Compensation or Aggravation: Pb and SO 2 Copoisoning Effects over Ceria-Based Catalysts for NO x Reduction.

Severe catalyst deactivation caused by multiple poisons, including heavy metals and SO 2 , remains an obstinate issue for the selective catalytic reduction (SCR) of NO x by NH 3 . The copoisoning effects of heavy metals and SO 2 are still unclear and irreconcilable. Herein, the unanticipated differential compensated or aggravated Pb and SO 2 copoisoning effects over ceria-based catalysts for NO x reduction was originally unraveled. It was demonstrated that Pb and SO 2 exhibited a compensated copoisoning effect over the CeO 2 /TiO 2 (CT) catalyst with sole active CeO 2 sites but an aggravated copoisoning effect over the CeO 2 -WO 3 /TiO 2 (CWT) catalyst with dual active CeO 2 sites and acidic WO 3 sites. Furthermore, it was uniquely revealed that Pb preferred bonding with CeO 2 among CT while further being combined with SO 2 to form PbSO 4 after copoisoning, which released the poisoned active CeO 2 sites and rendered the copoisoned CT catalyst a recovered reactivity. In comparison, Pb and SO 2 would poison acidic WO 3 sites and active CeO 2 sites, respectively, resulting in a seriously degraded reactivity of the copoisoned CWT catalyst. Therefore, this work thoroughly illustrates the internal mechanism of differential compensated or aggravated deactivation effects for Pb and SO 2 copoisoning over CT and CWT catalysts and provides effective solutions to design ceria-based SCR catalysts with remarkable copoisoning resistance for the coexistence of heavy metals and SO 2 .