Ni@C catalyzed hydrogenation of acetophenone to phenylethanol under industrial mild conditions in a flow reactor

The catalytic hydrogenation of organic substrates containing plenty of unsaturated functional groups is an important step in the industrial preparation of fine chemicals and has always been a hot spot in basic catalysis research. For example, phenylethanol obtained by the preferential hydrogenation of the C=O group of acetophenone is a valuable intermediate for the production of spices, flavors, and medicines. Furthermore, as the demand for 1-phenylethanol (PhE) continues to increase, the catalytic hydrogenation of acetophenone (AP) is becoming more and more important. At present, relatively few catalytic systems are used in this reaction as the hydrogenation of acetophenone is a complex multi-step reaction. Enantioselective hydrogenation on heterogeneous catalysts is remarkable due to its inherent operational and economic advantages, such as atom economy. It is one of the most ideal methods as the catalyst is easily separated and recycled. However, the traditional synthesis way in batch reactors usually takes a long time with unsatisfactory conversion which is not conducive to industrialization. Heterogeneous non-precious metal catalysts are advantageous for their implementation in flow reactor systems for industrial applications due to their ease of separation, low cost, and environmental friendliness. Herein, we report the first use of non-noble metal Ni-supported graphene-based catalysts for hydrogenation of acetophenone to phenylethanol with high efficiency in a flow reactor made of 316L stainless steel with a length of 200 mm and an inner diameter of 6 mm which can significantly improve mass and heat transfer. The conversion rate under the optimized reaction conditions can reach 99.14% with a satisfactory selectivity of 97.77% (the conversion and selectivity are in mol%). The magnetic catalyst has a compact structure, and the Ni particles coated with carbon on the surface are uniformly distributed. After 48 hours of uninterrupted continuous experiments, the conversion rate of acetophenone still reached 88.44%. The catalyst has good cyclability, and the Ni-based catalyst after the cycle still maintains high catalytic activity without obvious deactivation, and the catalyst structure remains intact and stable.