Study of phase transformation and catalytic performance on precipitated iron-based catalyst for Fischer–Tropsch synthesis

Abstract

Detailed phase transformation in syngas (H 2/CO = 1.2) on a precipitated iron-based catalyst was studied by N 2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (LRS). Fischer–Tropsch synthesis (FTS) performance of the catalyst was investigated in a slurry-phase continuously stirred tank reactor (STSR). The hematite in the fresh catalyst was reduced initially to magnetite, and then the magnetite in the bulk reached steady state slowly with increasing reduction time. Simultaneously, the Fe 3O 4 on the surface layers converted gradually to iron carbides, accompanied with the continual increase in the amounts of surface carbonaceous species. In the FTS reaction, the catalytic activity presented an increased trend with gradual carburization of the catalyst by keeping the stability in the bulk Fe 3O 4, suggesting that the conversion of magnetite to iron carbides in the near-surface regions provides probably the active sites for FTS. In addition, the chain growth reaction was restrained and the hydrogenation reaction was enhanced with increasing reduction duration.