Short cation−cation distances in zeolites − the case of K−LSX

Zeolites with the faujasite structure (FAU) are extensively used as catalysts and in gas separation. A detailed knowledge of their structure, particularly the positions of extra−framework cations in the case of gas adsorption, is therefore central to understanding their performance. Typically zeolites X (Si/Al ~.1.1−1.5) and Y (Si/Al ~5−11) are used. A common assertion of structural determinations is that the two partially occupied cation sites labelled SI and SI’ (Figure 1) are not occupied simultaneously.