Multiple strategies to decrease ignition temperature for soot combustion on ultrathin MnO2- nanosheet array

Diesel soot combustion suffers from ignition temperatures (T10) as high as > 450 °C in the absence of catalysts, which are unavailable in diesel exhaust during normal driving cycles (normally 200–400 °C). A catalytic diesel particulate filter (CDPF) could decrease T10 greatly, but it is often inadequate due to the poor contact associated with the solid (catalyst)-solid (soot) interactions. Herein, a highly significant T10, as low as ˜200 °C, was achieved on noble metal-free ultrathin MnO2-x nanosheet array fabricated by in situ etching of a La layer from LaMnO3 under loose contact conditions in a NO-containing atmosphere. A number of advantages were found with such a system including the improved reducibility. Then, the nanosheet array ensures high dispersion of soot on the catalyst. Finally, high NO-to-NO2 oxidation activity further facilitates contact between catalyst and soot via NO2, a stronger oxidant than O2.