Effect of reduction temperature on a spray-dried iron-based catalyst for slurry Fischer–Tropsch synthesis

An industrial iron-based catalyst (100Fe/5Cu/6K/16SiO2, by weight) was characterized after reduction at different temperatures and after Fischer–Tropsch synthesis (FTS) in a stirred tank slurry reactor (STSR). The BET surface area and pore volume of the catalyst decreases with increasing reduction temperature, and the contrary trend was found for pore size. The iron phase compositions of catalysts reduced with syngas were strongly dependent on pretreatment conditions employed. Pretreatment with syngas at lower temperature prevents iron catalyst activation. Carburization was intensified with the increase in reduction temperature. The formation of iron carbides in reduced catalyst was necessary for obtaining stable high FTS activity. The relationship between the amount of CO2 in tail gas during activation and the Fe3+ (spm) content in the reduced catalyst was observed. The rapid carburization at high reduction temperature resulted in the formation of a superparamagnetic Fe3+ core and an iron carbide layer of the reduced catalyst. FTS activity decreased with the increase in the reduction temperature, but the stability distinctly improved. It was found that the working catalyst loss in the heavier waxy products resulted in higher deactivation rate of the catalyst reduced at lower temperature. With the increase in the reduction temperature, the product distribution shifted towards the lower molecular weight products.

This investigation focused on the effects of catalyst pre-treatment on its FTS performance. It was found that the total content of carbides of the reduced catalysts increased with the increase in reduction temperature. FTS activity and deactivation rates decrease with the increase in the reduction temperature, while the reverse trend is found for WGS activity. With the increase in the reduction temperature, the hydrocarbon product distribution shifts towards the lower molecular weight products. Figure optionsDownload as PowerPoint slide