Study On Preparation Of Palladium Nanoparticles And Catalytic Hydrogenation Of Nitrobenzene

In this paper,hydrogenation of nitrobenzene catalyzed by PVA-Pd nanocatalyst in water phase to prepare aniline was explored by using polyving akohol(PVA)as stabilizer for the purpose of environment-friendly and efficient catalysis.Pd nanoparticles stabilized by PVA were prepared by hydrogen reduction method,and the average size of Pd nanoparticles was 3.2 nm.The optimal reaction temperature,reaction time,hydrogen pressure,and the molar ratio of substrate to catalyst(S/C)were 45 °C,2 MPa,3 h and 500:1,respectively.Under these optimal reaction conditions,the conversion of nitrobenzene was 99.30% and the selectivity for aniline was 100%.The conversion of nitrobenzene still exceeded 90% after four repeated cycles.With triblock copolymer P123(PEO20-PPO70-PEO20)as the stabilizer,P123-Pd nanocatalyst in water phase were prepared and applied in the hydrogenation of nitrobenzene to obtain aniline.Pd nanoparticles stabilized by P123 micelles were synthesized by hydrogen reduction method,and the average size of Pd nanoparticles was 2.5 nm.The optimal reaction temperature,reaction time,hydrogen pressure and S/C were 60 °C,3 MPa,1 h and 500:1,respectively.Under these optimal reaction conditions,the conversion of nitrobenzene was 99.40% and the selectivity for aniline was 100%.There was no obvious loss in both catalytic activity and selectivity for the hydrogenation of nitrobenzene after five repeated cycles.Based on the electrostatic and steric stabilization of ionic liquids.Pd nanoparticles stabilized by polyether octadecylamine ionic liquid were prepared and applied in the hydrogenation of nitrobenzene to obtain aniline.The effects of average degree of polymerization,alkyl chain and anion on the size and morphology of Pd nanoparticles were investigated.The optimal reaction temperature,reaction time,hydrogen pressure and S/C were 70 °C,2 MPa,3 h and 2000:1,respectively.Under these optimal reaction conditions,the conversion of nitrobenzene was 96.05% and the selectivity for aniline was 100%.The catalytic performance was almost unchanged for the hydrogenation of nitrobenzene after six cycles.The above research involved the polymer stabilization and ionic liquid stabilization for the preparation of Pd nanoparticles.Pd nanocatalysts were characterized by transmission electron microscopy(TEM),confocal laser scanning microscope(CLSM),X-ray diffraction spectroscopy(XRD)et al.There are physical and chemical adsorption between stabilizer and Pd nanoparticles.After encapsulating Pd nanoparticles,a local microenvironment is formed.This microenvironment plays a significant role in solubilizing the substrate and promoting contaction between substrate and catalyst.The three kinds of catalytic systems all had the advantages of high catalytic activity and excellent selectivity,showing good reusability.With water or ionic liquid as reaction medium,both the preparation of Pd nanocatalysts and hydrogenation of nitrobenzene were under mild and environmentally friendly conditions.Furthermore,the products were readily separated from the catalysts.This study provides an effective method for the catalytic hydrogenation of nitrobenzene to aniline,and also offers a reference for the catalytic hydrogenation of other aromatic nitro-compounds.