Evaluation of an Integrated Selective Catalytic Reduction-Coated Particulate Filter

Abstract

In this study, an SCR-coated particulate filter with soot loaded from engine bench experiments was evaluated. Prior to soot loading, the sample was hydro-thermally aged at 850 degrees C. Flow reactor measurements were performed under various reaction conditions to examine the impact of soot in an SCR-coated diesel particulate filter (DPF) on standard SCR, fast SCR, NH3 oxidation, and NO oxidation. In the presence of soot, NOx conversion was slightly lower at 200-300 degrees C due to the blocking of active sites. However, at higher temperatures, the NOx conversion was somewhat higher with soot, indicating that soot more strongly inhibited the oxidation of NH3 than the SCR reaction. When feeding equal amounts of NO and NO2 together with NH3, ammonium nitrates on the sample were formed. The presence of soot significantly decreased the formation or the stability of ammonium nitrate, resulting in higher conversion with soot. To further understand this interesting aspect, ammonium nitrate formation and decomposition experiments using model Cu/BEA catalyst with and without soot were performed. It was observed that less N2O was formed in the presence of soot, and this in combination with COx formation during the ammonium nitrate formation step suggested that soot reacted with the ammonium nitrates, and we propose that this occurs on CuO species on the outside of the zeolite particles.