Aerobic Oxidation of Cyclohexane over LaCoxFe1-xO3 Perovskites in the Liquid Phase

• LaCo x Fe 1-x O 3 nanoparticles were synthesized via co-precipitation and applied as slurry. • LaCo x Fe 1-x O 3 shows promising results in the selective oxidation of cyclohexane to KA oil. • At x = 0.7, 95 % KA oil selectivity was achieved at a conversion of 14.8 %. • Decrease in the induction period (< 1 h) in the presence of the catalysts. • Three consecutive runs confirm the reusability of LaCo 0.7 Fe 0.3 O 3 without any leaching. • Milder reaction conditions (≈ 120°C) favor the stability of the produced KA oil. • Spin-trap EPR measurements using DMPO confirm the free-radical mechanism. The aerobic oxidation of cyclohexane is a highly relevant reaction in polymer industry, which generates a mixture of cyclohexanol and cyclohexanone, together known as KA oil. It is further converted to adipic acid, which is used as monomer to produce Nylon-6,6. Herein, we report on the activity of LaCo x Fe 1-x O 3 perovskites synthesized by co-precipitation with Co contents in the range from x = 0.00 to x = 0.70. An increase in KA oil selectivity to 95% at a relatively high conversion of 15% compared with the conversion typically used in industry was achieved by increasing the Co content to 0.70. The standard reaction parameters in the three-phase batch reactor were set at 120°C, 1.00 mol/L cyclohexane in 40 mL acetonitrile, 20 mg catalyst, 15 bar O 2 , 600 rpm, and 6 h reaction time. In the presence of the LaCo 0.7 Fe 0.3 O 3 nanoparticles, the apparent activation energy was lowered by 47 kJ/mol to 123 kJ/mol. The kinetic investigation revealed an induction period of 2 h in the uncatalyzed cyclohexane oxidation, which was lowered to less than 1 h by adding the catalyst. A free-radical mechanism was identified by spin-trap EPR measurements where the cyclohexyloxy radical was found to be the main radical. Thus, the cobalt-based perovskite catalysts improve conversion, KA oil selectivity and free-radical generation in the aerobic oxidation of cyclohexane. Graphics : Aerobic oxidation of cyclohexane to KA oil over highly active and selective LaCo x Fe 1-x O 3 perovskite nanoparticles in the liquid phase using a high-pressure reactor.