Ordered Mesoporous Ni_<i>y</i>MnO_<i>x</i> Nanocatalysts for the Low-Temperature Selective Reduction of NO_<i>x</i> with NH₃

Abstract

Three-dimensional ordered mesoporous NiyMnOx catalysts were synthesized by the nanocasting method and tested for selective catalytic reduction (SCR) of NOx with ammonia. The addition of Ni could greatly enhance the low temperature performance of the catalysts. Various techniques (XRD, TEM, and HR-TEM, N2 adsorption–desorption, SEM, H2-TPR, NH3-TPD, XPS, DFT calculation and in situ DRIFTS), along with SCR performances, were used to evaluate the promotional role of Ni and establish the structural-activity relationship. The results suggested that the Ni addition could significantly increase the BET surface area through the formation of amorphous manganese oxide. Besides, Ni addition could improve the presence of Mn4+ and surface adsorbed oxygen species, both of which are important reactive species in the NH3–SCR. The highly ordered mesoporous Ni0.5MnOx exhibited approximately 100% NOx conversion in a temperature range of 150–275 °C with a GHSV of 60 000 h–1. On the basis of the in situ DRIFTS and physicochemical characterizations, the SCR reaction mechanism over the ordered mesoporous Ni0.5MnOx was proposed. Langmuir–Hinshelwood is expected to be the dominant pathway with the coexistence of Eley–Rideal mechanisms.