Selective hydrogenation of phenol for cyclohexanone: A review

Cyclohexanone from phenol attractively meets the requirements of green chemistry, through catalytic selective hydrogenation, the prevalent methodology in rapid progress recently. In this background, pathways under this methodology are reviewed herein, including possible cyclohexanone formation mechanisms proposed in those years, as well as the corresponding catalysts, such as noble metal, non-noble metal and emerging amorphous alloy and heteropoly acids. Among the common catalysts, Pd-based catalysts exhibit excellent performance in both conversion and selectivity. Usually, the conversion and selectivity reached almost 100% after the opportune treatment of the metal and support. Other catalysts such as Pt, Rh, Ni, etc., only perform well in conversion rather than selectivity and the product is mainly cyclohexanol. Amorphous alloys and heteropoly acids, although still relatively rare compared with traditional metal catalysts, are bright in prospects indicated by achievements in this field. The reaction mechanism on some catalysts, indistinct to the community, is still in the way of development to overcome the letdown of catalyst design for higher conversion and selectivity industrially. After horizontal comparison of different catalysts, this article manages to give some advice on possible methods contributing to the design of efficient and inexpensive catalytic systems.