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.