Study of NH4+ in the zeolite phillipsite by combined synchrotron powder diffraction and IR spectroscopy

The Rietveld refinement on synchrotron data of three natural hydrated NH4+-exchanged phillipsites with different Si/Al ratios allowed acceptable assignment of the NH4+ sites. These phillipsites display the typical monoclinic P2(1)/m cell, whose volume increases with increasing numbers of NH4+ ions, which are refined in the two sites labelled I and II. Some residual Na+ is retained in the site labelled II'. Distortion of the Si/Al tetrahedra, which affects some absorption bands in the IR spectra, seems to be mainly due to the distribution of Al in the framework, while the interaction of NH4+ with the O atoms of the framework seems to play a minor role. NH4+ in both sites acts as a donor in hydrogen bonding with O atoms of the framework and water molecules. NH4+ in site I has three H atoms interacting with O atoms of the framework and a number of interactions with water O atoms. In all three samples, monocentric and dicentric connections are formed. NH4+ in site II has one H atom interacting with O atoms of the framework and a number of interactions with water O atoms. Two monocentric connections and a quadricentric one were found in sample (1), three dicentric connections and a monocentric one in sample (2), and three monocentric connections and a dicentric one in sample (3).