Modification of the W/CeZrO_<i>x</i> Catalyst with Transition Metal Cu for Selective Catalytic Oxidation of NH₃

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/CeZrOx catalyst was modified with varying Cu loadings (5, 10, 20, and 40 wt %) to improve its low-temperature activity. Among these, 20Cu–W/CeZrOx (20 wt %) exhibited the optimal catalytic performance, achieving 97% NH3 conversion at 300 °C. On the other hand, the NH3 conversion of the W/CeZrOx catalyst was only 55% even at 400 °C. The N2 selectivity of the 20Cu–W/CeZrOx 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/CeZrOx catalyst, which played a crucial role in enhancing NH3-SCO activity. In situ DRIFTS results indicated that both W/CeZrOx and 20Cu–W/CeZrOx 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/CeZrOx 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.