C. Heath Turner

University of Alabama, Tuscaloosa, Alabama, United States

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Publications (61)153.97 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Previous work has characterized specific physical properties and CO2 solubility of 1-n-alkylimidazole solvents for use in pre- and post-combustion CO2 capture during gas treating. This research project explores the CO2 solubility and physical properties of multiply-branched alkylimidazole solvents to determine the effects of functional group position(s) on various chemical and physical attributes. Using this information, additional correlations between ring substitution and physical properties can be derived to optimize the characteristics. Synthesis and purification of these compounds were followed by tests to determine density, viscosity, and vapor pressure as functions of temperature and ring substitution, and these properties were shown to be comparable to previously-tested 1-n-alkylimidazoles. The solvents in general were found to have low viscosities (<15 cP) and negligible vapor pressures (<0.5 mbar). CO2 solubility experiments also showed that multiply-branched alkylimidazoles have similar if not improved absorption capacities relative to ionic liquids and 1-n-alkylimidazoles. In future work, polymeric membranes can be synthesized from these compounds to determine CO2 permeability and selectivity as a function of ring substitution. The ultimate goal of this research is to find an imidazole-based solvent with low volatility and high CO2 absorption capacity or an imidazole-based membrane structure with high CO2 permeability and selectivity that can be easily manufactured for application in large-scale industry for the reduction of atmospheric CO2 emissions.
    14 AIChE Annual Meeting; 11/2014
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    ABSTRACT: Imidazole-based polymers, such as poly(vinylimidazole), may provide useful properties for membrane-based CO2 capture applications, so it is becoming increasingly important to understand the formation mechanisms and underlying molecular structure of these materials. One of the challenges in the photopolymerization of 1-vinylimidazole (VIm) are slow rates and incomplete monomer conversion. We recently discovered that polymerization rate and overall conversion could be dramatically improved when VIm is in the presence of a bulky salt, lithium bis(trifluoromethylsulfonyl)imide [Li+][Tf2N-]. In this work, molecular dynamics simulations are used to model the intermolecular conformational behavior and thermophysical properties of the VIm-[Li+][Tf2N-] complexes. Molecular conformations of different ratios of [VIm] to salt were characterized in order to identify the structural ordering induced by [Li+][Tf2N-] on the polymerization of [VIm]. The same structural analyses were also performed on systems containing poly(vinylimidazole) [PVIm] in order to explore the conformations and thermophysical properties at different stages of the polymerization reaction. The calculated properties from the molecular dynamics simulations are compared against experimentally-derived structural features and found to be in agreement. Radial distribution functions indicate that [Li+] chelates with the “pyridine-like” nitrogen of the imidazole ring in both [VIm] and [PVIm], while the fluorine atoms of [Tf2N-] have strong interactions with the vinyl groups. Also, as the relative concentration of the salt increases, the probability of vinyl groups aggregating in favorable conformations to polymerization tends to increase (at all temperatures studied). Furthermore, electronic structure calculations have also been performed to identify electrostatic interactions in the systems, such as partial charge assignments and potential dipole interactions with [VIm] and [PVIm].
    14 AIChE Annual Meeting; 11/2014
  • Haining Liu, Christoffer Heath Turner
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    ABSTRACT: The properties of pristine carbon nanotubes (CNTs) can be modified in a number of different ways: covalent attachments, substitutional doping, induced defects, and non-covalent interactions with ligands. One unconventional approach is to combine CNTs with boron-nitride nanotubes (BNNTs) to form hybrid carbon and boron-nitride nanotube (CBNNT) materials. In this work, we perform a first-principles density functional theory study on the adsorption properties of NO2 on CBNNT heterostructures. It is found that the adsorption of NO2 is significantly increased on both zigzag CBNNT(8,0) and armchair CBNNT(6,6), as compared to either a pristine CNT or BNNT. For example, the chemisorption of NO2 on CNT(8,0) is found to be endothermic, while the chemisorption of NO2 on CBNNT(8,0) is an exothermic process with a very large binding energy of –27.74 kcal mol–1. Furthermore, the binding of NO2 on both CBNNT(8,0) and CBNNT(6,6) induces an increase in the conductivity of the nanotube. These characteristics indicate that the CBNNT heterostructures may have significant potential as an NO2 sensor or as a catalyst for NO2 decomposition reactions. Our calculations provide critical information for further evaluation, such as molecular-level adsorption simulations and microkinetic studies.
    Physical Chemistry Chemical Physics 09/2014; · 4.20 Impact Factor
  • Haining Liu, Jason E Bara, C Heath Turner
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    ABSTRACT: In this work, we report a computational study of the interactions between metal cations and imidazole derivatives in the gas phase. We first performed a systematic assessment of various density functionals and basis sets for predicting the binding energies between metal cations and the imidazoles. We find that the M11L functional in combination with the 6-311++G(d,p) basis set provides the best compromise between accuracy and computational cost with our metal-imidazole complexes. We then evaluated the binding of a series of metal cations, including Li+, Na+, K+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ba2+, Hg2+ and Pb2+, with several substituted imidazole derivatives. We find that electron-donating groups increase the metal binding energy while electron-withdrawing groups decrease the metal binding energy. Furthermore, the binding energy trends can be rationalized by the hardness of the metal cations and imidazole derivatives, providing a quick way to estimate the metal-imidazole binding strength. This insight can enable efficient screening protocols for identifying effective imidazole-based solvents and membranes for metal adsorption, and provide a framework for understanding metal…imidazole interactions in biological systems.
    The Journal of Physical Chemistry A 05/2014; · 2.77 Impact Factor
  • Haining Liu, C. Heath Turner
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    ABSTRACT: In this work, first-principles density functional theory (DFT) is used to predict oxygen adsorption on two types of hybrid carbon and boron-nitride nanotubes (CBNNTs), zigzag (8,0), and armchair (6,6). Although the chemisorption of O2 on CBNNT(6,6) is calculated to be a thermodynamically unfavorable process, the binding of O2 on CBNNT(8,0) is found to be an exothermic process and can form both chemisorbed and physisorbed complexes. The CBNNT(8,0) has very different O2 adsorption properties compared with pristine carbon nanotubes (CNTs) and boron-nitride nanotube (BNNTs). For example, O2 chemisorption is significantly enhanced on CBNNTs, and O2 physisorption complexes also show stronger binding, as compared to pristine CNTs or BNNTs. Furthermore, it is found that the O2 adsorption is able to increase the conductivity of CBNNTs. Overall, these properties suggest that the CBNNT hybrid nanotubes may be useful as a gas sensor or as a catalyst for the oxygen reduction reaction. © 2014 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 03/2014; · 3.84 Impact Factor
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    ABSTRACT: In this work, a variety of molecular simulation tools are used to help characterize the selective absorption of CO2 and CH4 in imidazole-based solvents. We focus our efforts on a series of 1-n-alkyl-2-methyl-imidazoles and ether-functionalized imidazoles, over a temperature range of 293 K to 353 K, and we perform detailed analysis of the free volume. We find that the electrostatic potential within the solvent free volume cavities provides a useful indication of the selective absorption of CO2 and CH4. The electrostatic potential calculation is significantly faster than the direct calculation of the chemical potential, and tests with the 1-n-alkyl-2-methyl-imidazoles and the ether-functionalized imidazoles indicate that this may be a useful screening tool for other solvents.
    The Journal of Physical Chemistry B 12/2013; · 3.61 Impact Factor
  • Haining Liu, Jason E. Bara, C. Heath Turner
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    ABSTRACT: There has been increasing interest in developing new materials for CO2 capture. One of the approaches is to synthesize polymer membrane using imidazole derivatives as the monomer. These imidazole derivatives are able to react with aqueous CO2 to form bicarbonate anions, thus enabling facilitated transport of CO2 through the membrane. In order to better understand the chemical and thermophysical properties of imidazole derivatives, we have employed quantum mechanics and molecular dynamics methods to calculate the proton affinities, 1H NMR chemical shifts, and absorption properties of a variety of imidazole derivatives. From our simulations, a quantitative characterization of the effect of various exocyclic substituents on the proton affinity of imidazole was achieved. In particular, we find that electron-donating groups are able to increase the proton affinity of imidazole. In addition, the calculated 1H NMR chemical shift and thermophysical properties are in excellent with experiment. These results will be helpful for future experimental design of new materials to be used for CO2 capture.
    13 AIChE Annual Meeting; 11/2013
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    ABSTRACT: Branched gold nanoparticles were synthesized via a soft-template directed process using a biological buffer, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). These branched Au nanoparticles are mainly tetrapods and show distinct absorption in the range of 700-900 nm. A combined experimental and computational study suggests that at high concentration, the HEPES molecules self-assemble into structures with long-range order, serving as soft-templates to direct the formation of the anisotropic gold nanoparticles. Detailed analyses of surface chemistry and structure indicate the formation of a molecular bilayer structure for the stabilization of the branched Au nanostructures. Our density functional theory (DFT) calculations predict that the sulfonate group of the HEPES molecules prefer to bind to the Au surfaces, while the free hydroxyl groups facilitate the self-assembly and bilayer formation through the formation of hydrogen bonds. By comparing three different buffer molecules, our study demonstrates the critical importance of ligand chemistry in the directed formation of anisotropic metallic nanoparticles.
    13 AIChE Annual Meeting; 11/2013
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    ABSTRACT: Despite the utility of imidazoles for a wide variety of chemical and biological applications as well as the growing research in imidazolium-based ionic liquids (ILs), synthetic studies and characterization data for N-functionalized imidazole derivatives with substituents present at the C(2) and/or C(4) and/or C(5) positions are generally unreported. Here, we modify our prior method for synthesizing monofunctionalized imidazoles and apply it to the production of a library of 30 di- and trifunctionalized alkylimidazoles using only commodity chemicals and avoiding anhydrous solvents or air/water-sensitive reagents. For all products, purities of >98% could be readily achieved, although yields were lower than in our prior work with imidazole, which may be due to mass transfer limitations and/or increased nucleophilicity of substituted imidazole products. Interestingly, we also observe that, when 4-methylimidazole or 2-ethyl-4-methylimidazole is used as a starting material, two regioisomers are inevitably formed. We employed electronic structural calculations to aid in identifying the chemical shifts and quantifying the relative presence of the regioisomers. In both series of compounds where regioisomers could be formed, the 4-methyl regioisomer was favored. Although the formation of similar regioisomers has been previously noted in the literature, it has perhaps not been fully considered in works related to imidazolium-based ILs.
    Industrial & Engineering Chemistry Research 08/2013; 52(34):11880–11887. · 2.24 Impact Factor
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    ABSTRACT: Branched gold nanoparticles are synthesized via a soft-template-directed process using a biological buffer, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). These branched Au nanoparticles are mainly tetrapods and show distinct absorption in the range of 700–1000 nm. A combined experimental and computational study suggests that at high concentration, the HEPES molecules self-assemble into structures with long-range order serving as soft templates to direct the formation of the anisotropic gold nanoparticles. Detailed analyses of surface chemistry and structure indicate the formation of a molecular bilayer structure for the stabilization of the branched Au nanostructures. Our density-functional theory (DFT) calculations predict that the sulfonate group of the HEPES molecules prefers to bind to the Au surfaces, while the free hydroxyl groups facilitate the self-assembly and bilayer formation through the formation of hydrogen bonds. By comparing three different buffer molecules, our study demonstrates the critical importance of ligand chemistry in the directed formation of anisotropic metallic nanoparticles.
    The Journal of Physical Chemistry C. 08/2013; 117(33):17143–17150.
  • Zhongtao Zhang, C. Heath Turner
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    ABSTRACT: In order to explore possible ways of using metallocene compounds in heterogeneous catalysis and in sensor applications, we present a theoretical characterization of cyclopentadienyl (Cp) + transition metal (TM) complexes adsorbed on boron-doped carbon nanotubes (B-CNTs) and boron-doped graphenes. Using spin-polarized density functional theory calculations, we present a systematic study of the geometries, energetics, and electronic properties of CpTM (where TM = Fe, Ni, Co, Cr, Cu) adsorbed on both pristine and boron-doped carbon supports. Our work reveals significant increases of the binding energies between CpTM and boron-doped CNTs and graphenes (versus pristine carbon supports), surpassing even the adsorption strength of the isolated metals atoms (by about 2 eV). According to our electronic structure analysis, both the delocalization of the TM-d state by the presence of the Cp ring and the interactions between the Cp ring and the carbon substrate are responsible for the enhancement of the binding energies. This stabilization may play an important role in immobilizing ferrocene-based catalysts. Moreover, tunable metallicities of CpTMs adsorbed on pristine and on B-CNTs are observed, indicating potential applications of CpTM/B-CNT complexes in nanoelectronics and as sensors. Using these complexes, we also probed the adsorption of O2 molecules, as an initial indicator of catalytic performance. Both chemisorption (with an elongated O–O bond) and dissociative chemisorption were found on CpFe/B-CNT (8,0) complexes.
    The Journal of Physical Chemistry C. 04/2013; 117(17):8758–8766.
  • Haining Liu, Jason E. Bara, C. Heath Turner
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    ABSTRACT: A deeper understanding of the acid/base properties of imidazole derivatives will aid the development of solvents, polymer membranes and other materials that can be used for CO2 capture and acid gas removal. In this study, we employ density functional theory calculations to investigate the effect of various electron-donating and electron-withdrawing groups on the proton affinity of 1-methylimidazole. We find that electron-donating groups are able to increase the proton affinity relative to 1-methylimidazole, i.e., making the molecule more basic. In contrast, electron-withdrawing groups cause a decrease of the proton affinity. When multiple substituents are present, their effects on the proton affinity were found to be additive. This finding offers a quick approach for predicting and targeting the proton affinities of this series of molecules, and we show the strong correlation between the calculated proton affinities and experimental pKa values.
    Chemical Physics 04/2013; 416:21–25. · 1.96 Impact Factor
  • Wei An, C. Heath Turner
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    ABSTRACT: Using density functional theory methods, we investigate the relative stability of three types of 1D Ni nanostructures. The first two are conceived from the growth of either Ih or Oh symmetry 0D nanoparticles of Ni, and the third, a Ni (6,3) nanorod (NR), is a hexagonal close-packed structure (both on the surface and along the axis direction). Our calculations show that 1D Ni NRs as well as Ni double-walled and triple-walled nanotubes, are more stable than comparable-sized Ni 0D nanoparticles. We explore the potential of NRs as a prototype catalyst by calculating the alloying effect of M (M = Mo, Fe, Co, and Cu) on the adsorption of C and S under full coverage of atomic O. The calculated results suggest that Ni-based 1D NRs are highly reactive toward O-binding, an indication that anode oxidation may be achieved at much lower temperatures. By forming a NiM surface alloy, the binding strength of C and S can be reduced. In particular, Fe and Cu seem to be the most promising metal dopants in Ni-based 1D NR systems for suppressing the formation of C and S (whereas Co promotes the binding of C). Also, it is found that the Ni0.75Mo0.25 (6,3) NR model collapses its tubular structure due to strong binding with O.
    The Journal of Physical Chemistry C 01/2013; 117(3):1315–1322. · 4.84 Impact Factor
  • Zhongtao Zhang, Wei An, C. Heath Turner
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    ABSTRACT: Characterizing the Structural and Electronic Properties of Cyclopentene -Metal- Singlewalled Carbon Nanotube Complexes: a DFT Study The complexes of metallocene(Cp2M) between single walled carbon nanotubes (SWCNT) on the surface or inside, graphene are studied thoroughly, and shown potential applications as sensors.CpM and SWCNT/ graphene complexes drawed our attentions due to the similarity with the tunable electronic structures of the complexes of SWCNT/ graphene and organic molecules/ metal atoms. Meanwhile, our previous research showed significantly stabilization of transition metals on B-doped nanocarbon, indicates that CpM may aslo be stabilized. Therefore, we perform a theoretical study on the structural and electronic properties of CpM (M= Fe, Co, Cr, V, Ni) and pristine or B-doped SWCNTs. A significant increasing of binding energies comparing with our previous work on metal atoms was observed (increased about 2eV). Also, density of states (DOS), and band strucutres of CpM (M= Fe, Co, Cr, V, Ni) ligands on the outer surface of 4 different SWCNTs: prinstine (6, 6), pristine (8, 0), B-doped (6, 6), B-doped (8, 0) SWCNTs were calculated using Density Functional Theory (DFT) to explore the potential application of CpM SWCNT complexes for sensors as well as the possibilities of immobilization of CpM based catalyst by B-doped SWCNTs.
    12 AIChE Annual Meeting; 10/2012
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    ABSTRACT: N-functionalized imidazoles are a class of heterocyclic organic molecules, and are well-known as components of pharmaceuticals and also serve as building blocks for imidazolium-based ionic liquids (ILs). While IL-based solvents have been the focus of many research efforts in areas such as CO2 capture, imidazoles have not been considered for these same applications. Imidazoles possess many of the same desirable characteristics as ILs such as tunable chemical structures, low vapor pressure and good chemical/thermal stability. Despite these promising features, it has only been very recently that reports on the the relationships between imidazole structure and physical properties were reported, and the study of imidazoles as tailored solvents is still dwarfed by the body of knowledge available for ILs. Our research in this area has focused on developing structure-property relationships for a wide range of N-functionalized imidazoles, with emphasis on density, viscosity, vapor pressure, pKa, heat capacity, solubility of CO2, CH4 and other gases, as well as the underlying thermodynamics. Because imidazoles possess such tunable structures, we also forsesee broad applications of this platform in polymers and self-assembling materials such as liquid crystals. Furthermore, we have utilized molecular dynamics as well as COSMOtherm simulations to computationally model and predict properties as well as parametrically study the influences of various functional groups (e.g. alkyl, ethers, nitriles, etc.) on physical properties. While imidazoles have some similar properties to ILs, other properties such as viscosity can be an order of magnitude (or more) different. Furthermore, some unique chemistries are available due to the basicity/nucleophilicty of imidazoles that are unavailable in ILs. This presentation will detail our synthetic methods, property characterizations, COSMO modeling and provide comparisons to these properties in ILs.
    12 AIChE Annual Meeting; 10/2012
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    ABSTRACT: Molecular simulations are used to probe the thermophysical properties of a series of N-functionalized alkylimidazoles, ranging from N-methylimidazole to N-heptylimidazole. These compounds have been previously synthesized, and their solvation properties have been shown to be potentially useful for CO2 capture from industrial sources. We report first-principles calculations, which are used to fit electrostatic charges to the molecular models, which are then implemented in a series of molecular dynamics simulations. Over a range of different temperatures, we benchmark the simulated densities and heat capacities against experimental measurements. Also, we predict the Henry’s constants for CO2 absorption and probe the solvents’ structures using molecular simulation techniques, such as fractional free volume analysis and void distributions. The simulations demonstrate excellent agreement when comparing density values, and the predictions of the heat capacities and Henry’s constants for CO2 absorption are in very good qualitative agreement with the experiments. Overall, we find that our simulations are able to closely reproduce the experimental benchmarks and add additional insight into the molecular structure of these fluids, with respect to their observed solvent properties.
    12 AIChE Annual Meeting; 10/2012
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    ABSTRACT: Molecular simulations are used to probe the thermophysical properties of a series of N-functionalized alkylimidazoles, ranging from N-methylimidazole to N-heptylimidazole. These compounds have been previously synthesized, and their solvation properties have been shown to be potentially useful for CO(2) capture from industrial sources. In this work, we use first-principles calculations to fit electrostatic charges to the molecular models, which are then used to perform a series of molecular dynamics simulations. Over a range of different temperatures, we benchmark the simulated densities and heat capacities against experimental measurements. Also, we predict the Henry's constants for CO(2) absorption and probe the solvents' structures using molecular simulation techniques, such as fractional free volume analysis and void distributions. We find that our simulations are able to closely reproduce the experimental benchmarks and add additional insight into the molecular structure of these fluids, with respect to their observed solvent properties.
    The Journal of Physical Chemistry B 05/2012; 116(22):6529-35. · 3.61 Impact Factor
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    ABSTRACT: The efficient capture of CO2 from industrial power generation sources is a major challenge. Current studies are investigating the adsorption of CO2 into ionic liquids (ILs). Imidazolium-based ILs have received a great deal of attention for CO2 capture due to their unique physical properties. However, it has recently been reported that imidazoles – neutral counterparts to imidazolium-based ILs – can offer enhancements in viscosity, cost, and CO2 capacity. However, the lack of thermophysical property data for neutral imidazole substitutions and chemical permutations makes it difficult to identify and develop future candidates for specific gas processing applications without having to obtain extensive experimental datasets. Using ab initio and molecular mechanics methods, we elucidate thermodynamic and structural properties of a variety of N-functionalized imidazole compounds. Ab initio calculations are used to determine parameters (such as partial charges) for the all-atom Optimized Potentials for Liquid Simulations (OPLS-AA) force field, followed by simulations using the molecular dynamics package Gromacs. We make comparisons with our experimentally-synthesized compounds, providing guidance towards new synthesis targets.
    2011 AIChE Annual Meeting; 10/2011
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    ABSTRACT: Iron oxide nanowhiskers with dimensions of approximately 2 × 20 nm were successfully synthesized by selectively heating an iron oleate complex. Such nanostructures resulted from the difference in the ligand coordination microenvironments of the Fe(III) oleate complex, according to our electronic structure calculations and thermogravimetric analysis. A ligand-directed growth mechanism was subsequently proposed to rationalize the growth process. The formation of the nanowhiskers provides a unique example of shape-controlled nanostructures, offering additional insights into nanoparticle synthesis.
    Nano Letters 02/2011; 11(3):1141-6. · 13.03 Impact Factor
  • Wei An, Daniel Gatewood, Brett Dunlap, C. Heath Turner
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    ABSTRACT: We present density-functional theory calculations of the chemisorption of atomic species O, S, C, H and reaction intermediates OH, SH, and CHn (n = 1, 2, and 3) on M/Ni alloy model catalysts (M = Bi, Mo, Fe, Co, and Cu). The activity of the Ni alloy catalysts for solid-oxide fuel cell (SOFC) anode oxidation reactions is predicted, based on a simple descriptor, i.e., the binding energy of oxygen. First, we find that the binding of undesirable intermediates, such as C and S, can be inhibited and the catalytic activity of planar Ni-based anodes can be tuned towards oxidation by selectively forming a bimetallic surface alloy. In particular, Cu/Ni, Fe/Ni, and Co/Ni anode catalysts are found to be most active towards anode oxidation. On the other hand, the Mo/Ni alloy surface is predicted to be the most effective catalyst in terms of inhibiting the deposition of C and S (while still preserving relatively high catalytic activity). The formation of a surface alloy, which has the alloy element enriched on the topmost surface, was found to be critical to the activity of the Ni alloy catalysts.Research highlights▶ Density-functional theory is used to model the activity of Ni-alloy catalysts. ▶ Chemisorption of O, S, C, H, OH, SH, and CHn is predicted. ▶ Catalytic activity for SOFC anode oxidation is strongly dependent upon surface alloy. ▶ Ni-alloy compositions include Bi, Mo, Fe, Co, and Cu.
    Journal of Power Sources 01/2011; 196(10):4724-4728. · 5.26 Impact Factor

Publication Stats

243 Citations
153.97 Total Impact Points

Institutions

  • 2005–2014
    • University of Alabama
      • Department of Chemical and Biological Engineering
      Tuscaloosa, Alabama, United States
  • 2008–2010
    • George Washington University
      • Department of Chemistry
      Washington, D. C., DC, United States
  • 2006
    • Tuskegee University
      • Department of Chemical Engineering
      Tuscaloosa, AL, United States
  • 2001–2003
    • North Carolina State University
      • Department of Chemical and Biomolecular Engineering
      Raleigh, NC, United States
    • University of Pittsburgh
      • Chemical and Petroleum Engineering
      Pittsburgh, PA, United States