Unraveling the contribution of acidic metal oxides modulating the CeO2/TiO2 catalyst acid sites for NH3-SCR activity and SO2 tolerance

Abstract

As a potential substitute for V₂O₅-WO₃/TiO₂ (V-W/Ti) catalyst, CeO₂/TiO₂ (Ce/Ti) catalyst still faces severe challenges regarding low-temperature denitrification performance and SO₂ tolerance. To this end, we report an effective strategy to modulate Ce/Ti catalyst acid sites by different acidic metal oxides. The modification of Nb, Mo and W species can well weaken the L-acid sites and enhance the B-acid sites of Ce/Ti catalyst, which helps more NH₃ adsorb to form the ionic NH₄⁺ for activation at low temperatures. Moreover, the improvement of redox performance well weakens the adsorption of low reactive nitrates and facilitates the NO oxidation of NO₂. The optimum sample (Ce-Nb/Ti) achieved 95 % NO_x conversion within the active temperature window (225 − 425 °C) and admirable SO₂-tolerant performance at 300 °C. The abundant surface acidity and strong interactions between metal ions not only suppress the adsorption of SO₂ on the Ce-Nb/Ti but also decrease the thermal stability of ammonia bisulfate and alleviate sulfate deposition. Moreover, the in situ DRIFTS experiments demonstrated that introducing these acidic metal oxides on Ce/Ti catalyst did not change the reaction pathway, following the Langmuir-Hinshelwood and Eley-Rideal mechanisms.