Synthesis Of Magnetic Hierarchical Core-shell LDH Supported PdAu Bimetallic Alloy Catalyst For C-C Coupling Reaction

Carbon-Carbon coupling reaction catalysed by supported mono-/ bimetallic catalysts as one of the indispensable and efficient methods in the synthesis of fine chemicals receives extensive interest in catalysis and organic synthesis areas. In this thesis, a series of supported PdAu bimetallic alloy catalysts PdAux/Fe₃O₄@MAl-LDH ?LDH:Layered double hydroxides? with magnetic hierarchical core@shell structure were synthesized for the first time by a simple polyol reduction-adsorption approach and systematically characterized by combinational techniques to study the catalyst structure, catalytic performance and recyclability of the catalyst in C-C coupling reaction. [Au]/[Pd] molar ratio ?x? and LDH layer compositions ?M=Mg, Ni, Co? of magnetic hierarchical core@shell support were highlighted to probe the effect on composition-structure, morphology and surface electronic density of the catalysts, revealing the intrinsic relationship between catalyst structure and catalytic performance. The main results and highlights of the thesis are as follows:?1? Polyol reduced PdAux-PVP alloy nanoparticles ?NPs? were adsorbed onto pre-prepared support via intermolecular forces to synthesize a series of bimetallic alloy catalysts PdAux/Fe₃O₄@MgAl-LDH ?x=[Au]/[Pd]=0.11,0.16,0.48? with honeycomb-like magnetic hierarchical core@shell structure for the first time. Combinational characterizations confirmed that the addition of gold owns three functions: ?to modulate favorably the size of PdAux alloy NPs in the range of 1-3 nm and PdAu0.16/Fe₃O₄@MgAl-LDH shows the smallest size at?1.8 nm; ?to adjust the surface electron density of PdAux alloy NPs and PdAuo.16/Fe304@MgAl-LDH exhibits the largest one;?to adjust surface elemental composition of PdAu alloy NPs and PdAu0.16/Fe₃O₄@MgAl-LDH shows the largest percentage of surface Au and favorably inhibit Pd0 oxidation.?PdAu0.16/Fe₃O₄@MgAl-LDH presents the best catalytic activity for Heck coupling reaction ?TOF:245 h-1? among the catalysts studied, four times as high as that of the corresponding monometallic catalyst Pd/Fe₃O₄@MgAl-LDH, owing to its smallest alloy NPs size, largest electron density of surface Pd0 and highest percentage of surface Au protecting Pd0. Identification of the ArPdAuxI intermediate by XPS and TGA-MS confirms that Heck reaction of iodobenzene with styrene occured on the surface of alloy NPs of the magnetic catalyst.?3? Applying PdAu0.16/Fe₃O₄@MgAl-LDH in the coupling reaction of bromobenzene and styrene shows that Ullmann homocoupling become the main reaction. Therefore, the effect of layer elemental kinds of shell LDH on Ullmann reaction activity of bromobenzene was investigated over the catalysts PdAu0.16/Fe₃O₄@M?Mg, Ni, Co?Al-LDH, and shows that PdAu0.16/Fe304@CoAl-LDH exhibits the best catalytic activity ascribing to the stronger PdAu alloy-CoAl-LDH interaction.?4? The present magnetic hierarchical PdAu bimetallic alloy catalyst has no obvious loss of activity after 5 times upon facile magnetic separation by external magnetic field rendering them the promising green catalysts with trait of high activity, easy recycling, environmental benign and so on.