Publications

Stewart, Constantine A.; Arrieta, Marie Y.

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Stewart, Constantine A.

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Stewart, Constantine A.

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Grainger, Lora A.; Imran, Thamer A.; Cook, Eric N.; Gaudioso, Jennifer M.; Stewart, Constantine A.

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Stewart, Constantine A.

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Stewart, Constantine A.; Garcia, Brooke M.

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Stewart, Constantine A.

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Stewart, Constantine A.

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Alley, William M.; Kottenstette, Richard K.; Stewart, Constantine A.

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Stewart, Constantine A.

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Cruz-Campa, Jose L.; Lavin, Judith M.; James, Conrad D.; Stewart, Constantine A.; Kemp, Richard K.; Nielson, Gregory N.; Okandan, Murat O.; Gupta, Vipin P.

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Stewart, Constantine A.

This late-start LDRD was broadly focused on the synthetic attempts to prepare novel ligands as complexing agents for main group metals for the sequestration of CO{sub 2}. In prior work we have shown that certain main group (p block elements) metals such as tin and zinc, when ligated to phosphinoamido- ligands, can bind CO{sub 2} in a novel fashion. Rather than simple insertion into the metal-nitrogen bonds to form carbamates, we have seen the highly unusual complexation of CO{sub 2} in a mode that is more similar to a chemical 'adduct' rather than complexation schemes that have been observed previously. The overarching goal in this work is to prepare more of these complexes that can (a) sequester (or bind) CO{sub 2} easily in this adduct form, and (b) be stable to chemical or electrochemical reduction designed to convert the CO{sub 2} to useful fuels or fuel precursors. The currently used phosphinoamido- ligands appear at this point to be less-stable than desired under electrochemical reduction conditions. This instability is believed due to the more delicate, reactive nature of the ligand framework system. In order to successfully capture and convert CO{sub 2} to useful organics, this instability must be addressed and solved. Work described in the late-start LDRD was designed to screen a variety of ligand/metal complexes that a priori are believed to be more stable to polar solvents and possible mild hydrolytic conditions than are the phosphinoamido-ligands. Results from ligand syntheses and metal complexation studies are reported.

Lavin, Judith M.; Stewart, Constantine A.; Kemp, Richard K.

This late-start LDRD was focused on the application of chemical principles of self-assembly on the ordering and placement of photovoltaic cells in a module. The drive for this chemical-based self-assembly stems from the escalating prices in the 'pick-and-place' technology currently used in the MEMS industries as the size of chips decreases. The chemical self-assembly principles are well-known on a molecular scale in other material science systems but to date had not been applied to the assembly of cells in a photovoltaic array or module. We explored several types of chemical-based self-assembly techniques, including gold-thiol interactions, liquid polymer binding, and hydrophobic-hydrophilic interactions designed to array both Si and GaAs PV chips onto a substrate. Additional research was focused on the modification of PV cells in an effort to gain control over the facial directionality of the cells in a solvent-based environment. Despite being a small footprint research project worked on for only a short time, the technical results and scientific accomplishments were significant and could prove to be enabling technology in the disruptive advancement of the microelectronic photovoltaics industry.

Stewart, Constantine A.; Kemp, Richard K.; Kemp, Richard K.

Group 12 metal cyclam complexes and their derivatives as well as (octyl){sub 2}Sn(OMe){sub 2} were examined as potential catalysts for the production of dimethyl carbonate (DMC) using CO{sub 2} and methanol. The zinc cyclams will readily take up carbon dioxide and methanol at room temperature and atmospheric pressure to give the metal methyl carbonate. The tin exhibited an improvement in DMC yields. Studies involving the reaction of bis-phosphino- and (phosphino)(silyl)-amido group 2 and 12 complexes with CO{sub 2} and CS{sub 2} were performed. Notable results include formation of phosphino-substituted isocyanates, fixation of three moles of CO{sub 2} in an unprecedented [N(CO{sub 2}){sub 3}]{sup 3-} anion, and rapid splitting of CS{sub 2} by main group elements under extremely mild conditions. Similar investigations of divalent group 14 silyl amides led to room temperature splitting of CO{sub 2} into CO and metal oxide clusters, and the formation of isocyanates and carbodiimides.

Stewart, Constantine A.; Kemp, Richard K.

Energy production is inextricably linked to national security and poses the danger of altering the environment in potentially catastrophic ways. There is no greater problem than sustainable energy production. Our purpose was to attack this problem by examining processes, technology, and science needed for recycling CO{sub 2} back into transportation fuels. This approach can be thought of as 'bio-inspired' as nature employs the same basic inputs, CO{sub 2}/energy/water, to produce biomass. We addressed two key deficiencies apparent in current efforts. First, a detailed process analysis comparing the potential for chemical and conventional engineering methods to provide a route for the conversion of CO{sub 2} and water to fuel has been completed. No apparent 'showstoppers' are apparent in the synthetic route. Opportunities to improve current processes have also been identified and examined. Second, we have also specifically addressed the fundamental science of the direct production of methanol from CO{sub 2} using H{sub 2} as a reductant.

Chemical Communications

Kemp, Richard K.; Stewart, Constantine A.

Abstract not provided.

Staiger, Chad S.; Cornelius, Christopher J.; Rice, Steven F.; Coker, Eric N.; Stewart, Constantine A.; Kemp, Richard K.; Pickett, Lyle M.

The United States produces only about 1/3 of the more than 20 million barrels of petroleum that it consumes daily. Oil imports into the country are roughly equivalent to the amount consumed in the transportation sector. Hence the nation in general, and the transportation sector in particular, is vulnerable to supply disruptions and price shocks. The situation is anticipated to worsen as the competition for limited global supplies increases and oil-rich nations become increasingly willing to manipulate the markets for this resource as a means to achieve political ends. The goal of this project was the development and improvement of technologies and the knowledge base necessary to produce and qualify a universal fuel from diverse feedstocks readily available in North America and elsewhere (e.g. petroleum, natural gas, coal, biomass) as a prudent and positive step towards mitigating this vulnerability. Three major focus areas, feedstock transformation, fuel formulation, and fuel characterization, were identified and each was addressed. The specific activities summarized herein were identified in consultation with industry to set the stage for collaboration. Two activities were undertaken in the area of feedstock transformation. The first activity focused on understanding the chemistry and operation of autothermal reforming, with an emphasis on understanding, and therefore preventing, soot formation. The second activity was focused on improving the economics of oxygen production, particularly for smaller operations, by integrating membrane separations with pressure swing adsorption. In the fuel formulation area, the chemistry of converting small molecules readily produced from syngas directly to fuels was examined. Consistent with the advice from industry, this activity avoided working on improving known approaches, giving it an exploratory flavor. Finally, the fuel characterization task focused on providing a direct and quantifiable comparison of diesel fuel and JP-8.

Kemp, Richard K.; Stewart, Constantine A.

Abstract not provided.

Kemp, Richard K.; Stewart, Constantine A.

This report summarizes our findings during the study of a novel homogeneous epoxidation catalyst system that uses molecular oxygen as the oxidant, a ''Holy Grail'' in catalysis. While olefins (alkenes) that do not contain allylic hydrogens can be epoxidized directly using heterogeneous catalysts, most olefins cannot, and so a general, atom-efficient route is desired. While most of the work performed on this LDRD has been on pincer complexes of late transition metals, we also scouted out metal/ligand combinations that were significantly different, and unfortunately, less successful. Most of the work reported here deals with phosphorus-ligated Pd hydrides [(PCP)Pd-H]. We have demonstrated that molecular oxygen gas can insert into the Pd-H bond, giving a structurally characterized Pd-OOH species. This species reacts with oxygen acceptors such as olefins to donate an oxygen atom, although in various levels of selectivity, and to generate a [(PCP)Pd-OH] molecule. We discovered that the active [(PCP)Pd-H] active catalyst can be regenerated by addition of either CO or hydrogen. The demonstration of each step of the catalytic cycle is quite significant. Extensions to the pincer-Pd chemistry by attaching a fluorinated tail to the pincer designed to be used in solvents with higher oxygen solubilities are also presented.