Mg-ZSM-5分子筛酸性的固体核磁表征

利用固体核磁共振(NMR)技术,以脱水分子筛及吸附氘代吡啶的1H MAS NMR谱,对MgZSM-5分子筛的表面羟基进行了表征,研究了酸性和羟基的H/D交换性能,并以三甲基膦为碱性探针分子,运用吸附三甲基膦的31P MAS NMR谱表征了分子筛表面的B酸中心和L酸中心,对其特征峰进行了归属。结果表明,在一定温度之上,氘代吡啶在被质子化的同时,会很容易与分子筛发生H/D交换反应,交换不但可以在桥式羟基上发生,也可以在其他非酸性羟基上发生;分子筛表面的L酸中心来源于Mg原子,其在分子筛表面的存在形式为Mg(OH)+。

Acidity characterization of Mg-ZSM-5 zeolite by solid-state nuclear magnetic resonance spectroscopy

The superficial hydroxyl groups of Mg-ZSM-5 zeolites were characterized by 1H MAS NMR spectrums of dehydrated zeolites and deuterated pyridine adsorbed samples using solid state nuclear magnetic resonance method.The acidities and the H/D exchange properties of hydroxyl groups were also studied.The B and L acid sites on the surface of zeolite were characterized by using 31P MAS NMR spectrums of trimethylphosphine adsorbed samples with trimethylphosphine as alkaline probe,and the assignments of characteristic peaks were given.The results showed that above a certain temperature,the deuterated pyridine was protonated,and at the same time,its H/D exchange with zeolite occurred easily not only on bridge hydroxyl group but also on other non-acid hydroxyl groups.The Lewis acid sites on Mg-ZSM-5 zeolite surface were derived from Mg atom and found itself in the form of Mg（OH） ＋.