Abstract: Nickel phosphate nanotubes (NiPO-NTs) with a uniform pore size distribution were prepared by urea-assisted hydrothermal synthesis in the absence of any organic template. Calculations from N2 adsorption-desorption isotherms of NiPO-NTs revealed a narrow pore distribution around 2.7–4.2 nm and a surface area of 96.6 m2/g. NiPO-NTs was used to catalyze the epoxidation of cyclohexene using hydrogen peroxide as the oxidant. Infrared spectroscopy of adsorbed pyridine and NH3 temperature-programmed desorption characterization results showed that the weak Lewis acid was predominant on the surface of NiPO-NTs. CH3CN was found to be a suitable solvent for the epoxidation. The reaction conversion increased with increasing reaction temperature and H2O2/cyclohexene molar ratio, whereas the selectivity for epoxycyclohexane increased with decreasing temperature and increasing H2O2/cyclohexene molar ratio. High cyclohexene conversion (50.6%) and selectivity for epoxycyclohexane (72.1%) were obtained at 60 oC, 6 h, and H2O2/cyclohexene of 3.

Key words: nickel phosphate, nanotube, urea, cyclohexene, epoxidation, epoxycyclohexane