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

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

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K2.3Fe2.3Ti5.7O16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(linearα-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(C2-4=/C2-40,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-FeZn-Ti催化剂具有较好的稳定性,经100 h在线反应后,仍保持LM O结构。

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 K2.3Fe2.3Ti5.7O16 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 C+5 hydrocarbons and especially C+4 linear alpha-olefins(LAOs);the content of LAOs in C+4 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.