Mechanism of NH-SCR over P/CeO Catalysts Investigated by Spectroscopies.

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