Preparation Of Palladium-based Nanocatalysts And Their Applications In Reduction Of Nitroarenes

Supported heterogeneous metal catalysts have been widely employed in the industrial catalysis,such as organocatalysis,electrocataylysis and environmental catalysis.Therefore,design of supported catalysts with both high activity and enhanced stability is of great significance.In principle,active spices and support play key roles to the catalytic performance of supported heterogeneous catalysts.As three basic but important issues,uniform-dispersion of active sites,accessibility of supports as well as their satisfied interactions between them should be taken into consideration for catalysts design.Over the past decades,great efforts have focused on increasing the catalytic efficiency by comprehensively investigation and understanding of catalytic process at molecular/atomic level.However,tiny metal nanoparticles(NPs)loaded in catalysts are prone to aggregate owing to their large surface-volume ratio,higher surface free energy and weak metal-support interaction(MSI),which inevitably lead to a deterioration of their catalytic performance.Nevertheless,the development of high-performance heterogeneous catalysts and effective catalytic methods are still remain challenging.In this thesis,double-layered multi-walled carbon nanotubes@nitrogen doped carbon(MWCNTs@NC)and NC functionalized Bi₂S₃ hollow spheres(Bi₂S₃@NC)were employed as supports to anchor bimetal Palladium-Iron or Palladium NPs to prepare corresponding catalysts.The structural properties and catalytic performance and of as-prepared MWCNTs@Pd-Fe@NC and Bi₂S₃@NC@Pd catalysts are discussed.The fabrication methods and detailed results are presented as follows:(1)We present an efficient encapsulation approach to fabricate a bimetallic nanocatalyst,in which Pd-Fe bimetal NPs were anchored and confined in the interface of double-layered MWCNTs@Pd-Fe@NC catalyst.The as-prepared MWCNTs@Pd-Fe@NC catalyst exhibites superior catalytic activity to its mono-metal counterparts(MWCNTs@Pd@NC and MWCNTs@Fe@NC)toward the nitroarenes reduction reactions,showing an enhanced synergetic effect.Typically,the turnover frequency(TOF)is as high as 70.36 min^-1 toward 4-nitrophenol(4-NP)reduction reaction,which was higher than that of many reported noble-metal based nanocatalysts in the last four years.Furthermore,the Pd-Fe bimetallic catalyst also exhibites an excellent stability and reusability due to the intrinsic confined structure.(2)We present a facile strategy to prepare a hollow structured Bi₂S₃@NC@Pd catalyst,in which Pd NPs were decorated on NC functionalized Bi₂S₃ hollow spheres.The resultant Bi₂S₃@NC@Pd hollow catalyst shows remarkably photothermal effect due to NC and Bi₂S₃,which is an effective photothermal material.Under irradiation of 808 nm laser,the surface temperature of catalyst increased from 25? to 32? within 3min40s,and thus exhibiting an enhanced catalytic activities for the reduction reactions of organic dyes,such as 4-NP,methylorange(MO),congro red(CR).The TOF is as high as 18.52 min^-1 toward 4-NP reduction reaction,which was higher than that of conventional catalytic process(11.66 min^-1)without laser irradiation.