Study on the hydrothermal and SO2 stability of Al2O3-supported manganese and iron oxide catalysts for lean CO oxidation

Abstract

This paper addresses the hydrothermal stability and SO2 poisoning resistance of Al2O3-supported manganese and iron oxide catalysts for lean CO oxidation. Catalysts were used in the form of powders and coated cordierite monoliths. Bare catalysts mostly comprised Mn and Fe loadings of 20wt% and were prepared by impregnation and flame spray pyrolysis (FSP). The hydrothermal treatment was conducted at 700°C. Monolithic catalysts were evaluated toward CO oxidation, and powders were characterized by X-ray diffraction, N2 physisorption, X-ray absorption near-edge spectroscopy and transmission electron microscopy. Catalytic tests indicated higher hydrothermal stability of the FSP samples, whereas the corresponding Mn catalyst was most stable and most active. The superior stability of the FSP catalysts was associated with the maintenance of their nanocrystallinity and high active surface area. Furthermore, the hydrothermal treatment of the manganese oxide catalysts was accompanied by formation of the thermodynamically preferred Mn3O4.The SO2 poisoning of selected Mn-based powders was performed at 150°C and led to strong decrease in catalytic performance, likely due to formation of sulfate species on Mn sites and alumina surface. The FSP catalyst could be partially regenerated by annealing at 700°C, related to its thermal stability and homogeneous dispersion of the manganese moieties.