Highly effective MFe2O4 (M=Zn, Mg, Cu and Mn) spinel catalysts for Fischer-Tropsch synthesis

Abstract

A series of spinel catalysts, including ZnFe2O4, MgFe2O4, CuFe2O4, and MnFe2O4, were prepared and applied to the Fischer-Tropsch synthesis (FTS). Zn, Mg, Cu and Mn easily form spinels with Fe. Among them, Zn and Mg can significantly maintain the spinel structure during the pretreatment and reaction, resulting in a low CO conversion. Cu and Mn are beneficial to the formation of iron carbide during the reaction, resulting in an apparent influence on FTS performance. ZnFe2O4 has little effect on the hydrocarbon distribution and the olefin/paraffin (O/P) ratio of C2–C4. MgFe2O4 exhibits low selectivity for C5+ hydrocarbons, and the selectivity of C= 2−C= 4 and the O/P ratio of C2–C4 in the product are increased due to the alkaline effect of Mg. Cu can promote the carbonization of the catalyst, so that CuFe2O4 has higher activity. Meanwhile, CuFe2O4 can significantly improve the selectivity of C5+ hydrocarbons. Moreover, Cu can promote the dissociation and activation of H2, which is beneficial to the secondary hydrogenation of olefins, thereby reducing the selectivity of C= 2−C= 4 and the O/P ratio of C2–C4. Mn promotes carbonization during the reaction, but MnFe2O4 has little effect on the chain growth of hydrocarbon. However, Mn can promote the generation of a certain amount of ɛ-Fe2C, which may explain the higher selectivity of C= 2−C= 4 and the O/P ratio of C2–C4 for MnFe2O4. All spinel catalysts exhibit low CO2 selectivity, which meets the current green environmental protection requirements.