|Full Name:||Oluwole O. Ajumobi|
|Thesis Title: ||DEVELOPMENT OF CERIA-ZIRCONIA NANOCOMPOSITES FOR CATALYTIC CRACKING OF HYDROCARBONS |
|Major Field:||Chemical engineering|
|Date of Degree:||April 2017|
Nano-sized iron- and cobalt-doped ceria-zirconia nanocomposites were synthesized via hydrothermal synthesis technique at 180 °C for 8 - 24 h, with the novel incorporation of both Co and Fe into ceria-zirconia (CZ), for n-hexane catalytic cracking. The intrinsic properties of ceria-zirconia were investigated using different characterization techniques. Influence of dopant ions on the improvement of basic properties of ceria-zirconia nanocomposites were also studied. Ceria-zirconia and its doped nanocomposites showed similar x-ray diffraction (XRD) patterns and significant to full fusion of the metal/dopant ions into the ceria-zirconia lattice structure. The prepared nanocomposite catalysts were tested for n-hexane cracking for 10 h time-on-stream. It should be noted that there has been no previous report or study on catalytic cracking of hexane via ceria-zirconia nanocomposites, highlighting the novelty of this application. Appreciably high ethylene and propylene selectivity, each > 31%, was obtained over CZ, FeCoCZ_A and FeCoCZ_B at the stipulated time-on-stream. Comparatively, FeCoCZ_A exhibited the best catalytic activity and stability with higher n-hexane conversions (49% at 1 h and 33% after 10 h) over time-on-stream. Temperature and catalyst weight per feed flowrate (W/F) variations were carried out on the best catalyst (FeCoCZ_A). Higher conversions were evaluated at higher reaction temperature and lower W/F. In addition, the spent catalysts were successfully regenerated via thermal approach by calcining the spent samples at 600 °C for 4 h. The regenerated samples were tested, repeating the regeneration and reusability procedure for two additional cycles. The XRD and scanning electron microscopy characterization results showed that the morphology (shape, phase structure and size) of the samples were restored after regeneration. Also, the regenerated samples were tested and exhibited catalytic activity for hexane cracking, with 9.1 % and 16.9 % loss in conversion after the first and second regeneration cycle, respectively.