摘要
制备了一系列用NaCl修饰的Cu/SiO2 催化剂 ,考察了它们对丙烯在空气中直接环氧化反应的催化性能 ,并利用TPR表征手段对催化剂的活性中心进行了初步探讨 .在最佳反应条件下 ,丙烯转化率为 0 16 % ,环氧丙烷选择性达到 4 4 % .在反应气中加入氢后 ,环氧丙烷的选择性显著提高 ,并且催化剂稳定性大大增强 .反应结果表明 ,还原态的低价铜可能是催化剂的活性中心 ,NaCl与铜离子结合而生成新物种可能在催化反应过程中起到关键作用 .
Propylene oxide (PO) is an important chemical intermediate, but its traditional production processes cause serious environmental problems. Direct epoxidation of propylene with molecular oxygen has attracted both industrial and academic interests. A series of NaCl modified Cu catalysts were prepared by impregnation method, and their catalytic performance for epoxidation of propylene with air as the oxidant was investigated. The results showed that SiO 2 is a suitable support and NaCl is an effective promoter for the epoxidation. The unmodified Cu/SiO 2 has no catalytic activity, while the modified Cu/SiO 2 with 20%NaCl gives 17 7% selectivity for PO. The unreduced Cu/SiO 2 is not active for this reaction, while the catalyst reduced with H 2 shows higher activity, which indicates that the reduced Cu species is very important for the reaction. Under the conditions of n (C 3H 6) ∶ n (O 2) ∶ n (H 2) =10∶1∶1, SV=1 5×10 4 h -1 and θ =215 ℃, the propylene conversion is 0 16% and PO selectivity reaches up to 44% on 10%Cu 2%NaCl/SiO 2 catalyst. The addition of hydrogen in the feedstock can remarkably increase the PO selectivity and stabilize the catalyst. It is proposed that H 2 reacts with oxygen species on the catalyst surface, thus keeps the catalyst from being oxidized. The results of temperature programmed reaction showed that there is a reduction peak at about 400 ℃ for Cu/SiO 2, when it was modified with NaCl, the peak shifts to 300 ℃, which implies that the interaction between CuO and NaCl takes place. The reduced copper species with low valence may be the active sites for epoxidation.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2004年第1期5-9,共5页
基金
国家自然科学基金资助项目 (2 0 0 73 0 45 )
关键词
铜
氧化硅
负载型催化剂
氧化钠
丙烯
环氧化
分子氧
copper, silica, supported catalyst, sodium chloride, propylene, epoxidation, molecular oxygen
