Preparation of hierarchical hollow structures assembled from porous NiCo₂O₄ nanosheets for diesel soot elimination

Construction of catalysts with designed microstructures is critically important in heterogeneous catalysis. The soot catalytic oxidation was considered as one of the most efficient methods for the diesel soot elimination, but its development has been hindered by the lack of efficient catalysts. The hierarchically porous materials with well-defined microstructures are expected to perform high-catalytic activity for the large-sized soot particulates elimination. Herein, we report a method to prepare a novel hierarchical hollow structure (HHS) assembled from porous NiCo2O4 NSs, referred to as NiCo2O4 HHS. The cation-exchange reaction and Kirkendall effect induce the conversion from the Co-Asp (Asp: aspartic acid) fibers to the Co,Ni-Asp HHSs. The NiCo2O4 HHSs are prepared through annealing the Co,Ni-Asp HHSs. As a proof-of-concept application, the unique NiCo2O4 HHS is used as a catalyst to eliminate the soot particulates and exhibits superior performance, which could be attributed to the improved soot-catalyst contact, sufficient active sites and strong active oxygen species.