Effects of Cr Promoter on Structure and Fischer-Tropsch Synthesis Performance over Fe-Based Catalysts

The effects of promoter Cr content in the Fe-based Fischer-Tropsch synthesis (FTS) catalysts on the textural properties, reduction behavior, and phase transformation of the catalysts during reduction and reaction were investigated by N(2) adsorption, X-ray diffraction, Mossbauer spectroscopy, X-ray photoelectron spectroscopy, H(2) differential thermogravimetric analysis, and CO temperature-programmed reduction over the coprecipitated Fe-based catalysts. The FTS performance of the Fe-based catalysts promoted with Cr was studied in a fixed-bed reactor under the conditions of H(2)/CO = 2.0, 260-300 degrees C, 1.5 MPa, and 2 000 ml/(g.h). The results showed that the strong interaction existed between Fe and Cr species by the formation of Fe-Cr solid solution, alpha-(Fe(1-x)Cr(x))(2)O(3). With the increase of promoter Cr content in the Fe-based catalysts, the phases of the catalysts gradually transformed to the Fe-rich phase and Cr-rich phase. Because the Fe-Cr solid solution strongly inhibited the reduction of the catalyst, Cr-promoted Fe-based catalysts exhibited low activity due to its lower extents of both reducibility and carburization. The promoter Cr enhanced the formation of methane and light hydrocarbon products but inhibited the activity of water-gas-shift reaction.