Synthesis And Application Of Fe₃O₄@C Supported Bimetallic Nanocatalyst Pd-Pt

The colloidal metal alloy nanoparticles, especially platinumand palladium alloys have been the outstanding choice of catalysts in many important chemical and electrochemical reactions. However, it is often the case that a sudden drop in catalytic activities is experienced after the catalytic transformation, Hence, a number of efforts have been devoted to develop feasible routes for immobilizing or grafting the bimetallic catalysts onto inorganic supports by physically adsorbing to improve their stabilization. But there are few reports about preparing the supported bimetallic catalysts by an in situ formation method which is beneficial to promote activity of the supported metallic nanocatalysts.To design high-performance of bimetallic catalysts in terms of activity, selectivity and resistance to deactivation, exploiting the unknown catalytic reaction have became the recent development tendency. The main objective of this thesis is investigation the preparation of bimetallic catalysts and searching for a facile approach to in situ synthesis of the supported Pd-Pt nanoalloys on the proper supports and then, we exploited application of the supported bimetallic nanocatalysts in the new field of catalysis.Firstly, we investigate the preparation of monometals Pd and Pt supported on the surface of carbon-encapsulated superparamagnetic colloidal nanoparticles Fe3O4@C by the method of ethanol reduction before supporting bimetallic nanocatalyst Pd-Pt on the surface of supports. We find that the precursor of Pd and Pt could be more easily reduced by ethanol and in situ grown on the surface of supports in the presence of supports than that in the absence of supports. And furthermore, the supporting amounts and distribution of noble metals Pd and Pt could be tuned easily by controlling the the supplied content of the precursor and temperature of experiment. As for the preparation of supported bimetallic nanoparticles Pd-Pt, we utilized the co-reduction method at the very start and it turned out that we obtained the monodispersity of bimetallic nanoparticles disperse on the surface of supports uniformly at the room temperature. And then, we developed a facile method called two-step synthesis method that the atomic diffusion between bimetallic platinum and palladium was applied. More succinctly, Firstly, Pt nanoparticles are in situ generation on the surface of the supports by the alcohol reduction and then, we take advantage of galvanic replacement reaction (GRR) and rapid interdiffusion of Pt and Pd atoms in the reduced dimension of nanoparticles due to the same face-centered cubic crystal structure and almost equal lattice constant between Pd and Pt crystal. Pd atoms in situ form on the surface of Pt nanoparticles and diffuse into the Pt nanoparticles at room temperature which finally bring about the formation of the PtPd nanoalloys on the surface of supports. The experiment result turns out the supported bimetallic nanocrystals have a definite alloy structure. Finally, we prepared bimetallic nanoparticles Pd-Pt supported on another kind of magnetic hybrid nanoparticles Fe3O4@C which have been reported by the two-step synthesis method in order to discuss the influence of surface property on the catalytic property for the same phase supports.It was found that the as-prepared samples by two-step synthesis method exhibit an ultrahigh activity in all of the samples prepared by various of method for the reduction of p-nitrophenol to p-aminophenol by NaBH4with the highest normalised rate constant about12.03πmol-1s-1, which is about two times higher than that of the supported bimetallic nanoparticles Pd-Pt prepared by co-reduction method and nine times higher than that of the supported bimetallic nanoparticles Pd-Pt on the Fe3O4@C prepared by two-step synthesis method. Further investigation of catalytic property of the supported bimetallic nanocatalyst in terms of alloy-composition dependent catalytic activity was investigated and the result shows that catalytic activity of the supported bimetallic nanoparticles Pd-Pt prepared by co-reduction method exhibit a linear increase relationship with Pd percentage. However, the relationship between catalytic activity and Pd percentage shows a volcano shape for the samples by prepared two-step synthesis method. We tend to attribute it to the employ of co-reduction which is likely to resulting in the generation of poor defined structures. Moreover, the recyclability the samples by prepared two-step synthesis method for the reduction of p-nitrophenol was studied and we found that a severe drop in rate constant is occured after the fourth reuse. We tend to consider that surface detachment for the bimetallic nanoparticles supported on the CMNPs and collapse of carbon shell of supports turn up in the harsh environment of reaction.