Macroporous SmMn2O5 mullite for NOx-assisted soot combustion

Abstract

A series of mullite SmMn₂O₅ oxides were prepared by citric acid (CA), hydrothermal (HT) and co-precipitation (CP) and combustion of ethylene glycol and methanol solutions (EG&M) methods, and tested for NO_x-assisted soot combustion. The catalyst performance tests were conducted under “loose” contact conditions and the physical and chemical properties characterized by XRD, FTIR, BET, SEM, XPS, and O₂-TPD and H₂-TPR measurements. The SmMn₂O₅-EG&M catalyst possessed a distinct morphology with slabs separated by interconnected macropores, and exhibited the overall highest catalytic activity for soot combustion. The corresponding T₁₀, T₅₀, and T₉₀ were 283 °C, 368 °C, and 420 °C, respectively, and the CO₂ selectivity was 99.6%. The soot combustion activation energy for the SmMn₂O₅-EG&M catalyst is 65 kJ mol⁻¹. O₂-TPD and H₂-TPR measurements demonstrated higher mobility and better reducibility of surface adsorbed oxygen for the EG&M sample. The soot combustion is greatly accelerated by the NO₂-assisted mechanism under a NO + O₂ atmosphere and further enhanced by the interconnected macropores of the catalyst, facilitating an intimate contact between the soot and the catalyst. Our study reveals that SmMn₂O₅ mullite is an effective catalyst for NO_x-assisted soot combustion.