Manganese-based catalysts have shown excellent low-temperature selective catalytic reduction (SCR) activity for NOx removal. However, they all suffer from the serious SO2 poisoning effect on activity. Ceria modification has been reported to be able to promote SO2 tolerance of SCR catalysts probably via the inhibition of surface sulfate species formation. In this study, in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigations were carried out to determine the role of Ceria in the improved resistance for a Ce-modified Mn/TiO2 catalyst. The results indicated that after the introduction of Ce, SOx, ad-species preferentially formed on Ceria as bulk-like sulfate species and lessened the sulfation of the main active phase (MnOx) during low-temperature SCR processes in the presence of SO2. Furthermore, the DRIFT and TG-DSC results also implied that Ce modification could reduce thermal stabilities of the sulfate species covered on catalyst surface, thereby promoting its decomposition. Both of these would be beneficial to the improved SO2 tolerance of Ce modified catalysts. (c) 2013 Elsevier B.V. All rights reserved.