Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science (Chemistry), 1990 / Deactivation studies; making use of fixed bed reactors, wet chemical analysis, surface area, pore volume determinations and X-ray diffraction—, scanning electron microscope— and secondary ion mass spectrometry techniques; were performed on a low temperature iron Fischer—Tropsch catalyst. It was revealed that this catalyst is mainly deactivated by sulphur poisoning, oxidation of the catalytic reactive phases, sintering of the iron crystallites and to a lesser extent deactivation through fouling of the catalytic surface by carbonaceous deposits. It was found that the top entry section of the catalyst bed deactivated relatively fast, the bottom exit section also deactivated, but not as fast as the top section The central portion of the catalyst bed was least affected. Sulphur contaminants in the feed gas, even though present in only minute quantities, results in a loss of catalyst performance of the top section of the catalyst bed, while water, produced as a product from the Fischer—Tropsch reaction, oxidized and sintered the catalyst over the bottom section of the catalyst bed.

The final objective of this project is to create an environmentally friendly solid alkylation catalyst to replace the commercially available liquid acid catalysts, such as hydrofluoric acid and sulfuric acid, which are used in the petroleum industry. My research target is to synthesize the diazonium PFSI zwitterions, which can be chemically grafted on the silica as the solid alkylation catalyst. A 4-steps synthesis is designed to prepare the diazonium PFSI zwitterions. The first two steps were successfully completed in the lab. The first one is to prepare the starting material of 4-nitrobenzenesulfonamide from an ammonolysis reaction between 4-nitrobenzene sulfonyl chloride and ammonium hydroxide. And next, a base catalyzed coupling reaction was carried out with 4-nitrobenzenesulfonamide and commercially available perfluorobutane sulfonyl fluoride with nitrogen gas (N2) protection. The coupling product (I in Figure 1) was then purified by extraction and recrystallization. All chemicals in the synthesis procedure were characterized with proton NMR, fluorine NMR, Infrared (IR) spectroscopy and melting points.

Novel anode catalysts have been developed for sour natural gas solid oxide fuel cell (SOFC) applications. Sour natural gas comprises light hydrocarbons, and typically also contains H2S. An alternative fuel SOFC that operates directly on sour natural gas would reduce the overall cost of plant construction and operation for fuel cell power generation. The anode for such a fuel cell must have good catalytic and electrocatalytic activity for hydrocarbon conversion, sulfur-tolerance, resistance to coking, and good electronic and ionic conductivity. The catalytic activity and stability of ABO3 (A= La, Ce and/or Sr, B=Cr and one or more of Ti, V, Cr, Fe, Mn, or Co) perovskites as SOFC anode materials depends on both A and B, and are modied by substituents. The materials have been prepared by both solid state and wet-chemical methods. The physical and chemical characteristics of the materials have been fully characterized using electron microscopy, XRD, calorimetry, dilatometry, particle size and area, using XPS and TGA-DSC-MS. Electrochemical performance was determined using potentiodynamic and potentiostatic cell testing, electrochemical impedance analysis, and conductivity measurements. Neither Ce0.9Sr0.1VO3 nor Ce0.9Sr0.1Cr0.5V0.5O3 was an active anode for oxidation of H2 and CH4 fuels. However, active catalysts comprising Ce0.9Sr0.1V(O,S)3 and Ce0.9Sr0.1Cr0.5V0.5(O,S)3 were formed when small concentrations of H2S were present in the fuels. The oxysuldes formed in-situ were very active for conversion of H2S. The maximum performance improved from 50 mW cm2 to 85 mW cm2 in 0.5% H2S/CH4 at 850 oC with partial substitution of V by Cr in Ce0.9Sr0.1V(O,S)3 . Selective conversion of H2S offers potential for sweetening of sour gas without affecting the hydrocarbons. Perovskites La0.75Sr0.25Cr0.5X0.5O3, (henceforth referred to as LSCX, X=Ti, Mn, Fe, Co) are active for conversion of H2, CH4 and 0.5% H2S/CH4. The order of activity in the different fuels depends on the substituent element: CH4, X=Fe>Mn>Ti; H2,X = Fe>Mn>Ti; and 0.5% H2S/CH4, X = Fe>Ti>Mn. The electrocatalytic activity for methane oxidation in a fuel cell correlates with ex-situ temperature programmed catalytic activity. A process is proposed to explain the difference in catalyst order and enhanced activities in H2S/CH4 as fuel compared to CH4 alone. The maximum power density of 250 mW cm2 was attained using a fuel cell with a composite anode, LSCFe-GDC | YSZ(0.3 mm) | Pt, operated at 850 oC (GDC is Ce0.9Gd0.1O3, a good mixed conductor under reducing conditions). / Materials Engineering

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Polymer electrolyte membrane (PEM) fuel cells have been viewed as promising power source candidates for transport, stationary, and portable applications due to their high efficiency and low emissions. The platinum is the most commonly used catalyst material for the oxygen reduction reaction (ORR) at the cathode of PEM fuel cells; however, the limited abundance and high cost of platinum hinder the large-scale commercialization of fuel cells. To overcome this limitation, it is necessary to enhance the catalyst utilization in order to improve the catalytic activity while decreasing or eliminating the use of platinum. The material on which the catalyst is supported is important for the high dispersion and narrow distribution of Pt nanoparticles as well as other non-precious metal active sites, and these characteristics are closely related to electrocatalytic activity of the catalysts. The support materials can influence the catalytic activity by interplaying with catalytic metals, and the durability of the catalyst is also greatly dependent on its support. A variety of support materials like carbons, oxides, carbides, and nitrides have been employed as supports materials for fuel cell catalysts, and much effort has been devoted to the synthesis of the novel carbon supports with large surface area and/or pore volume, including nanostructured carbons such as carbon nanotubes (CNTs), carbon nanofibers, and mesoporous carbon. These novel nanostructured carbon materials have achieved promising performance in terms of catalytic activity and durability. However, there is still enormous demand and potential for the catalysts to improve. In the first study, non-precious metal catalysts (NPMC) for the oxygen reduction reaction were synthesized by deposition of Fe/Co-Nx composite onto nanoporous carbon black with ethylenediamine (EDA) as nitrogen precursor. Two different nanoporous carbon supports, Ketjen Black EC300J (KJ300) and EC600JD (KJ600), were used as catalyst support for the non-precious catalysts. The results obtained from the optimized FeCo/EDA-carbon catalyst, using KJ600 as the support, showed improved onset, half-wave potentials and superior selectivity than that of the KJ300. Similarly, the catalyst showed good performance in the hydrogen-oxygen PEM fuel cell. At a cell voltage of 0.6 V the fuel cell managed to produce 0.37 A/cm2 with a maximum power density of 0.44 W/cm2. Fuel cell life test at a constant voltage of 0.40 V demonstrated promising stability up to 100 h. The X-ray photoelectron spectroscopy study indicated that pyridinic type nitrogen of the non-precious metal catalysts is critical for ORR catalytic activity and selectivity. These results suggest higher pore volume and surface area of carbon support could lead to higher nitrogen content providing more active sites for ORR and this type of catalyst has great potential used as a non-precious PEM fuel cell catalyst. In the second study, we report the development of a novel NPMC in acid electrolyte using pyrimidine-2,4,5,6-tetramine sulfuric acid hydrate (PTAm) as a nitrogen precursor and graphene nanosheets as catalyst supports. Graphene, consisting of a two-dimensional (2D) monolayer of graphitic carbon atoms, has been viewed as a promising candidate for the fuel cell catalyst support, due to its many intriguing properties such as high aspect ratios, large surface areas, rich electronic states, good electron transport, thermal/chemical stability and good mechanical properties. We investigate the effect of different pyrolysis temperatures on the catalysts’ ORR activity along with detailed surface analysis to provide insight regarding the nature of the ORR active surface moieties. This novel NPMC demonstrates promising electrocatalyst activity and durability superior to that of commercial catalyst for the ORR, rendering graphene nanosheets as a suitable replacement to traditional nanostructured carbon support materials. In the final study, we have developed Pt catalyst by combining the precious metal with nitrogen-doped activated graphene (N-AG) as the support. A transmission electron microscopy (TEM) image of the catalyst shows uniform size and distribution of platinum nanoparticles on a graphene layer. This novel catalyst demonstrates superior electrocatalyst activity and durability over Pt/XC72 catalyst for ORR under the studied conditions, rendering graphene as an ideal replacement to traditional nanostructured carbon support materials. In summary, several catalyst samples were made using novel nanostructured support materials to improve the ORR performance. Several recommendations for future work were suggested in the last section of this work to further apply the knowledge and understanding of nanostructured support materials to design a highly active, durable, and low-cost NPMCs and platinum catalysts.

Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resides in the fact that they can be used without major modifications in the polymerization reactors that previously used heterogeneous Ziegler-Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. Metallocene catalysts have been supported on a variety of carriers, but supporting late transition metal catalysts has not been investigated in detail, despite their very interesting properties such as tolerance to polar comonomers and impurities, activity in the absence of MAO, and the formation of short chain branches by the chain walking mechanism. The research work of this PhD thesis intends to fill this gap, by developing supported late transition metal catalysts with high catalyst activities towards ethylene polymerization and good polymer particle morphology. The effects of catalyst structure and polymerization conditions on silica-supported nickel diimine catalysts are discussed in Chapter 3. Compared with the equivalent homogeneous catalysts, the covalently-attached supported catalysts had high activities, produced spherical polyethylene particles with good morphologies, and polyethylene with higher melting temperatures, higher molecular weight averages, and broader molecular weight distributions. Borates used as internal activators during the synthesis of these supported catalysts successfully activated the nickel diimine complexes. In Chapter 4, MgCl2/alcohol adducts are recrystallized with alkylaluminum compounds and used as catalysts supports for nickel diimine complexes functionalized with amine groups. Polymerization results were compared with those of the equivalent SiO2-supported nickel diimine catalysts. MgCl2-based supported nickel diimine catalysts had high catalyst activity without the use of activators, and it was possible to control polymer molecular weight averages by changing the support composition. Although linear low density polyethylene made with metallocenes offers superior mechanical properties such as excellent toughness, impact strength and clarity, it suffers from poor processability. To overcome some of these disadvantages, Chapter 5 introduces methods to produce bimodal polyethylene resins using supported hybrid early and late transition metal catalyst systems. The presence of short chain branches in the higher molecular weight component is attributable to the incorporation of alpha-olefin molecules by the metallocene sites, while the nickel diimine catalyst sites produce chains with a distribution of short chain branch sizes through the chain walking mechanism. Finally, in Chapter 6 supporting a nickel diimine catalyst onto organo-modified montmorillonite (MMT) to prepare polyethylene/clay nanocomposites through in-situ polymerization is described. The thermal properties and crystallinity of the nanocomposites could be controlled by varying the fraction of MMT in the nanocomposite, and the dispersion of the MMT layers in the polymer matrix were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Homogeneous catalysts demonstrate the ability to perform extremely selective organic syntheses with high yields. These catalysts are usually quite expensive and the commercial viability of processes that use homogeneous catalysts depends on the efficiency of catalyst recovery, which is normally quite complex. This obstacle often excludes the use of homogene-ous catalysts from commercial processes. This work investigates the implementation of mem-branes as the unit operation for catalyst recovery as a means to expand the use of homogeneous catalysis. The commercial polyimide, Matrimid, has been examined for its suitability as a membrane material for the homogeneous catalyst recovery of a 1-dodecene hydroformylation reaction, catalyzed by a rhodium-triphenylphosphine transition metal catalyst. This reaction occurs in the liquid phase in solution with toluene. Because of the aggressive environment of the reaction, blends of Matrimid with a crosslinkable, diacetylene-functionalized oligomer have been formed to promote polymer stability through network formation. The diacetylene groups on the oligomer and acetylene end groups can be thermally activated at 250 ??o form distributed polymer networks. Compatible blends of Matrimid and the crosslinking agent can be formed with up to 10% (w/w) crosslinking agent content. Matrimid and the blends have been investigated in the form of dense, nonporous films to evaluate their membrane performance. In terms of material stabilization, it has been found that heat treatment of the neat Matrimid at 250 ??esults in a significant suppression of the material plasticization when exposed to toluene. Addition of the crosslinking oligomer to Matrimid promotes further reduction in swelling and toluene sorption. Transport studies of the reaction components in the materials show that addition of the crosslinking oligomer results in reduced diffusion of the permeating components in the mem-brane materials. However, some increases in solute sorption occur and this is attributed to the oligomer chemistry. A 10% blend of crosslinking agent and Matrimid gave a superior catalyst rejection of 91.5%. The catalyst rejection system has been modeled using Maxwell-Stefan transport equa-tions. Through the model it was found the flux coupling significantly influences the separation characteristics, with sorption of both the solvent and solute as key factors.

A new protocol for direct amination of N-Methyl-2-phenylindole catalyzed by copper(II) trifluoromethanesulfonate was presented. Both of (E)-N-(1,1'-Dimethyl-2,2' -diphenyl-2,3'-biindolin-3-ylidene)-4-methylbenzenesulfonamide¡]4¡^and 4-methyl -N-(1-methyl-2-phenyl-1H-indol-3-yl)benzenesulfonamide¡]2¡^were obtained under the optimal reaction conditions (2.5 mol% Cu(OTf)2, 1.2 equiv PhI=O, 0.7 equiv PhI=NTs heated at 25 ¢J in acetonitrile for 1 hour) in 78 % and 11 % yields, respectively. In addition, (E)-N-(2-hydroxy-1-methyl-2-phenylindolin-3-ylidene)-4-methylbenzene sulfonamide ¡]6¡^and (E)-N-(1,1'-dimethyl-2,2'-diphenyl-2,3'-biindolin-3-ylidene) -4-methylbenzenesulfonamide ¡]4¡^were synthesized in 47 % and 24 % yields, respectively, by using 5 mol% Cu(OTf)2, 2 equiv PhI=O, 1.2 equiv PhI=NTs at ambient temperature in acetonitrile for 1 hour. Finally, 4-methyl-N-(1-methyl-2-oxo-3-phenyl indolin-3-yl)benzenesulfonamide ¡]3¡^and 1,1'-dimethyl-2,2'-diphenyl-2,3'-biindolin -3-one ¡]7¡^can be formed under the following reaction condition, 5 mol% Cu(OTf)2, 2 equiv PhI=O, 1.2 equiv PhI=NTs and 3 equiv Ag2CO3 heated at 100 ¢J in acetonitrile for 1 hour, in 41% and 22% yields, respectively.

Biodegradable polyesters represent a class of extremely useful polymeric materials for many applications. Among these polyesters, the biodegradable and biocompatible, polylactide is very promising for many applications in both medical and industrial areas. Other biodegradable polymers such as polytrimethylene carbonate, polybutyrolactone, polyvalerolactone, and polycaprolactone can be blended or copolymerized with polylactide to fine tune the properties to fit the needs for their applications. The properties of these polymers and copolymers depend upon the tacticity of the polymers which can be directly controlled by the catalysts used for polymer production. Therefore, it has been of great interest to develop new selective catalytic systems for the ring-opening polymerization of lactide and other cyclic monomers. This dissertation focuses on developing new zinc and aluminum complexes and studying their selectivity and reactivity of these complexes for the ring-opening polymerization of lactide and other cyclic monomers, i.e. trimethylene carbonate, beta-butyrolactone, delta-valerolactone, and epsilon-caprolactone. Herein, aspects of the ring-opening polymerization of lactide and other cyclic monomers utilizing novel zinc and aluminum complexes will be discussed in detail. In the process for the ring-opening polymerization of lactide, chiral zinc half-salen complexes derived from natural amino acids have shown to be very active catalysts for producing polymers with high molecular weight and narrow polydispersities at ambient temperature. The chiral zinc complexes were found to catalyze rac-lactide to heterotactic polylactides with Pr values ranging from 0.68-0.89, depending on the catalyst and reaction temperature employed during the polymerization process. The reactivities of the various catalysts were greatly affected by substituents on the Schiff base ligands, with sterically bulky substituents being rate-enhancing. Furthermore, a series of both chiral and achiral aluminium half-salen complexes have been synthesized and characterized. These aluminum complexes all showed moderate selectivity to the ring-opening polymerization of rac-lactide to produce isotactic polylactide with Pm value up to 0.82 in toluene at 70 degrees C. Moreover, some of the studied aluminum complexes displayed epimerization of rac-lactide to meso-lactide during the polymerization process. Kinetic studies for the ring-opening polymerization of lactide utilizing these zinc and aluminum complexes are included in this dissertation. Along with these studies, the copolymerization of lactide with epsilon-caprolactone and delta-valerolactone will also be presented.

Organic – ordered mesoporous silica (OMS) hybrid materials have attracted great interest due to their potential applications for gas separations, and heterogeneous catalysis. Amine-functionalized OMS materials are active in a variety of base-catalyzed reactions. The key to successfully achieving the desired reactivity is the ability to rationally tether the targeted organic functionality onto the OMS surface. Understanding the organic-inorganic interface is crucial for rational design of heterogeneous catalysts, because the local structure and molecule dynamics are paramount in determining the reactivity of the organic groups attached to the OMS surface. This dissertation focuses on three goals that will lead to a description of the organic-OMS interface and designing hybrid catalysts: 1) Determining the dynamics of organic groups attached to the OMS surface, 2) Catalytic testing to understand how the local structure and dynamics of the organic moiety influence the catalytic properties of organic-OMS catalysts, 3) Designing more active hybrid catalysts by introducing higher loadings of organic group using dendrimer structures. Solid-state NMR is uniquely suited for quantifying dynamics in the milli- to nano-second time scale. Deuterium (2H) NMR is a powerful tool to obtain detailed information about the dynamics or organic molecules. In this study, several simple functional groups isotopically labeled with deuterium have been attached to MCM-41 and SBA-15. The spectra display different molecular motions for different organic moieties. The results have indicated that the interactions between the functional groups and silanol groups on the surface influence the mobility of the organic fragments. Also, the porosity of the solid supports effects dynamics via confinement. The catalytic properties of simple amine groups attached to MCM-41, containing primary, secondary, and tertiary amines have been compared in the Nitroaldol (Henry) reaction. The effects of amine identity, structure, loading, presence of surface silanols, and the substrate topology on the catalytic properties have been investigated. The dramatic decrease of the activity of amine-functionalized MCM-41 by capping the residual silanol groups with hexamethyldisilazane was ascribed to the decrease of the interactions of hydrogen bonding between the amine functional groups and surface silanols. The result was consistent with the changes of the molecular motions shown by 2H NMR measurements. Fabricating OMS hybrid materials with high densities of organic functional groups leads to challenges in realizing uniform, catalytically active sites. Our group has immobilized melamine-based dendrimers on the surfaces of amine-functionalized SBA-15 materials by iterative synthesis procedures. The current studies in this dissertation mainly describe the catalytic properties of these dendrimers on SBA-15 and MCM-41 in the Nitroaldol (Henry) reaction, the transesterification reaction of triglycerides and methanol to synthesize methyl esters, and the cross aldol reaction between acetone and 5-hydroxymethylfurfural. The results indicate that the OMS-dendron materials have potential as solid base catalysts for a range of reactions.