Aluminum distribution in high-silica mordenite

The Al distribution in high-silica MOR zeolites with various Si/Al ratios was investigated by FT-IR spectroscopy in the presence of CD3CN probe molecules and benzene adsorption. Two adsorption bands assigned to CN stretching vibration were observed at 2280-2295 and ≈ 2315 cm-1, which are due to interaction of CN with acidic hydroxyl groups in the main channels and the side pockets of H-MOR zeolite, respectively. The relative intensity of the peak at 2315 cm-1 increased with an increase in the Si/Al ratio, indicating that the proportion of Al atoms in the main channels relatively decreased with the Si/Al ratio. This was confirmed from the linear relationship between the number of benzene molecules adsorbed in a unit cell and the number of Al atoms in the main channels. In addition, this was also suggested from the computer simulation result that Al atoms are preferentially sitting in the T3 site