Facile Synthesis of Birnessite-type K2Mn4O8 and Cryptomelane-type K2-xMn8O16 Catalysts and Their Excellent Catalytic Performance for Soot Combustion with High Resistance to H2O and SO2

Abstract Soot particles emitted from the diesel exhausts have caused serious air pollution and catalytic soot combustion is promising for soot abatement. In this work, two kinds of soot oxidation catalysts, including phase-pure birnessite-type K2Mn4O8 (K-OL-1) and cryptomelane-type K2-xMn8O16 (K-OMS-2), were successfully prepared by a very simple method. In preparation of these catalysts, KMnO4 and glucose were used in various proportions and different calcination temperatures employed. The as-prepared catalysts exhibit excellent catalytic performance in the loose contact mode with the presence of water (10%). Specifically, most of them completely remove soot particles below 450 °C. More importantly, the birnessite-type K2Mn4O8 catalysts exhibit good tolerance for sulfur and water and the presence of water in the interlayer space is the reason for this property. The possible reaction mechanisms for soot combustion on K2Mn4O8 catalysts are related to reaction of active oxygen species and NO2-assisted oxidation. This work shed a light on the important role of the interlayer gallery species (K+, H2O) in the catalytic activity of the birnessite materials in soot combustion, which so far has not been recognized. Meanwhile, the birnessite-type K2Mn4O8 catalysts are low-cost, the excellent catalytic performance and simple synthesis method give them a great potential for industrial applications.