show that not all magic-numbered clusters can be readily obtained through conventional synthetic routes. For example, Au21(SR)14, a magic-numbered cluster, was only obtained as a minor product from a mixture of clusters but was never synthesized in pure form using a single-step synthetic approach. We have made several attempts, albeit without any success, using a variety of approaches to synthesize Au21(SR)14 clusters in a single step. We show in this communication that synthetic failure is not likely due to electronic instabilities based on computational investigation of its electronic structure. Our DFT calculations show that the optimized cluster consists of a center Au13 core cluster capped by two Au2(SCH2CH3)3 fragments and four Au(SCH2CH3)2 fragments and is energetically stable. The findings reported here should give more confidence for the synthetic chemists to successfully synthesize Au21(SR)14 in the near future.

A Comprehensive Multiphysics, Multiscale Study of Reactor Chamber and Substrate Orientation Effects on Carbon Nanotube Synthesis During Chemical Vapor Deposition Process

A comprehensive multiphysics, multiphase model of carbon nanotube (CNT) fabrication process by chemical vapor deposition (CVD) is utilized to study the effects of several physical phenomena inside the quartz tube. The investigations include fluid flow properties, temperature profile and heat transfer as well as diffusion and concentration of carbon species along the substrate. These properties are examined in a great detail for a horizontally placed substrate. For each physical property, the effects of substrate dislocation as well as the angle between substrate and reactor chamber longitudinal axis are investigated. It is shown that the temperature in the gas phase reactions region is significantly lower compared to the temperature profile around the substrate. Based on the obtained results, two new CVD system designs are proposed to enhance the temperature in the reactor chamber section where gas phase reactions take place. Moreover, it is shown that substrate dislocation and angle change result in physical property change such as species concentration on upper and lower substrate surfaces. This study is also applicable to other CVD-based fabrication process such as deposition of any layer, since the methodology of the fabrication process remains the same.Copyright

Basic Engineering Research for D and D of R Reactor Storage Pond Sludge: Electrokinetics, Carbon Dioxide Extraction, and Supercritical Water Oxidation

Large quantities of mixed low level waste (MLLW) that fall under the Toxic Substances Control Act (TSCA) exist and will continue to be generated during D and D operations at DOE sites across the country. The standard process for destruction of MLLW is incineration, which has an uncertain future. The extraction and destruction of PCBs from MLLW was the subject of this research Supercritical Fluid Extraction (SFE) with carbon dioxide with 5% ethanol as cosolvent and Supercritical Waster Oxidation (SCWO) were the processes studied in depth. The solid matrix for experimental extraction studies was Toxi-dry, a commonly used absorbent made from plant material. PCB surrogates were 1.2,4-trichlorobenzene (TCB) and 2-chlorobiphenyl (2CBP). Extraction pressures of 2,000 and 4,000 psi and temperatures of 40 and 80 C were studied. Higher extraction efficiencies were observed with cosolvent and at high temperature, but pressure little effect. SCWO treatment of the treatment of the PCB surrogates resulted in their destruction below detection limits.