Lignocellulosic biomass is a significant pool of energy resource, which can be harnessed to supplement or replace the dwindling fossil fuel reserves. This requires development of economically viable means to efficiently convert biomass to biofuels. A major requirement in biofuel industry is to develop highly active, selective and stable catalysts. Zeolites are an important class of micro-porous crystalline solids, and have proven to be effective and stable acid catalysts for a variety of petrochemical and fine-chemical processes. Nitrided zeolites -- i.e., those with Si-O-Si and Si-OH-Al groups substituted by Si-NH-Si and Si-NH2-Al -- have shown promise as shape-selective basic catalysts, and are potential candidates for biofuel production catalysts. In the first part of this dissertation, the stability and base characteristics of nitrided zeolites have been explored. The nitridation mechanism in HY and silicate type zeolites is computed by first time implementation of embedded-cluster procedure with nudged-elastic-band method of finding elusive transition states. The stability of nitrided sites is investigated by modeling the kinetics of nitridation in reverse, going back to untreated zeolite plus ammonia. Our calculations suggest that nitrided silicalite and HY zeolites require high temperatures to form, but once formed, they remain relatively stable, auguring well for their use as shape-selective base catalysts. In addition, a systematic study of base strength versus aluminium content or alkali cation of nitrided zeolites is also performed. Our studies suggest that K-N-Y (Si:Al = 11) optimizes the balance of activity, stability and cost. Pyrolysis of lignocellulosic biomass is a burgeoning technology to obtain renewable fuels. Commercializing pyrolysis would require efficient process design, especially reactors as they are one of the most energy intensive units in the whole process. This would in turn require detailed understanding of complex pyrolysis chemistries. Biomass is mainly composed of the biopolymer cellulose; therefore, understanding cellulose pyrolysis chemistries is important for efficiently modeling and optimizing pyrolysis reactors. In the second part of this dissertation, the mechanism(s) of conversion of crystalline cellulose to precursors of major products in cellulose pyrolysis have been explored. As the first step, the transformation of cellulose Iβ to a high-temperature (550 K) structure is modeled by computing infrared (IR) spectra as a probe of hydrogen bonding using constant-pressure classical molecular-dynamics simulations. To assist in the analysis of IR spectra, a novel synthesis of normal mode analysis and power spectrum methods is developed to assign the O-H stretches. Simulated IR spectra at elevated temperatures suggests a structural transformation above 450 K, a result in agreement with experimental IR results. The low-temperature (300-400 K) structure is found to be dominated by intrachain hydrogen bonds, whereas in the high-temperature structure (450- 550 K), many of these intrachain hydrogen bonds transform to longer, weaker interchain hydrogen bonds. Next, the subsequent decomposition of cellulose is modeled at 600 and 873 K using Car-Parrinello molecular- dynamics simulations and the metadynamics method. The computed nascent processes can explain the formation of precursors to major products observed during cellulose pyrolysis such as levoglucosan (LGA), hydroxy-methylfurfurral (HMF) and fragmentation products such as formic acid. LGA is found to be kinetically and thermodynamically favorable in comparison to other products, which explains why LGA is the major product observed during cellulose pyrolysis. The molecular insights presented in this part of the study will be helpful in developing detailed kinetic models for optimizing pyrolysis reactors.

Thesis (D. Min.)--Denver Seminary, 2006. / Includes bibliographical references (leaves 237-264).

Applied research project (D. Min.)--School of Theology and Missions, Oral Roberts University, 2006. / Includes abstract and vita. Translated from Korean. Includes bibliographical references (leaves 199-208).

Applied research project (D. Min.)--School of Theology and Missions, Oral Roberts University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 169-178).

Thesis (D. Min.)--Midwestern Baptist Theological Seminary, 1995. / Abstract. Appendices contain three sermons in Korean. Includes bibliographical references (leaves 181-182).

High temperature hydrogen attack (HTHA) is a damage mechanism that only affects carbon steel and low alloy material. Most of the data regarding HTHA are experimental-driven. Even though this approach has been successful, there are still much more things that the oil and gas industry does not understand about HTHA. The regions that were considered safe (below the Nelson curves) have experienced catastrophic failure. Our research consists of performing Molecular Dynamics (MD) and the Nudge Elastic Band (NEB) calculation of HTHA to better understand the atomistic behavior of this damage mechanism.

Texte remanié de: Dissertation Ph. D.--Madison--University of Wisconsin, 2001. / Bibliogr. p. 107-121.

Thesis (Ph. D.)--University of Wisconsin, Madison, 2001. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 297-332).

No description available.

Un alliage métallique complexe est un intermétallique dont la maille est constituée d'un nombre important d'atomes et dont la structure peut être souvent décrite comme un empilement de motifs d'atomes reliés par des liaisons de type covalent. Al5Co2 est l'un de ces composés et est un catalyseur potentiel pour la semi-hydrogénation d'acétylène. L'influence de la structure tridimensionnelle sur les surfaces bidimensionnelles et donc la réactivité est étudiée. Pour se faire, le système massif est analysé en utilisant la DFT afin d'éclaircir ses propriétés thermodynamiques, électroniques et vibrationnelles. Les valeurs calculées, expérimentales et celles de la littérature sont en bon accord. La structure des surfaces de bas indice, (001), (100) et (2-10) est étudiée. Une combinaison de techniques d'analyse de surface sous ultra-vide - LEED, STM - et de DFT est utilisée pour les déterminations structurales. Les résultats indiquent que: (i) la structure des surfaces dépend des conditions de préparation, comme la température de recuit, (ii) la structure des surfaces peut être interprétée comme étant constituée de motifs tronqués où certaines liaisons de type covalent sont brisées. Les sites et les énergies d'adsorption des molécules impliquées dans la réaction de semi-hydrogénation sont calculés pour les trois surfaces. Pour les sites favorables, des distances spécifiques entre atomes d'hydrogène adsorbés et atomes de Co de surface et de sous-surface peuvent être observées. Les atomes de Co de sous-surface ont un caractère donneur d'électrons, stabilisant les atomes adsorbés en surface. En se basant sur des calculs NEB, de possibles chemins réactionnels sur la surface (2-10) sont proposés. L'activité calculée est similaire à celle obtenue pour la surface d'Al13Co4, qui est considérée comme un bon catalyseur. La sélectivité - la compétition entre la désorption d'éthylène et son hydrogénation en éthyle - est discutée. / A complex metallic alloy is an intermetallic with a large unit cell and whose structure can often be seen as a stacking of motifs of strongly covalent-like bonded atoms. Al5Co2 is such a compound and is a potential catalyst for the semi-hydrogenation of acetylene. The influence of the 3-dimensional structure on 2-dimensional surfaces is investigated. Therefore, the bulk system is analysed using DFT to gain insight in the thermodynamic, electronic and vibrational properties. Good agreements between calculated results, experimental ones and results found in the literature are obtained. The low index (001), (100) and (2-10) surfaces are investigated. A combination of surface analysis techniques under ultra high vacuum - LEED, STM - and DFT calculations is used for the structural investigations. The results show that: (i) the surface structure depends on the preparation conditions, such as the annealing temperature, (ii) the surface structure can be interpreted as truncated motif parts, where the covalent-like bonds are broken. Adsorption sites and energies of molecules involved in the semi-hydrogenation reaction are calculated for all three surfaces. For favourable adsorption sites, specific distances of adsorbed H atoms with Co surface and subsurface atoms are observed. These Co subsurface atoms have an electron donor character, stabilising the adsorbed atoms at the surface. Based on NEB calculations, possible reaction paths on the (2-10) surface are proposed. The calculated activity is similar to the one obtained for the Al13Co4 surface, which is considered a good catalyst. The selectivity - the competition between desorption of ethylene and its further hydrogenation - is discussed.