Deactivation of a Ce/TiO₂ Catalyst by SO₂ in the Selective Catalytic Reduction of NO by NH₃

The effects of SO 2 on the selective catalytic reduction of NO by NH 3 over a Ce/TiO 2 catalyst were studied. Conversion of NO remained above 90% in the presence of 100 ppm SO 2 at 350 °C for 48 h. However, when 180 ppm SO 2 was added at 300 °C, NO conversion only remained above 90% during the first 12 h and then gradually decreased with time. Characterizations of fresh and SO 2 -poisoned Ce/TiO 2 catalysts were carried out using Brunauer−Emmett−Teller method, ion chromatography, X-ray photoelectron spectroscopy, and X-ray diffraction. The analytical results indicate that there was no obvious change in the crystal structure of the different samples; however, the specific area decreased with SO 2 poisoning time. Sulfates were formed and preferentially diffused from the surface to a bulk phase during the poisoning process. Temperature-programmed desorption and diffuse reflectance infrared Fourier-transform spectroscopy results show that in the presence of O 2, SO 2 could react with NH 3 to form NH 4 HSO 4, which is deposited on the surface of the catalyst and blocked the active sites. Moreover, the main reason for the deactivation is that SO 2 could react with the catalyst to form high thermally stable Ce(SO 4 ) 2 and Ce 2 (SO 4 ) 3, resulting in the disruption of the redox properties between Ce(IV) and Ce(III) and the inhibition of the formation and adsorption of nitrate species.