等离子体改性CuO/γ-Al_2O_3催化剂催化低浓度甲烷燃烧性能

为了研究CuO/γ-Al_2O_3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-Al_2O_3和CuO/γ-Al_2O_3-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、H_2-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。

Preparation of plasma modified CuO/γ-Al2O3 catalyst and its catalytic performance in the combustion of low-concentration methane

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.