层状K-Fe-Zn-Ti催化剂的制备及其对二氧化碳加氢制烯烃反应的催化性能

采用高温固相法制备了系列Zn改性的层状K-Fe-Zn-Ti催化剂，用于CO₂加氢经费托合成直接制烯烃反应。采用SEM、TEM、XRD、H₂-TPR、CO₂-TPD、XPS、N₂吸附-脱附和TG等手段对反应前后的催化剂进行了表征，对K-Fe-Zn-Ti催化剂的组成-结构-性能关系进行了关联研究。结果表明，所制备的催化剂均出现K_2.3Fe_2.3Ti_5.7O₁₆物相，为典型的层状金属氧化物（Layered Metal Oxides，LMO）结构；Zn改性后生成了ZnFe₂O₄物相，降低了催化剂样品结晶度，增强了表面碱性，促进了CO₂表面吸附。在CO₂加氢反应中，K-Fe-Zn-Ti系列催化剂均具有较高的烯烃选择性（O/P>6.5），Zn改性促进了C₅⁺的生成，显著提高了C₄⁺线性α-烯烃（linear α-olefins，LAOs）的选择性，C₄⁺烃中LAOs含量由Zn改性前的54.6%提高至75.2%。在所考察的范围内，随Zn/Fe比的增加，烯/烷比（C_2-4⁼/C_2-4⁰，O/P）先增加后降低，但对重烃含量以及LAOs选择性影响不明显。K-Fe-Zn-Ti催化剂具有较好的稳定性，经100 h在线反应后，仍保持LMO结构。

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.