Temperature sensitivity of the selective catalytic reduction (SCR) performance of Ce–TiO₂ in the presence of SO₂

Cerium titanate catalyst (Ce–TiO₂) is competitive as a substitute for the commercial SCR (selective catalytic reduction) catalysts VO₅–WO₂/TiO₂ due to its high SCR activity and excellent redox performance. The reaction mechanisms of Ce–TiO₂ at 180 °C, 240 °C, and 300 °C in the presence of SO₂ were systematically studied regarding the evolution of the SCR activity, quantitative analysis of sulfate compounds, and comprehensive identification of the fresh and poisoned catalysts. The results demonstrated that NO conversion at 180 °C in the presence of SO₂ is highly sensitive to the formation of cerium sulfates/sulfites, limiting the reactivity of NH₄⁺ adsorbed on S[dbnd]O Brønsted acid sites and inhibiting the E-R reaction pathway. At 240 °C, the degradation of NO conversion was commenced by the cumulative influence of cerium sulfates/sulfites. With the increase of the reaction temperature to 300 °C, the NO conversion is gradually immune to the formation of cerium sulfates in spite of the great amount of cerium sulfates deposited on the deeper interior of CeO₂. The high SCR activity of the Ce–TiO₂ catalyst in the presence of SO₂ at a higher reaction temperature might be ascribed to the synergistic catalysis between surface cerium sulfates and bulk CeO₂, where surface cerium sulfates act as acid sites for the adsorption of NH₃ and the bulk CeO₂ acts as the redox sites. The reaction mechanisms of the Ce–TiO₂ catalyst in the presence of SO₂ at different temperatures are proposed as the two reaction routes.