Publications

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We demonstrate that metal-organic frameworks (MOFs) can catalyze hydrogenolysis of aryl ether bonds under mild conditions. Mg-IRMOF-74(I) and Mg-IRMOF-74(II) are stable under reducing conditions and can cleave phenyl ethers containing β-O-4, α-O-4, and 4-O-5 linkages to the corresponding hydrocarbons and phenols. Reaction occurs at 10 bar H2 and 120 °C without added base. DFT-optimized structures and charge transfer analysis suggest that the MOF orients the substrate near Mg2+ ions on the pore walls. Ti and Ni doping further increase conversions to as high as 82% with 96% selectivity for hydrogenolysis versus ring hydrogenation. Repeated cycling induces no loss of activity, making this a promising route for mild aryl-ether bond scission.

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Product formation from R + O2 reactions relevant to low-temperature autoignition chemistry was studied for 2,5-dimethylhexane, a symmetrically branched octane isomer, at 550 and 650 K using Cl-atom initiated oxidation and multiplexed photoionization mass spectrometry (MPIMS). Interpretation of time- and photon-energy-resolved mass spectra led to three specific results important to characterizing the initial oxidation steps: (1) quantified isomer-resolved branching ratios for HO2 + alkene channels; (2) 2,2,5,5-tetramethyltetrahydrofuran is formed in substantial yield from addition of O2 to tertiary 2,5-dimethylhex-2-yl followed by isomerization of the resulting ROO adduct to tertiary hydroperoxyalkyl (QOOH) and exhibits a positive dependence on temperature over the range covered leading to a higher flux relative to aggregate cyclic ether yield. The higher relative flux is explained by a 1,5-hydrogen atom shift reaction that converts the initial primary alkyl radical (2,5-dimethylhex-1-yl) to the tertiary alkyl radical 2,5-dimethylhex-2-yl, providing an additional source of tertiary alkyl radicals. Quantum-chemical and master-equation calculations of the unimolecular decomposition of the primary alkyl radical reveal that isomerization to the tertiary alkyl radical is the most favorable pathway, and is favored over O2-addition at 650 K under the conditions herein. The isomerization pathway to tertiary alkyl radicals therefore contributes an additional mechanism to 2,2,5,5-tetramethyltetrahydrofuran formation; (3) carbonyl species (acetone, propanal, and methylpropanal) consistent with β-scission of QOOH radicals were formed in significant yield, indicating unimolecular QOOH decomposition into carbonyl + alkene + OH. (Chemical Equation Pesented).

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In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate process performance, and Monte Carlo analyses were carried out to identify key sources of uncertainty and variability. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. In the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars.

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The branched C 5 alcohol isopentanol (3-methylbutan-1-ol) has shown promise as a potential biofuel both because of new advanced biochemical routes for its production and because of its combustion characteristics, in particular as a fuel for homogeneous-charge compression ignition (HCCI) or related strategies. In the present work, the fundamental autoignition chemistry of isopentanol is investigated by using the technique of pulsed-photolytic Cl-initiated oxidation and by analyzing the reacting mixture by time-resolved tunable synchrotron photoionization mass spectrometry in low-pressure (8 Torr) experiments in the 550-750 K temperature range. The mass-spectrometric experiments reveal a rich chemistry for the initial steps of isopentanol oxidation and give new insight into the low-temperature oxidation mechanism of medium-chain alcohols. Formation of isopentanal (3-methylbutanal) and unsaturated alcohols (including enols) associated with HO 2 production was observed. Cyclic ether channels are not observed, although such channels dominate OH formation in alkane oxidation. Rather, products are observed that correspond to formation of OH via β-C-C bond fission pathways of QOOH species derived from β- and γ-hydroxyisopentylperoxy (RO 2) radicals. In these pathways, internal hydrogen abstraction in the RO 2 QOOH isomerization reaction takes place from either the -OH group or the C-H bond in α-position to the -OH group. These pathways should be broadly characteristic for longer-chain alcohol oxidation. Isomer-resolved branching ratios are deduced, showing evolution of the main products from 550 to 750 K, which can be qualitatively explained by the dominance of RO 2 chemistry at lower temperature and hydroxyisopentyl decomposition at higher temperature. © 2012 The Owner Societies.

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The convergence of micro-/nano-electromechanical systems (MEMS/NEMS) and biomedical industries is creating a need for innovation and discovery around materials, particularly in miniaturized systems that use polymers as the primary substrate. Polymers are ubiquitous in the microelectronics industry and are used as sensing materials, lithography tools, replication molds, microfluidics, nanofluidics, and biomedical devices. This diverse set of operational requirements dictates that the materials employed must possess different properties in order to reduce the cost of production, decrease the scale of devices to the appropriate degree, and generate engineered devices with new functional properties at cost-competitive levels of production. Nanoscale control of polymer deformation at a massive scale would enable breakthroughs in all of the aforementioned applications, but is currently beyond the current capabilities of mass manufacturing. This project was focused on developing a fundamental understanding of how polymers behave under different loads and environments at the nanoscale in terms of performance and fidelity in order to fill the most critical gaps in our current knowledgebase on this topic.

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Long chain alcohols possess major advantages over the currently used ethanol as bio-components for gasoline, including higher energy content, better engine compatibility, and less water solubility. The rapid developments in biofuel technology have made it possible to produce C{sub 4}-C{sub 5} alcohols cost effectively. These higher alcohols could significantly expand the biofuel content and potentially substitute ethanol in future gasoline mixtures. This study characterizes some fundamental properties of a C{sub 5} alcohol, isopentanol, as a fuel for HCCI engines. Wide ranges of engine speed, intake temperature, intake pressure, and equivalence ratio are investigated. Results are presented in comparison with gasoline or ethanol data previously reported. For a given combustion phasing, isopentanol requires lower intake temperatures than gasoline or ethanol at all tested speeds, indicating a higher HCCI reactivity. Similar to ethanol but unlike gasoline, isopentanol does not show two-stage ignition even at very low engine speed (350 rpm) or with considerable intake pressure boost (200 kPa abs.). However, isopentanol does show considerable intermediate temperature heat release (ITHR) that is comparable to gasoline. Our previous work has found that ITHR is critical for maintaining combustion stability at the retarded combustion phasings required to achieve high loads without knock. The stronger ITHR causes the combustion phasing of isopentanol to be less sensitive to intake temperature variations than ethanol. With the capability to retard combustion phasing, a maximum IMEP{sub g} of 5.4 and 11.6 bar was achieved with isopentanol at 100 and 200 kPa intake pressure, respectively. These loads are even slightly higher than those achieved with gasoline. The ITHR of isopentanol depends on operating conditions and is enhanced by simultaneously increasing pressures and reducing temperatures. However, increasing the temperature seems to have little effect on ITHR at atmospheric pressure, but it does promote hot ignition. Finally, the dependence of ignition timing on equivalence ratio, here called {phi}-sensitivity, is measured at atmospheric intake pressure, showing that the ignition of isopentanol is nearly insensitive to equivalence ratio when thermal effects are removed. This suggests that partial fuel stratification, which has been found effective to control the HRR with two-stage ignition fuels, may not work well with isopentanol at these conditions. Overall, these results indicate that isopentanol has a good potential as a HCCI fuel, either in neat form or in blend with gasoline.

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Today, carbon-rich fossil fuels, primarily oil, coal and natural gas, provide 85% of the energy consumed in the United States. The release of greenhouse gases from these fuels has spurred research into alternative, non-fossil energy sources. Lignocellulosic biomass is renewable resource that is carbon-neutral, and can provide a raw material for alternative transportation fuels. Plant-derived biomass contains cellulose, which is difficult to convert to monomeric sugars for production of fuels. The development of cost-effective and energy-efficient processes to transform the cellulosic content of biomass into fuels is hampered by significant roadblocks, including the lack of specifically developed energy crops, the difficulty in separating biomass components, the high costs of enzymatic deconstruction of biomass, and the inhibitory effect of fuels and processing byproducts on organisms responsible for producing fuels from biomass monomers. One of the main impediments to more widespread utilization of this important resource is the recalcitrance of cellulosic biomass and techniques that can be utilized to deconstruct cellulosic biomass.