Catalytic conversion of mercury over Ce doped Mn/SAPO-34 catalyst: Sulphur tolerance and SO₂/SO₃ conversion

A series of Mn-Ce/SAPO-34 catalysts were prepared to study the catalytic oxidisation of elemental mercury (Hg⁰). Sulphur tolerance and SO₃ formation over the catalyst were studied further. Hg⁰ was transported by compressed air from PSA Cavkit. NO, SO₂, and NH₃ are standard gases, and H₂O is produced by gas carrying. Mn could incorporate into the cerium oxide lattice to form capping oxygen and well-dispersed high valance manganese ions after the addition of Ce, which was conducive to NO removal and Hg⁰ oxidisation. 9 Mn-9Ce showed the best performance regarding Hg⁰ conversion, achieving more than 92% Hg⁰ conversion efficiency at 50-300 °C. The sulphur resistance of the Mn-based catalyst was significantly improved after the addition of cerium due to the high affinity of Ce for SO₂, and the relative content of HgSO₄ was exceeded 72% on the 9 Mn-9Ce catalyst with SO₂; SO₃ formation over the 9 Mn-9Ce decreased by 17% compared with the 9 Mn. H₂O not only reduced the available active site, but also decreased the oxidation rate of SO₂. The active sites were preferentially occupied by NH₃ rather than Hg⁰ and SO₂, generated NH₄⁺ occupied cation vacancies. Therefore, both H₂O and NH₃ have inhibitory effects on Hg⁰ conversion and SO₃ formation.