Preparation of nanometer CuO-ZnO-ZrO2 catalysts through citrate-gel process and their catalytic properties for methanol synthesis from CO2
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摘要: 采用柠檬酸盐凝胶法制备出纳米CuO-ZnO-ZrO2(CZZ) 催化剂, 应用XPS、BET、XRD、H2-TPR、H2-TPD、CO2-TPD和TG-DTA等检测手段对催化剂及前驱体的结构进行表征.研究了湿凝胶干燥时间和柠檬酸用量对催化剂结构的影响, 并与燃烧法制得的催化剂进行对比, 考察了不同催化剂CO2加氢制甲醇的性能.研究表明, 延长湿凝胶干燥时间可有效防止催化剂焙烧时发生喷溅, 有利于催化剂中各组分的分散, 提高催化剂对H2和CO2的吸附能力; 112℃干燥48h制得的催化剂(CZZ-48h) BET比表面积为43.5m2/g, 高于燃烧法; 柠檬酸用量等于化学计量比时催化剂的性能最佳, 在240℃、2.6MPa、空速为3600h-1、H2/CO2(体积比) 为3的条件下甲醇时空收率达109.4g/(kg·h); 柠檬酸过量会影响催化剂组分的分散度, 并造成分解残留覆盖催化剂表面活性位而不利于CO2加氢反应.
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关键词:
- 柠檬酸盐凝胶法 /
- CuO-ZnO-ZrO2 /
- CO2催化加氢 /
- 甲醇
Abstract: CuO-ZnO-ZrO2(CZZ) nanocatalysts were successfully prepared by citrate-gel method. The catalysts and their precursors were characterized by X-ray photoelectron spectroscopy (XPS), N2 adsorption specific surface area measurement (BET), X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2 and CO2-temperature-programmed desorption (H2 and CO2-TPD) and thermogravimetric analysis (TG-DTA). Drying time of the wet gel and the dosage of citric acid were systematicly studied, while combustion method was also conducted with the comparison of those obtained catalysts. Results show that, prolonged drying process can effectively prevent particle spattering during calcination, benefit the dispersion of different components in the catalyst, and improve the adsorption ability of catalyst for H2 and CO2. Sample CZZ-48h, which was dried at 112℃, 48h, maintained a much higher BET specific surface area than that prepared by combustion method. The CuO-ZnO-ZrO2 catalyst, in which 100% of stoichiometric amount of citric acid was added, exhibited an optimum catalytic behavior with a space-time-yield of methanol 109.4g·h-1·kg-1 under the condition of 240℃, 2.6 MPa, 3600h-1, H2/CO2=3. The detriment of the catalytic performance excessive amounts of citric acid is ascribed to decline dispersion of the catalyst component, and decomposition residual covering on the surface active species of the catalyst.-
Key words:
- citrate-gel process /
- CuO-ZnO-ZrO2 /
- CO2 catalytic hydrogenation /
- methanol
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图 1 不同湿凝胶干燥时间和方式制备催化剂的XRD谱图
Figure 1 XRD patterns of calcined CZZ catalysts prepared from different treatments
●: CuO; ■: ZnO; ▼: ZrO2
图 2 不同湿凝胶干燥时间和方式制备催化剂的SEM照片
Figure 2 SEM micrographs of calcined CZZ catalysts prepared from different treatments
(a): CZZ-24 h; (b): CZZ-48 h; (c): CZZ-72 h; (d): CZZ-bake; (e): CZZ-comb
图 3 不同湿凝胶干燥时间和方式制备催化剂的H2-TPR谱图
Figure 3 H2-TPR patterns of calcined CZZ catalysts prepared from different treatments
图 4 不同湿凝胶干燥时间和方式制备催化剂的H2-TPD谱图
Figure 4 H2-TPD patterns of calcined CZZ catalysts prepared from different treatments
图 5 不同湿凝胶干燥时间和方式制备催化剂的CO2-TPD谱图
Figure 5 CO2-TPD patterns of calcined CZZ catalysts prepared from different treatments
图 6 柠檬酸与催化剂前驱体的TG-DTG曲线
Figure 6 TG and DTG profiles of citric acid and the dried gel of catalysts
(a): citric acid; (b): CZZ-100; (c): CZZ-125; (d): CZZ-150
图 7 催化剂CZZ-100、CZZ-125、CZZ-150的XRD谱图
Figure 7 XRD patterns of CZZ-100、CZZ-125、CZZ-150
●: CuO; ■: ZnO; ▼: ZrO2
图 8 CZZ-100、CZZ-125和CZZ-150催化剂的Cu 2p谱图
Figure 8 XPS patterns of CZZ-100, CZZ-125 and CZZ-150
表 1 不同Cu-ZnO-ZrO2催化剂的催化性能
Table 1 Catalytic properties of different Cu-ZnO-ZrO2 catalysts
Catalyst CO2
conversation
x/%CH3OH
selectivity
s/%WTY of CH3OH
/(g· kg-1· h-1)CZZ-24 h 22.2 27.4 78.3 CZZ-48 h 22.3 38.1 109.4 CZZ-72 h 24.5 33.5 105.6 CZZ-bake 19.9 23.9 44.4 CZZ-comb 12.9 26.8 61.3 CZZ-125 26.4 24.5 83.2 CZZ-150 27.0 23.6 81.9 reaction conditions: t=240 ℃, p=2.6 MPa, WHSV=3 600 h-1, and CO2/H2(mol ratio)=1:3 
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表 2 不同凝胶干燥时间和方式制备CZZ催化剂的物化性质
Table 2 Physicochemical properties of calcined CZZ catalysts
Catalyst ABET
/(m2·g-1)v
/(cm3·g-1)CuO crystallite size
d /nmCZZ-24 h 38.7 0.20 14.9 CZZ-48 h 43.5 0.17 11.8 CZZ-72 h 39.7 0.09 12.0 CZZ-bake 15.9 0.09 23.9 CZZ-comb 16.3 0.06 16.2
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表 3 催化剂的还原峰温度及还原峰在H2-TPR谱图中所占的面积比例
Table 3 Temperatures of reduction peaks and their contributions to the H2-TPR profiles over catalysts
Catalyst tα /℃ tβ /℃ Aα/(Aα+Aβ) /% CZZ-24 h 238 257 72 CZZ-48 h 235 257 75 CZZ-72 h 232 257 73 CZZ-bake 226 257 59 CZZ-comb 230 257 74 Aα and Aβ represent the areas of α and β peaks，respectively
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表 4 不同柠檬酸用量制备CuO-ZnO-ZrO2的XPS数据
Table 4 Surface concentrations of CZZ catalysts prepared from different amounts of citric acid
Catalyst Surface concentrations wat/% Cu 2p Zn 2p Zr 3d C 1s O 1s CZZ-100 19.6 11.9 6.0 0 62.6 CZZ-125 17.1 10.3 4.1 15.2 53.3 CZZ-150 16.2 9.0 4.1 13.3 57.5
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