Biofuels Produced by Fischer-Tropsch Synthesis over Silica-supported Iron-Based Catalysts Prepared by Autocombustion Method

Abstract

The purpose of this study was to evaluate the effect of different silica types on iron (Fe)-based catalysts containing copper and potassium prepared by autocombustion for direct use in Fischer-Tropsch Synthesis (FTS) without a reduction step. The catalysts were characterized through nitrogen (N₂) adsorption, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The FTS performance of each catalyst was evaluated in a fixed-bed reactor at 300 ^◦C, 1.0 MPa, a catalyst weight to volume flow rate of 10 g_cat h/mol and a hydrogen (H₂)/carbon monoxide (CO) molar ratio of 1. The pore size of the silica had an important influence on the formation of the Fe active phases and subsequent FTS activity. The presence of iron carbide (Fe_xC), which is known to be one of the active Fe phases, was demonstrated by the XRD and TEM analyses. Larger crystallite sizes in the large pores were much easier to accommodate Fe_xC than the smaller crystallite sizes in the small pores. The Fe-based catalysts supported on the silica with the largest pores gave the highest CO conversion level at 86.5%, with a 28.1% C_2–4 selectivity and 17.3% C₅₊ selectivity under these operating conditions. Interestingly, this is an alternative approach to synthesize nanostructured metallic catalysts on silica and to produce clean biofuel for the fuel industry and transportation.