Preparation of layered K-Fe-Zn-Ti catalyst and its performance in the hydrogenation of carbon dioxide to light olefins

A series of layered K-Fe-Zn-Ti catalysts with different Zn/Fe molar ratios were prepared by high-temperature solid state reaction and characterized by SEM, TEM, XRD, H₂-TPR, CO₂-TPD, XPS, N₂ sorption and TG measurements; the performance of K-Fe-Zn-Ti catalysts in the hydrogenation of CO₂ to light olefins was investigated. The results indicate that the K-Fe-Zn-Ti catalysts have the typical layered structure with K_2.3Fe_2.3Ti_5.7O₁₆ as the main phase. ZnFe₂O₄ appears on the Zn promoted K-Fe-Zn-Ti catalysts, which may reduce the crystallinity, enhance the surface basicity, and promote the adsorption of CO₂. The K-Fe-Zn-Ti catalysts exhibit high selectivity to olefins in CO₂ hydrogenation; the ratio of olefins to paraffins in the products (O/P) is higher than 6.5. The addition of Zn can enhance the formation of C₅⁺ hydrocarbons and especially C₄⁺ linear alpha-olefins (LAOs); the content of LAOs in C₄⁺ hydrocarbons over Zn promoted K-Fe-Zn-Ti reaches 75.2%, in comparison with the value of 54.6% over the Zn-free K-Fe-Ti catalyst. In particular, the 0.8K-1.8Fe-0.6Zn-1.3Ti catalyst displays the highest O/P value (7.8), although the effect of Zn content in the Zn-promoted K-Fe-Zn-Ti catalysts on the yield of heavy hydrocarbons and selectivity to alpha-olefins is less significant. Moreover, the K-Fe-Zn-Ti catalysts display high stability in CO₂ hydrogenation and the LMO structure remains almost intact after a long term reaction test of 100 h.