Synthesis of MnO2/Mg-Al layered double hydroxide and evaluation of its NO-removal performance

The removal of toxic nitric oxide (NO) from exhaust gas is challenging and expensive. MnO2/Mg-Al LDH, a composite of manganese dioxide and Mg-Al layered double hydroxide, was synthesized via the rehydration method for potential application in NO removal. MnO2/Mg-Al LDH was found to be complexed with MnO2, pillared between the LDH layers and intercalated with CO32- and OH-. We investigated the performance of a MnO2/Mg-Al LDH treatment in removing NO from exhaust gas. The exhaust gas was circulated in a reaction tube filled with MnO2/Mg-Al LDH, CO3 center dot Mg-Al LDH, or a MnO2 + CO3 center dot Mg-Al LDH mixture, and the NO removal efficiency of the MnO2/Mg-Al LDH composite was compared with that of the other compounds. When NO gas (150 ppm, linear velocity 1.0 m/min) was distributed at 170 degrees C, treatment with the MnO2 center dot Mg-Al LDH composite and CO3 center dot Mg-Al LDH yielded removal rates of 83.9% and 0%, respectively. The significantly higher NO removal rate of MnO2/Mg-Al LDH was ascribed to the transformation of NO to NO2 via oxidation over MnO2. Further, the NO removal rate after 90 min through the application of a simple mixture of MnO2 and CO3 center dot Mg-Al LDH (Mn: 4.2 wt %) was only 1.4%, suggesting that a synergistic effect was generated by the MnO2/Mg-Al LDH composite. Though NO removal by MnO2/Mg-Al LDH was reduced at temperatures of 140 degrees C and higher, the results suggest that the synthesized compound can be much more effective than those commonly used for NO removal from exhaust gas. (C) 2021 Elsevier B.V. All rights reserved.