Synthesis Of Metal Nanoparticles Supported On MIL-101 And Their Catalytic Hydrogenation Applications

Metal-organic frameworks(MOFs) are a new type of porous materials, which are made by linking inorganic metal ions and organic units. Compared with other porous materials, MOFs have large specific surface area and porosity as well as tunable structure. Owing to these properties, MOFs have been intensely researched in adsorption, catalysis, luminescence, drugs, etc. What is more, MOFs and modified MOFs present a tempting prospect of application in heterogeneous catalysis.In this work, Cr(III)-based MIL-101 which has large specific surface area and high stability of structure was selected as a host matrix to incorporate well-dispersed palladium nanoparticles through an impregnation method. These catalysts were characterized by N2 adsorption, P-XRD, XPS and TEM. There were no significant differences in the structural properties between Pd/MIL-101 and MIL-101. The Pd/MIL-101 achieved the highest activity in the hydrogenation of acetophenone and the control experiments indicated that the catalyst with Pd loading of 2.04 wt% was the most active in absence of base under mild conditions(40 °C, 0.1MPa H2). The conversion of acetophenone was almost 100% with a selectivity of 96% over this catalyst, indicating its high activity and selectivity for this reaction.The materials based on noble metal nanoparticles are known as highly active catalysts that have been extensively applied in scientific research, chemical industry, biology, medicine, etc. Researchs show that catalytic reactions mainly occur on the surface of the nanoparticles, and a large fraction of metal in the cores of the nanoparticles are wasted. In the view point of “atom economy”, the synthesis of core-shell nanoparticles with a cheap metal core and a noble metal shell is desirable. Ni@Pd core-shell nanoparticles were synthesized through solvothermal reduction of bivalent nickel and palladium in oleylamine and trioctylphosphine. Then, Ni@Pd/MIL-101 catalysts, for the first time, were synthesized with the nanoparticles loaded on MIL-101 by a simple impregnation method. The catalyst exhibited extremely high performance for reduction of nitrobenzene at 30 °C and a hydrogen pressure of 1 bar, giving a turnover frequency(TOF) of 375 h-1, nearly twice more than the Pd/MIL-101 achieved. Meanwhile, the Ni@Pd/MIL-101 was highly active and chemoselective for the hydrogenation of a variety of substituted nitroarenes except for nitrostyrene. The achievement demonstrates it is feasible to use cheap metals to replace noble metals.