Study On The Carbon Nanotubes Supported And Promoted Co-based Fischer-Tropsch Catalyst

Currently the world's fuel production is based predominantly on petroleum crude oil. The presently known reserves of methane and of coal exceed that of crude oil by factors of about 1.5 and 25, respectively. Production of syngas from methane or coal and conversion of the syngas to a range of fuels could become increasingly of interest as the reserves of crude oil are depleted and/or the price of crude oil rises. One of the key processes in this path is Fischer-Tropsch (F-T) synthesis. Furthermore, fuels from F-T synthesis are cleaner with lower sulfur and aromatic compounds.Conventional F-T catalysts are supported on the oxide materials, and the main problem of this kind of catalysts is the formation of cobalt containing stable materials, which is very hard to be reduced. However, this problem can be eliminated by using Carbon nanotubes (CNTs) as the support. Additionally, more properties show that CNTs is very suitable for supporting metals. Therefore, more and more attention has been paid to CNTs supported cobalt-based F-T catalyst.The effects of different support on Co-based F-T catalyst, the effects of different preparation conditions on Co/CNTs catalyst, the effects of different treatment on CNTs and Co/CNTs catalyst were investigated via several characterization methods alongside with the F-T synthesis testing. Using CNTs as promoter or reducer were also studied.Results showed that Co/CNTs catalyst had the same CO conversion as the catalyst supported on oxide materials, but with lower selectivity to the higher hydrocarbons. For Co/CNTs catalyst, the cobalt acetate is a better precursor than cobalt nitrate, and an optimum cobalt loading value was observed. The CO conversion of Co/CNTs catalyst was decreased apparently and the selectivity slightly shifted to the higher hydrocarbons with the increasing of CNTs diameter. Cobalt particle dispersion was increased and cobalt particle size was decreased by addition of sucrose in Co/CNTs catalyst. The effects of calcination condition on Co/CNTs catalyst only exhibited in high temperature calcination. The Co/CNTs catalysts prepared by incipient wetness impregnation and high pH homogenous deposition precipitation exhibited the highest CO conversion and C5+ selectivity, respectively. And the catalytic activity was decreased by increasing the pH value in the impregnation solution. Results also showed that the specific surface area and the concentration of oxygen containing groups were both increase after chemical modification, and the best results was achieved by HNO₃ treatment. The specific surface area and the concentration of oxygen containing groups were also increased with increase of concentration of HNO₃ solution and the best HNO₃ treatment method was co-boiling reflux. The wet air plasma modification was better than hydrogen plasma modification. Co/CNTs catalyst supported on modified CNTs had higher CO conversion and the selectivity shifted to the lower hydrocarbons with higher CO₂ selectivity.It was shown that CNTs could be a potential promoter or reducer for Co-based F-T catalysts.