The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C−H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C−H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis. [Display omitted] •The morphology of Ni-MOF precursor can be controlled by changing solvent molecules.•NiO inherited the morphology of precursors and exposed different crystal facets.•DFT results show that the oxygen defects can be easily formed on the crystal facet of NiO (111).•Propane molecular can be easily adsorbed and activated on the defect NiO (111) facet.