Comparison of sulfuric acid- or phosphoric acid-modified CeO2 and the influence of surface acidity and redox property on its activity toward NH3-SCR

• Published in: Research on chemical intermediates Vol. 45; no. 2; pp. 645 - 661
• Main Authors: Song, Zhongxian, Wang, Junkai, Zhang, Qiulin, Ren, Dong, Liu, Hongpan, Ning, Ping, Zhang, Xuejun, Kang, Haiyan, Liu, Biao, Mao, Yanli
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 15.02.2019; Springer Nature B.V
• Subjects: Ammonia; Catalysis; Catalytic activity; Cerium oxides; Chemistry; Chemistry and Materials Science; Inorganic Chemistry; Nitrates; Oxidation; Phosphates; Phosphoric acid; Physical Chemistry; Selective catalytic reduction; Sulfates; Sulfuric acid; Phosphates; Redox property; Sulfates; Surface acidity; Mechanism
• ISSN: 0922-6168; 1568-5675
• DOI: 10.1007/s11164-018-3635-2

A series of CeO 2 prepared with H 2 SO 4 (C–S), H 3 PO 4 (C–P) and H 2 SO 4  + H 3 PO 4 (C–P–S) were investigated in selective catalytic reduction of NO x with NH 3 . The sulfates contributed to the improvement of Brønsted (B) acid sites, while phosphates were prone to the enhancement of Lewis (L) acid sites, which could improve the catalytic activity. Furthermore, sulfates existed in the surface of C–P–S and C–S; phosphates occurred on the subsurface region or were highly dispersed on the surface of C–P–S and C–P. Besides, the nitrates adsorbed on the CeO 2 and NH 3 contacted with the sulfates, which followed the L–H mechanism at 200 °C on C–P–S and C–S. The adsorption and activation of NO and NH 3 over C–P occurred at the same active sites, which obeyed the E–R mechanism at 200 °C. C–P–S possessed the best catalytic activity because of the appropriate surface acidity and redox property, and more than 80% conversion of NO x was obtained at 220–450 °C. Graphical abstract CeO 2 modified by H 2 SO 4 (C–S), H 3 PO 4 (C–P) and H 2 SO 4  + H 3 PO 4 (C–P–S) was prepared and used for selective catalytic reduction of NO x by NH 3 . The presence of sulfate species over C–S and C–P–S contributed to the formation of surface acidity. CeO 2 modified by phosphoric acid favored excellent oxidation ability.