Study On Cobalt Catalyst For Fischer- Tropsch Synthesis

The Fischer-Tropsch synthesis (FTS) is an important process for the conversion of syngas derived from carbon sources such as coal, peat, natural gas and biomass into high-grade, clean liquid fuels and high value chemicals. Cobalt catalysts are the potential catalysts for FTS catalyst because of their high activity, high selectivity to linear hydrocarbons, and low activity for the water-gas shift (WGS) reaction. A detail study on the preparation conditions such as the impregnation time, promoter, drying modes were studied in present work. The preparation of zeolite-enwrapped cobalt catalyst was also investigated. Characterization methods such as XRD, H2-TPR, BET and SEM were used in oreder to get insight into the relationship between the structural and catalytic performance. Main results from this work were as follows.The activity of catalyst is improved with the increasing of impregnation time in 24 h. But further extend the impregnation time has no significant effect on the activity. The catalyst dried in air has better activity than that dried in vacuum or in infrared. The catalytic activity increases first and then decreases with the increase of drying temperature. The catalyst drying at 90 ℃ showed the highest activity and best stability among studied catalysts.Content of La promoter had a significant effect on the activity and selectivity of cobalt catalyst for F-T synthesis. When a small quantity of La promoter was added, the activity and C5+ hydrocarbon products selectivity were improved and the CH4 selectivity was reduced. Impregnation of La first followed by Co inpregnation can eliminate the strong interaction between Co and SiO2, leading to good reducibility and therefore high catalytic activity of the catalyst.The surface of Co/SiO2 catalyst by zeolite-enwrapped, the CO conversion of catalyst would decreased, but the hydrocarbon distribution would significantly changed; C1-18 hydrocarbon products content increased, and C19+ hydrocarbon products content obviously reduced. Silica alumina ratio had an obvious effect on the hydrocarbon distribution; C1-12 and C19+ hydrocarbon products content increase gradually, but C13-18 hydrocarbon products content decrease with the increase of silica alumina ratio. High template concentration is favorable for the formation of zeolite. When the crystallization temperature was 180 ℃, Crystallization time had an obvious effect on the catalytic performance, with the increase of the crystallization time, the CO conversion of catalyst decreased.