Single Mo atoms paired with neighbouring Ti atoms catalytically decompose ammonium bisulfate formed in low-temperature SCR

Abstract

Selective catalytic reduction (SCR) of NO_x with NH₃ has been widely used for NO_x emission control, but commercial catalysts inevitably suffer severe deactivation in SO₂-containing stack gases at low temperatures because the ammonium bisulfate (NH₄HSO₄, ABS) formed in SCR blocks the surface active sites. We resolve this issue by developing a TiO₂-supported single-atom Mo catalyst (Mo₁/TiO₂) that decomposes ABS at ∼225 °C, far lower than the dew point of ABS (∼260 °C). Single Mo atoms paired with the neighboring surface Ti atoms function as Mo–Ti acid–base dual sites, which respectively adsorb the NH₄⁺ and HSO₄⁻ of ABS. After the oxidation of NH₄⁺ by surface lattice oxygen on the Mo sites, electrons left behind on the dual sites are localized around the Fermi level, which allows them to transfer to the adsorbed HSO₄⁻ on the Ti sites, thus releasing SO₂ at low temperatures. The Mo₁/TiO₂ catalyst with Mo–Ti acid–base dual sites enables the decomposition of ABS at low temperatures, and thus this work provides a way to effectively control NO_x emission particularly from industrial boilers.