Zn、Mn助剂对CuFe合成低碳醇催化剂的影响

研究了锌、锰助剂对CuFe合成低碳醇催化剂结构及性能的影响. 低温N2吸附、X射线衍射(XRD)和H2-程序升温还原(H2-TPR)结果表明, 锌的添加导致催化剂比表面下降, 不利于活性相的分散; 而锰则促进铜铁的分散, 增加了铜铁的接触面积, 有利于二者之间的相互作用. CO吸附的漫反射红外光谱(DRIFT)表明, 锌增强了铁对CO的吸附能力, 这种效应与ZnFe2O4的形成有直接关系; 而锰助剂由于稀释效应, 减弱了铁对CO吸附能力和链增长能力. 催化剂的反应性能测试表明, 与CuFe催化剂相比, CuZnFe催化剂的活性大幅度提高, 但C2+醇选择性下降; CuFeMn催化剂的活性却有所下降, C2+醇选择性也降低, 但总醇的选择性提高. 双助剂修饰的催化剂表现出明显的协同效应, 改变了催化剂的织构, 降低了Cu的还原温度, 修饰了Fe的还原性能. 更重要的是, Zn和Mn的添加显著增强了CO在催化剂表面的吸附量. 催化剂催化性能总体上优于CuZnFe和CuFeMn催化剂.

Effect of Zn and Mn Promoters on Copper-Iron Based Catalysts for Higher Alcohol Synthesis

The influences of zinc and manganese promoters on the structure and reaction behavior of CuFe catalyst for higher alcohol synthesis were investigated by N2 adsorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), in situ diffuse reflectance infrared spectroscopy (DRIFT) and CO+H2 reaction. It was found that the zinc additive suppressed the dispersion of active phases but improved their activation ability towards CO molecule due to the formation of a new spinel phase, ZnFe2O4. The presence of manganese showed a more favorable effect on the dispersion of active phases and then promoted the synergistic effect between copper and iron although the adsorption tendency towards CO declined due to the dilution effect of manganese. Compared with binary CuFe catalyst, CuZnFe catalyst had a higher activity with the decreasing of C2+OH selectivity, and CuFeMn catalyst showed improved total alcohol selectivity although both CO conversion and C2+OH selectivity decreased. The results of the doubly promoted CuFe catalyst evidently indicated the existence of synergistic effect between zinc and manganese, which modified the texture parameters, decreased the reduction temperature of Cu and altered the reduction behavior of Fe. More importantly, the abundance of CO adsorption on the CuFe catalyst was greatly increased due to the co-addition of zinc and manganese. Therefore, the overall catalytic performance of doubly promoted CuFe catalyst was superior to that of the single promoted CuFe catalyst.