High-efficiency catalytic oxidation of nitric oxide over spherical Mn-Co spinel catalyst at low temperature

The spherical Mn-Co spinel catalyst were prepared by (NH4)(2)CO3-assisted co-precipitation method and were used for the catalytic oxidation of NO at low temperature. The experimental results showed that the optimized Mn0.52Co2.48O4 spinel catalyst, preparing under conditions of Co/Mn molar ratio as 5 and calcination temperature at 450 degrees for 5 h, has the best catalytic activity with about 65% NO oxidation at 150 degrees C, 80% at 200 degrees C and 90% at 250 degrees C, respectively. The main reasons for good NO oxidation activity over Mn0.52Co2.48O4 spinel were attributed to the high surface area of 182.8m(2)/g, low apparent activation energy of 30.8 kJ/mol, high content of high surface concentrations of chemisorbed oxygen, Mn4+/Mn3+ and Co2+/Co3+, and the efficient synergetic effect between Co and Mn ions (Co2+ + Mn4+ <-> Mn3+ + Co3+; Co3+ + Mn2+ <-> Mn3+ + Co2+). The monodentate nitrite and bridged nitrate species were the important intermediates in the oxidation process of NO to NO2, and the adsorption-reaction pathways were further proposed over Mn-Co spinel catalyst.