Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 03/08/2010). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

Thesis (Ph.D.). / Written for the Dept. of Chemistry. Title from title page of PDF (viewed 2007/08/29). Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1942. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MSc. (Chemistry)) -- University of Limpopo, 2015 / In this study, the use of 10-member ring zeolites with different silica-to-alumina ratios (SARs) as supports for palladium (Pd) to produce hydrocracking catalysts was investigated. The syntheses of zeolites ZSM-22, ZSM-48, ZBM-30 and ZSM-23 were carried out under hydrothermal conditions, and the resulting materials were characterised with XRD, SEM and BET surface area measurements, prior to activity tests. Successful synthesis of ZSM-48 and ZBM-30 remained elusive for the major part of this study, and these zeolites could therefore not be catalytically tested. The XRD patterns showed pure ZSM-22 materials with different SARs (60, 80 and 120) were successfully synthesised using hexamethylenediamine (HMDA) as a structure-directing agent (SDA) and a synthesis gel with pH 12. However, at synthesis gel pH 13, cristobalite and ZSM-5 impurity phases tend to form in addition to ZSM-22. Relative % XRD crystallinity of the materials prepared at synthesis gel pH 12 decreased with a decrease in SAR, and there was no specific trend for the response of a particular SAR to changes in pH from 12 to 13. SEM micrographs showed needle-shaped crystals with lengths in the range 0.6 - 1.2 μm. The BET surface area of the ZSM-22 with SAR of 60 was found to be 189 m2/g, which is around the theoretical BET surface area of ZSM-22 materials and the presence of impurities lowered the surface area of the ZSM-22 materials. The synthesis of ZBM-30 using triethylenetetramine (TETA) and a (1 TETA : 1 pyrrolidine) mixture as SDAs was also attempted. The XRD patterns showed that a completely amorphous material was obtained when using TETA as SDA and ZSM-39 was produced when using the mixture as SDA. The XRD patterns revealed that impurity-free ZSM-23 materials were successfully synthesised with SAR > 60, and that with SAR of 60, ZSM-5 was produced instead. Relative % XRD crystallinity of the impurity-free ZSM-23 materials increased with an increase in SAR from 80 to 120. SEM micrographs of the impurity-free ZSM-23 materials showed needle-shaped crystals of around 0.9 μm in length. The predominantly ZSM-5 material had the highest BET surface area compared to the impurity-free ZSM-23 materials. ZSM-48 synthesis was attempted using HMDA (produced ZSM-22), pyrrolidine (produced ZSM-23) and hexamethonium bromide (HMBr2) as SDAs. The XRD and SEM vi analysis showed only HMBr2 successfully directed the synthesis of impurity-free crystalline ZSM-48 at prolonged synthesis time of 168 h. ZSM-48 crystals were also needle-shaped and 4.2 - 11.3 μm in length. The incipient wetness impregnation method was used to achieve 0.5 wt. % Pd loadings on the catalysts. The hydrocracking of n-hexadecane (n-C16) over the catalysts was studied at conditions typical of catalytic cracking of LTFT products. At 225 oC, the Pd/ZSM-22 (80) and Pd/ZSM-23 (80) were highly selective to cracking products, with excessive secondary cracking occurring over these catalysts, as indicated by the C4/C12 ratios of 11.3 and 5.2, respectively. Excessive secondary cracking (C4/C12 = 11.7) was also observed over Pd/ZSM-23 (60). However, the Pd/ZSM-22 (60) and Pd/ZSM-23 (120) catalysts achieved a C4/C12 ratio close to 1.0, suggesting closeness to ideal hydrocracking behaviour. The Pd/ZSM-22 (60) (C4/C12 of 1.9) catalyst, was physically mixed with Pd/ZSM-5 (90) (C4/C12 = 6.4) and catalytically tested for the hydrocracking of n-C16. This Pd/ZSM-5/ZSM-22 catalyst achieved a remarkable C4/C12 = 1.1, which is less than what was achieved over the individual catalysts. On the basis of the C4/C12, this catalyst’s behaviour is close to that of an ideal hydrocracking behaviour. In summary, Pd/ZSM-22 (80), Pd/ZSM-22 (120) and Pd/ZSM-23 (80) catalysts are promising for diesel-selective catalysis and need further exploration.

Thesis (M. Sc. (Chemistry)) -- University of Limpopo, 2016 / In this study, the use of synthetic hierarchical MFI zeolites as supports for palladium hydrocracking catalysts was investigated. Hierarchical zeolites were synthesised through two different routes, viz., (i) the indirect and (ii) direct routes. In (i) pristine ZSM-5 zeolites with different SiO2/Al2O3 ratios (SARs) were synthesised hydrothermally using tetrapropylammonium bromide as structure-directing agent (SDA), followed by a brief desilication of its calcined form in 0.2 M NaOH solution at 65 °C for 0.5 h. Procedure (ii) involved prior synthesis of three polyquaternary ammonium surfactants (containing 2 - 4 ammonium centres), followed by their use as SDAs in the hydrothermal synthesis of hierarchical MFI zeolites. The resulting materials were characterised by XRD, FT-IR, SEM and N2 adsorption isotherms (including BET surface area measurements). Successful synthesis of different classes of the hierarchical MFI zeolites was confirmed by XRD patterns, while successful synthesis of polyquaternary ammonium surfactants was confirmed by both their 1H NMR spectra and their ability to direct the MFI structure. On the basis of IR, peak intensities in the OH region between 3500 and 3800 cm-1, the surfactant-templated zeolites were inferred to be more acidic than zeolites prepared through the desilication route. Significant changes in crystal morphology were observed upon desilication of ZSM-5(50), while the ZSM-5(77) and ZSM-5(100) retained their agglomerated morphology upon a similar treatment. The micrograph pristine of ZSM-5(50) showed a predominant morphology of large and small spheroids, together with some ill-defined cubic shapes. After desilication, the zeolite did not retain the original morphology entirely, showing hexagonal prismatic crystals with twinning occurring in other areas and large spheroids “hatching” to reveal their contents upon treatment. Desilicated zeolites exhibited improved textural properties (i.e., increased SBET, pore volumes and pore diameters) and minor structural readjustments compared to their pristine counterparts. Textural properties of surfactant-templated zeolites were superior to those of desilicated zeolites, and improved with increasing number of quaternary ammonium centres in the surfactant template. These materials were generally more crystalline than the conventional zeolites. Hydrocracking catalysts containing 0.9 wt.% Pd loading on different MFI supports were prepared by the incipient wetness impregnation method. The n- v hexadecane hydrocracking conditions used were typical of LTFT process (i.e., Temperature = 215 - 310 °C, WHSV = 1 h-1, Pressure = 20 bar, in addition to the H2 /n-C16 ratio of 10). The catalytic activity in all catalyst systems increased with increasing reactor temperature and displayed C4/C12 ratios ≠ 1, evidence of the occurrence of secondary cracking (i.e., a non-ideal hydrocracking behaviour). This was also supported by the shapes of their product distribution profiles, which showed dominant C3 - C7 n-paraffins. Co-feeding H2O with n-C16 into the reactor was found to be detrimental to n-C16 conversion, but promoted the selectivity to iso-paraffins in the product spectrum. Simultaneous introduction of CO and H2O aggravated secondary cracking. Amongst the pristine ZSM-5 zeolite-based catalysts, Pd/P-ZSM-5(77) showed the best catalytic performance. Upon desilication, the performance order changed to favour Pd/D-ZSM-5(50*). For the surfactant-templated supports, Pd/HSZ(N4) showed the most superior hydrocracking performance. Comparison of catalytic activities of the best performing catalyst systems derived from the conventional and surfactant-templated zeolites in the hydrocracking of n-hexadecane, follow the order Pd/D-ZSM-5(50*) > Pd/P-ZSM-5(77) > Pd/HSZ(N4). That is, the pristine and desilicated zeolite-based catalysts performed better than their surfactant-templated zeolite-based counterparts. Therefore, the post-synthesis generation of mesoporosity through desilicating ZSM-5 with a SAR of 50 has proven beneficial for the resulting catalyst system. One of the possible reasons for the relatively inferior hydrocracking performance of the Pd/HSZ(N4) catalyst may be the aluminium-richness of the support (SAR = 40) compared to the conventional ZSM-5-based supports. In summary, catalysts Pd/D-ZSM-5(50*), Pd/P-ZSM-5(77) and Pd/HSZ(N4) are promising for diesel-selective catalysis and need further refinements and exploration.

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Graph Theory is a branch of mathematics that has a wealth of applications to other science and engineering disciplines, specifically Chemistry. The primary application of graphs to Chemistry is related to understanding of structure and symmetry at the molecular level. By projecting a molecule to the plane and examining it as a graph, a lot can be learned about the underlying molecular structure of a given compound. Using concepts of Graph Theory this masters project examines the underlying structures of two specific families of compounds, fullerenes and zeolites, from a chemical and mathematical perspective.

archives@tulane.edu / A catalyst is a substance that increases the rate of a reaction without itself being consumed. Catalysis is an enabling technology due to its importance in a wide range of industrial applications. Processes responsible for more than 95% of all produced chemical products by volume employ catalysis, more than 85% of the added value in the chemical industry is produced by means of catalysis, and ca. 20% of the world economy depends directly or indirectly on catalysis. Generally, catalysts are classified into three categories: heterogeneous, homogeneous, or bio catalysts. A heterogeneous catalyst is one that is not in the same phase as the reactants while in homogeneous catalysis, the catalyst is in the same phase as the reactants. Heterogeneous catalysis is currently the most dominant catalysis route due to its advantages. A very important feature is that heterogeneous catalysts can be regenerated and reused for several catalytic cycles, which makes their application highly economical. Zeolites, which are porous crystalline aluminosilicates, offer great potential as heterogeneous catalysts due to their unique structural characteristics. For example, they can be employed in important chemical reactions such as aromatization, alkylation, dehydration, disproportionation, hydroalkylation, hydrocracking, and hydrogenation. To achieve unique selectivities in these processes, knowing the topology of zeolites is essential because it controls the size and shape of molecules that can be admitted in the framework, and their possible pathways. Since the properties of zeolites are associated with their structure, the synthesis of zeolites with improved topologies and compositions and their fundamental understanding has been and continues to be the objective of many researchers. Even though significant improvements in zeolites have been achieved in the last century, there is still space for growth in some areas including the diversification of zeolite chemical compositions to expand their applications as catalyst. The present dissertation attempts to give an understanding of how different parameters can be linked to the activity of heteroatom-containing zeolites in certain oxidation reactions. Chapter (1) of the dissertation covers the fundamentals of zeolite materials science and their applications in industry. Chapter (2) describes the experimental methods and analytical tools used in this dissertation. Synthesis and detail characterization of Sn, Sn-Al, and Sn-B substituted into MFI zeolites are discussed in chapter (3). We found that Sn-Al- MFI have both Lewis and Brönsted acidities while Sn-B-MFI shows strong Lewis acidity and weak Brönsted acidity. Moreover, the presence of the second element (Al/B) impacts the Sn uptake. In chapter (4), we report the synthesis of Fe-ZSM-5 zeolites made by a novel method called steam-assisted crystallization and their use in benzene hydroxylation to phenol in the presence of hydrogen peroxide as the oxidant. These materials showed a superior catalytic activity for benzene hydroxylation as compared to conventional Fe- ZSM-5 zeolites. Chapter (5) describes the effect of different trivalent elements (Ga, Al, B) on the acidity of Fe-MFI materials and their relation to the catalytic activity methane partial oxidation to oxygenated compounds including formic acid, methanol, and methyl hydroperoxide. We found that acidity plays a crucial role in the activation of hydrogen peroxides and ultimately methane oxidation. Chapter (6) and (7) present conclusions and potential future works, respectively. / 1 / Meysam Shahami