Liquid‐Phase Cyclohexene Oxidation with O2 over Spray‐Flame‐Synthesized La1−x Sr x CoO3 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: Hoboken John Wiley and Sons Inc 14-10-2021
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202103381

La
1−
x
Sr
x
CoO
3
(
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 O
2
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 Co
2+
was also increased. However, Co
2+
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 O
2
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
: La
1−
x
Sr
x
CoO
3
nanoparticles were prepared by spray‐flame synthesis and applied in the liquid‐phase oxidation of cyclohexene with molecular O
2
. An optimum Sr doping of 20 at. % – with balanced amounts of oxygen vacancies and Co
2+
cations – was found to be beneficial for cyclohexene conversion. In situ ATR‐IR and EPR spectroscopy verified the complex radical reaction network.