Liquid‐Phase Cyclohexene Oxidation with O2 over Spray‐Flame‐Synthesized La1−xSrxCoO3 Perovskite Nanoparticles

• Published in: Chemistry : a European journal Vol. 27; no. 68; pp. 16912 - 16923
• Main Authors: Büker, Julia, Alkan, Baris, Chabbra, Sonia, Kochetov, Nikolai, Falk, Tobias, Schnegg, Alexander, Schulz, Christof, Wiggers, Hartmut, Muhler, Martin, Peng, Baoxiang
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 06-12-2021
• Subjects: Carbon dioxide; Catalysts; Cations; Chemistry; Cobalt; Cyclohexene; Cyclohexene hydroperoxide; Electron paramagnetic resonance; Electron spin; Electron spin resonance; flame-spray synthesis; Infrared reflection; Infrared spectroscopy; in situ ATR-IR; Liquid phase oxidation; Nanoparticles; Oxidants; Oxidation; Oxidizing agents; oxygen vacancies; Perovskites; Reaction kinetics; Reaction products; Selectivity; Spectrum analysis; spin trap EPR; Sr doping
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202103381

La1−xSrxCoO3 (x=0, 0.1, 0.2, 0.3, 0.4) nanoparticles were prepared by spray‐flame synthesis and applied in the liquid‐phase oxidation of cyclohexene with molecular O2 as oxidant under mild conditions. The catalysts were systematically characterized by state‐of‐the‐art techniques. With increasing Sr content, the concentration of surface oxygen vacancy defects increases, which is beneficial for cyclohexene oxidation, but the surface concentration of less active Co2+ was also increased. However, Co2+ cations have a superior activity towards peroxide decomposition, which also plays an important role in cyclohexene oxidation. A Sr doping of 20 at. % was found to be the optimum in terms of activity and product selectivity. The catalyst also showed excellent reusability over three catalytic runs; this can be attributed to its highly stable particle size and morphology. Kinetic investigations revealed first‐order reaction kinetics for temperatures between 60 and 100 °C and an apparent activation energy of 68 kJ mol−1 for cyclohexene oxidation. Moreover, the reaction was not affected by the applied O2 pressure in the range from 10 to 20 bar. In situ attenuated total reflection infrared spectroscopy was used to monitor the conversion of cyclohexene and the formation of reaction products including the key intermediate cyclohex‐2‐ene‐1‐hydroperoxide; spin trap electron paramagnetic resonance spectroscopy provided strong evidence for a radical reaction pathway by identifying the cyclohexenyl alkoxyl radical.
A complex for a complex reaction: La1−xSrxCoO3 nanoparticles were prepared by spray‐flame synthesis and applied in the liquid‐phase oxidation of cyclohexene with molecular O2. An optimum Sr doping of 20 at. % – with balanced amounts of oxygen vacancies and Co2+ cations – was found to be beneficial for cyclohexene conversion. In situ ATR‐IR and EPR spectroscopy verified the complex radical reaction network.