Fischer-Tropsch synthesis and XRD characterization of an iron carbide catalyst synthesized by laser pyrolysis

Abstract

Slurry phase Fischer-Tropsch synthesis (FTS) is conducted under industrially relevant conditions on an iron carbide catalyst of 30 nm particle size prepared by the laser pyrolysis of Fe(CO)₅ and C₂H₄. The activity and selectivity are compared to that obtained for a precipitated catalyst and an industrially prepared ultrafine Fe₂O₃ catalyst. In general, the iron carbide catalyst is not as active for FTS or water-gas shift reaction as the precipitated catalyst; however, it is more active for the FTS than the ultrafine Fe₂O₃. At similar CO conversion the iron carbide produces less methane and has a higher C₅+ and olefin selectivity than the precipitated catalyst. X-ray diffraction analysis shows that the iron carbide catalyst is composed of θ-Fe₃C and Fe₇C₃ at the start of synthesis, while the CO pretreated, precipitated and ultrafine Fe₂O₃ catalysts are composed of χ-Fe₅C₂, ε′-Fe_2.2C and Fe₃O₄. All three catalysts are rapidly oxidized to Fe₃O₄ during FTS.