Iron Fischer-Tropsch Catalysis

Application of Fe catalysts on a commercial scale using slurry bubble column reactors (SBCR) has been held back due to their poor attrition resistances. Recently, high attrition resistant catalysts have been successfully prepared using spray drying. Their improved physical strength was found to depend greatly on particle density, which was determined by type and concentration of SiO2 added to the catalysts. However, only Fe catalysts containing binder or binder + precipitated SiO2 were studied.To improve our understanding of the role of SiO2 on attrition properties of Fe catalysts, in general, attrition of spray-dried Fe catalysts prepared with only precipitated SiO2 was investigated. The amount of precipitated SiO2 that optimized catalyst performance (attrition resistance and activity) during an SBCR operation was suggested to be ca. 11 wt%. The strong relationship between catalyst attrition and particle density was consistent with the previous findings.Unlike high attrition resistant catalysts, whose physical and chemical attrition properties remained essentially unchanged after pretreatment, the physical strength of poor attrition-resistant catalysts was able to be improved significantly by pretreatment (CO or H2). This improvement was surprisingly decreased by the addition of water vapor during pretreatment. The presence of water vapor was found to prevent sintering of Fe pore structure but to provide no significant additional interaction between Fe and SiO2. The conventional CO-pretreatment was suggested as the best activation for Fe catalysts, since it results in high attrition resistance and reasonably high surface area.Different activation pretreatments (H2, CO, or syngas) result in different Fe phases, and the relationship of these phases with catalyst activity during FTS has been debated among researchers up to the present day. Steady-state isotopic transient kinetic analysis (SSITKA) was used to study at the site level the activity of differently activated Fe during CO hydrogenation. It was found that the H2-pretreated sample exhibited the highest concentration of surface reaction intermediates (NM) while those of CO- and syngas-pretreated ones were similar. The intrinsic site activity (kM) of differently pretreated catalyst samples was essentially identical. These results suggested that the active sites were on the surface of carburized Fe