Y型沸石脱铝机制和铝状态的NMR研究

对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,²⁹Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,²⁷Al MAS NMR谱、二维章动NMR及¹H-²⁷Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合²⁹Si和²⁷Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。

NMR STUDIES ON DEALUMINATED Y ZEOLITES

Dealuminated Y zeolites after mild steaming and (NH₄)₂SiF₆ treatments were studied by ²⁹Si,²⁷Al MAS NMR, ²⁷Al-¹H cross polarization MAS NMR and 2D nutation NMR. ²⁹Si MAS NMR shows that the Si, Al framework distributions of ultrastable Y zeolites and Y zeolites dealuminated by (NH₄)₂SiF₆ isomorphous substitution are different, even if they have almost the same framework Si/Al ratio. The reason is due to their different dealumination experience. Y zeolites with high Si/Al framework ratio can be obtained by a coorperation of isomorphous substitution and hydrothermal dealumination. Based on ²⁷Al MAS NMR, ²⁷Al-¹H CP/MAS NMR and 2D nutation ²⁷Al NMR observations, four aluminuous species, i.e. framework tetrahedral Al(AlFT),distortcd framework tetrahedral Al(Al^FDT), penta-coordinated non framework Al(AlNFP) and non framework octahedral Al(Al^NFO), in dealununated Y zeolites are supposed Si/Al frame ratios of dealuminated Y zeolites determined by ²⁷Al MAS NMR simulations are in good agreement with whose results of ²⁹Si MAS NMR