Improved NOxReduction over Phosphate-Modified Fe2O3/TiO2Catalysts ViaTailoring Reaction Paths by In SituCreating Alkali-Poisoning Sites

The deactivation issue arising from alkali poisoning over catalysts is still a challenge for the selective catalytic reduction of NOxby NH3. Herein, improved NOxreduction in the presence of alkaline metals over phosphate-modified Fe2O3/TiO2catalysts has been originally demonstrated viatailoring the reaction paths by in situcreating alkali-poisoning sites. The introduction of phosphate results in the partial formation of iron phosphate species and makes the catalyst to mainly exhibit the characteristics of FePO4, which is responsible for the widened temperature window and enhanced alkali resistance. The tetrahedral [FeO4]/[PO4] structures in iron phosphate act as the Brønsted acid sites to increase the catalyst surface acidity. In addition, the formation of an Fe–O–P structure enhances the redox ability and increases surface adsorbed oxygen. Furthermore, the created phosphate groups (PO43–) serving as alkali-poisoning sites preferentially combine with potassium so that iron species on the active sites are protected. Therefore, the enhanced NH3species adsorption capacity, improved redox ability, and active nitrate species remaining in the phosphate-modified Fe2O3/TiO2catalyst ensure the de-NOxactivity after being poisoned by alkali metals through the Langmuir–Hinshelwood reaction pathway. Hopefully, this novel strategy could provide an inspiration to design novel catalysts to control NOxemission with extraordinary resistance to alkaline metals.