铝在MCM-22分子筛骨架上分布的27Al MQ MAS NMR研究

利用二维多量子魔角旋转（2D MQ MAS）技术并结合量子化学计算，研究了铝在MCM-22分子筛骨架上的分布，并对铝的不等价四面体位进行了归属.在27Al 2D 5Q MAS NMR谱中骨架四配位铝的范围内观察到3个信号，证明MCM-22分子筛有3种骨架铝.经计算这3种骨架四配位铝的各向同性化学位移和四极作用常数分别为：δ 50.5、δ 57.3、δ 62.4和1.74、1.68、1.92 MHz. MCM-22分子筛结构中有8种结晶学不等价四面体（T）位.我们通过模拟MCM-22分子筛的27Al 2D 5Q MAS NMR谱，认为8种不等价T位分为3组. T2、T6位上的铝分别与δ 61、δ 49处的信号相关， T1、T3、T4、T5、T7、T8位上的铝对δ 56处的共振峰有贡献.当硅铝原子数比(Si/Al)在10～15之间变化时，铝在MCM-22分子筛的骨架上是无规占据的.

27Al Multiple Quantum MAS NMR Study on the Distribution of Aluminium in the Zeolite MCM-22

The distribution of aluminum in the zeolite MCM-22 lattice has been investigated by 27Al MQ MAS NMR and quantum chemical calculation. Three different aluminum species in tetrahedral coordination were clearly observed in the 2D 5Q MAS NMR spectrum of zeolite MCM-22. From the spectrum, we can calculate the isotropic chemical shifts(δ 50.5, δ 57.3, δ 62.4 ) and the quadrupolar coupling constant (1.74, 1.68, 1.92 MHz) of the three species. The structure of MCM-22 has the 8 crystallographically distinct T sites. From the simulated 27Al 5Q MAS NMR spectrum, it is evident that 8 T sites can be divided into 3 groups. Sites T2 and T6 correspond to the signals at δ 61, δ 49, respectively; while sites T1, T3, T4, T5, T7, T8 give rise to signal atδ 56. Al is randomly distributed in the framework of MCM-22 zeolite when the Si/Al atom ratio is varied from 10 to 15.