Synthesis of MgO@CeO2-MnOx core shell structural adsorbent and its application in reducing the competitive adsorption of SO2 and NOx in coal-fired flue gas

Abstract

Magnesium oxide (MgO) with different morphologies was prepared by oxalic acid sol-gel method and the MgO were used to prepare three different kinds of adsorbents for simultaneous SO2 and NOx removal from coal-fired flue gas. It was found that the core-shell coated adsorption material MgO@CeO2-MnOx prepared from MgO formed by calcination of magnesium oxalate at 650 ℃ had the best performance. The MgO@CeO2-MnOx exhibited an adsorption breakthrough time up to 50 min and dynamic adsorption capacity of 0.3507 mmol/g and 0.1407 mmol/g for SO2 and NOx respectively. This is better than any other composite material. The N2 adsorption-desorption isotherms result showed that core-shell structure material possessed the largest specific surface area, which could be its basic advantage for efficient adsorption. According to different operating conditions tests, it was found that the adsorption of SO2 and NOx by the adsorbent was dominated by chemisorption. Therefore, the surface metal material (MnOx, CeO2) played an important role in the adsorption process. According to FTIR and DRIFTS analysis, it was observed that the SO2 and NO were oxidized by hydroxyl groups on the absorbent surface and the oxidation was further aggravated by the presence of Mn4+, Mn3+, Ce3+and Ce4+. Core-shell materials successfully prepared can reduce or weaken the adsorption competition between SO2 and NOx in three aspects: 1. The surface oxidation ability is strengthened and it is easy to adsorb the two substances, which makes the metal oxides on the shell surface interact fully with the adsorbents; 2. More and more effective adsorption sites are provided; 3. The adsorbent provides greater specific surface area and appropriate pore size.