Comparative Study of Cu-SSZ-13 and V ₂ O ₅ –WO ₃ /TiO ₂ Catalysts on Ammonia Storage and Slip Behavior

This study compared the adsorption-desorption behavior of NH₃ on Cu-SSZ-13 and V₂O₅-WO₃/TiO₂ catalysts using an NH₃-SCR flow reactor, systematically investigating the effects of temperature, space velocity, and NH₃/NOx ratio on the ammonia storage performance and ammonia slip characteristics of catalysts. The relationship between ammonia storage capacity and NOx conversion efficiency as well as N₂O formation was further analyzed. The results indicate that increasing temperature and space velocity reduce the ammonia storage capacity of the catalysts. Under conditions of high temperature (500 °C) and high space velocity (60,000 h^-1), the saturated ammonia storage capacity of the catalyst decreases by 20-30%, leading to an increased risk of ammonia slip and causing ammonia slip to occur approximately 20% earlier during the NH₃-SCR process. Excessive NH₃/NOx ratios also exacerbate ammonia slip due to NH₃ overloading. In terms of reaction performance, higher ammonia storage capacity provides more active ammonia species on the catalyst surface, significantly enhancing the reduction activity. Particularly at temperatures below 300 °C, increased ammonia storage improves the NOx conversion efficiency of the catalyst. However, when the temperature exceeds 300 °C, due to the already high catalytic activity, the effect of ammonia storage on NOx conversion is not significant. It should be noted that excessive NH₃ adsorption not only improves NOx conversion efficiency but also leads to the formation of 15 ppm of the byproduct N₂O, leading to secondary emission issues. Overall, Cu-SSZ-13 demonstrates superior ammonia storage capacity and reaction stability compared to the vanadium-based catalyst over a wide range of temperatures and space velocities. Its ammonia storage capacity is less affected by operational variations, thereby more effectively delaying ammonia slip.