CeO2 nanoparticles were in-situ grown on the surface of Mn-Co mixed oxide micro-flowers to improve the resistance to SO2 and H2O poisoning. Display omitted •A new MnCoCeOx microflower was rationally designed for the SCR de-NOx.•The MnCoCeOx exhibited obviously enhanced low-temperature de-NOx performance.•CeO2 played important roles in improving low-temperature catalytic performance.•Both E-R and L-H mechanisms were included in the SCR de-NOx over the MnCoCeOx. A new MnCoCeOx microflower is rationally designed by a series of elaborate steps for the selective catalytic reduction (SCR) of NOx with NH3. The MnCoOx 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 MnCoOx microflower in Ce(NO3)3 solution followed by a heat-treatment. The resultant MnCoCeOx 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-NOx performance, such as decreasing the apparent activation energy, increasing the ratios of Ce3+/Cen+, Mn4+/Mnn+ and Oα/(Oα + Oβ), enhancing the oxidation ability of MnCoOx at low temperatures. Moreover, by preventing MnCoOx 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 MnCoCeOx catalyst, which occur SCR de-NOx reaction following both Eley-Rideal and Langmuir-Hinshelwood mechanisms.