Thermal decomposition of SO₄ ^2--intercalated Mg-Al layered double hydroxide: Elimination behavior of sulfur oxides

The thermal properties of SO₄ ^2--intercalated Mg-Al layered double hydroxide (SO₄.Mg-Al LDH) were investigated using simultaneous thermogravimetry-mass spectrometry (TG-MS), and the elimination behavior of sulfur oxides from this double hydroxide was examined. The TG-MS results showed that SO₄.Mg-Al LDH decomposed in five stages. The first stage involved evaporation of surface-Adsorbed water and interlayer water in SO₄.Mg-Al LDH. In the second, third, and fourth stages, dehydroxylation of the brucite-like octahedral layers in SO₄.Mg-Al LDH occurred. The fifth stage corresponded to the elimination of SO₄ ^2- intercalated in the interlayer of Mg-Al LDH, producing SO ₂ and SO₃. The thermal decomposition of SO ₄.Mg-Al LDH resulted in the formation of SO₂ and SO ₃ at 900-1000 °C, which then reacted with H₂O to form H₂SO₃ and H₂SO₄. The elimination of sulfur oxides increased with the decomposition time and temperature. Almost all of the intercalated SO₄ ^2- was desulfurized from SO ₄.Mg-Al LDH at 1000 °C; however, Mg-Al oxide was not formed due to the production of MgO and MgAl₂O₄.