Cation distribution in K,H-L zeolite prepared through ion-exchange with TMA ion

Structural analyses of hydrated K9-L and K7.5H1.5-L zeolites were carried out by measurements of X-ray powder diffraction patterns and Rietveld refinements, and distributions of potassium ion in the zeolites were investigated. K7.5H1.5-L was obtained by heating K7.5TMA1.5-L at 773 K in air, which was prepared through an ion-exchange of K9-L with TMA ion. In both K9-L and K7.5H1.5-L, potassium ion located only on sites B, D and E. The number of potassium ion on site D was the most remarkably different between K9-L and K7.5H1.5-L, that is, its number was 4.08 per unit cell (puc) in K9-L and 3.00 puc in K7.5H1.5-L. It was found from this result that TMA ion preferentially exchanges with potassium ion on site D. The potassium ion on site E also reduced to 2.52 puc in K7.5H1.5-L from 2.94 puc in K9-L. It was considered that the reduction arose in the ion-exchange between K+/E and the hydrogen ion (just) after converting to K,H-L from K7.5TMA1.5-L by heating, because TMA ion cannot access site E at all due to the location of site E and its ion size, but hydrogen ion can. All the nearest interatomic distance between a potassium ion and a framework oxygen showed the tendency which becomes longer in K7.5H1.5-L than K9-L. The results suggest that the Coulmbic attraction between the potassium ion and a negative chare of framework (AlO4−) becomes weaker in K7.5H1.5-L than K9-L.