Preparation of Ni/C Core-shell Nanoparticles through MOF Pyrolysis for Phenylacetylene Hydrogenation Reaction

Abstract

A series of Ni/C core-shell nano catalysts with abundant mesoporous and uniform size were prepared by Ni-MOF-74 pyrolysis. The Ni-MOF-74 was synthesized via hydrothermal method with nickel acetate and 2,5-dihydroxyterephthalic acid (DHTA) as raw materials. The pyrolysis process was carried out in a tube furnace under Argon (Ar) atmosphere with a heating rate of 2 degrees C/min. Completed pyrolytic product Ni/C can be obtained by extending the pyrolysis time (6 h) at 400. or increasing the pyrolysis temperature (>= 500 degrees C) based on the TG result. Moreover, the particle size of Ni/C varied with pyrolysis temperature from 3 nm (500 degrees C) to 17 nm (800 degrees C). The TEM images and Ar ion sputtering XPS indicated a core-shell structure of the pyrolysis product. Nickel species can be stable in the form of nickel (Ni-0) due to the electronic properties regulating and confinement effect of the carbon shell. Moreover, the carbon shell greatly weaken the interaction between particles, which is favorable for the dispersion of the catalyst in the reaction system. H-2-TPR results show that the interaction between nickel and amorphous carbon increases with the pyrolysis temperature, which is unfavorable to the interaction between Ni species and the reactant. The phenylacetylene (PA) hydrogenation reaction was carried out with 0.2 g catalyst, 10 mL of 1 mol/L ethanolic phenylacetylene solution and 1.0 MPa H-2 in a 50 mL high-pressure autoclave under 50 degrees C. Ni/C exhibits excellent catalytic activity and recyclability in phenylacetylene (PA) hydrogenation. In addition, we compared the activity of Ni/C with several reported catalyst system and found their activity increases in the order of Ni, NiSix, supported Ni2Si, Ni/C, Pd and Pt. With an activity of up to 0.833 mmol.min(-1).g(cat).(-1) at 50 degrees C (Ni/C-400-6, Ni/C-500-2), Ni/C is the most promising transition metal catalyst that can be comparable with noble metal.