Low-temperature NH3-SCR activity of M (M = Zr, Ni and Co) doped MnO supported biochar catalysts

Several metal (Zr, Ni and Co) oxides doped biochar (BC) supported Mn oxide (MnOx) catalysts were prepared by impregnation method, and their effects on the low-temperature selective catalytic reduction with NH3 (LT NH3-SCR) activity were studied. Zr-Mn/BC catalyst exhibited the highest NO conversion of around 87% at 200 oC and the best N2 selectivity of the four catalysts. Furthermore, Zr-Mn/BC catalyst showed better resistance of SO2 and H2O than that of Mn/BC catalyst. Metal oxides were evenly distributed on the surface of the four catalysts. Zr-Mn/BC catalyst, Ni-Mn/BC catalyst and Co-Mn/BC catalyst had lower surface area compared with Mn/BC catalyst. Moreover, the high activity of Zr-Mn/BC catalyst was related to its higher concentration of Mn4+, more surface oxygen (Oα), excellent redox property and more Lewis acid sites and Brønsted acid sites. From in situ DRIFTS, the Zr-Mn/BC catalyst followed Langmuir-Hinshelwood (L-H) reaction mechanism: the NH4+ species or NH3,ads reacted with the NxOy species (NO2,ads, NO2-, NO3-), finally generated N2 and H2O. In which the Zr doping could avoid the formation of N2O by restraining the decomposition of NH4NO3 intermediate.