Experimental study of emission characteristics and performance of SCR coated on DPF with different catalyst washcoat loadings

Abstract

To improve the NOx conversion efficiency (CE) and inlet temperature of selective catalytic reduction (SCR) under low-temperature conditions, SCR coated on diesel particulate filter, so called SDPF, is one of the important technologies to meet the future Euro Ⅶ ultra-low emission regulations for diesel engines. In this study, the effects of different Cu-SSZ-13 catalyst washcoat loadings (60, 90, and 120 g/L) on the SDPF performance were investigated. The results showed that as the catalyst washcoat loading increased, the inlet temperature and pressure drop of the SDPF rose, the high-NOx-conversion-efficiency area expanded toward the low-speed and low-load directions of the engine, and the NOx CE first increased and then decreased. The number of active sites of the catalyst and the SDPF pressure drop together determine the NOx CE. When the catalyst washcoat loading was increased, the nucleation-mode (NM) particle factor decreased significantly, while the accumulation-mode (AM) particle factor decreased slightly. The filtration efficiency of the three types of particles was NM > total > AM from high to low. The higher the washcoat loading, the higher the particle filtration efficiency and the larger the geometric mean diameter. The reduction of NM particles was the result of a combination of the chemical reaction and the physical collection mechanism.