One-pot synthesis of CexZr1-xO2 solid solution catalysts for the splitting of CO2 to CO via thermochemical cycling
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摘要: 采用一锅蒸发诱导自组装法（EISA）制备了一系列不同铈锆物质的量比的铈锆固溶体催化剂，用TGA研究了其热化学循环分解CO2制CO的催化性能，并采用XRD、Raman光谱、H2-TPR、XPS、SEM和N2吸附-脱附等手段对催化剂的物相结构、还原性能和表面化学性质进行了表征分析，用热重分析（TGA）研究了铈锆固溶体对热化学循环分解CO2制CO的催化性能。结果表明，随着Ce/Zr物质的量比增加，铈锆固溶体催化剂的CO2高温分解活性先增大后减小。Ce/Zr物质的量比为1的Ce0.5Zr0.5O2催化剂由于具有较多的晶格缺陷和氧空穴，氧迁移能力强，催化活性高，而Ce/Zr物质的量比为3的Ce0.75Zr0.25O2催化剂具有相对稳定的氧空穴数，循环稳定性好。循环反应后，所有的催化剂均出现了一定程度的烧结，且富锆固溶体发生了相分离，这可能会影响催化剂的性能。
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关键词:
- CexZr1-xO2 /
- CO2分解 /
- 热化学循环 /
- 氧空穴
Abstract: A series of CeO2-ZrO2 solid solutions with different Ce/Zr molar ratios were synthesized by one-pot evaporation-induced self-assembly (EISA) method and characterized by XRD, Raman spectroscopy, H2-TPR, XPS, SEM and N2 sorption. The catalytic activity of CeO2-ZrO2 solid solutions in the thermochemical splitting of CO2 to CO were investigated by thermogravimetric analysis. The results reveal that with the increase of Ce/Zr molar ratio, the catalytic activity of CeO2-ZrO2 in CO2 splitting increases first and then decreases. The Ce0.5Zr0.5O2 solution with a Ce/Zr molar ratio of 1 exhibits high activity in CO2 splitting, owing to its abundant lattice defects and oxygen vacancies which can promote the oxygen migration. In contrast, the Ce0.75Zr0.25O2 solution with a Ce/Zr molar ratio of 3 shows the best cyclic stability, due to its relatively stable number of oxygen vacancies. Sintering of particles was observed after the cycling reaction, accompanying with the phase separation in the Zr-rich solid solutions, which may influence the catalytic performance of CeO2-ZrO2 solid solutions in the CO2 splitting.-
Key words:
- CexZr1-xO2 /
- CO2 splitting /
- thermochemical cycle /
- oxygen vacancy
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图 3 新鲜铈锆固溶体的Ce 3d(a)、Zr 3d(b)和O 1s(c)的XPS谱图
Figure 3 Ce 3d(a), Zr 3d(b) and O 1s(c) XPS spectra of the fresh CexZr1-xO2 solid solutions
图 6 铈锆固溶体材料的平均CO产量和平均还原程度
Figure 6 Average amount of CO evolved and average reduction rate of various CexZr1-xO2 solid solutions
图 7 铈锆固溶体材料的平均还原程度与Ce3+/Ce4+物质的量比的关系
Figure 7 Average reduction rate of various CexZr1-xO2 solid solutions vs the Ce3+/Ce4+ molar ratio
图 10 循环反应前后样品的SEM照片
Figure 10 SEM images of fresh
(a): Ce0.2Zr0.8O2; (b): used Ce0.2Zr0.8O2; (c): fresh Ce0.33Zr0.67O2; (d): used Ce0.33Zr0.67O2; (e): fresh Ce0.67Zr0.33O2; (f): used Ce0.67Zr0.33O2; (g): fresh Ce0.75Zr0.25O2; (h): used Ce0.75Zr0.25O2; (i): fresh Ce0.8Zr0.2O2; (j): used Ce0.8Zr0.2O2
表 1 新鲜铈锆固溶体的BET比表面积及晶粒粒径
Table 1 BET surface area and crystal size of the CexZr1-xO2 solid solutions
Material Crystallite size
d/nmSurface
area A/(m2·g-1)Ce0.2Zr0.8O2 8.1 51 Ce0.33Zr0.67O2 9.3 33 Ce0.67Zr0.33O2 14.6 17 Ce0.75Zr0.25O2 17.7 14 Ce0.8Zr0.2O2 26.4 12 
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表 2 循环反应前后铈锆固溶体的表面元素组成及相对含量
Table 2 Surface chemical composition of the fresh and used CexZr1-xO2 solid solutions
Material Chemical composition /% Surface element molar ratio Ce Zr O OⅡ/O Ce3+/Ce4+ Ce0.2Zr0.8O2 4.1(6.8) 21.5(21.2) 74.4(72.0) 0.22(0.23) 0.30(0.31) Ce0.33Zr0.67O2 6.4(9.7) 18.7(17.7) 74.9(72.7) 0.24(0.26) 0.32(0.34) Ce0.67Zr0.33O2 13.9(13.7) 8.3(10.9) 77.8(75.4) 0.26(0.30) 0.33(0.36) Ce0.75Zr0.25O2 15.3(14.9) 6.5(9.4) 78.2(75.7) 0.21(0.22) 0.27(0.28) Ce0.8Zr0.2O2 15.8(15.4) 5.9(8.2) 78.3(76.4) 0.20(0.21) 0.25(0.27) *: the data for the used samples were supplied in parentheses
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表 3 TGA实验中产生的O2和CO体积
Table 3 O2 and CO yields over CexZr1-xO2 derived from the TGA results
Sample O2 /(mL·g-1) CO /(mL·g-1) Average
reduction rate /%2nd cycle 3rd cycle 4th cycle average 2nd cycle 3rd cycle 4th cycle average Ce0.2Zr0.8O2 1.18 1.11 1.00 1.10 2.52 2.49 2.46 2.49 13.1 Ce0.33Zr0.67O2 2.77 2.72 2.68 2.72 5.21 5.38 5.33 5.31 20.3 Ce0.67Zr0.33O2 3.23 3.35 3.28 3.29 5.36 5.84 5.99 5.73 13.7 Ce0.75Zr0.25O2 2.56 2.38 2.42 2.45 5.35 5.26 5.43 5.35 9.3 Ce0.8Zr0.2O2 2.42 2.41 2.39 2.41 4.12 4.47 4.44 4.34 8.7 Ce0.5Zr0.5O2* 3.94 3.65 3.89 3.83 6.67 6.76 7.04 6.82 20.2 CeO2[11] 1.28 1.12 1.19 1.20 2.20 2.28 2.35 2.28 3.7 *: from our previous work[19]
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