Improved Pd/CeO₂ Catalysts for Low-Temperature NO Reduction: Activation of CeO₂ Lattice Oxygen by Fe Doping

Developing better three-way catalysts with improved low-temperature performance is essential for cold start emission control. Density functional theory in combination with microkinetics simulations is used to predict reactivity of CO/NO/H₂ mixtures on a small Pd cluster on CeO₂(111). At low temperatures, N₂O formation occurs via a N₂O₂ dimer over metallic Pd₃. Part of the N₂O intermediate product re-oxidizes Pd, limiting NO conversion and requiring rich conditions to obtain high N₂ selectivity. High N₂ selectivity at elevated temperatures is due to N₂O decomposition on oxygen vacancies. Doping CeO₂ by Fe is predicted to lead to more oxygen vacancies and a higher N₂ selectivity, which is validated by the lower onset of N₂ formation for a Pd catalyst supported on Fe-doped CeO₂ prepared by flame spray pyrolysis. Activating ceria surface oxygen by transition metal doping is a promising strategy to improve the performance of three-way catalysts.