The insight into the role of CeO₂ in improving low-temperature catalytic performance and SO₂ tolerance of MnCoCeO_x microflowers for the NH₃-SCR of NO_x

A new MnCoCeO_x microflower is rationally designed by a series of elaborate steps for the selective catalytic reduction (SCR) of NO_x with NH₃. The MnCoO_x microflower is firstly synthesized by the self-assembly of Mn-Co mixed oxide nanosheets, and then CeO₂ nanoparticles are in-situ grown on the surface of Mn-Co mixed oxide nanosheets by dipping MnCoO_x microflower in Ce(NO₃)₃ solution followed by a heat-treatment. The resultant MnCoCeO_x microflower presents significantly enhanced low-temperature catalytic performance and SO₂ tolerance. It is revealed that the attached CeO₂ plays several important roles in the improvement of low-temperature de-NO_x performance, such as decreasing the apparent activation energy, increasing the ratios of Ce³⁺/Ceⁿ⁺, Mn⁴⁺/Mnⁿ⁺ and O_α/(O_α + O_β), enhancing the oxidation ability of MnCoO_x at low temperatures. Moreover, by preventing MnCoO_x from being vulcanized into metal sulfate species, CeO₂ plays an important role in enhancing the resistance to SO₂ poisoning. The in-situ DRIFTS results disclose that the NH₃ coordinated on Lewis acid sites, NH₄ ⁺ bound to Brønsted acid sites, the NO₂ and bidentate nitrates linked on metal oxides are the major reactive species on MnCoCeO_x catalyst, which occur SCR de-NO_x reaction following both Eley-Rideal and Langmuir-Hinshelwood mechanisms.