HZSM-5分子筛焙烧脱铝的^(27)Al MQMAS NMR研究  

Dealumination of HZSM-5 Zeolite by Calcination:~27Al Multiple Quantum MAS NMR Study

作　　者：陈雷[1] 邓风[1] 叶朝辉[1] 

机构地区：[1]中国科学院武汉物理与数学研究所

出　　处：《物理化学学报》2002年第9期786-790,共5页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(29973058)资助项目~~

摘　　要：用29Si、27Al魔角旋转固体核磁共振(MASNMR)结合二维多量子魔角旋转(2DMQMAS)技术对焙烧脱铝的HZSM-5分子筛中铝的配位状态进行了研究.结果表明,HZSM-5分子筛经焙烧后,在化学位移(δ)45处出现一宽峰信号,其主要来自扭曲四配位铝.通过二维三量子铝谱计算出扭曲四配位铝的四极作用常数约为5.2MHz.对700和750℃焙烧样品的铝谱进行分峰拟合,发现在δ30处又出现一个小峰,归属为非骨架五配位铝.同时,在750℃焙烧样品的二维多量子铝谱中直接观察到非骨架五配位铝的信号.焙烧温度低于700℃,脱铝不明显;高于700℃,引起分子筛骨架的显著脱铝.焙烧还造成部分骨架铝的信号变得“不可观测”.The coordination states of aluminum species in calcined HZSM 5 zeolites have been investigated using 29Si,27Al MAS and 2D MQMAS NMR methods.A broad peak at δ 45 in presents in the 27Al MAS NMR spectra of calcined HZSM 5 zeolites.From the 27Al 3QMAS NMR spectrum,it is evident that the peak at δ 45 comes mainly from the distorted tetrahedral Al with a quadrupolar coupling constant of 5.2 MHz.Simulation of the 27Al 1D MAS NMR spectra of samples calcined at 700 and 750 ℃ shows that a small peak at about δ 30 emerges,which is probably due to 5 coordinated non framework Al.The existence of this Al species is also confirmed by 27Al 3QMAS NMR.HZSM 5 zeolite calcined at temperature higher than 700 ℃ suffers severe dealumination.Calcination causes part of the Al species “NMR invisible” in the corresponding 27Al MAS spectra.

关 键 词：分子筛 HZSM-5 NMR MQMAS 脱铝 焙烧 核磁共振 配位状态 

分 类 号：O657.2[理学—分析化学]