Effect of Sulfates on the Reaction Pathway Over CeO2-Based Catalyst for NH3-SCR

CeO₂-H₂SO₄ (C-S), CeO₂-TiO₂ (C-T), and CeO₂-TiO₂-H₂SO₃ (C-T-S) were used for the selective catalytic reduction of NO with NH₃ (NH₃-SCR). Nearly 100% NO_x conversion of C-T-S was achieved at 250°C–450°C. When the concentration of Ce₂(SO₄)₃ was excessively high, it causes tightly binding with Ce³⁺ ions in CeO₂, prevents some Ce³⁺ ions from effectively participating in redox reactions, and results in the inferior SCR activity. Consequently, C-T-S possessed the superior catalytic performance due to the optimal content of sulfates. Furthermore, the presence of NO₂ facilitated the rapid SCR reaction on C-T-S, thereby further enhancing the catalytic activity. Additionally, the formation of Ce₂(SO₄)₃ on C-T-S could increase the number of acid sites, particularly Brönsted acid sites, resulting in the improvement of SCR performance. C-S, C-T, and C-T-S mainly followed the Langmuir–Hinshelwood (L–H).