Synthesis and Catalytic Properties of Au-Based Noble Metal and Ceria Composite Nano-Materials

Author:Li Jian

Supervisor:zhang hong jie


Degree Year:2019





Because of their unique optical and chemical properties,Au based nanomaterials have been applied in various areas including optic,biomedicine,and especially catalysis.In their catalytic applications,Au-based nanomatrials could catatlysize various organic reactions,such as selective oxidations,selective hydrogenations,C-C coupling reactions etc.The improvment of these applications can benefits from the advancement of synthetic methods of nanomaterials.Over the past few years,many methods have been developed to achieve the synthesis of nanomaterials with controllable morphology,structure and properties.At the same time,new challenges about synthetic methods have emerged,for instance,how to develope new methods with clean and simple fabrication process.And how to achieve synthesis of nanomaterials with complicated structures and components.Additionally,exploring the influence of chemical modification,component and structure on selectivity and activity of catalysts is also important for designing effective catalysts.This thesis focused on developing new methods to achieve simple and clean fabrication of complicated Au-based nanomaterials.Furthermore,we explored the influence of chemical modification,component and structure on selectivity and activity of Au-based catalysts.The main achievements are listed as follows:1.We have developed two unique autoredox routes to the fabrication of CeO2-encapsulated Au nanocatalysts.Route A is the synthesis of well-defined CSNs by a one-step redox reaction.The process involves an interesting phenomenon in which Ce3+ can act as a weak acid to inhibit the hydrolysis of Ce3+ under the condition of OH-shortage.Route B is the fabrication of monodispersed YSNs by a two-step redox reaction with Co3O4 as an in-situ template.Furthermore,the transfer coupling of nitrobenzene was chosen as a probe reaction to investigate their catalytic difference.The CSNs can gradually achieve the conversion of nitrobenzene into azoxybenzene,while the YSNs can rapidly convert nitrobenzene into azobenzene.The different catalytic results are mainly attributed to their structural distinctions.2.We report a general one-pot strategy for the synthesis of Au@multi-MxOy(M=Co,Ce,Fe,Sn)yolk@shell nanospheres.Without any additional protecting molecule or reductant,the whole reaction is a clean redox process that happens among the inorganic metal salts in an alkaline aqueous solution.By using this method,Au@Co3O4/CeO2(Au@Co-Ce),Au@Co3O4/Fe2O3(Au@Co-Fe),Au@CeO2/SnO2(Au@Ce-Sn)yolk@shell nanospheres with binary oxides as shell,Au@Co3O4/CeO2/Fe2O3(Au@Co-Ce-Fe)yolk@shell nanospheres with ternary oxides as shell and Au@Co3O4/CeO2/Fe2O3/SnO2(Au@Co-Ce-Fe-Sn)yolk@shell nanospheres with quaternary oxides as shell can be obtained.Subsequently,the catalytic CO oxidation was selected as the catalytic model,and the Au@Co-Ce system was chosen as the catalyst.It was found that the catalytic activity of Au@Co-Ce yolk@shell nanospheres can be optimized by altering relative proportion of Co and Ce oxides.3.We describe a robust self-template strategy for simple synthesis of multishell Au with net-like shell structure,controllable shell number and sphere size.The process involves the rapid reduction of novel Au-melamine colloidal templates with a great amount of NaBH4 in suitable solvent.The further experiment demonstrated that the relatively slow separation of residual melamine-based polymers played a vital role in assisting the formation of completed structures.In the hydrogenation of 4-nitrostyrene using NH3BH3 as a reducing agent,the porous triple-shell Au with surface modification(S-PTSAu)exhibited great improvement of selectivity(97%)for 4-aminostyrene in contrast with unmodified Au/ZrO2.Furthermore,it also showed higher enhancement of catalytic activity under irradiation of visible light as compared to similar catalysts with less shell number.This work opens up a new route in designing and synthesizing noble metal and alloy multishell structures for various applications.