Beta分子筛催化桥式双环戊二烯异构研究

Beta Zeolite Catalytic Isomerization of endo-Dicyclopentadiene

采用Hβ分子筛为催化剂,在液相体系中将桥式双环戊二烯(endo-DCPD)异构为挂式双环戊二烯(exo-DCPD)。无催化剂时双环戊二烯主要发生聚合反应,加入催化剂后生成了大量exoDCPD。在分子筛表面沉积SiO2可提高反应选择性,说明异构反应发生在分子筛孔道内,而外表面主要引发聚合副反应。低n(硅)/n(铝)的分子筛含有大量强度较弱的Lewis酸性位,在异构反应中的活性最高,说明弱酸性位是异构的活性中心。对分子筛焙烧温度考察发现,焙烧温度过低时分子筛的L酸位较少,温度过高时L酸变强而且结晶度急剧下降,500℃焙烧的分子筛异构化性能最佳,证明分子筛异构是孔结构和弱L酸性中心协同作用的结果。

Hβ-catalytic isomerization of endo-dicyclopentadiene（endo-DCPD） to exo-dicyclopentadiene（exo-DCPD） in liquid phase was studied.With the absence of zeolite,DCPD is converted into oligomers and the formation of exo-DCPD is neglectable.With the presence of Hβ,considerable amount of exo-DCPD is formed.Passivation of the external surface with amorphous silica layer improves the selectivity of isomerization reaction with a little decline in conversion.This means that the isomerization reaction occurs inside the pore of zeolite,meanwhile the external acidity accelerates the undesired oligomerizations.Hβ with low SiO2/Al2O3ratio contains highest concentration of weak Lewis acid,and exhibits highest activity,confirming that weak L acidity is the active site for the isomerization.The calcination temperature has great influence on the acidity and porous structure of zeolite.The amount of weak L acid is not enough at low temperature,while the framework and pores are destroyed at high temperature.Calcination at 500 ℃ produces enough weak L acid and keeps relatively well crystallinity,thereby providing best catalytic performance.