Location of Brønsted and cation sites in dehydrated zeolites: a comparison

To date, the location and population of protons in acid forms of zeolites and those of exchangeable cations in dehydrated zeolites have been investigated as two distinct topics. This paper intends to highlight the analogies and differences in the siting of protons and extraframework cations in dehydrated zeolites. The starting point is that a framework oxygen whose bond strength from tetrahedral cations is low and/or whose bond strength from extraframework cations is high presumably has a higher probability of hosting a proton. A comparison between the bond strength on oxygen atoms and the location of hydroxyl groups in mordenite, ferrierite, chabazite, faujasite, and rho showed that this assumption is supported in the majority of cases. Consequently, bond strength information can be utilized to locate Brønsted acid sites even if neutron diffraction data are not at our disposal.