Promoted stability of Cu/ZnO/Al2O3 catalysts for methanol production from CO2 hydrogenation by La modification
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摘要: CO2加氢制甲醇反应中Cu/ZnO/Al2O3催化剂的失活是限制其应用的主要原因之一，实验通过向Cu/ZnO/Al2O3催化剂中添加不同含量的La，合成了一系列La改性的Cu/ZnO/Al2O3催化剂，以提高其对 CO2加氢制甲醇反应的催化稳定性。在温度200 ℃，压力3 MPa，空速12000 mL/(g·h)条件下进行的100 h短期稳定性测试中，未改性的Cu/ZnO/Al2O3催化剂在100 h内活性衰减明显，添加La后催化剂稳定性逐渐得到提高，当La添加量为5% 时活性最佳（CO2转化率4%，甲醇选择性85%），并且该催化剂在1000 h长期稳定性测试中表现出较高的稳定性（在190−220 h失活 17% 后保持稳定）。通过X射线衍射（XRD）、X射线光电子能谱（XPS）表征发现，加入5% La提高了Cu/ZnO/Al2O3催化剂中Cu、ZnO的分散度，抑制了催化剂中Cu的烧结；同时稳定了Cu0/+，延缓了催化剂中Cu的氧化，从而提高了催化剂的稳定性。
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关键词:
- Cu/ZnO/Al2O3 /
- La 助剂 /
- 稳定性
Abstract: Deactivation of Cu/ZnO/Al2O3 catalysts in CO2 hydrogenation to methanol reaction is one of the main reasons limiting their application. We synthesized a series of La modified Cu/ZnO/Al2O3 catalysts by adding different contents of La to improve the stability. In the 100 h short-term stability test at 200 ℃ under 3 MPa with a GHSV of 12000 mL/(g·h), the unmodified Cu/ZnO/Al2O3 catalysts degraded obviously over 100 h. In sharp contrast, the stability was significantly promoted by the addition of La. The best activity was achieved with 5% La added samples (4% CO2 conversion and 85% methanol selectivity). Which also showed impressive stability over 1000 h except about17% deactivation during the initial 190−220 h. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results revealed that the addition of 5% La improved the dispersion of Cu and Zn , inhibited the sintering of Cu, stabilized the Cu0/+ species and retarded oxidation of Cu in catalysts, which attributed to the high stability of the catalysts.-
Key words:
- Cu/ZnO/Al2O3 /
- La promoter /
- stability
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图 1 La改性的Cu/ZnO/Al2O3 催化剂 100 h稳定性测试
Figure 1 La modified Cu/ZnO/Al2O3 catalyst 100 h stability test Reaction condition: 200 ℃, 3 MPa, 12000 mL/(g·h).
图 2 5% La Cu/ZnO/Al2O3 催化剂的稳定性
Figure 2 250 h and 1000 h stability tests of 5% La Cu/ZnO/Al2O3 catalyst Reaction condition: 200 ℃, 3 MPa, 12000 mL/(g·h).
图 3 0% La、5% La Cu/ZnO/Al2O3催化剂煅烧后、还原后及稳定性测试后的XRD谱图
Figure 3 XRD patterns of 0% La and 5% La Cu/ZnO/Al2O3 catalysts after calcination, reduction and stability tests.
图 4 0% La、5% La Cu/ZnO/Al2O3催化剂煅烧后、还原后及稳定性测试后的XPS谱图
Figure 4 XPS spectra of 0% La and 5% La Cu/ZnO/Al2O3 catalysts after calcination, reduction and stability tests
(a): Cu 2p; (b): Cu LMM; (c): La 3d; (d): O 1s.
图 5 添加5% La 提高 Cu/ZnO/Al2O3 稳定性
Figure 5 Schematic diagram of adding 5% La to improve the stability of Cu/ZnO/Al2O3
表 1 0%、5% La Cu/ZnO/Al2O3催化剂还原后及稳定性测试后的不同价态Cu含量和煅烧后、还原后及稳定性测试后的不同O物种含量
Table 1 0%, 5% La Cu/ZnO/Al2O3 catalysts with different valence Cu contents after calcination, reduction and stability tests and different O species contents after calcination, reduction and stability tests
Samples Cu/% O/% Cu0 Cu+ Cu2+ Olat Oads Owea 0% La calcined − − 100.0 18.8 63.0 18.2 0% La reduced 27.6 7.9 64.5 23.2 76.8 − 0% La after 100 h 13.1 7.0 79.9 36.5 63.5 − 5% La calcined − − 100.0 18.5 70.0 11.5 5% La reduced 32.8 16.8 50.4 11.6 88.4 − 5% La after 100 h 19.8 20.0 60.2 12.4 87.6 − 5% La after 250 h 13.4 15.2 71.4 32.6 67.4 − 5% La after 1000 h 12.8 14.3 72.9 34.0 66.0 − 
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