Alumina-pillared montmorillonite (Al-PILC) was treated with NH 3 in order to extract charge-balancing protons from the octahedral layer and form NH + 4 species between the clay sheets. The adsorbed ammonia gas on the clay after a treatment of 15 min results in a NH + 4 content of ±0.8 mmol/g, as was detected by Kjeldahl N analysis and Fourier transform infrared (FTIR) spectroscopy. Besides NH + 4 cations, the Al-PILC also contains an amount of physisorbed NH 3 , which is removed after degassing under vacuum at room temperature during 30 min. The FTIR data show that NH + 4 species are present in a C 3 v configuration, located in the hexagonal Si-O rings of the tetrahedral clay layers. There was an indication that the NH 3 also interacted with the Al-(OH)-Mg configuration in the octahedral layers. The deammoniation process starts at 200°C and is completed near 500°C. After the decomposition of the NH + 4 , the remaining protons interact with the Si-O bridges of the tetrahedral layer, breaking these bonds and forming Si-OH species. The ammonium treatment has no effect on the dehydroxylation temperature of the PILC, but induces additional hydrophilicity in the pillared clay.