12元环硅铝分子筛酸性及其B酸中心可接近性探究

摘要

采用原位红外光谱技术,以吡啶(Py)、2 ,6‐二甲基吡啶(DMPy)、2 ,6‐二叔丁基吡啶(DTPy)为探针分子,考察了 HY 、HMOR 、Hβ 3种12元环孔道结构分子筛的表面酸性及其孔道内B酸中心的可接近性.结果表明, HY分子筛表面酸密度最大,存在丰富的强B酸中心、强L酸中心,以及较多的弱B酸中心,而HMOR和Hβ分子筛表面酸密度较低,且主要为强B酸中心和强L酸中心;以孔道内硅铝桥羟基的变化规律计算B酸中心可接近性指数,结果发现,3种分子筛孔道内B酸中心对大分子碱性探针的可接近性顺序为HMOR＞ Hβ＞ HY .%Acidity and accessibility of three commercial zeolites (HY ,HMOR ,Hβ) were characterized by using in situ FTIR spectroscopy with pyridine (Py) ,2 ,6‐dimethylpyridine (DMPy) and 2 ,6‐di‐tert‐butylpyridine (DTPy) as the probing molecules .The results indicate that the surface acid density of HY molecular sieve is the highest ,and there are abundant strong B acid centers ,strong L acid centers ,and many weak B acid centers .However ,the surface acid density of HMOR and Hβ is low ,and it is mainly the strong B acid center and the strong L acid center .The accessibility index of B‐acid center is calculated by changing the hydroxyl group of Si‐Al bridge.The results show that the order of accessibility of macromolecule probes to Br?nsted acid sites in these three type of zeolites is HMOR＞ Hβ＞ HY.