Novel Synthesis of Silica-Supported Fischer-Tropsch Catalysts for Second Generation Biofuels

The objective of this study is to improve the catalytic performance of silica-supported Fischer-Tropsch cobalt based catalyst. Iron and nickel catalyst were also briefly studied.
Initial work focused on synthesis of porous silica via oxidative thermal decomposition of polydimethylsiloxane (PDMS) and its characterisation. It was shown that PDMS undergoes at least two thermal degradation steps to form silica powder. It was also demonstrated that increase in isothermal time at constant temperature and increase in temperature at constant time could be used to tune the surface area and pore volume of the synthesized silica powder.
Subsequently, a novel one pot technique called the swelling in method (SIM) was developed, and employed to synthesize silica-supported cobalt, iron and nickel based Fischer-Tropsch catalyst. The results of silica-supported cobalt based catalyst prepared by the swelling in method were compared with those synthesized by incipient wet impregnation method. The colloidal method was also combined with the swelling in method to prepare silica-supported cobalt nanoparticles catalyst.
Characterisation of cobalt, iron and nickel based catalyst prepared by the swelling in method showed that PDMS as the initial catalyst support converted to silica powder after oxidative calcination. Physicochemical properties of silica-supported cobalt, iron and nickel catalyst prepared by the swelling in method suggest that the oxides of each metal were present inside the silica pores while cobalt based catalyst prepared by the same method had better surface area and pore volume compared to the catalyst synthesized by the incipient wetness impregnation technique.
Catalytic performance of the catalyst synthesized by the swelling in and incipient wetness methods were studied in High Temperature Fischer-Tropsch synthesis reaction condition. The results showed that silica-supported cobalt based catalyst prepared by the swelling in method was overall more active, generated less methane and less susceptible to deactivation by sintering and carbon deposition when compared to the catalyst prepared by the impregnation technique. Silica-supported cobalt nanoparticles catalyst had the best catalytic activity in comparison to all the catalyst studied in this work. Silica-supported cobalt based catalyst prepared by the swelling in method using cobalt nitrate exhibited the best catalytic activity while the catalyst synthesized from cobalt acetate had the least activity. The addition of ruthenium to silica-supported cobalt catalyst contributed in minimising the formation of methane when compared to the catalyst without ruthenium. Silica-supported iron and nickel based catalyst showed reasonable catalytic activity, and as expected the amount of methane generated by nickel catalyst was relatively very high compared to all the catalyst studied in this thesis.