Preparation of ZrO2 modified Al2O3 nano-sheets supported cobalt catalyst and its performance in Fischer-Tropsch synthesis
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摘要: 通过水热法合成了Al2O3纳米片（Al2O3-CN），采用浸渍法制备20%（质量分数）钴基催化剂，并应用于费托合成反应。制备的Al2O3-CN（226 m2/g）与商业氧化铝（Al2O3-C，249 m2/g）具有相近的比表面积，但Al2O3-CN孔尺寸分布更加集中。浸渍钴后，与Co/Al2O3-C催化剂相比，Co/Al2O3-CN催化剂表现出较高的还原度及更均匀的钴颗粒粒径分布。因此，Co/Al2O3-CN催化剂表现出更高的CO转化率和低的甲烷选择性。为了进一步提高Co/Al2O3-CN的催化性能，采用不同含量ZrO2对Al2O3-CN进行修饰。表征结果表明，随着ZrO2修饰量的增加，Al2O3-CN载体比表面积变化不明显，孔体积和孔径增大；相对应催化剂的钴颗粒粒径减小，活性位点数目增加。在相同反应条件下，经ZrO2修饰催化剂CO转化率进一步提高，甲烷选择性降低。Abstract: Al2O3 nano-sheet (Al2O3-CN) was synthesized under hydrothermal condition. The cobalt-based catalyst of 20% (mass fraction) was prepared by impregnation method and applied to Fischer-Tropsch synthesis. The Al2O3-CN (226 m2/g) and commercial alumina (Al2O3-C, 249 m2/g) have similar specific surface area, but Al2O3-CN has more narrow pore size distribution. Compared with Co/Al2O3-C catalyst, Co/Al2O3-CN catalyst showed higher reduction degree and more uniform cobalt particle size distribution after impregnation. Thus, Co/Al2O3-CN catalyst exhibited higher CO conversion and lower methane selectivity. In order to further improve the catalytic performance of Co/Al2O3-CN, Al2O3-CN was modified with ZrO2. The characterization results showed that with the increase of ZrO2, the specific surface of Al2O3-CN did not change significantly, and the pore volume and pore diameter increased. The cobalt particle size decreased and the number of active sites increased. Under the same reaction conditions, the CO conversion rate of catalysts modifield by ZrO2 was farther improved and selectivity of methane was decreased.
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Key words:
- Fischer-Tropsch synthesis /
- zirconium additives /
- alumina /
- nano-sheets
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图 1 载体的SEM照片
Figure 1 SEM images of the supports
(a): Al2O3-C; (b): Al2O3-CN; (c): Al2O3-2.5Zr-CN; (d): Al2O3-5Zr-CN; (e): Al2O3-7.5Zr-CN; (f): Al2O3-10Zr-CN
图 2 不同反应时间的SEM照片
Figure 2 SEM images of different reaction times
(a): 1.5 h; (b): 2 h; (c): 3 h
图 3 载体N2吸附-脱附等温线及孔径分布
Figure 3 N2-sorption isotherms and pore size distribution of the supports
a: Al2O3-C; b: Al2O3-CN; c: Al2O3-2.5Zr-CN; d: Al2O3-5Zr-CN; e: Al2O3-7.5Zr-CN; f: Al2O3-10Zr-CN
图 4 载体的XRD谱图
Figure 4 XRD patterns of the supports
a: Al2O3-C; b: Al2O3-CN; c: Al2O3-2.5Zr-CN; d: Al2O3-5Zr-CN; e: Al2O3-7.5Zr-CN; f: Al2O3-10Zr-CN
图 5 载体的EDS照片
Figure 5 EDS photos of the supports
(a): Al2O3-2.5Zr-CN; (b): Al2O3-10Zr-CN
图 6 催化剂的XRD谱图
Figure 6 XRD patterns of the catalysts
a: Co/Al2O3-C; b: Co/Al2O3-CN; c: Co/Al2O3-2.5Zr-CN; d: Co/Al2O3-5Zr-CN; e: Co/Al2O3-7.5Zr-CN; f: Co/Al2O3-10Zr-CN
图 7 催化剂的TEM照片
Figure 7 TEM images of the catalysts
(a), (d): Co/Al2O3-C; (b), (e): Co/Al2O3-CN; (c), (f): Co/Al2O3-10Zr-CN
图 8 催化剂的H2-TPR谱图
Figure 8 H2-TPR profiles of various catalysts
a: Co/Al2O3-C; b: Co/Al2O3-CN; c: Co/Al2O3-2.5Zr-CN; d: Co/Al2O3-5Zr-CN; e: Co/Al2O3-7.5Zr-CN; f: Co/Al2O3-10Zr-CN
图 9 催化剂Co 2p XPS谱图
Figure 9 Co 2p XPS spectra of various catalysts
a: Co/Al2O3-C; b: Co/Al2O3-CN; c: Co/Al2O3-2.5Zr-CN; d: Co/Al2O3-5Zr-CN; e: Co/Al2O3-7.5Zr-CN; f: Co/Al2O3-10Zr-CN
表 1 ZrO2在载体中的含量分析
Table 1 Quantitative analysis of the ZrO2 in the supports
Catalyst ZrO2 w/% XPS ICP Al2O3-2.5Zr-CN 11.9 2.2 Al2O3-5Zr-CN 14.6 5.7 Al2O3-7.5Zr-CN 15.3 7.5 Al2O3-10Zr-CN 17.4 10.1 
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表 2 载体和催化剂的物化性质
Table 2 Physico-chemical properties of the supports and the catalysts
Sample ABET/
(m2·g-1)vpore/
(cm3·g-1)dpore/
nmCo crystalline a
/nmH2-TPR reducibilityb/% H2-TPD dispersionc
/%Co0accd
(10-2mol·gcat-1)Al2O3-C 249 0.75 10.1 - - - - Al2O3-CN 226 0.29 6.3 - - - - Al2O3-2.5Zr-CN 186 0.29 7.5 - - - - Al2O3-5Zr-CN 179 0.29 6.3 - - - - Al2O3-7.5Zr-CN 181 0.26 7.1 - - - - Al2O3-10Zr-CN 192 0.28 6.8 - - - - Co/Al2O3-C 176 0.49 10.3 9.3 30.1 7.5 5.06 Co/Al2O3-CN 142 0.25 10.6 10.6 36.0 5.5 3.70 Co/Al2O3-2.5Zr-CN 138 0.35 11.7 9.9 38.9 6.0 4.04 Co/Al2O3-5Zr-CN 137 0.35 12.8 9.4 40.3 6.1 4.16 Co/Al2O3-7.5Zr-CN 146 0.39 15.0 8.9 42.8 6.6 4.50 Co/Al2O3-10Zr-CN 132 0.31 13.3 8.6 38.9 6.7 4.60 a: d(Co) = 0.75 d(Co3O4); b: calculated by H2-TPR from 373 to 673 K; c, d: calculated from H2 chemisorption
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表 3 催化剂的表面组成
Table 3 Surface composition of the catalysts
Catalyst Co 2p3/2 EB/eV ICSS/
ICo3O4Co3O4 cobalt surface species Co/Al2O3-C 780.085 781.898 0.862 Co/Al2O3-CN 780.228 782.070 0.786 Co/Al2O3-2.5Zr-CN 780.202 782.034 0.736 Co/Al2O3-5Zr-CN 780.160 782.031 0.716 Co/Al2O3-7.5Zr-CN 780.109 781.828 0.697 Co/Al2O3-10Zr-CN 780.039 781.927 0.712
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表 4 不同催化剂的费托反应性能
Table 4 Performance of different catalysts on Fischer-Tropsch synthesis
Catalyst Temperature t/℃ CO conversion x/% Hydrocarbon selectivity s/% TOF/(10-3·s-1) CH4 C2-4 C5+ Co/Al2O3-C 200 22.8 13.9 12.0 74.1 5.0 210 49.6 14.1 13.1 72.8 10.7 Co/Al2O3-CN 200 42.0 8.0 10.0 81.9 13.2 Co/Al2O3-2.5Zr-CN 200 53.7 7.3 9.2 83.5 16.4 Co/Al2O3-5Zr-CN 200 58.5 6.8 9.0 84.2 18.2 Co/Al2O3-7.5Zr-CN 200 79.3 6.5 8.9 84.6 20.7 Co/Al2O3-10Zr-CN 200 78.9 7.6 8.7 83.7 20.3 reaction conditions: H2/CO(molar ratio)=2.0, GHSV=1000 h-1, p=2.0 MPa, time on stream=48 h
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