Effect of calcination temperature on the catalytic performance of the hydrotalcite derived Ce/Cu/Zn-Al catalysts for hydrogen production via methanol steam reforming
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摘要: 采用原位合成法在γ-Al2O3载体表面上合成了Zn-Al水滑石，再采用顺序浸渍法制备了一系列Ce/Cu/Zn-Al催化剂，并采用XRD、BET、H2-TPR和XPS等手段对催化剂进行了表征，考察了焙烧温度对Ce/Cu/Zn-Al催化剂表面结构及其催化甲醇水蒸气重整制氢性能的影响。结果表明，焙烧温度主要影响了催化剂的Cu比表面积、表面氧空穴含量和Cu-Ce间相互作用。当焙烧温度为500℃时，催化剂Cu的比表面积较大，表面氧空穴含量较多，Cu-Ce间相互作用较强，因此，催化甲醇水蒸气重整制氢活性较好。当焙烧温度升高到700℃时，Cu物种主要以稳定的CuAl2O4尖晶石形式存在，不利于甲醇水蒸气重整制氢反应的进行，因此，催化活性较差。Abstract: ZnAl-LDHs was prepared by in-situ synthesis method on the surface of γ-Al2O3, and then a series Ce/Cu/Zn-Al catalysts were prepared by ordinal wet impregnation method. All the catalysts were characterized by XRD, BET, H2-TPR and XPS to investigate the effects of calcination temperature on the surface structure of Ce/Cu/Zn-Al catalyst and its catalytic performance in methanol steam reforming. The results showed that calcination temperature mainly influenced the specific surface area of copper, surface oxygen vacancy content and the interaction between Cu and Ce. When the calcination temperature is 500℃, the specific surface area of Cu is larger, the content of oxygen vacancy is higher and the interaction between Cu and Ce is stronger. Therefore, the catalytic activity of the catalysts for methanol steam reforming is the best. When the calcination temperature rises to 700℃, the Cu species mainly exist in the form of stable CuAl2O4 spinel, which is not conducive to the reaction of methanol steam reforming, resulting in lower catalytic activity.
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Key words:
- calcination temperature /
- hydrotalcite /
- Cu-Al spinel /
- methanol steam reforming /
- hydrogen
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图 1 不同焙烧温度下制备催化剂的XRD谱图
Figure 1 XRD patterns of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 2 不同焙烧温度下制备催化剂的H2-TPR谱图
Figure 2 H2-TPR profiles of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 3 不同焙烧温度下制备催化剂的Zn 2p的XPS谱图
Figure 3 Zn 2p XPS spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 4 不同焙烧温度下制备催化剂的Al 2p的XPS谱图
Figure 4 Al 2p XPS spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 5 不同焙烧温度下制备催化剂的Cu 2p的XPS谱图
Figure 5 Cu 2p XPS spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 6 不同焙烧温度下制备催化剂的Cu俄歇谱图
Figure 6 Cu Auger spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 7 不同焙烧温度下制备催化剂的Ce 3d的XPS谱图
Figure 7 Ce 3d XPS spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 8 不同焙烧温度下制备催化剂的O 1s的XPS谱图
Figure 8 O 1s XPS spectra of the catalysts calcined at various temperatures
a: Ce/Cu/Zn-Al-400; b: Ce/Cu/Zn-Al-500; c: Ce/Cu/Zn-Al-600; d: Ce/Cu/Zn-Al-700
图 10 反应温度对催化剂CO浓度的影响
Figure 10 CO molar concentration as a function of the reaction temperature
: Ce/Cu/Zn-Al-400; : Ce/Cu/Zn-Al-500; : Ce/Cu/Zn-Al-600; : Ce/Cu/Zn-Al-700; : thermodynamic equilibrium
(reaction conditions: W/M=1.2 :1, GHSV=800 h-1, no carrier gas)表 1 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 1 Physical characteristics of the prepared catalysts and hydrogen production rate in methanol steam reforming
Catalyst ABET
/(m2·g-1)Pore volume
v/(cm3·g-1)Pore size
d/nmCu dispersiona/% Cu surface areaa
A/(m2·g-1)H2 production rateb
/(cm3·kg-1·s-1)Ce/Cu/Zn-Al-400 84.7 0.35 15.6 4.8 2.7 603.3 Ce/Cu/Zn-Al-500 109.6 0.41 15.3 11.5 \6.3 810.7 Ce/Cu/Zn-Al-600 77.2 0.38 18.8 3.7 2.0 505.4 Ce/Cu/Zn-Al-700 72.2 0.37 20.7 2.7 1.5 330.3 a: determined by N2O experiments;
b: reaction conditions: atmospheric, 240 ℃, W/M=1.2 : 1, GHSV=800 h-1, no carrier gas
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表 2 不同焙烧温度下制备催化剂的Ce 3d和O 1s XPS拟合结果
Table 2 Ce 3d and O 1s XPS curve-fitting results of catalysts calcined at various temperatures
Catalyst Ce3+ /(Ce3++ Ce4+)/% Oads/(Oads+O-OH+Olatt)w/% Ce/Cu/Zn-Al-400 21.77 0.62 Ce/Cu/Zn-Al-500 21.89 0.40 Ce/Cu/Zn-Al-600 21.61 0.39 Ce/Cu/Zn-Al-700 20.58 0.27
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