The Superior Performance of Sol–Gel Made Ce–O–P Catalyst for Selective Catalytic Reduction of NO with NH₃

In this paper, a sol–gel made Ce–O–P catalyst (referred to as Ce–O–P-SG) was employed for selective catalytic reduction (SCR) of NO_x with NH₃, which was directly compared with two other Ce–O–P samples as synthesized via hydrothermal and coprecipitation routes (referred to as Ce–O–P-HT and Ce–O–P-CP, respectively). Experimental results revealed that the Ce–O–P-SG catalyst yielded a more than 90% NO conversion at 200 °C in the presence of 10 vol % H₂O, whereas Ce–O–P-HT and Ce–O–P-CP catalysts only showed 50% and 20% NO conversions under the same conditions, respectively. After subjected to a series of characterization technologies (e.g., XRD, BET-BJH, XPS, NH₃-TPD, py-IR, and H₂-TPR), it was found that more enriched surface Ce­(4+) species were formed except for the two main CePO₄ phases (monazite and rhabdophane phases) of the Ce–O–P-SG catalyst compared to the other two samples, resulting in the increase of surficial active oxygen ions content. This could lead to an enhancement in surface acidity and redox capacity of the Ce–O–P-SG catalyst, effectively promoting the NH₃–SCR activity of the catalyst. Further analyses on SO₂ and H₂O tolerance revealed that the Ce–O–P-SG possessed a higher sulfur resistance than the other two samples, which could be attributed to the SO₂ trapping effect by the abundant active oxygen species over Ce–O–P-SG catalyst.