Mechanistic and Structural Insights into the Liquid-Phase Oxidation of Cyclohexane over LaCo_<b>0.7</b>Fe_<b>0.3</b>O_<b>3</b> Perovskite Nanoparticles

The aerobic liquid-phaaCo0.7Fe0.3O3 perovskite under mild conditions exhibited an enhanced selectivity toward KA oil (mixture of cyclohexanol and cyclohexanone) at high conversion. Mechanistic investigations revealed a partial reduction of Co3+ to Co2+ in the surface region during the activation of the C–H bond. The selectivity differences induced by adding the catalyst were qualitatively analyzed using in situ ATR-IR spectroscopy. The radical scavenging studies and spin trap EPR confirmed the crucial role of cyclohexylperoxyl (C6H11OO•), cyclohexyloxyl (C6H11O•), hydroxyl (HO•) and cyclohexyl (C6H11•) radicals in the reaction. Scavenging C6H11OO• during the uncatalyzed reaction strongly increased the stability of KA oil. Postreaction characterization by XRD, XPS, TPR, Mössbauer, magnetometry, EPR, and Raman spectroscopy confirmed the partial reduction of Co3+ and the formation of an additional Co-rich LDH phase during cyclohexane oxidation. DFT calculations of the cyclohexyl hydroperoxide (CHHP) decomposition pathways provided evidence that α-H abstraction is highly favored (33 kJ/mol) compared with the homolytic O–O cleavage (127 kJ/mol) in the absence of a catalyst and validated the influence of the catalyst on the homolytic O–O cleavage of CHHP via the Haber-Weiss reaction. A catalytic cycle based on mixed oxyhydroxy Co dimers is proposed to rationalize the influence of the catalyst in controlling highly oxidizing C6H11OO• radicals, thus favoring KA oil stability.