CeO_2修饰α-Al_2O_3载体对银催化剂结构及性能的影响

Influence of CeO_2 Modification of α-Al_2O_3 Support on Structures and Properties of Silver Catalysts

采用浸渍法用含Ce溶液对α-Al2O3载体进行修饰得到CeO2修饰的α-Al2O3(Ce/α-Al2O3)载体,再将Ce/α-Al2O3载体浸渍Ag溶液,制得负载型Ag催化剂;采用XRD,BET,SEM,O2-TPD等方法对载体和催化剂的结构进行了表征,在微型固定床反应器中对催化剂的乙烯环氧化性能进行了评价。实验结果表明,与α-Al2O3载体相比,Ce/α-Al2O3载体的比表面积增大,孔体积和侧压强度变化不大。Ce/α-Al2O3载体负载Ag后,Ag颗粒分布较均匀,经260℃热处理后,Ag颗粒粒径分布变窄,能形成对乙烯环氧化反应有利的Ag颗粒粒径及其分布。经900℃焙烧、Ce加入量为0.56%(相对于α-Al2O3和CeO2的总质量)的载体负载Ag后得到的催化剂具有很好的催化性能。在反应温度为196℃时,环氧乙烷的选择性可达82.7%,反应温度比载体未经修饰的Ag催化剂降低了4℃,环氧乙烷选择性提高了0.7个百分点。

a-Al2O3 support was modified through impregnating the support in cerium-containing solution and a series of silver catalysts with the modified a-Al2O3 as support were prepared. The structures of both the supports and silver catalysts were characterized by means of XRD, BET, SEM, and O2-TPD. The catalytic performances of the catalysts in ethylene epoxidation were evaluated in a micro-reactor. Experimental results indicated that the specific surface areas of the modified supports increased, and both the pore volume and the crush strength were not changed. The silver particles were well dispersed on the catalysts with CeO2 modified supports. After calcination at 260 ℃, the silver particle size distribution was in a relative narrow range, which was beneficial to the ethylene epoxidation. Under the optimal conditions of Ce content in the support 0.56% （ based on total mass of a-Al2O3 and CeO2） and calcination temperature 900 ℃, selectivity to ethylene oxide in the ethylene epoxidation at 196 ℃ could achieve 82. 7%. Compared with the unmodified silver catalyst, the epoxidation temperature lowered 4 ℃ and selectivity to ethylene oxide increased by 0.7%.