Interphase strengthening birnessite MnO₂ coating on three-dimensional Ni foam for soot removal

The soot particulates emitted from diesel engines have been ultimately evidenced cancerogenic and successive rigorous emission legislations have been approved in many countries. Monolithic metal-based purification materials are able to tackle the harsh working conditions. Hence, monolithic birnessite MnO₂/Ni foam catalysts were facilely synthesized via a hydrothermal route and characterized by XRD, Raman spectroscopy, SEM, HRSTEM, XPS, H₂-TPR, et al. The coating weights are in proportion to hydrothermal temperatures. And the catalyst synthesized at 160 °C displays the lowest T₅₀ (418 °C) with the coating exfoliation rates of only 0.45 ± 0.11 wt. %. Porous Ni substrates tightly covered with a layer of crosslinked flowerlike birnessite MnO₂ coating would provide many available sites capturing soot particulates. The interphase NiMnO₃ between nanoflowers and Ni substrate could intensify nanoflowers against exfoliation, and inhibit transformation into disordered nanorods. Potassium in the birnessite may activate gas O₂ effectively forming active oxygen species and improve the redox properties. Moreover, nickel dopants inhibit K⁺ thermal evaporation and water dissolution via strengthening K–O bonds, thus endowing good reusability. This candidate is likely a promising monolithic catalyst purifying the real diesel exhaust. And the method will be employed to synthesize novel monolithic metallic catalysts for other catalytic applications.