Preparation of Fe3O4@PI and its catalytic performances in Fischer-Tropsch synthesis
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摘要: 分别采用水热、水热-包覆、球磨法制备了Fe3O4、聚酰亚胺（PI）改性的Fe3O4@PI和Fe3O4-PI催化剂用于费托合成反应，对比研究了PI改性及其含量变化对Fe基催化剂催化CO加氢产物分布的影响规律。结合XRD、SEM、TEM、H2-TPR、CO-TPD、FT-IR、XPS、TG和接触角实验等手段对催化剂样品进行了表征。结果表明，Fe3O4、Fe3O4@PI和Fe3O4-PI样品均为球形颗粒；PI改性促进了Fe3O4的还原，亲水性增强。Fe3O4@PI样品中，PI均匀包覆于Fe3O4表面，具有较好的热稳定性；与Fe3O4、Fe3O4-PI相比，Fe3O4@PI样品CO吸附增强。在CO加氢反应中，与Fe3O4相比，PI改性的Fe3O4@PI和Fe3O4-PI样品催化活性下降，二次加氢能力受到抑制，烯烃选择性提高；Fe3O4@PI样品烯烃选择性增加明显，烯烷比（O/P）由改性前的0.50提高至2.15；适宜含量的PI改性促进C5+烃生成。
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关键词:
- Fe3O4@PI催化剂 /
- 费托合成 /
- 低碳烯烃 /
- 产物分布
Abstract: Polyimide (PI) modified Fe3O4@PI and Fe3O4-PI catalyst samples were prepared by hydrothermal-coating and ball milling methods, respectively. The effect of PI modification on the product distribution of the Fe-based catalysts for Fischer-Tropsch synthesis was investigated. The catalysts were characterized by XRD, SEM, TEM, H2-TPR, CO-TPD, FT-IR, XPS, TG and contact angle measurements. The results showed that Fe3O4, Fe3O4@PI and Fe3O4-PI were spherical with uniform particle size, and the Fe3O4@PI particle size was smaller. PI modification promoted the reduction and the hydrophilicity of Fe3O4. For Fe3O4@PI sample, PI was uniformly coated on Fe3O4 surface, which led to good thermal stability. Compared with Fe3O4 and Fe3O4-PI samples, CO adsorption was promoted on Fe3O4@PI. Compared with Fe3O4, the catalytic activity of Fe3O4@PI and Fe3O4-PI decreased, and the secondary hydrogenation ability was inhibited, resulting in increase of olefin selectivity. For Fe3O4@PI, the olefin selectivity was enhanced significantly with olefin to alkane ratio in C2-4 fraction increased from 0.50 to 2.15. PI modification with suitable content favored the formation of C5+ hydrocarbons.-
Key words:
- Fe3O4@PI catalyst /
- Fischer-Tropsch synthesis /
- light olefins /
- product distribution
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图 2 样品的SEM照片
Figure 2 SEM images of the fresh catalyst samples
(a): Fe3O4; (b): Fe3O4@PI-1;(c): Fe3O4@PI-2;(d): Fe3O4@PI-3;(e): Fe3O4-PI
图 3 样品的TEM照片
Figure 3 TEM images of the fresh catalyst samples
(a): Fe3O4; (b): Fe3O4@PI-1;(c): Fe3O4@PI-2;(d): Fe3O4@PI-3;(e): Fe3O4-PI
图 8 催化剂样品的接触角
Figure 8 Contact angle of the catalyst samples
(a): Fe3O4; (b): Fe3O4-PI; (c): Fe3O4@PI-1; (d): Fe3O4@PI-2; (e): Fe3O4@PI-3
图 9 反应前后催化剂样品的XPS全谱图
Figure 9 XPS survey spectra of the fresh (a) and used (b) catalyst samples
a: Fe3O4; b: Fe3O4@PI-1; c: Fe3O4@PI-2; d: Fe3O4@PI-3; e: Fe3O4-PI
图 10 Fe 2p反应前后样品的XPS谱图
Figure 10 Fe 2p XPS spectra of the fresh:
a: Fe3O4; b: Fe3O4@PI-1; c: Fe3O4@PI-2; d: Fe3O4@PI-3; e: Fe3O4-PI and used: f: Fe3O4; g: Fe3O4@PI-1; h: Fe3O4@PI-2; i: Fe3O4@PI-3; j: Fe3O4-PI catalyst samples
图 11 催化剂CO加氢反应性能
Figure 11 Catalytic performances of the catalyst samples
reaction conditions: 300℃, 1.5 MPa, 1000h-1, H2/CO=2, TOS=45h
表 1 样品表面元素组成
Table 1 Surface composition of the fresh and used catalyst samples
Catalyst Surface atom content wmol/%a Fe C O N Fe3O4 3.82 23.15 73.03 - Fe3O4@PI-1 6.07 56.80 32.02 5.11 Fe3O4@PI-2 10.24 48.71 36.95 4.10 Fe3O4@PI-3 10.61 47.65 37.51 4.23 Fe3O4-PI 5.30 68.62 24.50 1.58 AR-Fe3O4 12.49 52.03 35.48 - AR-Fe3O4@PI-1 19.41 42.09 36.75 1.75 AR-Fe3O4@PI-2 16.24 42.74 39.31 1.71 AR-Fe3O4@PI-3 23.47 27.38 47.02 2.13 AR-Fe3O4-PI 21.91 32.95 43.65 1.49 a: calculated from the peak area of XPS spectra 
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