Performance of hierarchical ZSM-5 supported cobalt catalyst in the Fischer-Tropsch synthesis
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摘要: 采用水蒸气辅助转晶（SAC）法合成了粒径均一（180 nm）的纳米ZSM-5颗粒，颗粒间堆积形成大量的开放介孔，与ZSM-5的微孔共同形成多级孔结构。以该材料为载体采用满孔浸渍法制备了负载量为15%（质量分数）的钴催化剂。采用XRD、SEM、TEM、N2物理吸附-脱附等表征技术对多级孔ZSM-5载体及其负载催化剂的形貌和结构进行了表征，并对催化剂的费-托合成催化性能进行了测试。结果表明，相比于大颗粒的ZSM-5和商业ZSM-5，多级孔ZSM-5负载的钴催化剂的费-托合成活性最高，CH4选择性最低，C5-20产物的选择性高达68.9%，这归因于多级孔ZSM-5的介孔孔道有效地促进反应过程中产物的传质扩散以及ZSM-5微孔骨架上的酸中心促进了长链烃产物的二次加氢裂解。Abstract: Uniform ZSM-5 nanoparticles (around 180 nm) were synthesized by steam assisted crystallization method (SAC), which have a hierarchically porous structure, composed of abundant open mesopores from the stacking of ZSM-5 particles and micropores in the ZSM-5 crystallites. The hierarchical ZSM-5 supported cobalt catalyst, with a cobalt loading of 15%, was then prepared through incipient impregnation and used in Fischer-Tropsch synthesis (FTS). The hierarchical ZSM-5 support and Co-based catalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 sorption. The results indicate that the hierarchical ZSM-5 supported cobalt catalyst performs excellently in FTS, since the mesoporous structure in the hierarchical ZSM-5 support can enhance the mass transfer of the reaction products and the acid sites on the microporous ZSM-5 framework can promote the hydrocracking of long chain hydrocarbon products. In comparison with the cobalt catalysts supported on bulk ZSM-5 and commercial ZSM-5, the hierarchical ZSM-5 supported cobalt catalyst exhibits much higher activity in FTS, lower selectivity to CH4, and higher selectivity to C5-20 hydrocarbons (68.9%).
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图 1 载体的XRD谱图
a: ZSM-5-C; b: ZSM-5-H; c: ZSM-5-S
Figure 1 XRD patterns of various supports
图 2 载体的SEM照片
(a): ZSM-5-C; (b): ZSM-5-H; (c): ZSM-5-S
Figure 2 SEM images of various supports
图 4 载体微孔(SF)、介孔(BJH)孔径分布
Figure 4 Micropore (SF, left) and mesopore (BJH, right) size distributions of various supports
图 5 载体的NH3-TPD谱图
a: ZSM-5-C; b: ZSM-5-H; c: ZSM-5-S
Figure 5 NH3-TPD profiles of various supports
图 6 催化剂的XRD谱图
a: 15%Co-ZSM-5-C; b: 15%Co-ZSM-5-H; c: 15%Co-ZSM-5-S
Figure 6 XRD patterns of various catalysts
图 7 催化剂的TEM照片
(a): 15%Co-ZSM-5-C; (b): 15%Co-ZSM-5-H; (c): 15%Co-ZSM-5-S
Figure 7 TEM images of various catalysts
图 8 催化剂的催化活性随反应时间的变化
Figure 8 CO conversions with the time on stream for FTS over various catalysts
表 1 载体的孔结构参数
Table 1 Textural parameters of various supports
表 2 催化剂的费-托合成反应数据性能
Table 2 Performance of various cobalt-based catalysts in FTS
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