Modification of the W/CeZrOx Catalyst with Transition Metal Cu for Selective Catalytic Oxidation of NH3

Abstract

NH₃ selective catalytic oxidation (NH₃-SCO) is an effective technology for solving the ammonia slip problem from NH₃-fueled engines. However, achieving high activity and high N₂ selectivity during catalytic reactions remains a significant challenge. Herein, the W/CeZrO_x catalyst was modified with varying Cu loadings (5, 10, 20, and 40 wt %) to improve its low-temperature activity. Among these, 20Cu–W/CeZrO_x (20 wt %) exhibited the optimal catalytic performance, achieving 97% NH₃ conversion at 300 °C. On the other hand, the NH₃ conversion of the W/CeZrO_x catalyst was only 55% even at 400 °C. The N₂ selectivity of the 20Cu–W/CeZrO_x catalyst was higher than 82% over a wide temperature range of 225–400 °C. Various characterization techniques revealed that Cu introduction increased the proportion of surface-adsorbed oxygen on the W/CeZrO_x catalyst, which played a crucial role in enhancing NH₃-SCO activity. In situ DRIFTS results indicated that both W/CeZrO_x and 20Cu–W/CeZrO_x catalysts followed an internal selective catalytic reduction (i-SCR) mechanism in the NH₃-SCO reaction. The abundance of surface-adsorbed oxygen facilitated the overoxidation of NH₃ species on the surface of the 20Cu–W/CeZrO_x catalyst to NO, thereby accelerating the NH₃-SCO reaction. Meanwhile, NO further reacted with the amide (−NH₂) to produce harmless N₂ and H₂O, and only a small amount of NO was further oxidized to form N₂O and NO₂, which contributed to maintaining excellent N₂ selectivity.