Study On Direct Syngas To Olefins Over Iron-based Catalysts

Catalyst is the crucial points of technology for the direct preparation of olefins from syngas.The modification of iron-based catalysts and the modified catalyst performance in the process of CO hydrogenation to produce the olefins was studied in this paper.Four kinds of Al2O3-based carriers were used in the catalysts preparation process.Manganese,potassium,thorium as well as the manganese-potassium were used as promoter to modify the catalysts by means of co-impregnation.The influence of the different carriers,the active component content,catalyst precursor calcination temperature,and the promoters were studied.The performance of catalyst with different potassium compound promotors and the reaction condition were investigated and optimized.In addition,the concrete composition of liquid product was analyzed used GC-MS measrues.The catalysts were characterized by means of BET,XRD,temperature programmed,SEM,TEM.The main product from the optimized catalyst was ?-olefins(55.06%),while it contained parafins(22.88%)and higher alcohols(22.06%)at the same time.The results proved that the catalysts prepared with high BET surface area carrier and strong basic promotor have quite high activity and olefins selectivity.The best catalytic performance could be obtained when the iron loading amount was 10.0 wt.% under following conditions: T = 320 °C,P = 2.0 MPa and GHSV = 1000 h-1.Among all the promoters,high-loading potassium could enhangce the dispersion of active metal and improve the reductivity of catalysts.The adsorption and decomposition of CO were strengthened due to the the increasing electron density of iron arise from the the electron-donating effect of promotor.The growth capacity of carbon chain was largely improved while the selectivity of the methane was decreased.Moreover,the addition of potassium could raise the selectivity of C5+ olefins and higher alcohols.