Magister Scientiae - MSc (Nanoscience)
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Item type: Item , Olefin oligomerization over nanostructured ZSM-5(University of the Western Cape, 2025) Mazamelela, YolisaZSM-5 type zeolites are widely used as catalysts in oligomerization reactions due to its unique pore structure and high acidity, which enables it to selectively convert light alkenes (C2-C6) into larger oligomers in the gasoline, jet fuel and diesel hydrocarbon range. In oligomerization processes such as PetroSA’s Conversion of olefins to Distillate (COD) typical feeds consist of propylene and C5 to C6 olefins. Recently, there has been much interest in converting low-value naphtha streams, such as Light Cracked Naphtha (LCN) rich in C5 to C6 olefins, to high-value transportation fuels. Furthermore, the growing demand for longer-chain jet and diesel fuels requires that the properties of ZSM-5 be optimized to meet these demands. However, conventional microporous ZSM-5 catalysts are subject to diffusion limitations and rapid deactivation, particularly when processing C₅-C₆ olefins, due to their small pore size and high acid strength, which often led to coke formation and pore blockage. To overcome these limitations, this study investigates the catalytic performance of nano-sized ZSM-5 zeolites synthesized via hydrothermal methods, focusing on the effect of synthesis parameters such as alkalinity, aging time, and choice of structure-directing agent on the resulting crystal size and morphology. The primary objective was to enhance mass transport and catalytic efficiency in the oligomerization of 1-hexene, a model C₆ olefin, by reducing crystallite size and promoting external surface accessibility. The structural and physicochemical properties of the synthesized materials were extensively characterized using techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, thermogravimetric analysis (TGA), and X-ray fluorescence (XRF). XRD confirmed the formation of a pure MFI-type crystalline phase, while TEM revealed nano-sized crystals (~90 nm) with well-faceted cubic to rectangular morphology. BET analysis showed a high surface area of 371 m²/g for the nano ZSM-5 catalyst, with an external surface area of 194 m2/g greater than its micropore area of 177 m2/g, indicative of enhanced external surface exposure. NH3-TPD also revealed nano-ZSM05 to have more weak/medium acid sites compared to the commercial catalyst with higher strong acid site density.