Positions of cations and molecules in zeolites with the mordenite-type framework VII dehydrated cesium mordenite

Abstract

Natural mordenite was ion-exchanged with CsCl solution and dehydrated at 300°C. The crystal structure [ a 18.194(19) b 20.470(17) c 7.506(9): Cs 7 4Al∼ 8Si∼ 40O 96] probably belongs to space group P2 1cn but was refined in the average space group Cmcm. Site occupancies for Cs are site II 3.8, IV 1.9, VI 1.8 atoms. Combined occupancies of sites IV and VI are less than 4 in dK-, dRb- and dCs- varieties. Cations larger than 1.3Å have not been found in site I. Cations in site VI block diffusion of large molecules in the main channel, and conversion of Na-mordenite from small-port to large-port variety by “decationization” towards H-mordenite might be explained by emptying sites IV and VI while up to 4 Na could remain in site I.