Effect of impregnation sequence of Ce on the performance of Cu/Zn-Al catalysts derived from hydrotalcite precursor in methanol steam reforming
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摘要: 采用原位合成法在γ-Al2O3载体上合成了锌铝水滑石，再经浸渍法制备了Cu/Zn-Al、Ce/Cu/Zn-Al、Cu/Ce/Zn-Al和Cu-Ce/Zn-Al催化材料，使用XRD、XRF、SEM、氮吸附，XPS、H2-TPR和N2O滴定等手段对其进行了表征，探讨了Ce的浸渍顺序对Cu/Zn-Al水滑石衍生材料甲醇水蒸气重整制氢反应催化性能的影响。结果表明，Ce的浸渍顺序主要影响催化剂的还原性质，进而影响了其催化性能。其中，Ce/Cu/Zn-Al催化剂的催化性能最佳，在250℃、水醇物质的量比为1.2、甲醇气体空速为800 h-1的条件下，甲醇转化率达到100%；与Cu/Zn-Al催化剂相比，甲醇转化率提高了近40%。Abstract: ZnAl-LDHs was prepared by in-situ synthesis method on γ-Al2O3 and the Cu/Zn-Al, Ce/Cu/Zn-Al, Cu/Ce/Zn-Al and Cu-Ce/Zn-Al catalysts were then obtained by wet impregnation method for methanol steam reforming. The catalysts were characterized by XRD, XRF, SEM, N2 sorption, XPS, H2-TPR and N2O titration; the effect of impregnation sequence of Ce on the performance of the Cu/Zn-Al catalysts in methanol steam reforming to produce hydrogen was investigated. The results showed that the impregnation sequence of Ce has a significant influence on the reducibility of resultant catalyst, which subsequently affects the catalytic performance. The Ce/Cu/Zn-Al catalyst exhibits the highest activity; over it, the methanol conversion reaches 100% under 250℃ and with a water/methanol molar ratio of 1.2 and gas hourly space velocity of 800 h-1, which is almost 40% higher than that achieved on the Cu/Zn-Al catalyst.
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Key words:
- impregnation sequence /
- hydrotalcite /
- ceria /
- methanol steam reforming /
- hydrogen
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图 1 γ-Al2O3和Zn-Al-LDHs/γ-Al2O3的XRD谱图
Figure 1 XRD patterns of γ-Al2O3 and Zn-Al-LDHs/γ-Al2O3
a: γ-Al2O3; b: Zn-Al-LDHs/γ-Al2O3
图 2 不同浸渍顺序制备催化剂的XRD谱图
Figure 2 XRD patterns of the catalysts prepared with different impregnation sequences
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al; c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
▼: CeO2; ■: ZnO; ▲: CuO; ◆: Al2O3
图 3 γ-Al2O3和Zn-Al-LDHs/γ-Al2O3的SEM照片
Figure 3 SEM image of γ-Al2O3 and Zn-Al-LDHs/γ-Al2O3
(a): γ-Al2O3; (b): Zn-Al-LDHs/γ-Al2O3
图 4 不同浸渍顺序催化剂的H2-TPR谱图
Figure 4 H2-TPR profiles of the catalysts prepared with different impregnation sequences
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al; c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 5 催化剂Cu 2p的XPS谱图
Figure 5 Cu 2p XPS spectra of various catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al;
c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 6 催化剂的Cu俄歇电子能谱谱图
Figure 6 Cu Auger spectra of various catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al;
c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 7 催化剂Ce 3d的XPS谱图
Figure 7 Ce 3d XPS spectra of the catalysts
a: Ce/Cu/Zn-Al; b: Cu-Ce/Zn-Al; c: Cu/Ce/Zn-Al
图 8 催化剂Zn 2p的XPS谱图
Figure 8 Zn 2p XPS spectra of the catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al;
c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 9 催化剂Al 2p的XPS谱图
Figure 9 Al 2p XPS spectra of the catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al;
c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 10 催化剂O 1s的XPS谱图
Figure 10 O 1s XPS spectra of the catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al;
c: Cu-Ce/Zn-Al; d: Cu/Ce/Zn-Al
图 11 反应温度对催化剂性能的影响
Figure 11 Catalytic activity (methanol conversion) as a function of reaction temperature for the methanol steam reforming over various catalysts
a: Cu/Zn-Al; b: Ce/Cu/Zn-Al; c: Cu-Ce/Zn-Al;
d: Cu/Ce/Zn-Al; e: equil(reaction conditions:
W/M=1.2:1, GHSV=800 h-1, no carrier gas)表 1 不同浸渍顺序催化剂的元素含量
Table 1 Components of the catalysts prepared with different impregnation sequences
Catalyst Element content w/% Cu Zn Al Ce O Cu/Zn-Al 9.66 14.60 36.90 - 38.84 Ce/Cu/Zn-Al 9.19 13.88 35.42 3.50 38.01 Cu-Ce/Zn-Al 8.68 13.59 35.80 3.74 38.19 Cu/Ce/Zn-Al 8.98 13.44 35.70 3.73 38.15 
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表 2 催化剂的物化性质及其催化甲醇水蒸气重整反应中氢气产率
Table 2 Physical characteristics of the prepared catalysts and and their hydrogen production rate in methanol steam reforming
Catalyst ABET
/(m2·g-1)Pore volume
v/(cm3·g-1)dCuO
/nmCu dispersiona
/%Cu surface areaa
A/(m2·g-1)H2 production rateb
/(cm3·kg-1·s-1)Cu/Zn-Al 147.0 0.47 34 10.3 5.9 446.2 Ce/Cu/Zn-Al 109.6 0.41 23 11.5 6.3 810.7 Cu-Ce/Zn-Al 96.4 0.46 24 11.1 6.1 673.1 Cu/Ce/Zn-Al 101.5 0.43 24 11.3 6.2 723.3 a: Cu dispersion and Cu surface area are determined by N2O sorption;
b: the reactions are carried out under atmospheric pressure, 240 ℃, water/methanol ratio of 1.2, GHSV of 800 h-1; no carrier gas was used
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表 3 高斯拟合后还原峰位置
Table 3 Positions of the reduction peaks by a Gauss fit of the H2-TPR profiles
Catalyst Peak position t/℃ peak 1 peak 2 peak 3 Cu/Zn-Al 266 324 - Ce/Cu/Zn-Al 242 266 281 Cu-Ce/Zn-Al 276 288 - Cu/Ce/Zn-Al 254 294 306
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表 4 甲醇转换率大致相同时CO浓度和选择性
Table 4 Comparison of CO molar concentration and selectivity at similar methanol conversion
Catalyst Conversion x/% CO molar concentration/% CO selectivity s/% Temperature t/℃ Cu/Zn-Al 93 0.60 2.4 280 Ce/Cu/Zn-Al 92 0.22 0.9 240 Cu-Ce/Zn-Al 85 0.44 1.8 260 Cu/Ce/Zn-Al 88 0.92 3.6 250
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