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.