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Call number: LD2668 .T4 1957 C35 / Master of Science

The Fischer-Tropsch process in South Africa, used for producing chemicals from synthesis gas, which is mostly derived from the gasification of coal, gives a large amount of medium chain length alkanes (C4-C8), which have little commercial value. Internationally, industry has recently placed more focus on the conversion of alkanes to value-added products. Two important routes to achieving this are dehydrogenation and oxidative dehydrogenation. The latter is an economically feasible route, in which there is growing interest by the international research community, and was investigated in this study. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2007.

Ball State University LibrariesLibrary services and resources for knowledge buildingMasters ThesesThere is no abstract available for this thesis.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Adelaide, Dept. of Chemical Engineering, 1990. / Includes bibliographical references (leaves 168-174).

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Transition metals are known to be the essential part in most of the catalysts, the heterogeneous and the homogenous catalysts; however, the ligands that attached to the metal centers can also alter the reactivity of the catalyst, and that is widely observed in nature. In our project, we are interested in the metal-ligand cooperation of a special type of ligand called the pincer ligand. Our focus is mainly on the tridentate Pincer Ligands with a pyridine backbone. Also, it contains a spacer that could be deprotonated and protonated during the aromatization and dearomatization process. Aromatization and dearomatization of the pincer ligand are responsible for the unique reactivity of the pincer complexes, especially in the hydrogenation and dehydrogenation reactions. Recently, huge developments have been made in the dehydrogenative coupling of aniline and benzyl alcohol via manganese pincer complexes. The most recent papers on that subject have been done by Beller in 2016[1], Kempe 2018 [2], and Hultzsch 2019 [3]. However, rhenium complexes have not been studied enough even though it is in the same seventh row of the transition metal. Therefore, the rhenium was studied as a possible alternative. Then, the synthesis of a well-defined PN3 rhenium complex was performed from the bipy-tBu ligand and the metal precursor Re(CO)5Cl. The ligand has a unique deformity as the phosphine sidearm is not attached to the metal center. Further investigation of the aniline and benzyl alcohol dehydrogenative coupling via PN3 rhenium pincer complex has been done. An optimal reaction condition was achieved, and the substrate scope was further examined with various alcohols and amines, and the result shows good to moderate conversion with decent selectivity towards the imine. Except for the secondary alcohols.

Liquid organic chemical hydride is a promising candidate for hydrogen storage and transport. Methylcyclohexane (MCH) to toluene (TOL) cycle has been considered as one of the feasible hydrogen carrier systems, but selective dehydrogenation of MCH to TOL has only been achieved using the noble Pt-based catalysts. The aim of this study is to develop non-noble, cost-effective metal catalysts that can show excellent catalytic performance, mainly maintaining high TOL selectivity achievable by Pt based catalysts. Mono-metallic Ni based catalyst is a well-known dehydrogenation catalyst, but the major drawback with Ni is its hydrogenolysis activity to cleave C-C bonds, which leads to inferior selectivity towards dehydrogenation of MCH to TOL. This study elucidate addition of the second metal to Ni based catalyst to improve the TOL selectivity. Herein, ubiquitous bi-metallic nanoparticles catalysts were investigated including (Ni–M, M: Ag, Zn, Sn or In) based catalysts. Among the catalysts investigated, the high TOL selectivity (> 99%) at low conversions was achieved effectively using the supported NiZn catalyst under flow of excess H2. In this work, a combined study of experimental and computational approaches was conducted to determine the main role of Zn over Ni based catalyst in promoting the TOL selectivity. A kinetic study using mono- and bimetallic Ni based catalysts was conducted to elucidate reaction mechanism and site requirement for MCH dehydrogenation reaction. The impact of different reaction conditions (feed compositions, temperature, space velocity and stability) and catalyst properties were evaluated. This study elucidates a distinctive mechanism of MCH dehydrogenation to TOL reaction over the Ni-based catalysts. Distinctive from Pt catalyst, a nearly positive half order with respect to H2 pressure was obtained for mono- and bi-metallic Ni based catalysts. This kinetic data was consistent with rate determining step as (somewhat paradoxically) hydrogenation of strongly chemisorbed intermediate originating from TOL. DFT calculation indicated that Zn metal prefers to occupy the step sites of Ni where unselective C–C bond breaking was considered to preferentially occur, explaining suppression of hydrogenolysis activity. Additionally, it confirmed that the H-deficient species at methyl position group (C6H5CH2) was stable on the surface, making its hydrogenation being rate determining step, consistent with positive order in H2 pressure on TOL formation rate. This may explain the conclusive role by H2 in facilitating desorption of the H-deficient surface species that was produced through further dehydrogenation of TOL.

The thermally induced reaction of chlorinated ethanes on the nearly-stoichiometric α-Cr₂O₃ (102) surface results in the formation of gas phase hydrocarbons including ethylene, ethane, acetylene, 2-butene, 2-butyne and dihydrogen, and deposition of surface chlorine adatoms. No surface carbon or combustion products are observed in any reactions indicating that no thermally induced C-C bond cleavage occurs and surface lattice oxygen is not incorporated into surface intermediates. A combination of photoemission and Auger electron spectroscopies indicates the surface reactions of the chlorinated ethanes proceed via C-Cl bond cleavage to form surface chlorine adatoms and surface C₂-alkyl hydrocarbon fragments (i.e. ethyl, ethylidene and ethylidyne). Temperature programmed desorption studies indicate that both ethyl and ethylidene intermediates are selective towards ethylene. However, ethylidyne is more selective towards acetylene, but also produces ethylene in significant quantities. Chlorine adatom deposition leads to deactivation of surface Cr reaction centers by simple site blocking. The interaction of water with nearly-stoichiometric α-Cr₂O₃ (001) and (102) surfaces is structure sensitive. Water is sensitive to the difference in coordination number of Cr surface cations between the two surfaces, and on the α-Cr₂O₃ (001) surface, water has also demonstrated sensitivity to the degree of surface Cr cation reduction (and/or reduced coordination). These observations allowed for the development of a surface treatment recipe for the nearly-stoichiometric (001) surface. / Ph. D.