Bi-functional Hierarchical Zeolite-based Catalysts for Upgrading Bio-oil into Fuels

  • Abdulla Ahmed Alhendi

Student thesis: Master's Thesis

Abstract

Self-pillared pentasil (SPP) is a hierarchical zeolite synthesized using organic structure directing agents to template the zeolite for obtaining self-pillared nanosheets of the MFI structure. Self-pillared MFI supports with transition metal catalysts provide good candidates for the hydrodeoxygenation (HDO) reaction. However, transition metal catalysts, such as nickel, can cause coke formation at high conversions, which is why they are often co-loaded with noble metals, such as platinum, to reduce coke formation. The bi-metallic catalyst can secure low deactivation rates, while the hierarchical MFI support provides good diffusion rates in addition to possible enhancements in metal dispersion, stability, and activity. This work aims at preparing and carefully characterizing the physiochemical properties of bi-metallic MFI catalysts with different morphologies for the potential application for the hydrodeoxygenation of oleic acid. Specifically, mono-metallic nickel catalysts and platinum-nickel bi-metallic catalysts with different platinum content are loaded on conventional and self-pillared MFI supports. For this project, the synthesis of a viable self-pillared MFI zeolite was successfully completed following an optimization protocol according to the literature. The microstructure, porosity, and surface acidity of the zeolite-based catalysts were studied by employing X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), N2 adsorption at 77K, NH3- and H2-temperature programmed desorption (TPD), and temperature programmed reduction (TPR). From TEM imaging, it was observed that the metal dispersion for impregnated self-pillared samples was much better than that achieved by the impregnated conventional MFI samples, where the metal particles for all SPP samples were mostly smaller than 10 nm. On the other hand, the metal particles observed on the external surfaces of impregnated commercial MFI samples were too big to fit into the pores of the support (> 100 nm) causing a drop in porosity due to blocking of pore entrances. Additionally, the bimetallic samples achieved enhanced reducibility and higher acidity as compared to monometallic samples. Moreover, H2-TPD experiments revealed that the bimetallic samples demonstrated stronger metal sites than monometallic samples when prepared using the self-pillared MFI support. However, for the commercial MFI samples, the strongest metal sites where observed for monometallic samples.
Date of AwardMay 2022
Original languageAmerican English

Keywords

  • MFI; zeolite; bi-functional; catalysts; nickel; platinum; nanoparticles; encapsulation; surface acidity; porosity; bio-oil; hydrodeoxygenation.

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