Dùng phương pháp cộng hưởng từ hạt nhân (NMR) để xác định độ axit, phân bố nhôm trong vật liệu ZSM-5 và ZSM-5/MCM-41

Abstract

ZSM-5/MCM-41 composite was prepared by using a dual-template synthetic gel system -   Tetrapropylamoniumhydroxit TPAOH and cetyltrimetylamoniumbromide CTMAB. The structure of that material was investigated by IR, XRD, TEM, and TPD-NH₃ and nitrogen adsorption/desorption [1]. The results of IR, XRD, NMR showed that the most of aluminum atoms distributed in the framework In this paper, ²⁷Al, ¹H MAS NMR are used to determine the geometry of the Bronsted acid and the distribution of aluminum atoms in ZSM-5/MCM-41. Acidic (“bridging”) OH groups in ZSM-5/MCM-41 are responsible for the catalytic activity. They can exist in materials in four forms: SiOHAl (d = 4.1 ppm), AlOH (d = 2.7ppm), SiOH1 (d = 1.8 ppm), and SiOH2 (d = 2.2 ppm).  Here, we can see the differences of acidities between ZSM-5 and ZSM5-/MCM-41 base on the signals of the formation of bridging OH groups (SiOHAl).