In high temperature in situ FT-IR (HTFTIR) spectra of Mg and Al layered double hydroxide with interlayer naphthalene-2,6-disulfonate ( Mg / Al / N 26 DS - LDH ), one S - O stretching vibration band of the non-coordinating - SO 3 group in the interlayer N 26 DS dianion is observed below 400 °C at 1035 cm-1 with keeping intensity. High temperature in situ X-ray diffraction (HTXRD) indicates that the basal spacing remains also constant up to 400 °C, MgSO 4 appears after the LDH collapses at 500 °C and some metal oxides are formed at higher temperature. Both results in HTXRD and HTFTIR indicate that the layered structure in this LDH is stable against heating up to 400 °C.