Balancing acid and redox sites of phosphorylated CeO catalysts for NO reduction: The promoting and inhibiting mechanism of phosphorus.

The role of phosphorus in metal oxide catalysts is still controversial. The precise tuning of the acidic and redox properties of metal oxide catalysts for the selective catalytic reduction in NO using NH is also a great challenge. Herein, CeO catalysts with different degrees of phosphorylation were used to study the balance between the acidity and redox property by promoting and inhibiting effects of phosphorus. CeO catalysts phosphorylated with lower phosphorus content (5 wt%) exhibited superior NO reduction performance with above 90% NO conversion during 240-420 °C due to the balanced acidity and reducibility derived from the highest content of Brønsted acid sites on PO to adsorb NH and surface adsorbed oxygen species. Plenty of PO over CeO catalysts phosphorylated with the higher phosphorus content (≥ 10 wt%) significantly disrupted the balance between the acidity and the redox property due to the reduced acid/redox sites, which resulted in the less active NO species. The mechanism of different structural phosphorus species (PO and PO) in promoting or inhibiting the NO reduction over CeO catalysts was revealed. This work provides a novel method for qualitative and quantitative study of the relationship between acidity/redox property and activity of catalysts for NO reduction.