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

Selective catalytic reduction (SCR) of NOx with NH3 has been widely used for NOx 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 NOx emission particularly from industrial boilers.