Novel hollow microspheres MnxCo3-xO4 (x=1, 2) with remarkable performance for low-temperature selective catalytic reduction of NO with NH3

Hollow microspheres MnCo2O4 and CoMn2O4 have been synthesized by a facile solvothermal route followed by pyrolysis of the carbonate counterparts and carbon microspheres, using carbon microspheres as the template. The NH3-selective catalytic reduction reaction was used to test the catalytic activity. The obtained hollow microspheres are composed of numerous primary particles with sizes of tens of nanometers, giving a porous shell. The obtained CoMn2O4 microsphere shows better low-temperature catalytic activity and N-2 selectivity than MnCo2O4 microsphere in the NH3-selective catalytic reduction reaction. The X-ray photoelectron spectroscopy results demonstrate that CoMn2O4 microsphere has a relatively higher number content of Mn3+ and chemisorbed oxygen species. The temperature-programmed desorption by ammonia and in situ diffuse reflectance infrared Fourier transform spectroscopy results indicate that the CoMn2O4 microsphere possesses stronger Lewis acid strength than the MnCo2O4 microsphere. Additionally, the CoMn2O4 microsphere also presented outstanding stability, H2O resistance and SO2 tolerance. The NH3-SCR reaction mechanism is proposed that NH3(g) is adsorbed on the surface of Lewis acid sites and Bronsted acid sites in the shape of NH4 (+) ions and gaseous NH3. Besides, the adsorption of NO could exist in the form of gaseous or oxide ions NO2 (-) on the surface of catalysts.The adsorbed NH3 species could react with NO2 (-) species easily to produce NH4NO2, which subsequently to produce the innocuous N-2 and H2O.