High-entropy layered double hydroxide for the coupling cyclohexanol dehydrogenation with phenol hydrogenation

Coupling dehydrogenation of cyclohexanol (CHOL) and hydrogenation of phenol (PhOH) for the production of cyclohexanone (CHON) was seldom reported as the separated dehydrogenation of CHOL and hydrogenation of PhOH require different active sites, varied surface acidity and opposite conditions. High-entropy layered double hydroxides (HE-LDHs) might be a promising candidate for this coupling reaction via the synergistic effect of all components and modulated acidity/basicity. In this work, a series of well-structured Ru-containing HE-LDHs were synthesized and utilized in the coupling dehydrogenation of CHOL with hydrogenation of PhOH for the first time. Characterizations revealed that the hexa-metallic Cu₁Co₁Mg₄Ru_0.2Al_0.9Sc_0.9(OH)₁₆CO₃·4.8 H₂O catalyst possesses large surface area (231 m²/g), enhanced acidity/basicity (254 µmol/g acid sites and 674 µmol/g basic sites), improved hydrogen adsorption capacity than those catalysts composed of two-, three-, four-, and five-metal components. It showed excellent activity under optimized reaction conditions (100 mmol CHOL + 5 mmol PhOH, 230 °C, 15 min), and the apparent conversion of PhOH reached 93.1 % with a formation rate of CHON as high as 661.5 g-CHON/g-Ru/h. Additionally, it was found that the dehydrogenation of CHOL could be accelerated when PhOH was added as a hydrogen acceptor, and hydrogen dehydrogenated from CHOL was utilized by PhOH which increased formation rate of CHON. The best hydrogen utilization achieved 86 %.