Preparation of plasma modified CuO/γ-Al2O3 catalyst and its catalytic performance in the combustion of low-concentration methane
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摘要: 为了研究CuO/γ-Al2O3催化低浓度甲烷燃烧性能，采用普通浸渍法和低温等离子体改性的方法分别制备了CuO/γ-Al2O3和CuO/γ-Al2O3-P催化剂，并用于低浓度甲烷燃烧，考察了Cu负载量和等离子体改性工艺对其催化活性的影响。结果表明，Cu负载量为7%时，催化剂的活性最强。改性气体、气体空速、放电电压、放电频率、等离子体处理时间均是影响催化剂活性的因素。氧气适合用作催化剂的改性气体，而氮气不宜作为改性气体使用。氧气作为改性气体时，最佳的改性工艺条件为峰峰值电压45 kV、放电频率14.71 kHz、等离子体处理时间30 min、氧气空速20 mL/（min·g）。在此工艺条件下制备的催化剂用于低浓度甲烷催化燃烧，可使t10降低23 ℃、t50降低6 ℃、t90降低19 ℃，同时，可使反应的活化能由79.27 kJ/mol降低为76.12 kJ/mol。催化剂的SEM、BET、XRD、XPS、H2-TPR表征结果表明，等离子体对催化剂的改性作用主要在于增大了催化剂的比表面积、促使催化剂中Cu周围电子云密度降低及体相氧向表面氧迁移，从而利于甲烷在催化剂表面的吸附、活化和转化。Abstract: A series of CuO/γ-Al2O3 catalysts were prepared by conventional impregnation and then modified with low temperature plasma at atmospheric pressure in a dielectric barrier discharge (DBD) reactor. These modified catalysts were used in the catalytic combustion of low-concentration methane. The effects of Cu loading and plasma modification process on the activity of CuO/γ-Al2O3 catalyst were investigated. The results show that the catalytic activity is the best when the loading of Cu is 7%. Modification gas and its space velocity, discharge voltage, discharge frequency, plasma treatment time are the factors that affect the activity of the catalyst. O2 plasma treatment has effect on increasing the activity of CuO/γ-Al2O3 catalyst, and N2 plasma treatment reduces the catalytic activity. When oxygen as the modification gas, the optimum modification process conditions are 45 kV of the discharge voltage, 14.71 kHz of the discharge frequency, 30 min of the plasma treatment time, and 20 mL/(min·g) of the oxygen space velocity. The catalyst, which is modified under the above process conditions, exhibits excellent catalytic activity for the combustion of low-concentration methane. Using this catalyst, t10, t50 and t90 are decreased by 23, 6 and 19 ℃, respectively. Compared with the conventional CuO/γ-Al2O3 catalyst, the plasma modified CuO/γ-Al2O3 catalyst can depress the apparent activation energy of the catalytic combustion reaction of low-concentration methane from 79.27 to 76.12 kJ/mol. The parent and modified samples were characterized by diverse techniques including SEM, BET, XRD, XPS and H2-TPR. The results show that the O2 plasma can adjust specific surface area, the electron density around atom Cu and mobility of bulk phase oxygen of the catalyst, thereby affect the adsorption, activation and conversion of methane on the surface of the catalyst in the combustion of low-concentration methane.
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Key words:
- CuO/γ-Al2O3 /
- plasma /
- catalyst /
- ventilation air methane /
- catalytic combustion /
- modification
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图 1 固定床反应器示意图
Figure 1 Diagram of the fixed bed reactor
1: gas cylinder; 2: pressure regulator; 3: mass flow controller; 4: electric furnace; 5: reactor; 6: thermocouple and temperature controller; 7: cooling trap; 8: gas chromatography; 9: computer
图 2 Cu负载量对催化剂性能的影响
Figure 2 Effect of Cu loading on the catalytic performance of the CuO/γ-Al2O3 catalyst
图 3 不同催化剂的SEM照片
Figure 3 SEM images of different catalysts
(a): γ-Al2O3; (b): 7%CuO/γ-Al2O3; (c): 10%CuO/γ-Al2O3
图 4 改性气体对催化剂性能的影响
Figure 4 Effect of modification gas on the catalytic performance of the 7%CuO/γ-Al2O3 catalyst
图 5 放电电压对催化剂性能的影响
Figure 5 Effect of discharge voltage on the catalytic performance of the 7%CuO/γ-Al2O3 catalyst
图 6 放电频率对催化剂性能的影响
Figure 6 Effect of discharge frequency on the catalytic performance of the 7%CuO/γ-Al2O3 catalyst
图 7 等离子体处理时间对催化剂性能的影响
Figure 7 Effect of plasma treatment time on the catalytic performance of the 7%CuO/γ-Al2O3 catalyst
图 8 氧气空速对催化剂性能的影响
Figure 8 Effect of space velocity of O2 on the catalytic performance of the 7%CuO/γ-Al2O3 catalyst
图 9 改性前后催化剂的SEM照片
Figure 9 SEM images of catalyst before and after modification
(a): 7%CuO/γ-Al2O3; (b): 7%CuO/γ-Al2O3-P
图 10 改性前后催化剂的XRD谱图
Figure 10 XRD patterns of catalyst before and after modification
a: 7%CuO/γ-Al2O3; b: 7%CuO/γ-Al2O3-P
图 11 改性前后催化剂的Cu 2p XPS谱图
Figure 11 Cu 2p spectra of the catalysts before and after modification
图 12 改性前后催化剂的Cu LMM XPS谱图
Figure 12 Cu LMM spectra of the catalysts before and after modification
图 13 改性前后催化剂的H2-TPR谱图
Figure 13 H2-TPR profile of the catalysts before and after modification
表 1 不同催化剂的催化活性
Table 1 Catalytic activity of different catalyst
Catalyst t10/℃ t50/℃ t90/℃ 7%CuO/γ-Al2O3-P 377 466 531 7%CuO/γ-Al2O3 400 472 550 
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