Mechanism of NH3‑SCR over P/CeO2 Catalysts Investigated by Operando Spectroscopies

• Published in: Environmental science & technology Vol. 57; no. 43; pp. 16289 - 16295
• Main Authors: Zhang, Ningqiang, Tong, Jiahuan, Miyazaki, Shinta, Zhao, Shirun, Kubota, Hiroe, Jing, Yuan, Mine, Shinya, Toyao, Takashi, Shimizu, Ken-ichi
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 31.10.2023
• Subjects: Ammonia; Catalysts; Cerium oxides; Chemical reduction; Density functional theory; Energy and Climate; Infrared analysis; Infrared spectroscopy; Intermediates; Investigations; Oxidation; Reaction mechanisms; Selective catalytic reduction; Species; Spectrum analysis; X ray absorption; X-ray absorption spectroscopy; phosphate; ceria dioxide; NH3-SCR; density functional theory (DFT); operando spectroscopy
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.3c05787

This study reports a comprehensive investigation into the active sites and reaction mechanism for the selective catalytic reduction of NO by NH3 (NH3-SCR) over phosphate-loaded ceria (P/CeO2). Catalyst characterization and density functional theory calculations reveal that H3PO4 and H2P2O6 species are the dominant phosphate species on the P/CeO2 catalysts under the experimental conditions. The reduction/oxidation half-cycles (RHC/OHC) were investigated using in situ X-ray absorption near-edge structure for Ce L3-edge, ultraviolet–visible, and infrared (IR) spectroscopies together with online analysis of outlet products (operando spectroscopy). The Ce4+(OH–) species, possibly adjacent to the phosphate species, are reduced by NO + NH3 to produce N2, H2O, and Ce3+ species (RHC). The Ce3+ species is reoxidized by aqueous O2 (OHC). The results from IR spectroscopy suggest that the RHC initiates with the reaction between NO and Ce4+(OH–) to yield Ce3+ and gaseous HONO, which then react with NH3 to produce N2 and H2O via NH4NO2 intermediates.