Manganese-cerium mixed oxides supported on rice husk based activated carbon with high sulfur tolerance for low-temperature selective catalytic reduction of nitrogen oxides with ammonia.

Abstract

A rice husk-derived activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/RAC) was prepared by an impregnation method and tested for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). 5 wt% Mn–Ce/RAC catalyst showed the highest activity, yielding nearly 100% NOx conversion and N2 selectivity at 240 °C at a space velocity of 30 000 h−1. Compared with commercial activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/SAC), a higher SCR performance with good SO2 tolerance could be observed in the tested temperature range over the Mn–Ce/RAC catalyst. The characterization results revealed that the Mn–Ce/RAC catalyst had a higher Mn4+/Mn3+ ratio, amount of chemisorbed oxygen and more Brønsted acid sites than the Mn–Ce/SAC catalyst. The XRD analysis indicated that Mn–Ce oxides were highly dispersed on the RAC support. These properties of Mn–Ce/RAC assisted the SCR reaction. Moreover, in situ DRIFTS results demonstrated that sulfate species formation on Mn–Ce/RAC was much less in the presence of SO2 than that of Mn–Ce/SAC, which might be ascribed to the reduced alkalinity of the catalyst by the presence of SiO2 in RAC.