Experimental Studies on NOx Removal and Soot Regeneration Characteristics of a Selective Catalytic Reduction Filter

Abstract

Herein, the NO_x removal capability of SCRF based on the Cu/SSZ-13 catalyst and its influencing factors were comprehensively explored. The reaction characteristics of important reactions in SCRF including SCR, fast SCR, NH₃ oxidation, etc. under different soot contents were studied under quasi-steady-state experimental conditions, as well as the influence of reactant conditions on soot regeneration. The results indicated the following: Cu/SSZ-13 SCRF achieves NO_x conversion efficiency exceeding 90% at 250 °C, comparable to through-flow SCR. Fast SCR performance is over 20% better than that of standard SCR at 200 °C, while NO₂–SCR shows the lowest NO_x removal. A significant amount of N₂O is generated, with NH₄NO₃ formation impeding the SCR reaction. An NO₂/NO_x ratio of 0.4 enhances NO_x removal. To limit NH₄NO₃ formation at low temperatures, an NH₃/NO_x ratio of 0.8 or lower is advised below 200 °C; above this temperature, the ratio should exceed 1 due to strong ammonia oxidation. Soot loading hinders NO_x removal at 200–500 °C but enhances it above 500 °C. NH₃-TPD, NH₃-TPO, and N₂O generation experiments indicate that NH₃ adsorption sites exist on soot, covering the Cu-based catalyst surface. Quasi-steady state SCR tests show that while the SCR reaction does not actively regenerate soot, it strongly inhibits passive regeneration. Under NO₂ intake, the level of CO₂ from passive regeneration at 300 °C increased by 175 ppm, indicating competition with NO₂.