Herein, we describe a simple and environmentally friendly method for the preparation of thin graphene spheres with a uniformly encapsulated Ni nano-alloy catalyst (Ni@C) with nickel citrate as the precursor. The resulting catalysts are stable and reusable and have been successfully used in the hydrogenation reduction process of acetophenone to phenylethanol. This reaction is under very mild industrially feasible conditions (100 °C and 1 MPa H2 pressure), in a high-efficiency flow reactor system at a flow rate of 0.4 mL/min to hydrogenate the easily available carbonyl compound acetophenone to phenethyl alcohol, which provides a feasible way of economical and efficient industrialization. In order to prevent the small catalyst particles from clogging the flow reactor pipeline, we adsorb the magnetic Ni@C catalyst on the magnetic stirring rod to leave room for liquid flow. Under optimized conditions, a continuous 48hour hydrogenation experiment of acetophenone was carried out in a flow reactor with non-toxic and cheap solvent ethanol, and the catalytic activity and product selectivity of the catalyst are not significantly reduced.