Prominent difference in the deactivation rate and mechanism of V2O5/TiO2 under H2S or SO2 during selective catalytic reduction of NOx with NH3

Selective catalytic reduction (SCR) over V2O5/TiO2-based catalysts is the most efficient technology to remove nitrogen oxides from stationary sources, where H2S coexists with NOx under variable combustion conditions. For the first time, the poisoning effect of H2S was observed to be almost six-fold that of SO2. Catalyst deactivation under SO2 was mainly caused by ammonium bisulfate while sulfates, especially polymeric sulfate, were the main contributors to H2S poisoning. Theoretical calculations showed that the generation of sulfates was much more energetically favorable under H2S than under SO2, resulting in massive deposition of sulfates and serious damage to vanadyl (V--O). Polymeric sulfate could inhibit the charge transfer between the occupied and unoccupied orbitals of V--O and suppress NH3 activation, thereby significantly restraining SCR activity. Furthermore, unstable sulfur species were shown to be responsible for the temporary deactivation during H2S poisoning. This work provides crucial information for solving catalyst deactivation.

Automated summary

Selective catalytic reduction (SCR) over V2O5/TiO2-based catalysts is an efficient technology for removing nitrogen oxides from stationary sources in the presence of H2S and NOx. H2S was found to be six times more poisonous than SO2, with polymeric sulfate being the main contributor to H2S poisoning. The generation of sulfates was energetically more favorable under H2S, causing deposition and damage to V--O. Polymeric sulfate inhibited charge transfer and NH3 activation, resulting in significant SCR activity suppression. Unstable sulfur species were responsible for temporary deactivation during H2S poisoning. This work provides crucial insights for solving catalyst deactivation.