Study on the effect and mechanism of Fe doping on Fe0.2Ce0.8O2-δ CDPF catalyst for NOx-assisted soot catalytic oxidation

Abstract

Herein, FeCeO_2-δ catalyst samples with different Fe doping content were prepared by self-propagation high-temperature synthesis, and the physical and chemical properties of different FeCeO_2-δ catalyst samples were characterized by XRD, BET, TEM, H₂-TPR, XPS and NO-TPO, and the catalytic oxidation performance of FeCeO_2-δ catalyst samples for the oxidation of soot particles was studied. Besides, the catalytic oxidation mechanism of soot particles by NO_x-assisted FeCeO_2-δ catalyst was studied by In-situ DRIFTS. The results show that the Fe_0.2Ce_0.8O_2-δ catalyst sample shows the best catalytic activity of soot particles, and T_10 %, T_50 % and T_90 % are 345 °C, 433 °C and 518 °C, respectively. The calculated activation energy E_a is 58.30 kJ/mol. FeCeO_2-δ catalyst samples with less Fe content are beneficial to the formation of solid solution and have higher specific surface area. The lattice constant and average crystallite size of Fe_0.2Ce_0.8O_2-δ reach the minimum, and the surface particles are uniformly dispersed, forming the most Fe–Ce solid solution with a specific surface area of 54.8 m²/g. Among all FeCeO_2-δ catalyst samples, Fe_0.1Ce_0.9O_2-δ and Fe_0.2Ce_0.8O_2-δ samples are the most easily oxidized and reduced, but when the Fe content in the samples is further increased, it is unfavorable to the redox cycle of Fe³⁺ and Fe²⁺ because of the aggregation of Fe₂O₃ particles on the catalyst surface. The contents of reduced Ce³⁺ and adsorbed oxygen on the surface of Fe_0.2Ce_0.8O_2-δ samples are the highest, and their changing rules are consistent. The doping of Fe can obviously enhance the activity of CeO₂ in catalytic oxidation of NO, and the Fe_0.2Ce_0.8O_2-δ catalyst sample shows the best NO oxidation activity. Due to the weak adsorption of NO_x on FeCeO_2-δ catalyst samples, NO is the main desorption product in the temperature range of 50 °C–200 C NO_x adsorbed on FeCeO_2-δ catalyst surface mainly exists in the form of nitrite and nitrate species, and the stability of nitrate species on the surface is stronger than that of nitrite species.