双功能催化剂γ-Al_2O_3-MgO-K_2CO_3中MgO的负载方法及协调作用

Loading Method and Coordinated Catalysis of MgO in Bi-functional Catalyst γ-Al_2O_3-MgO-K_2CO_3

研究了用于环戊二烯 ( CPD)和甲醇制备甲基环戊二烯 ( MCPD)的双功能催化剂。制备的催化剂是在 γ- Al2 O3 上分别用混合、沉淀、浸渍法负载 Mg O,焙烧后再负载 1 6% K2 CO3 (摩尔分数 ,下同 )。研究 Mg O负载方法及含量对催化剂活性的影响 ,进行了比表面、XRD和程序升温脱附( TPD)测定。结果表明三种方法形成的催化剂均在含 1 5 %～ 30 % Mg O时呈现高活性。从活性和比表面结果看 ,沉淀法最好 ,混合法次之 ,而浸渍法最差。性能最优化的催化剂是用沉淀法负载 2 5 %Mg O,其 MCPD产率达 76% ,比表面为 1 1 0 .4m2 /g。 XRD分析表明浸渍法的多次焙烧使催化剂表面烧结并形成镁铝尖晶石 ( Mg Al2 O4)。 TPD测定表明在 γ- Al2 O3 - K2 CO3 中负载 Mg O使催化剂表面酸中心强度增强 ,碱中心数量明显增多 ,由此使催化剂酸碱催化功能很有效地“匹配”。

A bi functional catalyst was developed for preparation of MCPD from CPD and methanol. MgO was loaded onto γ Al 2O 3 by the methods of mixing, precipitation and impregnation respectively, before the bi functional catalyst was loaded with 16% K 2CO 3. The effect of different loading methods and the amount of MgO on catalytic activity was investigated and the catalysts were characterized with specific surface area measurement, XRD and TPD. The catalyst loaded with 15%~30% MgO show high activity. The catalytic activity and specific surface area of the catalyst prepared by precipitation method are thehighest, where as those of the catalyst prepared by impregnation method are the lowest. The optimized catalyst with 76% yield of MCPD and 110.4 m 2/g specific surface area is obtained by loading 25% MgO with precipitation method. MgAl 2O 4 is formed in the catalyst by impregnation method, leading to a decrease in both catalytic activity and specific surface area. Adding MgO to γ Al 2O 3 K 2CO 3 increases the acid strength of the acid centers and the number of the base centers and, thus, renders an effective match between the acid centers and the base centers.