Promoting Diesel Soot Combustion Efficiency over Hierarchical Brushlike α-MnO₂ and Co₃O₄ Nanoarrays by Improving Reaction Sites

Improving the accessible reaction sites of catalysts is vital to diesel soot elimination. Herein, hierarchical brushlike α-MnO₂ and Co₃O₄ nanoarrays were in situ grown on AISI304 stainless steel wire-mesh via a two-step hydrothermal method. Morphology investigation displayed that compared with sole α-MnO₂ or Co₃O₄ nanoarrays, α-MnO₂ and Co₃O₄ nanoarrays provided 8-fold reaction sites. XRD, Raman spectroscopy, XPS, H₂-TPR, and soot-TPR techniques proved the synergistic effect between cobalt and manganese, namely, weaker Mn-O bonds, more surface active oxygen species, and better redox ability. Kinetic data also showed that the activation energy was decreased, and the pre-exponential factor was increased. α-MnO₂ and Co₃O₄ nanoarrays displayed superior catalytic performance (T₅₀ = 354 °C, T₉₀ = 395 °C), durability, and isothermal regeneration activity. In a simulated diesel exhaust at 400 °C, 90% of soot would be eliminated at 12 min, and the regeneration would be finished within 30 min. Finally, the catalyst coating was tightly anchored on the substrate without exfoliation or crazing.