Elimination behavior of nitrogen oxides from a NO3−-intercalated Mg-Al layered double hydroxide during thermal decomposition

The thermal properties of NO3−-intercalated Mg-Al layered double hydroxide (NO3·Mg-Al LDH) were investigated using simultaneous thermogravimetry-mass spectrometry (TG-MS), and the elimination behavior of nitrogen oxides from this double hydroxide was examined. The TG-MS results showed that NO3·Mg-Al LDH decomposed in four stages. The first stage involved evaporation of surface adsorbed water and interlayer water in NO3·Mg-Al LDH. In the second and third stages, dehydroxylation of the brucite-like octahedral layers in NO3·Mg-Al LDH occurred. The fourth stage mainly corresponded to the elimination of NO3− intercalated in the Mg-Al LDH interlayers to afford NO2. Thermal decomposition of NO3·Mg-Al LDH at 400-600 °C resulted in the formation of Mg-Al oxide, and the produced NO2 reacted with H2O and O2 to form HNO3 and HNO2. The elimination of nitrogen oxides was found to increase with time and decomposition temperature. The synthesized Mg-Al oxide mixture could be used to remove nitric acid from aqueous solutions.