铁助剂对纳米ZSM-5负载钴催化剂的费-托合成催化性能的影响

Effect of iron promotion on Fischer-Tropsch synthesis performance of nano-ZSM-5 supported cobalt catalysts

以蒸气转晶法制备的纳米ZSM-5为载体,采用共浸渍法负载钴,并通过不同方法引入铁助剂,制备了纳米ZSM-5负载钴基费-托合成催化剂.采用XRD、N2-物理吸附、H2-TPR、NH3-TPD、XPS、TEM等方法表征催化剂,并对催化剂的费-托合成(FTS)催化性能进行评价,研究了铁离子直接掺杂ZSM-5分子筛骨架、铁钴共浸渍、铁钴分步浸渍等三种铁助剂引入方式对钴基催化剂结构、性质及费-托合成催化性能的影响.结果表明:铁助剂引入方式影响了催化剂中钴物种的分散和还原性以及载体的酸性,由此影响催化剂的费-托合成催化性能.分步浸渍法所制备的催化剂的钴物种分散度最高,但是还原性最低,使其达到稳态后具有最高的CO转化率、最低的CH4选择性和最高的C5+产物选择性.此外,以浸渍法(共浸渍和分步浸渍)引入的铁助剂更有利于iso-C5的生成,而直接掺杂法引入的铁助剂不利于异构烃的生成.

Using Nano-ZSM-5 prepared by water vapor-assisted crystallization as carrier,cobalt-based Fischer-Tropsch synthesis(FTS)catalysts were prepared by impregnation methods with the iron promoter introduced by different means.The catalysts were characterized by XRD,N2-adsorption,H2-TPR,NH3-TPD,XPS,TEM and tested in FTS reactions.The effects of different ways of iron incorporation,such as direct doping on ZSM-5 molecular sieve framework,co-impregnation or consecutive impregnation with iron and cobalt,on the structure,properties and FTS performance were investigated.The results showed that the introduction methods of iron promoter could affect the reduction capacity and acidity of the Co support,thus change the FTS performance.The catalysts prepared by consecutive impregnation had the highest cobalt dispersion but the lowest reducibility,and resulted in highest CO conversion,lowest CH4 selectivity,and the highest C5+selectivity after reaching the steady state.Moreover,iron introduced by co-impregnation or consecutive impregnation methods was conducible for the generation of iso-C5+,while direct doping of iron on ZMS-5 hindered the generation of iso-paraffin.