Preparation of layered K/Mg-Fe-Al catalysts and its catalytic performances in CO hydrogenation
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摘要: 采用共沉淀法制备了系列不同Mg/Fe/Al配比MgFeAl-HTLcs前驱体,经焙烧、浸渍K改性、二次焙烧后用于CO加氢反应。采用N2吸附-脱附、SEM、TG、XRD、H2-TPR、XPS等手段对催化剂进行了表征。结果表明,共沉淀法制备的不同配比MgFeAl-HTLcs类水滑石前躯体均具有典型层状结构;焙烧后生成MgO、Fe2O3以及少量MgFeAlO4物相,三组元间相互作用增强,反应后以MgCO3和Fe3O4物相为主,同时出现较弱的Fe5C2相;K改性后发生结构重构,热稳定性增强,且随Al含量增加,比表面积显著单调下降;与K/Mg-Fe相比,K/Mg-Fe-Al样品中Fe2O3到Fe3O4的还原受到抑制;二次焙烧后,反应前表面相对富Fe,反应后表面富K。在CO加氢反应中,K/Mg-Fe-Al系列催化剂均表现出较高的反应活性以及烯烃选择性,随Fe/Al配比相对增加,C5+含量呈降低趋势,O/P值增加;与K/1.5Mg-0.67Fe相比,K/1.5Mg-0.67Fe-0.33Al催化剂C5+含量由22.17%降至10.90%,C2-4=含量由40.98%提高至47.28%。
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关键词:
- 费托合成 /
- K/Mg-Fe-Al催化剂 /
- CO加氢 /
- 低碳烯烃
Abstract: A series of K promoted K/MgFeAl-HTLcs catalysts with different Mg/Fe/Al molar ratios were prepared by means of coprecipitation and impregnation method for direct synthesis of light olefins from CO hydrogenation. The samples were characterized by XRD, N2 adsorption-desorption, SEM, TG, H2-TPR and XPS measurements. The results show that MgFeAl-HTLcs catalyst precursors has typical layered structure. MgO, Fe2O3 and small amount of MgFeAlO4 are formed after calcination. MgCO3 and Fe3O4 could be observed after reaction, and a little Fe5C2 iron carbide with broad and weak peaks appear simultaneously. Thermal stability of K/MgFeAl-HTLcs is improved due to recovery of hydrotalcite-like structure after K promotion. With increase of Al content, specific surface area of the precursors decreases monotonically after structure reconstruction. Reduction of Fe2O3 to Fe3O4 is inhibited with addition of Al, compared with K/Mg-Fe sample. Fe enrichment before reaction and K enrichment after reaction are observed on secondary calcination samples. During CO hydrogenation, the prepared samples show high activity and C2-4= selectivity with low C5+ weight fraction. C5+ hydrocarbons decrease and olefin selectivity increases with increasing Fe/Al molar ratio. The C5+ decreases from 22.17% to 10.90%, and C2-4= weight content increases from 40.98% to 47.28% on K/1.5Mg-0.67Fe-0.33Al sample compared with that of K/1.5Mg-0.67Fe sample.-
Key words:
- Fischer-Tropsch synthesis /
- K/Mg-Fe-Al catalyst /
- CO hydrogenation /
- light olefins
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表 1 催化剂的织构性质
Table 1 Textural properties of the catalysts
Catalyst BET surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Average pore size d/nm 1.5Mg-0.67Fe-0.33Al 83.06 0.60 28.39 K/1.5Mg-0.2Fe-0.8Al 131.09 0.23 7.11 K/1.5Mg-0.2Fe-0.8Al-Ha 11.00 0.05 18.91 K/1.5Mg-0.33Fe-0.67Al 167.58 0.25 5.96 K/1.5Mg-0.33Fe-0.67Al-Ha 15.74 0.05 13.07 K/1.5Mg-0.5Fe-0.5Al 116.85 0.21 7.26 K/1.5Mg-0.67Fe-0.33Al 49.84 0.16 12.50 K/1.5Mg-0.67Fe-0.33Al-Ha 33.20 0.08 9.78 K/1.5Mg-0.8Fe-0.2Al 64.56 0.20 12.38 K/1.5Mg-0.8Fe-0.2Al-Ha 17.32 0.06 13.19 K/1.5Mg-0.67Fe 103.15 0.24 9.37 K/1.5Mg-0.67Fe-Ha 50.95 0.10 7.86 K/2.0Mg-0.67Fe-0.33Al 83.14 0.19 9.28 K/3.0Mg-0.67Fe-0.33Al 84.77 0.19 9.06 a: K promoted samples without calcination 表 2 不同条件下催化剂的表面组成
Table 2 Surface composition of different samples
Sample Surface atom content wartom/%a Mg Fe Al K O C Mg/Fe Fe/Al Fe/K K/1.5Mg-0.2Fe-0.8Alb 17.20 0.84 10.33 - 53.94 17.69 20.48 0.08 - K/1.5Mg-0.2Fe-0.8Al-Hb 17.04 1.18 8.80 0.14 55.25 17.60 14.44 0.13 8.43 K/1.5Mg-0.67Fe-0.33Alb 17.87 3.66 5.90 0.29 53.03 19.26 4.88 0.62 12.62 K/1.5Mg-0.67Fe-0.33Al-Hb 19.60 4.45 4.18 0.31 51.94 19.53 4.40 1.06 14.35 K/1.5Mg-0.8Fe-0.2Alb 18.96 6.57 5.14 0.38 53.95 15.00 2.89 1.28 17.29 K/1.5Mg-0.67Feb 21.89 9.00 - 0.26 52.31 16.55 2.43 - 34.62 K/2.0Mg-0.67Fe-0.33Alb 21.60 4.81 5.88 0.25 54.20 13.27 4.49 0.82 19.24 K/1.5Mg-0.2Fe-0.8Alc 9.73 0.63 11.95 - 40.49 37.21 15.44 0.05 - K/1.5Mg-0.2Fe-0.8Al-Hc 8.78 0.45 7.56 - 31.47 51.75 19.51 0.06 - K/1.5Mg-0.67Fe-0.33Alc 1.16 0.36 1.63 0.22 17.35 79.29 3.22 0.22 1.64 K/1.5Mg-0.67Fe-0.33Al-Hc 14.84 3.00 5.95 0.17 43.70 32.35 4.95 0.50 17.65 K/1.5Mg-0.8Fe-0.2Alc 1.84 0.77 1.96 0.48 22.98 71.97 2.39 0.39 1.60 K/1.5Mg-0.67Fec 1.84 0.56 - 0.62 18.44 78.54 3.29 - 0.90 K/2.0Mg-0.67Fe-0.33Alc 3.56 0.81 2.43 0.15 23.14 78.54 4.40 0.33 5.40 a: calculated from the peak area of XPS spectra; b: fresh samples; c: used samples 表 3 催化剂的CO加氢反应性能
Table 3 Catalytic performance of the catalysts
Catalyst CO Conv. x/% Selectivity s/% Product w/% O/P CH4 CO2 CH4 C2-4= C2-40 C5+ K/1.5Mg-0.2Fe-0.8Al 87.78 15.71 24.36 29.18 39.51 18.63 12.68 2.12 K/1.5Mg-0.33Fe-0.67Al 82.60 20.22 16.55 30.62 35.92 19.30 14.15 1.86 K/1.5Mg-0.5Fe-0.5Al 77.86 20.76 14.73 29.48 41.79 15.88 12.85 2.63 K/1.5Mg-0.67Fe-0.33Al 69.47 22.41 10.06 30.48 47.28 11.35 10.90 4.16 K/1.5Mg-0.67Fe-0.33Al-H 96.70 12.53 18.18 30.57 38.61 18.43 12.39 2.10 K/1.5Mg-0.8Fe-0.2Al 73.09 22.57 15.94 32.88 46.18 10.73 10.21 4.30 K/1.5Mg-0.8Fe-0.2Al-H 74.97 23.50 14.99 33.22 44.40 11.59 10.79 3.83 K/2.0Mg-0.67Fe-0.33Al 67.54 28.14 8.11 35.52 42.01 12.79 9.68 3.29 K/3.0Mg-0.67Fe-0.33Al 61.13 29.67 5.90 35.30 41.17 13.52 10.01 3.05 K/1.5Mg-0.67Fe 81.45 22.04 10.11 27.00 40.98 9.86 22.17 4.16 K/1.5Mg-0.67Fe-H 93.39 12.64 32.06 20.86 35.87 10.50 32.77 3.41 reaction conditions: H2/CO=2, GHSV=1 000 h-1, t=320 ℃, p=1.5 MPa; -
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