载体SiO_2孔径及助剂对Co/SiO_2催化剂微观结构及费托合成反应性能的影响  

Effects of SiO_2 Pore Size and Additives on the Microstructure of Co/SiO_2 Catalysts and Their Catalytic Performance in the Fischer-Tropsch Reaction

作　　者：江云辉 付廷俊[1] 吕静[1] 李振花[1] 

机构地区：[1]天津大学化工学院,绿色合成与转化教育部重点实验室,天津300072

出　　处：《高校化学工程学报》2014年第3期553-560,共8页Journal of Chemical Engineering of Chinese Universities

基　　金：国家自然科学基金(21076151)

摘　　要：以三种不同孔径的SiO2为载体,等体积浸渍法制得三种Co/SiO2催化剂用于费托合成反应,采用氮气物理吸附、H2-TPR、H2-TPD、XRD、SEM和TEM等手段对催化剂的微观结构进行了表征。结果表明,载体的孔径对催化剂中钴的分散度和还原度有显著影响。小孔径SiO2为载体时,钴颗粒多堆积在孔外部,不利于钴颗粒的分散,还原度低;大孔径SiO2为载体时,钴颗粒粒径较大,致使钴分散度降低;两者均不利于CO的转化。而孔径适中的B型SiO2为载体制备的催化剂有较高的钴还原度和分散度,具有较高的费托反应活性和链增长能力。以孔径适中的SiO2为载体,进一步考察了助剂La、Ce和Zr对催化剂微观结构及催化性能的影响。结果表明,三种助剂的加入均改变了SiO2表面的性质,C5+选择性均有所提高,其中以锆为助剂效果最佳。研究表明钴锆界面的生成促进了钴颗粒的分散,提高了催化剂的活性,且有利于重质烃的生成。Co/SiO2 catalysts supported by three kinds of silica with different pore sizes were prepared using an incipient wetness impregnation method and their performances in the Fischer-Tropsch synthesis were tested. These catalysts were characterized by N2-physisorption, H2-TPR, H2-TPD, XRD, SEM and TEM. The results show that the SiO2 pore size have a significant influence on cobalt dispersion and reducibility. When SiO2 have smaller pore size, most cobalt species are accumulated on the outer surface of the support to form large clusters that leads to a poor cobalt dispersion and lower cobalt reducibility. While for SiO2 with the largest pore size, larger Co3O4 crystallites are formed, which also results in poor cobalt dispersion. Both these two Co/SiO2 catalysts displayed lower Fischer-Tropsch activity. However, the Co/SiO2B catalyst with medium support pore size exhibits better cobalt dispersion and reducibility, which results in an enhanced Fischer-Tropsch activity and hydrocarbon chain growth ability. Furthermore, the effect of additives like lanthanum, zirconium and ceria on the structure and properties of Co/SiO2B catalyst was studied. The results show that these additives can modify the silica surface property and increase the selectivity of C5＋. The results show that zirconium is the best additive tested, and the cobalt-zirconium interface can increase the cobalt dispersion, Fischer-Tropsch activity and hydrocarbon chain growth ability.

关 键 词：费托合成反应 钴 硅胶 孔径 助剂 

分 类 号：O643[理学—物理化学]