Abstract: The steamed and acid-leached mordenite samples were examined by high-resolution solid state ¹H, ²⁹Si, ²⁷Al magic angle spinning (MAS) and ¹H/ ²⁹Si cross polarization (CP) NMR spectroscopic techniques in order to study the aluminum species and evaluate the dealumination process during steaming and leaching. The NMR experiments provide a direct evidence for the existence of nonframework four-coordinated Al species,Al(OH)₃·H₂O,giving rise to a ¹H resonance at δ 3.0 and a ²⁷Al shoulder peak at δ 45,which are different from the distorted four-coordinated Al species. At a high temperature,water molecules will favor the formation of these Al species and extra-framework penta- and hexa-coordinated Al species in the ²⁷Al spectrum at δ 30 and δ 0,respectively. ¹H/ ²⁹Si CP and ¹H MAS NMR showed the presence of an abundance of SiOH and AlOH groups in the dealuminated mordenites during the steaming process.

Key words: ¹H,²⁹Si, ²⁷Al MAS NMR, ¹H/ ²⁹Si CP, Steaming/acid-leaching dealumination, Nonframework four-coordinated Al, Dealumination mechanism