The deactivation of noble metal catalysts by SO 2 and H 2 O is a common issue in the post combustion treatment of flue gases from sintering processes in the steel industry. In an effort to develop SO 2 -tolerant CO-oxidation catalysts, herein, we investigated the effect of SO 2 and H 2 O on the catalytic activity of Pt/TiO 2 (P-25) catalysts for CO oxidation using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and diffuse-reflectance infrared Fourier-transform (DRIFT) spectroscopy. Pt/TiO 2 (P-25) catalysts, in the absence of SO 2 and presence of H 2 O, enhanced the activity and stability of CO oxidation, while being largely suppressed and irreversibly deactivated in the presences of SO 2 . The XPS and TEM results suggested that variations in the Pt particle size and oxidation state were not major causes of the deactivation. Instead, according to DRIFT spectra, the interaction between CO and H 2 O at the metal-support interface was weakened after the formation of TiOSO 4 on the TiO 2 surface in the presence of SO 2 . This resulted in a loss of the previously observed enhancement of CO oxidation under humid conditions. These results indicate that in the presence of SO 2 , the formation of TiOSO 4 is the major cause of irreversible deactivation. Therefore, removal of the TiOSO 4 layer from the TiO 2 surface is a crucial step for catalyst regeneration. Graphical Abstract: [Figure not available: see fulltext.].
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