Hydrodeoxygenation of phenol using nickel phosphide catalysts. Study of the effect of the support

This work studied the performance of nickel phosphide phases supported on various supports (SiO2, Al2O3, TiO2, CeO2 and CeZrO2) for the hydrodeoxygenation of phenol in gas phase at 300 °C and 1 atm. The nature of the phosphide phase obtained by the temperature programmed reduction at 700 °C depended on the type of support. Only Ni2P was formed on SiO2, TiO2, and CeZrO2, whereas the Ni12P5 was the preferred phase on Al2O3. A mixture of both Ni2P and Ni12P5 phases was obtained on CeO2. Unsupported Ni2P exhibited high selectivity to benzene (95%), indicating that the Ni2P phase is responsible for the direct deoxygenation of phenol. Ni12P5 phase promoted the formation of cyclohexanone, cyclohexane and cyclohexene. However, the supported catalysts showed lower selectivity to benzene, even when the Ni2P was the only phase present. The supports favored the formation of hydrogenation products via the tautomerization route. All catalysts only slightly deactivated with time on stream, which is likely due to the high activity of the phosphide phase.