Nickel(II) nitrate hexahydrate (Ni(NO3)2•6 H2O, 0.03 mol) and citric acid (C6H8O7, 0.03 mol) were dissolved in 20 mL of absolute ethanol, and then the mixture was stirred at 70 ºC (300 rpm) Aging for 4-8 hours until a bubble-like green gel is obtained. Place it in a drying oven at 100 ºC for 24 to 72 hours to remove excess water. Then the green solid obtained was calcined in a fixed bed at 700 ºC under 40 mL min -1 of high-purity N2 (99.999%) atmosphere for 3 h, and the heating rate was controlled at 2 ºC min -1 . The resulting black solid was treated in a 1M H2SO4 aqueous solution at 70 °C until the solution became colorless to remove unsafe and uncovered Ni particles. Then, the black solid was washed thoroughly with deionized water until the pH value of the waste liquid was 7. Finally, the black solid was dried in a freeze dryer at -48 ºC for 12 h to obtain Ni@C-700-EtOH catalyst.