▎ 摘　　要

NOVELTY - Ultrasonically-assisted preparation of oxygen-enriched defect graphene encapsulated metal nickel catalyst, involves: (i) adding a nickel salt and an organic ligand into a mixed solvent of alcohol and N,N-dimethyl formamide and stirring to obtain a mixed solution; (ii) transferring the obtained mixed solution to polytetrafluoroethylene lining and sealing into a hydrothermal reaction vessel, heating, cooling, taking out the solution, decompressing and filtering to obtain a powder sample; (iii) vacuum drying the powder sample to obtain a powder precursor material; (iv) grinding the obtained precursor material and roasting to obtain a roasted product; (v) washing the roasted product using hydrochloric acid or hydrofluoric acid and drying; and (vi) providing the dried product into an ultrasonic reflux device, adding nitric acid solution and performing ultrasonic reflux treatment to obtain oxygen-enriched defect graphene encapsulated metal nickel catalyst. USE - Method for preparing oxygen-enriched defect graphene encapsulated metal nickel catalyst that is utilized for synthesizing 4-aminoindole (claimed). ADVANTAGE - The method provides oxygen-enriched defect graphene encapsulated metal nickel catalyst with high conversion rate, high selectivity, high stability and high acid resistance for synthesizing 4-aminoindole. DETAILED DESCRIPTION - Ultrasonically-assisted preparation of oxygen-enriched defect graphene encapsulated metal nickel catalyst, involves: (i) adding a nickel salt and an organic ligand into a mixed solvent of alcohol and N,N-dimethyl formamide to dissolve and stirring at 10-60°C for 1-10 hours using a magnetic stirrer to make it fully and uniformly mix and to obtain a mixed solution; (ii) transferring the obtained mixed solution to polytetrafluoroethylene lining and sealing into a hydrothermal reaction vessel, heating the reaction vessel in blast oven at 120-200°C for 2-15 hours, cooling to room temperature, opening the reaction vessel, taking out the solution from the polytetrafluoroethylene lining, decompressing and filtering and fully washing using alcohol and dimethylformamide (DMF) to obtain a powder sample; (iii) adding the obtained powder sample into a vacuum drying box for vacuum drying to obtain a powder precursor material; (iv) grinding the obtained precursor material in an agate mortar until there is no obvious granules, raising the temperature from room temperature to 300-900°C at a heating speed of 1-10°C/minute, under the condition of inert gas and roasting for 2-10 hours and cooling to room temperature to obtain a roasted product; (v) washing the roasted product using 0.5-3 mol/l hydrochloric acid or hydrofluoric acid for 2-12 hours, decompressing and filtering the acid washed product and drying the product in the drum air oven; and (vi) providing the dried product into an ultrasonic reflux device comprising a three-necked flask and a spherical condensing tube, adding 1-10 wt.% nitric acid solution, placing the ultrasonic reflux device, adjusting the ultrasonic frequency at 20-40 KHz and ultrasonic temperature at 20-90°C, performing ultrasonic reflux treatment with a catalyst for 1-8 hours, decompressing and filtering the ultrasonic reflux product, drying the product in the drum air oven to obtain oxygen-enriched defect graphene encapsulated metal nickel catalyst, where the value of oxygen defect peak intensities (ID/IG) in the graphene shell layer is more than 1.17, and the organic ligand in step (i) is terephthalic acid, 2-amino terephthalic acid, 4-pyridine formic acid, pyrrole-2-formic acid or oxalic acid. An INDEPENDENT CLAIM is included for an application of oxygen-enriched defect graphene encapsulated metal nickel catalyst for catalytic hydrogenation of 4-nitro-indole to synthesize 4-amino-indole.