Rb-exchange and thermal stability of the microporous titanosilicate AM-2 were analysed by powder X-ray diffraction, thermogravimetric analysis, and chemical analysis of the mother liquid after exchange. The dehydration and thermal stability of the exchanged structure were monitored with in situ high temperature powder X-ray diffraction. Crystal structures were refined with Rietveld methods at 25 and 400 degrees C. The AM-2 structure was found to incorporate Rb(+) by replacing K(+). After four exchange cycles and 166 h reaction time at 90 degrees C, the chemical composition was refined to K(0.18)Rb(1.82)TiSi(3)O(9)center dot H(2)O. Extrapolation suggests that higher exchange ratios may be obtained after further cycles. H(2)O was expelled by heating, leading to a dehydrated structure at 360 degrees C. Dehydration was associated with a change of space group symmetry from orthorhombic P2(1)2(1)2(1) to monoclinic P2(1), which proved to be reversible after rehydration. This change of symmetry leaves the AM-2 characteristic structural topology uninfluenced and causes only minor distortions. The monoclinic AM-2 structure breaks down above 600 degrees C to become X-ray amorphous, and at 750 degrees C a wadeite-type phase (K(x)Rb(2-x)TiSi(3)O(9)) crystallises. This transformation is irreversible and leads to immobilisation of Rb(+). (C) 2006 Elsevier Ltd. All rights reserved.