Abstract:

Mordenite catalysts were studied by solid-state ²⁹Si and ²⁷ Al NMR. The relative d istribution of the Si and Al atoms in the framework and the framework Si/Al rati o were obtained by ²⁹Si MAS NMR, and the aluminum species were charact erized by ²⁷Al MAS NMR. 34.3% of the aluminum is lost from the structure fol lowi ng a calcination at 500℃, but only 10.1% of the aluminum became non-framew ork octahedral a luminum that is NMR visible, and 24.2% of the aluminum became non-framework alu minum that is NMR invisible. Possible mechanism of dealumination was suggeste d. After binding with Al₂O₃, the ²⁹Si MAS NMR spectrum is similar  to that of pur e NH₄-MOR, but the ²⁷Al MAS NMR spectrum is different from the simp le addition  of the ²⁷Al MAS NMR spectrum of NH₄-MOR and Al₂O₃. Short pulse length was used to quantify the ²⁷Al MAS NMR experiment, and ²⁷Al MAS NMR wi th various pulse widths (0.5μs, 2μs, 3.5μs and 3.9μs) were used to character ize aluminum sites. With the increase in pulse width, a sharp peak appears on a broad resonance at 0ppm, indicating that there are two different nonframework sites at 0ppm, the broad on e is d u e to octahedrally coordinated aluminum of Al₂O₃, and the narrow one may be some Al³⁺ cations, possibly arising from Al₂O₃ in the process of binding.

Key words: ²⁹Si MAS NMR,  ²⁷Al MAS NMR, Mor denite catalysts