Promoter not inhibitor: The antidotal effects of arsenic on lead-poisoning V₂O₅−WO₃/TiO₂ catalyst for selective catalytic reduction of NO_x with NH₃

Arsenic has been considered a strong inhibitor for a variety of catalysts for the selective catalytic reduction of NO_x with NH₃ (NH₃−SCR). However, in this work, we found arsenic exhibits a remarkable detoxification effect on lead-poisoning V₂O₅−WO₃/TiO₂ catalysts. With only 0.9 wt% arsenic introduction, the NO_x conversion over Pb–V₂O₅−WO₃/TiO₂ (lead: 2 wt%) could be raised from 35% to 81% at 250 °C under a GHSV of 100,000 h⁻¹. More surprisingly, the negative effect of arsenic on N₂ selectivity was greatly inhibited simultaneously. The catalyst characterizations and DFT simulation manifest that arsenic could not only extricate VO_x sites and related Lewis acid sites from lead shackles but also promote the redox property through its stronger electronic interaction with the lead. On the basis of in situ DRIFTS and kinetic study, regenerated V=O sites were profitable to the adsorption and activation of NH₃ species, thus greatly improving the SCR activity. We demonstrate that the antidotal effect of arsenic to lead poisoning V₂O₅−WO₃/TiO₂ catalyst is the increase of active site amount rather than the change of reaction pathway. It is believed that the novel findings above could open up an innovative pathway for toxic heavy metals reduction and catalyst designing with virtuous anti-poisoning performance.