Oxidation of dimethyl-ether and ethylene in the atmosphere and combustion environment and thermodynamic studies on hydrofluorocarbons using ab initio calculation methods

Reaction pathways and kinetics are analyzed on CH3OC·H2 unimolecular decay and on the complete CH3OC·H2 + O2 reaction system using thermodynamic properties (ΔHf°298, S°298, and C(T) 300≤T/K≤1500) derived by two ab initio calculation methods, CBS-q and G2. These are used to determine thermodynamic properties of reactants, intermediate radicals and transition state (TS) compounds. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculate energy dependent rate constants, k(E), and master equation is used to account for collisional stabilization. Comparison of calculated fall-off with experiment indicates that the CBS-q and G2 calculated Ea,rxn for the rate controlling transition state (-scission reaction to C·H2O + C·H2OOH) needs to be lowered by factor of 3.3 kcal/mol and 4.0 kcal/mol respectively in order to match the data of Sehested et al. Experimental results on dimethyl-ether pyrolysis and oxidation reaction systems are compared with a detailed reaction mechanism model. The computer code CHEMKIN II is used for numerical integration. Overall agreement of the model data with experimental data is very good. Reaction pathways are analyzed and kinetics are determined on formation and reactions of the adduct resulting from OH addition to ethylene using the above ab initio methods. Hydrogen atom tunneling is included by use of Eckart formalism. Rate constants are compared with experimentally determined product branching ratios (C·H2CH2OH stabilization : CH2O + CH3 : CH3CHO + H). ab initio calculations are performed to estimate thermodynamic properties of nine fluorinated ethane compounds (fluoroethane to hexafluoroethane), eight fluoropropane (1-fluoropropane, 1,1- and 1,2-difluoropropane, 1,1,1- and 1,1,2-trifluoropropane, 1,1,1,2- and 1,1,2,2-tetrafluoropropane and 1,1,2,2-pentafluoropropane), and 2- fluoro,2-methylpropane. Standard entropies and heat capacities are calculated using the rigid-rotor-harmonic-oscillator approximation with direct integration over energy levels of the intramolecular rotation potential energy curve. Enthalpies of formation are estimated using G2MP2 total energies and isodesmic reactions. Thermodynamic properties for fluorinated carbon groups C/C/F/H2, C/C/F2/H, C/C/F3, C/C2/F/H, C/C2/F2 and C/C3/F for fluorinated alkane compounds, CD/F/H and CD/F2 for fluorinated alkene compounds and CT/F for fluorinated alkyne compounds are estimated. Fluorine-fluorine interaction terms F/F, 2F/F, 3F/F, 2F/2F, 3F/2F and 3F/3F for alkane compounds, F//F, 2F//F and 2F/2F for alkene compounds, and F///F for alkyne compound are also estimated

Toward Computing Accurate Free Energies in Heterogeneous Catalysis: a Case Study for Adsorbed Isobutene in H-ZSM-5

Herein, we propose a novel computational protocol that enables calculating free energies with improved accuracy by combining the best available techniques for enthalpy and entropy calculation. While the entropy is described by enhanced sampling molecular dynamics techniques, the energy is calculated using ab initio methods. We apply the method to assess the stability of isobutene adsorption intermediates in the zeolite H-SSZ-13, a prototypical problem that is computationally extremely challenging in terms of calculating enthalpy and entropy. We find that at typical operating conditions for zeolite catalysis (400 °C), the physisorbed π-complex, and not the tertiary carbenium ion as often reported, is the most stable intermediate. This method paves the way for sampling-based techniques to calculate the accurate free energies in a broad range of chemistry-related disciplines, thus presenting a big step forward toward predictive modeling

Density Functional Theory and the Quantum Chemistry of Gas Separation, Magnetism, and Catalysis in Metal–Organic Frameworks

University of Minnesota Ph.D. dissertation. September 2017. Major: Chemistry. Advisor: Donald Truhlar. 1 computer file (PDF); xii, 206 pages.This dissertation uses theoretical and computational methods, mainly the quantum mechanical density functional theory of electronic structure, to explore three functionalities of metal-organic frameworks (MOFs), namely, purification and separation of gaseous mixtures, catalysis of C–H bond activation, and potential use of MOFs as magnetic materials. The dissertation also includes the development and analysis of computationally efficient quantum mechanical and molecular mechanical methods that are more accurate than previously available methods

Studies on the Decomposition of Selected Brominated Flame Retardants (BFRs) and Formation of Polybrominated Dibenzo-p-dioxins and Dibenzofurans (PBDD/Fs) and Mixed Halogenated Dibenzo-p-dioxins and Dibenzofurans (PXDD/Fs)

Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment or recycling activities are common disposal methods for BFR-laden objects, it is essential to determine the precise decomposition chemistry of BFRs at elevated temperatures, and their transformation pathways into hazardous pollutants. Sunlight can trigger the photodecomposition of BFRs, either during the life cycle of treated objects, or when emitted to the environment after disposal. Therefore, knowledge of the geometric and electronic structures of BFRs is of chief importance when tracking their fate in the ambient environment. Although BFR decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to their overall decay and subsequent fragmentation into brominated pollutants. Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Therefore, under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade to form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs produces potent precursors to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Co-combustion of BFR-containing objects with a chlorine source (e.g., polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e., PXDD/Fs; X = Br, Cl). In this thesis, we investigated the thermochemical parameters of bromochlorophenols (BCPhs) and the photodecomposition properties of major BFRs and their derived brominated phenols (BPhs). We scrutinised the formation of brominated and non-brominated products that evolved during the thermal decomposition of major BFR i.e., tetrabromobisphenol A (TBBA), through experimental measurements coupled with accurate quantum chemical calculations. We acquired thermo-kinetic parameters as well as mechanistic routes pertinent to the destruction of TBBA. We illustrated reaction networks for the synthesis of PXDD/Fs from BPhs and chlorinated phenols (CPhs). Similarly, we described pathways leading to the formation of PBDFs and polybrominated diphenylethers (PBDEs) from brominated benzenes (BBzs). We critically reviewed the literature on BFR thermal decomposition with specific foci on underlying mechanisms, decomposition products, the influence of the polymeric matrix, metallic content and operational conditions. As BCPhs are direct building blocks for the formation of PXDD/Fs, we computed the thermochemical parameters of their complete series. We calculated standard enthalpies of formation, entropies, heat capacities and bond dissociation enthalpies (BDHs) of O-H bonds for the complete series of BCPhs. Values of the acid dissociation constant (pKa) were estimated based on an accurate thermodynamic cycle incorporating solvation and protonation energies. Calculated values of BDHs of O-H bonds in BCPhs vary slightly with the change in degree and pattern of halogenation. Gibbs energies of solvation of BCPhs in water are highly exergonic, with their values increasing with the degree of halogen substitution. Values of pKa dictate that BCPhs characterised by high degrees of halogenation display stronger acidity and dissociate more easily in aqueous media (i.e., they are stronger acids than lower substituted phenols). Photolysis and photochemical decomposition are important channels for the degradation of halogenated organic pollutants in the environment. Therefore, we performed density functional theory (DFT) and time-dependent density functional theory (TDFT) calculations in order to derive the photodecomposition properties of major deployed BFRs and congeners of BPhs in both gaseous and aqueous media. We clarified the effect of degree and pattern of bromination on the photodebromination of selected brominated aromatic compounds based on several molecular descriptors; namely, geometries of the ground (S0) and electronically first excited (S1) states, values of the HOMO-LUMO energy gap (EH-L) and atomic charges on bromine atoms (qBr). Molecules exhibit different geometries in the S0 and S1 states and C-Br bonds elongate upon S0 → S1 transitions. In agreement with the recent findings on PBDEs, we found that the photoreactivity of bromine atoms in investigated BFRs and BPhs followed the sequence of ortho > meta > para. The bromine atom connected to the ortho-position holds the highest positive atomic charge and, thus, experiences the greatest lengthening of C-Br bonds in the S1 state, in both gaseous and an aqueous media, prompting their reductive debromination. Excitation energies decrease linearly with increasing numbers of bromine substituents, and congeners with a high degree of bromination photodecompose more readily than lower brominated isomers. Computed values of EH-L for major BFRs and their non-brominated molecules inferred that the number of bromine substituents and the nature of the structure (aromatic/non-aromatic) contributes significantly towards the photoreactivity of molecules. We conducted gas phase thermal decomposition of TBBA using a laboratory-scale tubular reactor. Our main focus was to identify pollutants arising in the temperature range of 673 – 1123 K following evaporation of TBBA in the gas phase. The identification and quantitation involved the use of a gas chromatograph – triple quadrupole mass spectrometer (GC-QQQMS) instrument, functioning in multiple reaction monitoring (MRM) and total ion current (TIC) modes. Product analysis revealed that thermal decomposition of TBBA commenced at 723 K. The major decomposition products were HBr, di-tribrominated bisphenols, benzene, phenol, mono-tribrominated congeners of benzene and phenol, brominated and non-brominated alkylated benzenes, benzofuran, bromobenzofuran, dibenzofuran, bromine substituted polyaromatic hydrocarbons (PAHs), biphenyl and biphenylene. We observed that, most of the decomposition products evolved in trivial concentrations at a temperature of 773 K and peaked at around 923 – 973 K. Higher temperatures favour the generation of non-brominated products. In this chapter, we have performed quantum chemical calculations to derive the degradation pathways of TBBA and to illustrate routes for the formation of brominated and non-brominated species. We constructed formation mechanisms related to the emission of PBDD/Fs in systems involving BFRs. In particular, we investigated formation corridors of (i) PXDD/Fs from the coupling reactions of 2-chlorophenoxy (2-CPhxy) and 2-bromophenoxy (2-BPhxy) radicals, (ii) PBDFs and PBDEs synthesis from the condensation reaction of monobromobenzene (MBBz) and a 2-BPhxy radical. The coupling reactions of 2-BPhxy and 2-CPhxy radicals produce keto-ether (through the additions of a phenoxy O at ortho C(H), C(Cl) and C(Br) sites) and diketo (at ortho positions to C–C bridges) structures. Keto-ethers act as direct intermediates for the formation of dioxin moieties such as dibenzo-p-dioxin (DD), 1-monochlorodibenzo-p-dioxin (1-MCDD), 1-monobromodibenzo-p-dioxin (1-MBDD), 1-bromo-6-chlorodibenzo-p-dioxin (1-B,6-CDD) and 1-bromo-9-chlorodibenzo-p-dioxin (1-B,9-CDD) molecules. Diketo adducts initiate the formation of furan species, i.e., 4-monochlorodibenzofuran (4-MCDF), 4-monobromodibenzofuran (4-MBDF) and 4-bromo-6-chlorodibenzofuran (4-B,6-CDF) compounds, through interconversion and rearrangement reactions. We found that, these mechanisms of formation, commencing from halogenated phenoxy radicals, are largely insensitive to patterns and degrees of halogenation on meta and para sites. It follows that, our developed mechanistic and kinetic factors of reactions involving 2-BPhxy and 2-CPhxy should also apply to higher halogenated phenoxy radicals. We explored the initial oxidative decomposition pathways of monobromobenzene (MBBz) in the generation of BPhxy radicals and examined the possible dimerisation reactions of MBBz and 2-BPhxy. It was found that, the coupling of MBBz and 2-BPhxy results in the generation of twelve pre-PBDF intermediates, of which four can also serve as building blocks for the synthesis of PBDEs. The resonance-stabilised structure of the o-BPhxy radical accumulates more spin density character on its phenoxy O atom (30.9 %) in reference to ortho-C and para-C sites. Thus, the formation of the pre-PBDE/pre-PBDF structures via O/o-C couplings advances faster, as it requires lower activation enthalpies (79.2 – 84.9 kJ mol-1) than the pre-PBDF moieties, which arise via pairing reactions involving o-C(H or Br)/o-C(H or Br) sites (97.2 – 180.2 kJ mol-1). Kinetic analysis indicates that the O/o-C pre-PBDE/pre-PBDF adducts self-eject the out-of-plane H atoms to produce PBDEs, rather than undergo a three-step mechanism that forms PBDFs. Since the formation mechanisms of PBDFs and PBDDs are typically only sensitive to the bromination at ortho positions, the results reported herein also apply to higher brominated isomers of BBzs. Overall, this thesis provides novel and comprehensive information on the thermochemical properties of the complete series of BCPhs (potential precursors to PXDD/Fs) and the electronic/structural characteristics of BFRs and their derived BPhs, with regards to their photodecomposition. To gain an insight into the degradation of TBBA once it has evaporated, this thesis examines the pure gas phase decomposition of TBBA and suggests mechanisms by which the experimentally-detected volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) are generated. Furthermore, this thesis explores the role of BPhs and CPhs as building blocks for the formation of PXDD/Fs, and computes their parameters. We also elucidate reaction pathways and thermo-kinetic parameters for PBDFs and PBDEs produced by the oxidation of BBzs

Development and application of force fields for molecular simulations

Simulationen weicher Materie umfassen ein breites Spektrum von Anwendungen, wie z. B. die Modellierung von Biomolekülen, Polymeren und Materialien für die organische Elektronik. Um die Längen- und Zeitskalen relevanter Phänomene zu erreichen, werden die Wechselwirkungen in diesen Systemen üblicherweise durch recheneffiziente analytische Kraftfelder berechnet. Ein Teil dieser Arbeit beschreibt eine Beispielanwendung für die kraftfeldbasierte Modellierung von amorphen organischen Halbleitern. Der konventionelle Kraftfeldansatz führt jedoch Parameter ein, die aus für das betrachtete Molekül geeigneten Parametersätzen zugewiesen werden müssen. Vor allem aufgrund der einfachen Funktionsausdrücke für die nicht-kovalenten Wechselwirkungen erfordert das Verfahren zur Bestimmung dieser Parametersätze empirische Zielwerte, die nicht immer verfügbar sind. Bottom-up-Ansätze, wie z. B. Bottom-up-Kraftfelder mit festen Funktionsausdrücken oder Potentiale basierend auf neuronalen Netzen, zielen darauf ab, die experimentellen Daten durch Ergebnisse aus ab initio Rechnungen zu ersetzen. Für die Anwendung in umfangreichen Molekulardynamiksimulationen weisen diese Methoden noch offene Herausforderungen auf. Feste Funktionsausdrücke leiden unter einer begrenzten Flexibilität, die ab initio Potentialenergieoberfläche zu reproduzieren und erfordern manuelle Typdefinitionen, um die Anzahl der Parameter zu reduzieren. Potentiale, die auf neuronalen Netzen basieren, verbessern beide Aspekte, aber ihre hohen Rechenanforderungen begrenzen die zugänglichen Längen- und Zeitskalen. In dieser Arbeit wird ein neuartiger Bottom-up-Ansatz zur Modellierung nicht-kovalenter Wechselwirkungen vorgestellt, der für großskalige Simulationen konzipiert ist. Das Konzept effizienter additiver Wechselwirkungen wird mit der Flexibilität künstlicher neuronaler Netze für die Interpolation verschiedener chemischer Zusammensetzungen und geometrischer Anordnungen kombiniert. Die Anwendung des Modells wird in Molekulardynamiksimulationen demonstriert, und der Vergleich der berechneten thermodynamischen Eigenschaften mehrerer kleiner organischer Moleküle mit experimentellen Daten und konventionellen Kraftfeldern zeigt eine vielversprechende Vorhersageleistung. Zusätzlich bewahrt das Modell die Energiezerlegung in physikalisch motivierte Komponenten, die von der symmetrieangepassten Störungstheorie, die für die ab initio Referenzrechnungen verwendet wird, bereitgestellt wird. Diese Trennbarkeit und die Unabhängigkeit von empirischen Daten machen dieses Modell potenziell nützlich für zukünftige Materialdesign-Anwendungen

Models and Computational Methods Applied to Industrial Gas Separation Processes and Enhanced Oil Recovery

[eng] Two main topics are treated in this doctoral thesis from a theoretical and computational point of view: the gas capture and separation from post-combustion flue gases, and the enhanced oil recovery from oil reservoirs. The first topic evaluates the separation of CO2 using three different materials. First, several zeolites from the Faujasite family are studied with a combination of Density Functional Theory (DFT) and Monte Carlo methods. The former is employed to understand the driving mechanisms of adsorption, whereas the latter served to assess the separation of CO2 from a flue gas formed by a ternary mixture of CO2, N2 and O2. Second, the adsorption of CO2, N2 and SO2 into Mg-MOF-74 obtained through DFT calculations is presented to determine the most fundamental gas/MOF interactions. The results are then coupled to a Langmuir isotherm model to derive the macroscopic adsorption isotherms of the three gases in Mg-MOF-74. Finally, the absorption of CO2 and SO2 into three different phosphonium-based Ionic Liquids (ILs) is addressed by using the soft-SAFT equation of state and the COSMO-RS model. From the calculated adsorption/absorption isotherms several properties are obtained, such as the purity in the recovered gas, the working capacity of the materials and their selectivity to capture CO2 in the presence of other contaminant species. The main results obtained from this part of the thesis reveal that the cations of microporous materials are very strong sites of absorption for polar gases (i.e., the Na+ cations in Faujasites or the Mg2+ cations in Mg-MOF-74). This feature makes them very good candidates for CO2 capture, but they can be easily poisoned by other polar gases such as SO2. For this reason, it is highly recommended to desulphurize the flue gas before using any of these adsorbents. Similarly, ILs have higher affinity for SO2 than for CO2. However, the gas/IL interactions are significantly weaker, so they do not become poisoned by SO2. This fact implies that SO2 can be captured and separated from the flue gas by using a phosphonium-based IL. The second topic describes via Molecular Dynamics simulations the interactions of several model oils with different rocks and brines. The obtained insight can be applied in better understanding the interactions of the species present at oil reservoirs, with direct application in enhanced oil recovery processes. To that end, two wettability indicators are monitored to determine the potential recovery of the model oils. First, the oil/water interfacial tension (IFT) under different conditions of temperature, pressure and salinity (i.e., from pure water to 2.0 mol/kg of NaCl or CaCl2). And second, the oil/water/rock contact angle (CA) on calcite (10-14) and kaolinite (001) also as a function of salinity (i.e., from pure water to 2.0 mol/kg of NaCl or CaCl2). The different model oils are built with molecules of different chemical nature representing the Saturate/Aromatic/Resin/Asphaltene (SARA) fractionation model. In a final stage of the doctoral thesis the effect of non-ionic surfactants at the oil/brine IFT is also included. The main results obtained show that the most polar components of oil migrate to the oil/water interface and reduce the IFT. However, the same compounds feel attracted to the rock, who increase the CA and hamper the oil recovery. Some of these interactions are affected by the presence of salt. Specifically, if a water layer is formed between the oil and the rock in a reservoir, electrolytes can diffuse into it and attract the polar components of oil, ultimately increasing the CA. Finally, cations can be attracted to the oil/water interface due to salt/surfactant interactions. Both species interact synergistically to modify their orientation/distribution at the interface and reduce the oil/water IFT.[cat] En aquesta tesi doctoral s’han tractat dos temes principals des d’una perspectiva teòrica i computacional: la captura i separació de gasos de post-combustió, i la recuperació millorada de petroli. El primer tema avalua la separació de CO2 utilitzant tres materials diferents. Primer, s’han estudiat diverses zeolites de la família de les Faujasites amb una combinació de teoria del funcional de la densitat (TFD) i mètodes Monte Carlo per entendre els mecanismes d’adsorció separació de CO2 d’una mescla ternària que conté CO2, N2 i O2. Seguidament, s’ha presentat un estudi TFD d’adsorció de CO2, N2 i SO2 en Mg-MOF-74 per determinar les interaccions fonamentals del MOF amb cada gas. Aquesta informació s’ha acoblat a un model d’isoterma de Langmuir per tal de derivar les isotermes d’adsorció macroscòpiques dels tres gasos en Mg-MOF-74. Finalment, s’ha analitzat l’absorció de CO2 i SO2 en tres Líquids Iònics (LIs) basats en fosfoni mitjançant l’equació d’estat soft-SAFT i el model COSMO-RS. D’altra banda, el segon tema descriu les interaccions de diferents models de petroli amb roques i salmorres, via simulacions de Dinàmica Molecular. El coneixement adquirit en aquesta part de la tesi doctoral es pot aplicar directament a la recuperació millorada de petroli i per entendre millor les interaccions de les espècies presents als pous. Amb aquesta finalitat, s’han controlat dos indicadors de la mullabilitat per determinar la recuperació potencial d’aquests models de petroli. Primer la tensió interfacial (TIF) oli/aigua sota diferents condicions de temperatura, pressió i salinitat (des d’aigua pura a 2.0 mol/kg de NaCl o CaCl2). I segon, l’angle de contacte oli/aigua/roca en calcita (10-14) i caolinita (001) en funció de la salinitat (des d’aigua pura a 2.0 mol/kg de NaCl o CaCl2). Els diferents models de petroli s’han construït amb molècules de diferent naturalesa química representant el model de fraccionament Saturat/Aromàtic/Resina/Asfaltè (SARA). En una etapa final de la tesi doctoral s’ha inclòs l’efecte en la TIF induïda pels surfactants no-iònics a la interfase oli/salmorra

Poster Session

Posters presented by: P01: Adam S. Abbott, University of Georgia P02: Yasmeen Abdo, University of Mississippi P03: Vibin Abraham, Virginia Tech P04: Asim Alenaizan, Georgia Institute of Technology P05: Isuru R. Ariyanthna, Auburn University P06: Brandon W. Bakr, Georgia Institute of Technology P07: [Matthew Bassett, Georgia Southern University] P08: Alexandre P. Bazanté, University of Florida P09: Andrea N. Becker, University of Tennessee P10: Randi Beil, University of Tennessee P11: Andrea N. Bootsma, University of Georgia/Texas A&M University P12: Adam Bruner, Louisiana State University P13: Lori A. Burns, Georgia Institute of Technology P14: Chanxi Cai, Emory University P15: Katherine A. Charbonnet, University of Memphis P16: Marjory C. Clement, Virginia Tech P17: Wallace D. Derricotte, Emory University P18: Harkiran Dhah, University of Tennessee P19: Manuel Díaz-Tinoco, Auburn University P20: Vivek Dixit: Mississippi State University P21: Eric Van Dornshuld, Mississippi State University P22: Katelyn M. Dreux, University of Mississippi P23: Narendra Nath Dutta, Auburn University P24: William Earwood, University of Mississippi P25: Thomas L. Ellington, University of Mississippi P26: Marissa L. Estep, University of Georgia P27: Yanfei Guan, Texas A&M University P28: Andrew M. James, Virginia Tech P29: Yifan Jin, University of Florida P30: Dwayne John, Middle Tennessee State University P31: Sarah N. Johnson, University of Mississippi P32: Noor Md Shahriar Khan, Auburn University P33: Monika Kodrycka, Auburn University P34: Ashutosh Kumar, Virginia Tech P35: Elliot Lakner, University of Alabama P36: Robert W. Lamb, Mississippi State University P37: S. Paul Lee, University of Mississippi P38: Zachary Lee, University of Alabama P39: Conrad D. Lewis, Middle Tennessee State University P40: Guangchao Liang, Mississippi State University P41: Chenyang Li, Emory University P42: Hannah C. Lozano, University of Memphis P43: SharathChandra Mallojjala, University of Georgia/Texas A&M University P44: Zheng Ma, Duke University P45: Elvis Maradzike, Florida State University P46: Ashley S. McNeill, University of Alabama P47: Stephen R. Miller, University of Georgia P48: W. J. Morgan, University of Georgia P49: Apurba Nandi, Emory University P50: Daniel R. Nascimento, Florida State University P51: Brooke N. Nash, Mississippi College P52: Carlie M. Novak, Georgia Southern University P53: Young Choon Park, University of Florida P54: Kirk C. Pearce, Virginia Tech P55: Rudradatt (Randy) Persaud, University of Alabama P56: Karl Pierce, Virginia Tech P57: Kimberley N. Poland, University of Mississippi P58: Chen Qu, Emory University P59: Duminda S. Ranasinghe, University of Florida P60: Hailey B. Reed, University of Mississippi P61: Matthew Schieber, Georgia Institute of Technology P62: Jeffrey B. Schriber, Emory University P63: Thomas Sexton, University of Mississippi P64: Holden T. Smith, Louisiana State University P65: Aubrey Smyly, Mississippi College P66: B. T. Soto, University of Georgia P67: Trent H. Stein, University of Alabama P68: Cody J. Stephan, Georgia Southern University P69: Thomas Summers, University of Memphis P70: Zhi Sun, University of Georgia P71: Monica Vasiliu, University of Alabama P72: Jonathan M. Waldrop, Auburn University P73: Tommy Walls, Southern Louisiana University P74: Qingfeng (Kee) Wang, Emory University P75: Constance E. Warden, Georgia Institute of Technology P76: Jared D. Weidman, University of Georgia P77: Melody Williams, University of Memphis P78: Donna Xia, University of Alabama P79: Qi Yu, Emory University P80: Boyi Zhang, University of Georgia P81: Tianyuan Zhang, Emory University P82: Michael Zott, Georgia Institute of Technolog

Liquid Phase Modeling in Heterogeneous Catalysis

Conversion of lignocellulosic biomass into transportation fuels or commodity and specialty chemicals will be an important and fast-growing industry within the United States over the coming decades. Its growth will be driven by a variety of factors, including increased energy demands, environmental considerations, national security, and government mandates. To achieve the desired energy efficiency and economic impact, the emerging biorefining industries need novel heterogeneous catalysts with exceptional activity, selectivity, and stability. Catalytic materials developed in the petrochemical industries are generally not suitable for processing highly functionalized feedstocks typical of the biorefinery landscape. Due to the characteristics of this biomass feedstock (aqueous, highly water soluble, very reactive, and thermally unstable), liquid-phase processing technologies are exceedingly sought after to reduce the process cost as well as to increase the targeted product selectivity. Despite making considerable progress in our understanding of the stability and the surface properties of metal-supported nanoparticles in vapor phase environments, the effect of condensed phase is less investigated and not well-understood due to the added complexity of the reaction system containing both a complex heterogeneous catalyst and a condensed phase. In order to gain fundamental understanding of the solvation phenomena occurring at solid-liquid interfaces, our research is primarily focused on the development, validation, and application of solvation methods for the rational design of novel heterogeneous transition metal catalysts for biomass conversion processes. As prototypical reactions with relevance to biomass catalysis, we investigated the hydrodeoxygenation (HDO) of various model biomolecules such as ethanol, ethylene glycol, and guaiacol under vapor and aqueous phase processing conditions to elucidate the reaction mechanism and the effect of condensed phase on the reaction kinetics. Using first principles calculations, continuum solvation models, and mean-field microkinetic modeling, we characterized the solvent effects on the kinetics of reactions and product distributions. An important outcome of our study is the identification of uncertainty in computed solvent effects due to the uncertainty of the cavity radius of transition metal atoms in implicit solvation schemes. To further elucidate the role of water on the reaction mechanism, we performed solvation calculations with our explicit solvation scheme for metal surfaces (eSMS). We found that implicit solvation models are most appropriate whenever directional hydrogen bonding is not present or does not change significantly along the reaction coordinate. Explicit solvation calculations agree with the implicit solvation models for C-H and C-OH bond cleavages of polyols where they both predict a small (\u3c0.10 eV) solvent effect. In contrast and unlike the implicit solvation models, our explicit solvation model predicts a larger solvent stabilization (\u3e0.35 eV) for the O-H bond cleavage due to its ability to approximately describe hydrogen bonding. Consequently, O-H bond dissociations are significantly favored over C-H and C-OH bond dissociations of polyols under aqueous processing conditions of biomass