Effective solvent-free oxidation of cyclohexene to allylic products with oxygen by mesoporous etched halloysite nanotube supported Co.

One dimensional mesoporous etched halloysite nanotube supported Co is achieved by selective etching of AlO from halloysite nanotube (HA) and immersing the etched HA (eHA) into the Co(NO)·6HO solution consecutively. By facilely tuning the etching time and the weight ratio of Co(NO)·6HO to eHA, the morphology, specific surface area and the supported Co content of the mesoporous material can be tuned. The method for mesoporous material is scaled up and can be extended to other clay minerals. The mesoporous eHA supported Co is used as catalyst for the selective catalytic oxidation of cyclohexene in solvent-free reaction system with O as oxidant. The results shows the catalytic activity is dependent on etching time, weight ratio of Co(NO)·6HO to eHA, calcination treatment and reaction time/temperature. Among them, mesoporous eHA supported Co prepared with 18 h etching time and 2 : 1 Co(NO)·6HO/eHA weight ratio without calcination (HA/HCl-18 h/Co-2 : 1) demonstrates the highest catalytic activity under 75 °C reaction temperature and 18 h reaction time (58.30% conversion and 94.03% selectivity to allylic products). Furthermore, HA/HCl-18 h/Co-2 : 1 has exhibit superior cycling stability with 37.69% conversion and 92.73% selectivity to allylic products after three cycles.