Versatile heterogeneous dipicolinate complexes grafted into kaolinite: Catalytic oxidation of hydrocarbons and degradation of dyes

Abstract

New heterogeneous catalysts were prepared by immobilization of Me(II)-dipicolinate complexes (Me=Co, Mn or Ni) on kaolinite (Ka). The precursor material was kaolinite grafted with dipicolinic acid (dpa) obtained via melting of the acid. The catalysts were prepared by suspending the Ka-dpa precursors (lamellar or exfoliated) in Me2+ solutions with a cation/ligand ratio of 1:3. The grafted complexes were characterized by thermal analyses, X-ray diffraction, UV/Vis and infrared spectroscopies, and transmission electron microscopy. The catalysts were tested in three reactions: (i) epoxidation of cis-cyclooctene to cis-cyclooctenoxide reaching 55% yield, with total selectivity to cyclooctenoxide; (ii) oxidation of cyclohexane, reaching 22% yield, with total selectivity towards cyclohexanone; and (iii) Fenton-like decolorization of the dyes metanil yellow, methylene blue and green light, reaching 70–100% decolorization, the maximum effectiveness being observed for methylene blue degradation. The high conversion in the oxidation reactions and the high levels of decolorization of dyes confirmed the versatility of these heterogeneous catalysts based on kaolinite.