Effect of preparation methods on the performance of MnO_x-TiO₂ adsorbents for Hg⁰ removal and SO₂ resistance

Aiming at the difficulty of elemental mercury (Hg⁰) removal from flue gas due to its indissolubility in water and the problem of lower SO₂ resistance performance of manganese-based adsorbent, the MnO_x-TiO₂ adsorbents prepared with impregnation (IM), sol-gel (SG) and deposition-precipitation method (DP) were employed to remove Hg⁰ in the absence and presence of SO₂. The adsorbents were characterized by N₂ adsorption-desorption, TG-DSC, XRD, TEM, H₂-TPR, and XPS techniques. The results showed that Hg⁰ removal performance over MnO_x-TiO₂ adsorbents was markedly influenced by the preparation methods. The adsorbent prepared by DP method exhibited a superior activity for Hg⁰ adsorption and the best SO₂ resistance performance. The characterization results indicated that the Hg⁰ removal activity did not correlate with the BET surface area. The preparation method of deposition-precipitation could not only lead to an increase of reducibility and high dispersion of MnO_x, but also significantly enhance a migration of well-dispersed active phase from bulk to surface, resulting in a higher Mn⁴⁺/Mn ratio and the presence of abundant chemisorbed oxygen, which would play an important role in promoting Hg⁰ removal.