氧化/还原预处理对Cu2O/AC催化甲醇氧化羰基化的影响

将醋酸铜热解制备的Cu₂O/AC(活性炭)催化剂,在氧化(O₂/N₂)和还原(H₂/N₂、CO/N₂)气氛下进行预处理。350 ℃下预处理4 h,氧化气氛中Cu₂O完全被氧化为CuO,还原气氛中Cu₂O被还原为单质铜。经CO/N₂预处理的催化剂表面Cu⁰分散性好,催化活性显著升高。在常压固定床微型反应装置上测试,在140 ℃的反应温度下,碳酸二甲酯的时空收率和选择性分别达到了261.9 mg/(g·h)和74.7%。反应后,还原气氛(H₂/N₂、CO/N₂)预处理的催化剂与Cu₂O/AC催化剂中铜物种价态组成趋于一致,催化活性亦趋于一致。关联反应前后催化剂表面铜物种的变化和催化活性的差异,可以认为Cu⁰具有较高的初始催化活性,Cu₂O活性和价态均较为稳定,CuO活性较低。

Effect of oxidative/reductive pretreatment on the performance of Cu2 O/AC catalyst for oxidative carbonylation of methnol

The Cu₂O/AC catalyst prepared by pyrolysis of copper acetate supported on activatede carbon was pretreated under oxidative (O₂/N₂) or reductive (H₂/N₂ and CO/N₂) atmospheres. The oxidation/reduction of Cu₂O was completed through pretreatment at 350 ℃ for 4 h, the Cu₂O in catalyst could be completely oxidized to CuO by oxidative atmosphere, or reduced to metallic copper by reductive atmosphere. The catalyst activities were evaluated in a continuous fixed-bed tubular micro reactor under atmospheric pressure at 140 ℃. The catalyst pretreated by CO/N₂ had good Cu⁰ dispersion on its surface and exhibited the highest activity. The space-time yield and selectivity of DMC reached 261.9 mg/(g·h) and 74.7%, respectively. After 58 h reaction, the valence state of copper species and the catalytic activity of catalysts pretreated by reductive atmosphere were found to be close to that of the Cu₂O/AC catalyst. Comparing the catalytic performance, the characterization of surface and bulk copper species before and after reaction, it was obvious that metallic copper exhibited a high initial activity, while Cu₂O was stable in catalytic activity and valence state, and CuO was low in activity.