Starting Material for Products Formed over an Iron Fischer-Tropsch Catalyst

摘要

The morphological reactions of iron Fischer-Tropsch catalysts during reaction have been well studied (1-4). The motivation for learning about phase changes during reaction is twofold: 1. Activity and selectivity may be enhanced by understanding the property-structure relationship of iron phase versus activity, and 2. Attrition of the iron catalyst during synthesis gas reaction is caused primarily by the morphological changes of the catalyst during reaction as well as the deposition of carbon on the catalyst. The changes occurring during reaction are shown schematically in Figure 1. Initially, an iron FT catalyst, which may have additives and promoters such as copper, silica, and/or potassium begins as an oxide. As the freshly calcined iron is reduced (in H_2, CO or H_2/CO) it initially transforms quickly from hematite (Fe_2O_3) to magnetite (Fe_3O_4). If the catalyst is reduced further in hydrogen, #alpha#-iron is formed. If the catalyst is reduced in either CO or synthesis gas, the result is iron carbide. No hydrocarbon products are formed unless iron carbide is present (1).