Enhancing the Understanding of a State-of-the-Art Fe/zeolite Selective Catalytic Reduction Catalyst

Fe/zeolite selective catalytic reduction (SCR) catalysts are commercially used for NO_x emissions reduction from diesel engines. In comparison to Cu/zeolite, these catalysts are widely reported to form less N₂O as a byproduct of the SCR reactions. However, Fe/zeolite SCR is less active than Cu/zeolite for low temperature NO_x conversion under standard SCR conditions. In this study, a state-of-the-art Fe/zeolite SCR catalyst is probed with a combination of N₂ physisorption, SEM/EDX, reactor-based performance and active site quantification. Measurements investigate the impact of degreening, mild and extreme hydrothermal aging. In a degreened condition, the impact of water vapor on standard and fast SCR and isothermal desorption of NH₃ is assessed. The Fe/zeolite catalyst’s hydrothermal durability is studied following hydrothermal aging at temperatures from 550°C up to 950°C. NH₃ adsorption and temperature programmed desorption (TPD) and NO₂ adsorption and TPD experiments are used to quantify the surface acidity and active Fe sites of the catalysts, respectively. Kinetic analysis of the standard SCR data is conducted to elucidate the mechanisms responsible for SCR activity loss upon hydrothermal aging. The authors believe the results presented herein can support the industry wide efforts to continue to improve diesel emissions control.