STUDY ON AN IRON-BASED FISCHER-TROPSCH SYNTHESIS CATALYST PROMOTED WITH MANGANESE

摘要

The Fischer-Tropsch synthesis (FTS) provides a promising route for the production of clean liquid fuels and chemicals by conversion syngas (CO + H_2). Iron-based catalysts are more suitable for the conversion of syngas with low H_2/CO ratio derived from coal due to their high FTS activity as well as high water-gas shift (WGS) reactivity, which helps to make up the deficit of H_2 in the syngas [1]. Iron-based catalysts for F-T synthesis are often incorporated with certain amounts of potassium, manganese and copper as promoters to improve its activity and selectivity [2]. The promotion effects of manganese have been extensively investigated on unsupported or supported iron catalysts. Kreitman et al. [3] had reported that manganese-supported iron catalyst showed higher lower olefins selectivity than the un-supported iron catalysts. Maiti et al. [4] reported that a single phase (a-(Fe_(1-x)Mn_x)_2O_3) was formed over the coprecipitated iron-manganese catalysts. The surface enrichment of MnO during calcination and reduction of iron-manganese catalysts was reported by Grzybek et al. [5]. Leith and Howden [6] indicated that the addition of manganese retarded the reduction of iron oxides. Das et al. [7] reported that the presence of manganese reduces the crystallite size of iron oxide and suppresses the carbonization of iron oxide. However, the studies on the incorporation manner of manganese into a precipitated iron-based catalyst prepared with ferrous sulfate are rarely reported. The objective of the present study is to investigate the effect of the incorporation manner of manganese on the performances of an iron-based catalyst.