Ultrahighly Alkali-Tolerant NO_<i>x</i> Reduction over Self-Adaptive CePO₄/FePO₄ Catalysts

Abstract

Catalyst deactivation caused by alkali metal poisoning has long been a key bottleneck in the application of selective catalytic reduction of NO_<i>x</i> with NH₃ (NH₃-SCR), limiting the service life of the catalyst and increasing the cost of environmental protection. Despite great efforts, continuous accumulation of alkali metal deposition makes the resistance capacity of 2 wt % K₂O difficult to enhance via merely loading acid sites on the surface, resulting in rapid deactivation and frequent replacement of the NH₃-SCR catalyst. To further improve the resistance of alkali metals, encapsulating alkali metals into the bulk phase could be a promising strategy. The bottleneck of 2 wt % K₂O tolerance has been solved by virtue of ultrahigh potassium storage capacity in the amorphous FePO₄ bulk phase. Amorphous FePO₄ as a support of the NH₃-SCR catalyst exhibited a self-adaptive alkali-tolerance mechanism, where potassium ions spontaneously migrated into the bulk phase of amorphous FePO₄ and were anchored by PO₄^3- with the generation of Fe₂O₃ at the NH₃-SCR reaction temperature. This ingenious potassium storage mechanism could boost the K₂O resistance capacity to 6 wt % while maintaining approximately 81% NO_<i>x</i> conversion. Besides, amorphous FePO₄ also exhibited excellent resistance to individual and coexistence of alkali (K₂O and Na₂O), alkali earth (CaO), and heavy metals (PbO and CdO), providing long durability for CePO₄/FePO₄ catalysts in flue gas with multipollutants. The cheap and accessible amorphous FePO₄ paves the way for the development and implementation of poisoning-resistant NO_<i>x</i> abatement.