Solid-state 1H NMR studies of the acidity of mordenites

Abstract

The interaction of known numbers of water molecules with the acidic OH groups of H-form commercial mordenites, giving H₃O⁺ and H₂O⋯HO, is studied using ¹H broad-line NMR at 4 K and MAS NMR at 300 K. The H₃O⁺ concentration for one adsorbed water molecule per Brønsted-acid site is related to the Si/Al ratio. The differences between the H₃O⁺ concentrations for the two samples at a higher water concentration is associated, semi-quantitatively, with synergy between Brønsted- and Lewis-acid sites.