Modification of MnCo2Ox catalysts by NbOx for low temperature selective catalytic reduction of NO with NH3

Abstract

A series of MnCo₂O_x catalysts modified with different Nb ratios were synthesized by co-precipitation and sol–gel method. The effects of niobia on the low-temperature NH₃-SCR performances of the catalysts were investigated. The MnCo₂O₄ spinel phase was identified according to XRD and Raman results. Niobates including Mn₂NbO_x and Co₂NbO_x appeared with the increase of the Nb loading based on the Raman and H₂-TPR results. Among the obtained catalysts, MnCo₂Nb_0.5O_x presented the best catalytic performance with a broad operation temperature window, high N₂ selectivity and good H₂O resistance. It was found that the addition of niobia weakened the redox properties of the catalysts to some extent, resulting in the decrease of NO conversion at 50 °C. This, as well as the enhanced surface acidity, inhibited the unselected oxidation of NH₃ to N₂O and increased the N₂ selectivity over the modified catalysts. Consequently, the modification of MnCo₂O_x catalyst by NbO_x promoted the low-temperature NH₃-SCR performance.