Catalytic combustion of soot over Cu, Mn substitution CeZrO2-delta nanocomposites catalysts prepared by self-propagating high-temperature synthesis method

摘要

This study concentrates on improving the low temperature performance of CDPF catalysts. The self-propagating high temperature combustion synthesis method was applied to synthesize a series of CeZrO2-delta, CuCeZrO2-delta, and MnCuCeZrO2-delta catalysts, which were coated on DPF substrate. The performance of the catalysts was fully investigated by the soot temperature programmed combustion, which showed that these catalysts with nanometer size have a high catalytic activity of soot combustion at low temperatures. Compared with Ce0.05Zr0.005O2-delta, Cu0.9Ce0.005Zr0.005O2-delta and Mn0.09Cu0.81Ce0.05Zr0.005O2-delta showed excellent low temperature soot oxidation activities and much higher CO2 selectivity. BET, XRD, TEM, and XPS were employed to characterize the structural and physical-chemical properties of catalysts. The XRD results indicated that catalysts with 90% Cu possess evenly distributed crystalline grains and small particle size, which is responsible for its excellent oxidation activity by providing more active sites as well as forming good connection between the catalyst and soot. The XPS results demonstrated that the Cux+ has a significant association with the formation of NO2, thus promoting the soot oxidation, and that the synergetic effect between Cux+ and Mnx+ contributes most to the improvement of the catalytic activity. The partial substitution with Mn could enhance the chemisorbed oxygen, which further improved NO oxidation and CO2 selectivity. Furthermore, the soot combustion reaction mechanism was examined with in situ DRIFTS. The results exhibited that the active sites of Cu0.9Ce0.05Zr0.05O2-delta and Mn0.09Cu0.81Ce0.05Zr0.05O2-delta could generate more reactive oxygen for NO oxidation and that the uniformly dispersed Cux+ and Mnx+ in Ce lattice could adsorb NO2 to form nitrite and nitrates, which behaved as a carrier of NO2 and transported it around the surface of soot, thus facilitating the soot combustion, especially at low temperatures. (C) 2