La-promoted oxygen vacancy formation in CePO4 catalysts: Unraveling Ce-La interactions and reaction mechanisms for enhanced low-temperature NH3-SCR performance

Abstract

Developing CePO₄-based NH₃-SCR catalysts with superior low-temperature performance represents a significant challenge. While CePO₄ has garnered substantial interest due to its abundant surface acidic sites, its limited redox capacity severely restricts low-temperature denitrification efficiency. To address this, a Ce_0.75La_0.25PO₄ catalyst was rationally designed and successfully synthesized. Studies demonstrated that La doping enhances surface oxygen vacancy concentration, boosts redox capability, and improves low-temperature NH₃-SCR activity, achieving over 95 % NO_x conversion at 250 °C. Combined experimental and computational investigations were performed to explore the atomic-level surface structure of Ce_0.75La_0.25PO₄ and the adsorption behaviors of NH₃ and NO molecules. Characterization results further validated the feasibility of La-doped CePO₄ solid solutions as efficient catalysts, revealing that La doping induces surface oxygen vacancies to enhance redox properties, thereby promoting low-temperature NH₃-SCR performance. DRIFTS analysis confirmed that La doping facilitates NO adsorption and activation on the catalyst surface, accelerating the L-H mechanism. These findings provided mechanistic insights into the superior low-temperature NH₃-SCR activity of Ce_0.75La_0.25PO₄. DFT calculations indicated that the (111) crystal plane was the most stable surface of Ce_0.75La_0.25PO₄, with NH₃ and NO adsorbing on Brønsted and Lewis acid sites; notably, NO exhibited the strongest adsorption on La atoms.