Encapsulating spinel nancrystals in Laponite cages and applications in molecular oxidation of cyclohexane

Abstract The Co-based spinel nanocrystals were fabricated by thermal decomposition of clay cages comprised with Laponite (LP) that were assembled on ZIF-67 frameworks (LP@ZIF-67). Spinel phases included Co3O4, FeCo2O4 and MgCo2O4 were produced and encapsulated within the Laponite cages (LP@spinel). The prepared materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analyses (TGA). It was indicated that the porous structure of Laponite and ZIF-67 was preserved after annealing at the temperature of ~400 °C. The XPS showed the binding energy of Co2P in sample of LP@spinel shifted to lower values compared to the Co3O4 which was obtained by annealing the pure phase of ZIF-67, and this demonstrates the catalytically active Co-centers were (220) facet-exposed in spinel nanocrystals. The material LP@spinel shares mesoporous structure with surface area of 135 m2·g−1. The LP@spinel was found to exhibit brilliant performance on aerobic oxidation of cyclohexane to get cyclohexanone and cyclohexanol (KA oil). At a preset O2 pressure of 2.0 MPa, the catalysis showed an outstanding conversion at 17.2% and the selectivity was found to reach 95.3% of KA oil for a typical reaction t = 5.0 h at T = 150 °C.