Effect of Al_2O_3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

摘要

A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al_2O_3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N_2 physical adsorption, temperature-programmed reduc-tion/desorption (TPR/TPD) and Moessbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al_2O_3 content and passes through a maximum at the Al_2O_3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al_2O_3 content. The incorporation of Al_2O_3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al_2O_3 and Fe-Al_2O_3 interactions. Furthermore, the H_2 adsorption ability of the catalysts is enhanced with increasing Al_2O_3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260℃, 1.5 MPa, 1000 h~(-1) and molar ratio of H_2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al_2O_3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al_2O_3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al_2O_3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al_2O_3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.