Hydrogenation of phenol to cyclohexanol and cyclohexanone on ZrO2-supported Ni-Co alloy in water

ZrO 2 -supported Ni and Ni-Co alloy catalysts were synthesized by co-precipitation method and tested for the hydrogenation of phenol in aqueous phase. Cyclohexanol and cyclohexanone are dominatingly generated on all the catalysts, and the deoxygenation products are minor. The Ni-Co alloy gives higher phenol conversion and the total yield of cyclohexanol and cyclohexanone compared to the metallic Ni. This is attributed to high metal dispersion due to the formation of Ni-Co alloy and the synergetic effect of Ni and Co in the alloy. ZrO 2 -supported Ni-Co alloy with the Ni/Co atomic ratio of 1 and the metal mass loading of 15% possesses the best performance. The total yield of cyclohexanol and cyclohexanone reaches 91.3% with the cyclohexanol/cyclohexanone molar ratio of 2.79. The phase composition of ZrO 2 -supported Ni-Co alloy remains stable during recycling, while the slight sintering of ZrO 2 and Ni-Co alloy particles can account for the catalyst deactivation. It has also been found that the presence of water may facilitate the keto-enol tautomerization and stabilize the ketone intermediates, leading to higher cyclohexanone yield than using n-octane as solvent.