原位负载稀土三元催化剂催化环氧丙烷和二氧化碳的共聚合研究

采用2种方法制备了原位负载稀土三元催化剂,即先将均相的Y(CCl3OO)3-Glycerin体系负载在载体上,后逐滴加入ZnEt2(标记为Y(CCl3OO)3-Glycerin/γ-Al2O3/ZnEt2);或先将ZnEt2与载体反应,再与均相的Y(CCl3OO)3-Glycerin体系反应(标记为ZnEt2/γ-Al2O3/Y(CCl3OO)3-Glycerin).研究发现原位负载催化剂催化环氧丙烷和二氧化碳共聚合反应的活性比未负载前低24%～36%,通过分析催化剂制备过程中所生成的乙烷量的变化,证明原位负载时催化剂组分如Y(CCl3OO)3、Glycerin或ZnEt2发生了向载体孔隙内的扩散渗透,使得催化剂各组分配比与未负载催化剂相比发生了偏差,从而降低了催化活性;另一方面,表面羟基与ZnEt2反应形成了低效率的活性种,也是原位负载催化剂活性不高的原因之一.提出了影响原位负载稀土三元催化剂活性的2个主要因素,即活性种的反应活性和活性种的数量.通过调节催化剂组分配比、负载化阶段的振荡研磨时间、原位负载时的活性种状态、载体的表面状态等,可使负载催化剂的活性比未负载的稀土三元催化剂提高3.5%.

COPOLYMERIZATION OF CARBON DIOXIDE AND PROPYLENE OXIDE UNDER in situ SUPPORTED RARE EARTH TERNARY CATALYST

Copolymerization of propylene oxide and carbon dioxide to form poly(propylene carbonate) was carried out under in-situ γ-Al2O3 supported rare earth ternary catalyst.Two in situ supporting routes were employed,one was dropping ZnEt2into γ-Al2O3pre-supported Y(CCl3OO)3-Glycerin system(Y(CCl3OO)3-Glycerin/γ-Al2O3/ZnEt2),the other was reacting γ-Al2O3pre-supported ZnEt2with Y(CCl3OO)3-Glycerin system(ZnEt2/γ-Al2O3/Y(CCl3OO)3-Glycerin).However,the two supported catalysts showed unexpected 24%~36% lower catalytic activity than their unsupported analog.By monitoring the ethane evolution during catalyst preparation,it was observed that the diffusion of three components of rare earth ternary catalyst into pores of γ-Al2O3 leading to molar ratio disparity of the components and decrease in number of active species,and subsequently loss of the catalytic activity.Moreover,the surface hydroxyl groups react with ZnEt2 forming low active species,also leading to catalytic activity loss.Therefore,two main factors were proposed for improving the catalytic activity of supported catalysts,one was the activity of the active species,the other was the number of active species.By adjusting the molar ratio of three components,the time for grinding-stirring during supporting process,the active species of the in situ supported catalyst,the surface chemistry of the support,the catalytic activity of the supported catalyst may be improved significantly,a state-of-the-art optimal catalytic activity for the in situ supported catalyst showed 3.5% increase over the unsupported analog.