Gas phase oxidative dehydrogenation of cyclohexane over Alumina-Supported Copper-Manganese oxide Catalyst: in-situ DRIFTS studies

Abstract

Oxidative dehydrogenation (ODH) is a promising technique for converting Cyclohexane (Cy-H) to Cyclohexene (Cy-ene). However, this reaction yields undesired byproducts (Benzene and CO2) due to deep-dehydrogenation and over-oxidation. Therefore, controlling reaction parameters, comprehending intermediate species, and optimizing catalyst design are crucial for enhancing selective Cy-ene formation. Copper-manganese oxide catalysts were synthesized via the incipient wetness impregnation technique. A solid solution (CuMnOδ) exhibited superior catalytic activity due to synergistic interaction and active site formation. The study elucidated that copper oxide facilitates the deep-dehydrogenation of Cy-H. While manganese oxide incorporation inhibits CO2 and benzene formation, promoting partial dehydrogenation to Cy-ene. The studies unveiled Cy-H activation via hydrogen abstraction, forming Cyclohexanolate intermediates interacting with surface hydroxyls, yielding Cy-ene via dehydration. Notably, Cy-one formation via Enolate intermediates was also observed. The catalyst 10Cu0.25Mn0.75Oδ/Al2O3 exhibited the highest Cy-ene yield (∼12.1 %), facilitated by the synergistic effect, with a Cy-H conversion (∼15.7 %) at 300 °C.