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

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 L-3-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 N-2, H2O, and Ce3+ species (RHC). The Ce3+ species is reoxidized by aqueous O-2 (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 N-2 and H2O via NH4NO2 intermediates.

Automated summary

This study investigates the active sites and reaction mechanism for the selective catalytic reduction of NO by NH3 over phosphate-loaded ceria catalysts. The results reveal the presence of H3PO4 and H2P2O6 species on the catalysts, which interact with Ce4+(OH-) species and undergo reduction/oxidation half-cycles to produce N2, H2O, and Ce3+ species.