Macroporous SmMn2O5 mullite for NOx-assisted soot combustion

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 NOx-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 O-2-TPD and H-2-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 T-10, T-50, and T-90 were 283 degrees C, 368 degrees C, and 420 degrees 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). O-2-TPD and H-2-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 + O-2 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 NOx-assisted soot combustion.