Ce regulated surface properties of Mn/SAPO-34 for improved NH3-SCR at low temperature

Abstract

Ce modified MnO_x/SAPO-34 was prepared and investigated for low-temperature selective catalytic reduction of NO_x with ammonia (NH₃-SCR). The 0.3Ce–Mn/SAPO-34 catalyst had nearly 95% NO conversion at 200–350 °C at a space velocity of 10 000 h⁻¹. Microporous SAPO-34 as the support provided the catalyst with increased hydrothermal stability. XPS and H₂-TPR results proved that the Mn⁴⁺ and O_α content increased after incorporation of Ce, this promoted the conversion of NO at low temperature via a ‘fast SCR’ route. NH₃-TPD measurements combined oxidation experiments of NO, NH₃ indicated the reduction of both the surface acidity and the amount of acid sites, which effectively decreased the NH₃ oxditaion to NO or N₂O at elevated temperature and promoted the catalytic selectivity for nitrogen. A redox cycle between manganese oxide and Ce was assumed for the active oxygen transfer and facilitated the catalyst durability.