Balancing acid and redox sites of phosphorylated CeO2 catalysts for NOx reduction: The promoting and inhibiting mechanism of phosphorus
2023
Zhang, Pan | Chen, Aling | Lan, Weitian | Liu, Xiangyu | Yan, Tingting | Ren, Wei | Zhang, Dengsong
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 NOₓ using NH₃ is also a great challenge. Herein, CeO₂ 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. CeO₂ catalysts phosphorylated with lower phosphorus content (5 wt%) exhibited superior NOₓ reduction performance with above 90% NOₓ conversion during 240–420 °C due to the balanced acidity and reducibility derived from the highest content of Brønsted acid sites on PO₄³⁻ to adsorb NH₃ and surface adsorbed oxygen species. Plenty of PO₃⁻ over CeO₂ 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 NOₓ species. The mechanism of different structural phosphorus species (PO₄³⁻ and PO₃⁻) in promoting or inhibiting the NOₓ reduction over CeO₂ 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 NOₓ reduction.
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