Brief Review of Precipitated Iron-Based Catalysts for Low-Temperature Fischer–Tropsch Synthesis

Abstract

Fischer–Tropsch synthesis (FTS) is a promising way to produce clean liquid fuels and high value-added chemicals from low-value carbon-containing resources such as coal, natural/shale gas, waste wood/plastics, and CO2 via syngas (CO + H2). Precipitated iron-based catalysts are one group of commercially viable FTS catalysts that are important in academic circles as well as in industry. Here, we briefly review the promoters for precipitated iron-based FTS catalysts, which critically influence the catalyst performance. Precipitated iron-based catalysts typically contain three types of promoters: reduction promoters, alkali promoters, and structural promoters. The major effects of reduction promoters on catalytic performance include shortening of the induction period and increasing the CO conversion. Alkali promoters significantly influence the catalyst activation and product selectivity. They facilitate carburization of iron and increase selectivity for the target hydrocarbons C5+ and 1-olefin. The heavier the alkali metal, the stronger the effect. The structural promoters are effective for increasing the resistance of precipitated iron-based catalysts to thermal sintering and physical attrition. However, the impact of structural promoters on chemical properties and resultant catalytic performance is still considered a matter of debate. In the case of alkali promoters and structural promoters, the optimal amount of loading is very important for obtaining high catalytic performance, and this deteriorates severely if loading exceeds the optimal range.