Strong Interaction of CoO x with PO x for Enhanced N 2 Selectivity in Selective Catalytic Oxidation of Ammonia

Selective catalytic oxidation of ammonia (NH 3 –SCO) over transition metal oxide catalysts with high NH 3 conversion and N 2 selectivity at low temperatures is important but remains a significant challenge. Herein, we propose a novel strategy for depositing phosphate (PO x ) onto CeO 2 nanorods, and PO x acts as a host for CoO x (CoO x -P 0.05 /CeO 2 ). The CoO x -P 0.05 /CeO 2 enables an NH 3 conversion of 84% and a N 2 selectivity of 86% at a low temperature of 200 °C, obviously outperforming CoO x /CeO 2 (N 2 selectivity of 40%) and P 0.05 /CeO 2 (NH 3 conversion of 7% even at 250 °C). The strong interaction of CoO x with PO x strengthens the Co–O bond and generates medium-strong acid sites, which are found to play an important role in improving N 2 selectivity. Density functional theory (DFT) calculations and in situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) reveal that the introduction of PO x enhances the binding energy with NH 3 and significantly alters the bidentate nitrate of CoO x /CeO 2 to monodentate nitrate of CoO x -P 0.05 /CeO 2, thereby substantially suppressing the formation of byproducts N 2 O and NO and enhancing N 2 selectivity.