Li⁺ Exchange into Zeolite Na–Y (FAU) from Aqueous Methanol. Single-Crystal Structures of Fully Dehydrated Li,Na–Y

Abstract

The ion exchange of Li+ into zeolite Na–Y, |Na75|[Si117Al75O384]-FAU, was attempted using methanol–water mixed solvents. Four solvents ranging in composition from as-purchased (undried) methanol (water concentration 0.02 M) to pure water were used. Four single crystals of Na–Y were treated with 0.1 M LiNO3 in each of the four solvents at 333 K, followed by vacuum dehydration at 673 K. Their structures were determined by single-crystal synchrotron X-ray diffraction techniques at 100(1) K in the space group Fd3̅m. In the four structures, Li+ and Na+ fill sites I′ and II; the remaining cations, when they can be found, occupy III′ sites. The site preference for Li+ over Na+ is approximately I′ > II > III′. The greatest degree of exchange of Li+ for Na+, 96%, was achieved from undried methanol under the conditions employed. The extent of Li+ exchange decreases with increasing water content and was least, 72%, from pure water. The low water content of the undried methanol appears to play an essential role in the ion exchange process.