Direct synthesis of light olefins from CO hydrogenation over K/MgFeZn-HTLcs catalysts

A series of K promoted K/MgFeZn-HTLcs catalysts with different Mg/Fe/Zn molar ratios were prepared by means of precipitation method and impregnation method for the direct synthesis of light olefins from CO hydrogenation. The samples were characterized by N₂ adsorption-desorption SEM, TG, XRD, XPS and H₂-TPR measurements. The results showed that the MgFeZn-HTLcs catalyst precursors have typical lamellar structure, larger specific surface area and average pore diameter compared with Fe/Zn catalyst. The BET surface area and the average pore diameter decreased after calcination and K promotion. The bulk composition of the calcined samples was mainly metal oxide and ferrite. Fe₅C₂, MgCO₃ and ZnO were formed in K/MgFeZn-HTLcs catalysts after reaction. However, the main phase in K/2Fe-1Zn catalyst was stabilized in ZnFe₂O₄. During CO hydrogenation, the prepared samples showed high C_2-4⁼ selectivity and low C₅⁺ weight fraction compared with that of K/2Fe-1Zn sample. The product distribution was greatly improved. Over the sample K/2Mg-2Fe-1Zn, an olefin to paraffin ratio of 5.15 and the C_2-4⁼ weight olefin content of 48.56% could be obtained.