Effect of the activation atmosphere on the activity of Fe catalysts supported on SBA-15 in the Fischer-Tropsch Synthesis

摘要

An iron catalyst supported on SBA-15 was prepared and activated in H _2 stream and in synthesis gas (H_2:CO = 2:1) stream, in order to be used in the Fischer-Tropsch Synthesis. The different activation treatments led to different Fe species in fresh catalysts: α-Fe, Fe _3O_4 and Fe~(2+) diffused into the SBA-15 walls in H2-Fe/SBA-15 and χ-Fe_5C_2, Fe_3O_4 and Fe~(2+) in H2:CO-Fe/SBA-15. These initial differences in the "bulk" structure of the solids disappear when both catalysts are "working". However, a higher production of total hydrocarbons, higher CO conversion and more CH_4 and light gases were obtained for H2-Fe/SBA-15 over 6 days. Besides, a higher selectivity toward light olefins was obtained with H2-Fe/SBA-15 during the first 24 h on reaction stream, but this selectivity decreases with the reaction time. These results are explained considering that the iron carbides produced from α-Fe are more active and/or have smaller sizes than that obtained from α-Fe_2O _3.